The Synthesis of Kinetically Stabilised Heavy

Group 13 Hydride Complexes

Thesis as partial fulfilment of the requirements of

Doctor of Philosophy (Chemistry)

by

Alasdair Iain McKay

(Student Number: 3188803)

Supervisor: Assoc. Prof. Marcus L. Cole

School of Chemistry

The University of New South Wales

Sydney, Australia

16th April 2015

Certificate of Originality

‘I, Alasdair Iain McKay, hereby declare that this submission is my own work and to the best of my knowledge it contains no materials, previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the projects’ design and conception or in style, presentation and linguistic expression is acknowledged.’

Signed......

Date......

ii Table of Contents

Acknowledgements ix Abstract x Abbreviations xi

Chapter One: General Introduction 1 1.1 Group 13 Element Structure 1 1.2 Group 13 Metal Hydrides 3 1.2.1 Bonding and Structure in Group 13 Trihydrides 4 1.2.2 The Thermodynamics of Group 13 Hydrides 5 1.2.3 Lewis Base Adducts of Group 13 Trihydrides 7 1.2.4 Group 13 Halohydride Chemistry 8 1.2.5 Donor Complexes of Group 13 Hydrides 9 1.3 Industrial Applications of Group 13 Hydrides 10 1.3.1 Semiconductor Materials 10 1.3.2 Organic Functional Group Reductions 11 1.4 Low Oxidation State Group 13 Chemistry 12 1.4.1 Synthesis 12 1.4.2 Chemistry 13 1.5 References 14

Chapter Two: Quantification of the Steric and Electronic Character of Monoanionic Bidentate N,Nʹ-Ligands 21 2.1 Introduction 21 2.1.1 Cone Angle 21 2.1.2 Solid Angle 22 2.1.3 Molecular Volumes 25 2.1.4 The Quantification of the Steric Character of High Denticity Ligands 27 2.2 Project Outline 29 2.3 Results and Discussion 30 2.3.1 The Development of a Metal-Based Probe for the Quantification of Monoanionic Bidentate N,N'-Ligands’ Steric Character 30 2.3.1.1 Steric Measurements 31 2.3.1.2 Evaluation of Aluminium as the Basis for a Steric Probe 31 2.3.1.3 Evaluation of Dimethylaluminium as a Steric Probe 34 2.3.1.4 Ligand Intermeshing - A Menacnac Case Study 36 2.3.2 The Preparation of Novel Super-Bulky Bidentate N,N'-Ligands and Evaluation of their Steric Character 40 2.3.2.1 The Synthesis of a 1,3-Bis(2,6-terphenyl)triazene 40 2.3.2.2 The Synthesis of C-2,6-terphenyl Substituted Amidine Ligands 42 2.3.2.3 The Synthesis of Dimethylaluminium Complexes of 1-3 and Popular Ligands 46

iii Table of Contents

2.3.2.4 Steric Measurements of Anionic Bidentate N,N'-Ligands 49 2.3.3 The Development of a Metal-Based Probe to Quantify the Electronic Character of Monoanionic Bidentate N,N'-Ligands 54 2.3.3.1 The Synthesis of Rhodium Bis(carbonyl) Complexes 57 2.3.3.2 Electronic Measurements for the Monoanionic Bidentate N,N'-Ligands Studied Herein 60 2.3.3.3 Structural Studies of Rhodium Complexes 11-18 63 2.3.4 The Development of a Second Generation Steric Probe 69 2.4 Conclusions 73 2.5 Future Directions 75 2.6 Experimental 76 2.6.1 General Synthetic Procedures 76

2.6.2 Synthesis of Dmp2N3H (1) 76 2.6.3 Synthesis of DitopACyH (2) 76 2.6.4 Synthesis of DmpACyH (3) 77 2.6.5 General Procedure for the Preparation of Dimethylaluminium Complexes 78 Me 2.6.6 Synthesis of [AlMe2( Aiso)] (10) 80 2.6.7 General Procedure for the Preparation of Rhodium Carbonyl Complexes 81 2.6.8 Synthesis of [Rh(Fiso)(cod)] (17) 82

2.6.9 Synthesis of [Rh(N3Dipp2)(cod)] (18) 83 2.6.10 General Procedure for the Carbonylation of Rhodium 1,5-cod Complexes 84 2.7 References 85

Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands 96 3.1 Introduction 96 3.1.1 β-Diketiminate Complexes 96 3.1.2 Amidinate, Guanidinate and Triazenide Complexes 97 3.2 Project Outline 101 3.3 Results and Discussion 102 3.3.1 The Synthesis of Ether Solvated Lithium Amidinate Complexes 102 3.3.2 The Synthesis of Ether Solvated Lithium Triazenide Complexes 106 3.3.3 Donor-Free Monomeric Alkali Metal Triazenide Complexes and a Less Hindered Aggregate 109 3.3.4 Bimetallic Triazenide Complexes 120 3.4 Conclusions 123 3.5 Future Directions 125 3.6 Experimental 126 3.6.1 General Synthetic Procedures 126 3.6.2 General Synthetic Procedure for the Preparation of Lithium Amidinate Complexes 126 3.6.3 General Synthetic Procedure for the Preparation of Ether Solvated Lithium Triazenide Complexes 127

iv Table of Contents

3.6.4 Synthesis of [{Li(N3Dipp2)}x] (28) 128 3.6.5 Synthesis of [{K(N3Dipp2)}x] (29) 129 3.6.6 Synthesis of [Li(N3Dmp2)] (30) 129 3.6.7 Synthesis of [Na(N3Dmp2)] (31) 130 3.6.8 Synthesis of [K(N3Dmp2)] (32) 130 3.6.9 Synthesis of [Rb(N3Dmp2)] (33) 131 3.6.10 Synthesis of [Cs(N3Dmp2)] (34) 131 1 n 3.6.11 Synthesis of [Li2(μ-κ -N3Dmp2)(μ- Bu)] (36) 132 3.7 References 133

Chapter Four: Stabilisation of Low Oxidation State Group 13 Complexes by Kinetic Control 138 4.1 Introduction 138 4.1.1 Halides 138 4.1.2 Alkyl, Amide, Cyclopentadienyl and Silyl Clusters 139 4.1.3 Bulky Aryl and Amide Complexes 141 4.1.4 Anionic Polydentate N-Donor Ligands 142 4.1.5 The Oxidative Chemistry of MIL Species 144 4.1.6 The Coordination Chemistry of MIL Species 145 4.2 Project Outline 148 4.3 Results and Discussion 149 4.3.1 Attempted Stabilisation of Low Oxidation State Group 13 Metals using a 1,3-Bis(aryl)triazenide 149 4.3.2 Kinetic Stabilisation of Low Oxidation State Group 13 Metals using a 1,3-Bis(2,6-terphenyl)triazenide 156 4.3.3 The Chemistry of Group 13 Metal(I) Triazenide Complexes 160 4.4 Conclusions 162 4.5 Future Directions 163 4.6 Experimental 165 4.6.1 General Synthetic Procedures 165

4.6.2 Synthesis of [GaI(N3Dipp2)2] (37) 165 4.6.3 Synthesis of [{GaI(N3Dipp2)}2] (38) 165 4.6.4 Synthesis of [GaCl(N3Dipp2)2] (39) 166 4.6.5 Synthesis of [InCl(N3Dipp2)2] (40) 166 4.6.6 Synthesis of [InI(N3Dipp2)2] (41) 167 4.6.7 The Reaction of InCp with Dipp2N3H 168 4.6.8 Synthesis of [{Tl(N3Dipp2)}2] (42) 168 4.6.9 Synthesis of [Ga(N3Dmp2)] (43) 168 4.6.10 Synthesis of [In(N3Dmp2)] (44) 169 4.6.11 Synthesis of [Tl(N3Dmp2)] (45) 169 4.6.12 Attempted Preparation of B(C6F5)3 Adducts of 42-45 170 4.6.13 The Reaction of [Ni(cdt)] with 44 170

v Table of Contents

4.6.14 The Reaction of [Pd2(dvds)3] with 44 170 4.7 References 171

Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls 180 5.1 Introduction 180 5.1.1 β-Diketiminate Complexes 180 5.1.2 Amidinate Complexes 181 5.1.3 1,3-Triazenide Complexes 183 5.1.4 Reactivity 184 5.2 Project Outline 185 5.3 Results and Discussion 186 5.3.1 Triazenide Complexes of the Dihalo Group 13 Metals 186 5.3.2 Triazenide Complexes of the Dimethyl Group 13 Metals 192 5.4 Conclusions 197 5.5 Future Directions 198 5.6 Experimental 199 5.6.1 General Synthetic Procedures 199

5.6.2 Synthesis of [AlCl2(N3Dmp2)] (46) 199 5.6.3 Synthesis of [GaCl2(N3Dmp2)] (47) 199 5.6.4 Synthesis of [InBr2(N3Dmp2)] (48) 200 5.6.5 Synthesis of [SiMe3(N3Dmp2)] (49) 200 5.6.6 Attempted Synthesis of [TlX2(N3Dmp2)] (X = halide) 201 5.6.7 Synthesis of [GaMe2(N3Dmp2)] (50) 202 5.6.8 Synthesis of [InMe2(N3Dmp2)] (51) 202 5.6.9 Synthesis of [TlMe2(N3Dmp2)] (52) 203 5.7 References 204

Chapter Six: Stabilisation of Group 13 Hydrides with Triazenide Ligands 208 6.1 Introduction 208 6.1.1 β-Diketiminate Complexes 208 6.1.2 Amidinate and Guanidinate Complexes 210 6.1.3 Triazenide Complexes 213 6.1.4 The Reactivity of Group 13 Hydride Complexes 215 6.2 Project Outline 216 6.3 Results and Discussion 217 6.3.1 The Stabilisation of M-H Bonds with C-2,6-Terphenyl Substituted Amidinate Ligands 217 6.3.2 The Stabilisation of M-H Bonds by N-Aryl Triazenide Ligands 221 6.3.3 The Stabilisation of M-H Bonds with an N-2,6-Terphenyl Triazenide Ligand 231 6.4 Conclusions 238

vi Table of Contents

6.5 Future Directions 240 6.6 Experimental 241 6.6.1 General Synthetic Procedures 241

6.6.2 Preparation of [LiInH4] 241 Ditop 6.6.3 Synthesis of [AlH( ACy)2] (53) 241 6.6.4 Synthesis of [AlH(N3Dipp2)2] (54) 242 6.6.5 Synthesis of [GaH(N3Dipp2)2] (55) 242 6.6.6 Synthesis of [InH(N3Dipp2)2] (56) 243 6.6.7 Synthesis of [TlCl(N3Dipp2)2] (57) 243 6.6.8 Synthesis of [TlBr(N3Dipp2)2] (58) 244 6.6.9 The Attempted Synthesis of [TlH(N3Dipp2)2] 244 6.6.10 Synthesis of [AlH2(N3Dmp2)] (59) 245 6.6.11 Synthesis of [GaH2(N3Dmp2)] (60) 245 6.6.12 Attempted Synthesis of [InH2(N3Dmp2)] 246 6.7 References 247

Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with N-Heterocyclic Carbenes 251 7.1 Introduction 251 7.1.1 Amine and Phosphine Complexes of Group 13 Metallanes 251 7.1.2 NHC Complexes of Group 13 Metallanes 254 7.1.3 The Stabilisation of 6th Period Metal Hydride Moieties with NHCs 256 7.1.4 Super Bulky NHCs 258 7.2 Project Outline 259 7.3 Results and Discussion 260 7.3.1 The Role of Sterics in the Stability of NHC Complexes of Alane 260 7.3.2 The Stability of NHC Complexes of Indane 262 7.3.3 Preliminary Studies of the Reactivity of the Indane and Gallane Complexes Developed Herein with Group 6 Carbonyls 284 7.4 Conclusions 293 7.5 Future Directions 295 7.6 Experimental 296 7.6.1 General Synthetic Procedures 296

7.6.2 Synthesis of [AlH3(IMe)] (61) 296 7.6.3 Synthesis of [InH3(7Dipp)] (62) 296 7.6.4 Intentional Synthesis of 7Dipp·HH (63) 297

7.6.5 Synthesis of [GaH3(7Dipp)] (64) 297 7.6.6 Synthesis of [InBr3(7Dipp)] (65) 298 7.6.7 Synthesis of [InH3(IPr)] (66) 298 7.6.8 Synthesis of [GaH3(IPr)] (67) 299 7.6.9 Synthesis of [InD3(IPr)] (68) 299 7.6.10 Synthesis of [InH3(IPr*)] (69) 299

vii Table of Contents

7.6.11 Spectroscopic Data for IPr*·HH (70) 300

7.6.12 Synthesis of [GaH3(IPr*)] (71) 300 7.6.13 Synthesis of [TlCl3(IPr*)] (72) 300 7.6.14 The Attempted Synthesis of [TlH3(IPr*)] 301 7.6.15 The Photochemical Reaction of 69 with Tungsten Hexacarbonyl 301 7.6.16 The Photochemical Reaction of 71 with Tungsten Hexacarbonyl 302

7.6.17 The Reaction of 66 with [Mo(CO)4(cod)] 302 2 7.6.18 Synthesis of [Mo(CO)4(κ -H3Ga·IPr)] (76) 302 7.6.19 The Reaction of [InH3(IMes)] with [Mo(CO)4(cod)] 303 7.7 References 304

Chapter Eight: N-Heterocyclic Carbene Complexes of Low Oxidation State Group 13 Metals 310 8.1 Introduction 310 8.1.1 The Stabilisation of Reactive Main Group Molecules using NHCs 310 8.1.2 The Stabilisation of Low Oxidation State Group 13 Elements using NHCs 311 8.2 Project Outline 314 8.3 Results and Discussion 315 8.3.1 NHC Complexes of Low Oxidation State Gallium and Indium 315 8.3.2 NHC Complexes of Thallium(I) 319 8.4 Conclusions 326 8.5 Future Directions 327 8.6 Experimental 328 8.6.1 General Synthetic Procedures 328

8.6.2 Synthesis of [{GaCl2(IMes)}2] (78) 328 8.6.3 Synthesis of [{GaI2(IMes)}2] (79) 328 8.6.4 Synthesis of [{InCl2(IMes)}2] (80) 329 t F 8.6.5 Synthesis of [Tl(C6H5F)2.5][Al(O Bu )4] (82) 329 t F 8.6.6 Synthesis of [Tl(IMes)2][Al(O Bu )4] (83) 329 t F 8.6.7 Synthesis of [Tl(IPr)2][Al(O Bu )4] (84) 330 8.7 References 331

Appendix One: General Experimental Procedures S1 Appendix Two: Crystallographic Data S5 Appendix Three: Revised Steric Parameters S48 Appendix Four: Assignment of M-π-arene Hapticities S49 Appendix Five: Publications, Oral and Poster Presentations in Support of this Thesis S52

viii Acknowledgements

I would first and foremost like to thank my supervisor, Assoc. Prof. Marcus Cole, whose guidance, encouragement and enthusiasm has been instrumental throughout the course of this project. I would also like to thank my co-supervisor Dr Graham Ball, for being my NMR guru.

I must also thank various other academics who have helped me in one form or another; Dr Jason Harper and Dr Ron Haines. I would also like to thank the staff of the NMR facility and Dr Mohan Bhadbhade for the X-ray diffraction department.

I would like to thank the members of the ‘Cole Group’ for being my second family over the past five years and encouraging me through the course of this project. Thanks to Trung, Sam, Matt, Erika, Maggie, Ren, Raj, Steve, Jo, Pete, Anthony, Kai, Dan, Chris, Doug and Damon for your friendship through this period.

I would like to thank my family. They have seen me at my best and at my worst over the years and have stuck with me all the way.

And last but not least I would like to thank Oanh, who has been there for me from start to finish. Thank you for helping me print and collate the thesis, for being the straight thinking guide when I am sleep deprived, for putting up with my crazy moods of late and for being my rock.

ix Abstract

The work presented in this thesis describes the synthesis and stability of a range of hydrido and low oxidation state complexes of the group 13 elements. The underlying theme is the stabilisation of these species. The work upon this subject is divided into eight chapters. Chapter One provides a general introduction to the members of group 13, with particular emphasis on the development of group 13 metal trihydrides and low oxidation group 13 metals. The reasons behind the inherent instability of these species are discussed, and is the development of stabilising ligands.

Chapter Two discusses the variability in the stereoelectronic character of stabilising ligands and describes the development of a number of probes to quantify the stereoelectronic character of monoanionic bidentate N,Nʹ-ligands. This Chapter also describes the syntheses of a new super bulky 1,3-bis(2,6-terphenyl)triazene and two C-2,6-terphenyl substituted amidines.

Chapter Three introduces the alkali metal chemistry of monoanionic bidentate N,Nʹ-ligands. Alkali metal complexes of the aforementioned super bulky ligands (Chapter Two) have been prepared.

Chapter Four introduces the +1 oxidation state chemistry of the group 13 metals. The stabilisation of +1 oxidation state group 13 species with triazenide ligands was found to be dependent on the steric character of the ligand employed.

Chapter Five introduces the coordination chemistry of trivalent group 13 complexes. The syntheses and crystallographic characterisations of dihalo- and dimethyl group 13 complexes featuring a super bulky triazenide are presented.

Chapter Six describes the kinetic stabilisation of group 13 heavy hydrides with monoanionic bidentate N,Nʹ-ligands. The impact of the ligand’s steric character on the thermal stabilities of these complexes is discussed.

Chapter Seven introduces the known hydride chemistry of indium and describes the synthesis of a number of NHC adducts of indane (InH3). The decomposition pathways and reactivities of these species were studied.

Chapter Eight introduces the stabilisation of low oxidation state main group species by

NHCs. A series of dimeric metal dihalide NHC complexes of the form [{MX2(NHC)}2] (M = Ga, In) have been prepared and characterised. Novel bis(NHC) complexes of thallium(I) were also characterised.

x Compounds by Number

br Broad

BTMA·ICl2 Benzyltrimethylammonium dichloroiodate nBu n-Butyl- nBuLi n-Butyllithium tBu tert-Butyl- tBuLi tert-Butyllithium ca. Circa, latin for ‘about’ cdt trans,trans,trans-1,5,9-cyclododecatriene cin Cinnamyl- cis Cisoid cm-1 Wavenumber, unit of frequency (= ν/c) cm3 Cubic centimetre

COD & cod 1,5-Cyclooctadiene, free and coordinated respectively

COE & coe cis-Cyclooctene, free and coordinated respectively

Cp Cyclopentadienyl-

Cp* 1,2,3,4,5-Pentamethylcyclopentadienyl-

Cy Cyclohexyl-

δ NMR chemical shift in ppm d Doublet dd Doublet of doublets

-dn Deuterated solvent

DCC Dicyclohexylcarbodiimide

DCM Dichloromethane dec. Decomposition temperature

ºC Degree Celsius

Dipp 2,6-Diisopropylphenyl-

xi Compounds by Number

DippNH2 2,6-Diisopropylaniline

Dipp* 2,6-Bis(diphenylmethyl)‐4-methylphenyl-

Ditop 2,6-Di(4-tolyl)phenyl-

Dmap Dimethylaminopyridine

DME & dme 1,2-Dimethoxyethane

Dmp Dimesitylphenyl- (2,6-di(2,4,6-trimethyl)phenyl-) dvds 1,1,3,3-tetramethyldisiloxane equiv. Equivalents

Et Ethyl-

Et2O Diethyl ether

EtOAc Ethyl acetate

EtOH Ethanol g Gram

η Hapticity of a ligand

HMBC Heteronuclear multiple bond correlation

HMDS Hexamethyldisilazane or hexamethyldisilazide anion h Hours

Hypersilyl Tri-trimethylsilyl-silyl-

Hz Hertz (s-1)

IAd 1,3-Bis(1-adamantyl)imidazol-2-ylidene

IPr 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene

IPr·HCl 1,3-Bis(2,6-diisopropylphenyl)imidazolium chloride

IiPrMe 1,3-Diisoproyl-4,5-dimethylimidazol-2-ylidene

IPr* 1,3-Bis(2,6-Bis(diphenylmethyl)‐4-methylphenyl)imidazol-2- ylidene

IDitop 1,3-Bis(2,6-di(4-tolyl)phenyl)imidazol-2-ylidene

xii Compounds by Number

IDitop·HCl 1,3-Bis(2,6- di(4-tolyl)phenyl)imidazolium chloride

IMes 1,3-Bis(2,4,6-trimethylphenyl)imidazol-2-ylidene

IMesBr 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dibromoimidazol-2-ylidene

IMes·HCl 1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride iPr Isopropyl-

IMe 1,3-Dimethylyl-imidazol-2-ylidene

IMe4 1,3-Dimethyl-4,5-dimethylimidazol-2-ylidene

IR Infrared

ItBu 1,3-Bis-tert-butylimidazol-2-ylidene

J Joule n JXY Coupling constant between nuclei X and Y, over n bonds, in Hz k Kilo- (103)

κn Denotes binding mode for polydentate ligands, n denotes the bridging index

KOtBu Potassium tert-butoxide lit. Literature value

L General Lewis base or litre (dm-3) m Medium, milli- (10-3) or multiplet

M Molar (mol dm-3) or mega- (106)

Me Methyl-

MeLi Methyllithium

MeOH Methanol

Mes Mesityl- (2,4,6-trimethylphenyl-)

Mes* super mesityl- (2,4,6-tri-tbutylphenyl-)

MesNH2 Mesitylamine or 2,4,6-trimethylaniline mins Minutes

xiii Compounds by Number

mol Moles m.p. Melting point (°C)

µn Bridging ligand, n denotes the bridging index

µ Micro- (10-6)

NBD & nbd Bicyclo[2.2.1]hepta-2,5-diene (2,5-norbornadiene), free and coordinated respectively

NHC Imidazol-2-ylidene

NMR Nuclear magnetic resonance

NPA Natural population analysis

NQR Nuclear quadrupole resonance

PCy3 Tricyclohexylphosphine

PPh3 Triphenylphosphine

Ph Phenyl- ppm Parts per million ppt Precipitate

QI Quadrupolar interaction

Quin Quinuclidine (1-azabicyclo[2.2.2]octane)

Quin∙HCl Quinuclidine hydrochloride r.t. Room temperature s Singlet or strong sh Sharp t Triplet

TEP Tolman electronic parameter

THF & thf Tetrahydrofuran, free and coordinated respectively

TLC Thin layer chromatography

xiv Compounds by Number

TMEDA & tmeda N,N,N’,N’-Tetramethylethylenediamine, free and coordinated respectively

Trans Transoid

Trip 2,4,6-Triisopropylphenyl-

UHP Ultra high purity

ν Frequency in Hz

V Volt

Via Latin for ‘by the way of’ v.i. Vide infra, latin for ‘see below’ v.s. Vide supra, latin for ‘see above’ vis-á-vis French for ‘in relation to’

Viz. Videlicet, latin for ‘namely’

VT Variable temperature w Weak

X Halide

XPS X-Ray photoelectron spectroscopy

XRD X-Ray diffraction

xv

“ Science, the most potent distraction of all ”

xvi Chapter One: General Introduction

1.1 Group 13 Element Structure

The first group of the p-block elements, group 13, comprises the elements boron, aluminium, gallium, indium and thallium. All group 13 elements possess the ground 2 1 2 [1] state valence electron configuration ns np and ground state electronic term P1/2. Aside from this commonality, the properties of the group 13 elements vary substantially. Some selected physical and electronic properties of the group 13 elements are listed in Table 1.1.[2]

B Al Ga In Tl

Atomic Number 5 13 31 49 81

Melting Point (°C) 2075 669.3 29.8 156.6 302.4

Covalent Radius (M3+, Å) 0.88 1.25 1.25 1.50 1.55 Electronegativity 2.01 1.47 1.82 1.49 1.44 (Allred and Rochow) Ionisation Energies (kJ mol-1) M → M1+ 800.6 577.5 578.8 558.3 589.4 M → M2+ 2427.1 1816.7 1979.4 1820.7 1971.0 M → M3+ 3659.8 2744.8 2963.0 2704.0 2878.0 Table 1.1 - Selected properties of the group 13 elements[2]

Boron, the lightest element of the group, is the only non-metal and is generally classed as a metalloid. The broad structural diversity of boron chemistry results from the inherent electron deficiency incurred by the provision of four valence orbitals and only three valence electrons. This, in combination with boron’s relatively high electronegativity, gives rise to the formation of covalently bonded molecular networks and boron’s metalloid character. Indeed, all crystalline allotropes of boron exhibit multicentre boron-boron bonding.[3]

The remaining elements of group 13 are soft, low melting metals that display high electrical conductivity and ductility.[1] An interesting feature of group 13 is that gallium (29.8 °C) and indium (156.6 °C) exhibit melting points much lower than those of

1 References for this chapter begin on pg. 14 Chapter One: General Introduction

aluminium (660.3 °C) and thallium (302.4 °C) (Table 1.1). These two examples are at odds with periodic trends, vis-à-vis groups 1 and 2, where the melting points decrease incrementally down the group.

The four metallic elements of group 13 exhibit close-packed structures, where each metal atom has 12 neighbouring atoms. Aluminium and indium are the only elements in the group which crystallise in single space groups (Fm3m and I4/mmm respectively).[4] The most prevalent thallium morphology is hexagonal α-Tl with space group [4] P63/mmc. Indium has a slightly distorted close-packed structure with four atoms slightly closer (3.25 Å) than the remaining eight (3.38 Å).[1] By contrast, the most prevalent gallium morphology (orthorhombic α-Ga, Fm3m) has a single close neighbour (2.48 Å), with the other neighbouring galliums in pairs at 2.70, 2.73 and 2.79 Å.[5] It is therefore unsurprising that gallium melts are thought to include pseudo-diatomic Ga2 molecules.[6] In this respect the structure of solid gallium displays similarities to the solid-state nature of iodine, which contains discrete I2 units. This incipient bond localisation is typical of metalloids, and goes some way to explaining some of the metalloid characteristics of gallium and the low melting points of both gallium and indium.

The ionisation energies (M → M3+) of the group 13 metals (Table 1.1) are also noteworthy. The variation in these can be explained on the basis of the electronic configurations of the respective elements. Generally the ionisation energies of elements decrease as a group is descended because of the increasing distance of the valence electrons from the nucleus , which serves to eclipse the increased effective nuclear charge. This trend is observed between boron and aluminium, where a considerable reduction in ionisation energy is observed. However, the corresponding move from aluminium to gallium fails to follow this trend. This is rationalised by the ‘d-block contraction’, wherein the filling of the highly directional and poorly shielding 3d-orbitals fails to compensate for the increase in effective nuclear charge. This translates to a more compact atom as the valence electrons are drawn closer to the nucleus, and can be seen in the near identical atomic radii of aluminium and gallium, the greater electronegativity of gallium and the increase in the ionisation energies (M → M3+) of gallium relative to those of aluminium and indium (Table 1.1). A similar phenomenon exists upon descending from indium to thallium due to the so-called

2 References for this chapter begin on pg. 14 Chapter One: General Introduction

‘f-block contraction’. The f-orbitals, like the d-orbitals, are poorly shielding, leading to a greater increase in effective nuclear charge and hence, smaller changes in atomic radius, electronegativity and ionisation energies are observed upon moving from the 5th to the 6th period (Table 1.1).

Group 13 elements commonly exhibit the 3+ oxidation state, the exception being thallium which exhibits a stable 1+ oxidation state. This may be attributed to the ‘inert pair effect’. The notion of a tightly bound and inert 6s2 electron pair was first articulated by Grimm and Sommerfeld[7] and popularised by Sidgwick.[8] This theory was later challenged by Drago, who noted that the ionisation energies of the 6th period elements are inconsistent with an unreactive s electron pair.[9] Drago contended that the lower oxidation state was in fact due to a fall in intrinsic bond energy as a consequence of a decrease in the covalent contribution from the heavier elements. Schwerdtfeger later revealed that relativistic effects also contribute to this phenomenon.[10]

1.2 Group 13 Metal Hydrides

[11] Alane (aluminium trihydride) was first reported as an oligomer, [(AlH3)n], in 1939.

This was followed by reports of polymeric alane, [(AlH3)∞], and the trimethylamine [12] adduct of alane, [AlH3(NMe3)], by Stecher and Wiberg. In 1947, the ether adduct of [13] alane (Scheme 1.1, top) and [LiAlH4] were reported by Finholt. A simple route to large quantities of alane, as the THF adduct, was achieved in 1966 (Scheme 1.1, bottom).[14] Indeed, alane adducts have become very important chemical reagents in synthesis and materials science.[15]

Scheme 1.1 - Preparation of alane ether adducts[13-14]

The chemistry of gallane (gallium trihydride) has been overshadowed by that of alane due to its relative instability and difficult preparation. For instance, digallane, [16] [H2Ga(μ-H)2GaH2], was first characterised in the vapour phase in 1989. By contrast, [17] [LiGaH4] can be straightforwardly synthesised from GaCl3 and LiH. This fuelled an

3 References for this chapter begin on pg. 14 Chapter One: General Introduction

in-depth study of gallium hydride chemistry primarily focusing on the use of the trihydride species as precursors for III/V semiconductor materials.[18]

The chemistry of indane (indium trihydride) is still in its infancy. The first reported synthesis of solid indane was by Wiberg in 1957.[19] However, recent studies conducted by Andrews indicate that solid indane decomposes above 180 K, which casts doubt on [20] Wiberg’s report. The synthesis of [LiInH4] was also reported contemporaneously by [21] Wiberg. The in situ preparation of [LiInH4] was later reported by Meller, who [22] employed different conditions to those of Wiberg. Indium subhydride species, InHn (n = 1-2), have thus far only been characterised under matrix isolation conditions.[20,23]

The hydride chemistry of thallium is yet to materialise. Early reports of the preparation [24] [25] [26] of thallium hydrides by Wiberg and Kumar have not been corroborated.

Thallium hydride species, TlHn (n = 1-3), have thus far only been characterised under matrix isolation conditions.[27] The reaction of laser-ablated thallium with dihydrogen formed primarily the diatomic molecule, TlH, which subsequently dimerised upon annealing at 6.5 K. This process also produced a very low yield of TlH3 (thallane), which likely reflects the decreased stability of the 3+ oxidation state.

At-a-glance, one can see that the majority of the research conducted in this area has centred upon boron and aluminium. There is a distinct pattern in thermal stability as the group is descended. In every-case the decomposition temperatures of the three metallic species decrease in the order alane > gallane > indane. For example, the trimethylamine adduct of alane decomposes at 87 °C,[28] whilst those of gallane and indane decompose at ~ 25 °C[28] and ~ -22 °C[29] respectively. By this precedent it is easy to see that stability, and therefore the scope for investigation and the development of viable applications, considerably favours alane complexes above those of gallane and, in-turn, indane. In-order to establish legitimate applications for gallane, indane and perhaps even thallane, examples that possess thermal stabilities approaching, if not exceeding, ambient temperature must be discovered.

1.2.1 Bonding and Structure in Group 13 Trihydrides

The structural compositions of alane and gallane are outlined in Figure 1.1 (pg. 5). Alane, owing to its highly Lewis acidic metal centre, forms ‘hypercoordinate’ (coordination number > 4) complexes featuring multiple M-H-M bridges, with each

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[30] aluminium atom bound to six hydrides (Figure 1.1, A). Dialane, [H2Al(μ-H)2AlH2] has been characterised as a short-lived intermediate in the preparation of [{AlH3}n] from the reaction of laser-ablated aluminium with dihydrogen at 3.5 K under matrix isolation conditions.[31] The greater electronegativity of gallium lessens the need for gallane to form hypercoordinate complexes; thus, a tetrahedral geometry at the gallium centre is typically observed. Gallane exists as a dimer (Figure 1.1, B) in the vapour phase and a tetramer (Figure 1.1, C) in the condensed phase.[16] Infrared spectra of

[{InH3}n] display stretches due to bridging In-H bonds but lack those assignable to terminal In-H bonds. This indicates the solid-state structure of indane likely closely [20] resembles that of [{AlH3}n] (Figure 1.1, A). Diindane, [H2In(μ-H)2InH2], was [20] characterised as a short-lived intermediate in the preparation of [{InH3}n].

Figure 1.1 - Known structures of uncoordinated alane and gallane[16,30]

1.2.2 The Thermodynamics of Group 13 Hydrides

The formation of monomeric alane and gallane from their respective elements is an endothermic process and, given allowances for entropy, should not occur at room temperature (Table 1.2, pg. 6).[26] Delocalised hydride bridge formation (M-H-M) is believed to be the instrument of stabilisation for the uncoordinated lighter group 13 metallanes. Bridge bond formation is enabled by the partial donation of electron density from the electron rich hydride ligand into the empty valence p-orbital of an adjacent metal, thereby forming the so-called three centre two electron “M-H-M” bond.

5 References for this chapter begin on pg. 14 Chapter One: General Introduction

-1 ΔfHᶿ298 K (kJ mol ) Al Ga In Tl

[2] MH3 +123 +151 +222 +297

[2] M2H6 +92 +105 +175 +245

Table 1.2 - Standard enthapies of formation of group 13 hydrides

Whilst these bridges play an essential part in the structure of donor-free group 13 metallanes, they are also believed to be a likely factor in facilitating the decomposition [26] of heavier metallanes (MH3), and therefore their overall instability. It is noteworthy that In-H and Tl-H bonds are calculated to be stronger than their analogous M-C bonds (Table 1.3), and yet donor free trimethyl species of all of the group 13 metals are well authenticated and long-lived at room temperature.[26,32] The reason for this disparity is thought to hinge on the formation strong M-X-M bridges in group 13 trihydrides (X = H) relative to their trimethyl counterparts (X = Me).

Mean Bond Enthalpy (kJ mol-1) Al Ga In Tl

M-H[2] 282 260 225a 180a

M-C[2] 280 245 162 125

Table 1.3 - Mean bond enthalpies of group 13 trihydride and trimethyl species a Calculated bond values[10,33]

It has been proposed that an associative transition state, preceding the concerted elimination of H2 (Scheme 1.2, pg. 7), provides a lower barrier to decomposition than a dissociative mechanism.[26] This is consistent with the greater stability of group 13 trimethyl species relative to their trihydride counterparts despite of the inferior strength of M-C bonds vis-à-vis M-H bonds. Thus the stabilisation of the heavier group 13 hydrides may be achieved (i) electronically by the coordination of strongly Lewis basic, and (ii) sterically by the use of bulky ligands that spatially frustrate the formation of M-H-M bridges.

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Scheme 1.2 - Proposed decomposition pathway of heavy group 13 hydride complexes[34]

1.2.3 Lewis Base Adducts of Group 13 Trihydrides

The unoccupied p-orbital of monomeric group 13 trihydrides gives rise to their Lewis acidity. Due to the respective electronegativities of the group 13 elements, the Lewis acidity of alane is greater than that of gallane, and by this rationale, irrespective of the electronegativity scale used, indane exhibits intermediate Lewis acidity to those of alane and gallane.[3]

Lewis base adducts of alane and gallane were first studied in the 1960s.[35] This area of research remained dormant until the 1990s, when a considerable amount of research on the structure, synthesis and reactivity of Lewis base adduct complexes of alane and gallane was undertaken by Atwood and Raston.[28,36] More recently, a number of Lewis base adducts of indane have been synthesised by Jones and their reactivities have likewise been explored.[37]

The coordination chemistries of alane and gallane display one striking feature; both entities can display differing coordination when provided with the same ligand environment.[28,36a] Due to its greater Lewis acidity, a 1:1 alane Lewis base complex may form intermolecular hydride bridges to satisfy electronic demands.[38] By contrast, 1:1 gallane Lewis base complexes do not feature intermolecular hydride bridges and typically maintain a tetrahedral geometry about the gallium centre.[28] The few reported 1:1 indane Lewis base complexes stable enough to be crystallographically characterised are monomeric and display a tetrahedral coordination geometry at indium.[37]

The greater Lewis acidity of alane also enables the formation of very stable 2:1 Lewis [39] base complexes, e.g. [AlH3(NMe3)2]. 2:1 Lewis base complexes of gallane can be prepared but, in contrast to alane, the second Lewis base remains labile. For example, [16b] [GaH3(NMe3)2] loses an equivalent of NMe3 above -23 °C. A 2:1 phosphine adduct

7 References for this chapter begin on pg. 14 Chapter One: General Introduction

of indane has been prepared but demonstrates decreased thermal stability over its 1:1 analogue.[40]

In contemporary chemistry, N-heterocyclic carbenes (NHCs) have featured prominently as superior support ligands to phosphines and amines in transition metal catalysis.[41] The facile steric variation of the NHC N-substituent, coupled with the high nucleophilicity of the carbenic position make these species an attractive ligand for group 13 hydride stabilisation. This was realised by the considerable enhancement in metallane thermal stability afforded by the NHC 1,3-bis(2,4,6- trimethylphenyl)imidazol-2-ylidene (IMes) (Figure 1.2).[42] These adducts remain the most thermally stable group 13 trihydride complexes reported to date.

Figure 1.2 - Group 13 trihydride complexes coordinated by IMes[42]

1.2.4 Group 13 Halohydride Chemistry

Substitution of one or two hydride ligands with a substituent of greater electronegativity, usually a halide, can be used as an alternative method for group 13 hydride stabilisation. The substitution of hydrides for halides results in increased bond enthalpies to the remaining M-H bonds due to inductive polarisation of the MXn core.[43] As the thermal decomposition of lighter group 13 Lewis base adducts is thought to be principally initiated by Lewis base dissociation,[44] the increased Lewis acidity of group 13 halohydrides serves to improve the thermal and aerobic stability of the halohydride relative to its trihydride counterpart (Figure 1.3, pg. 9). The greater Lewis acidity of group 13 halohydrides also promotes further ligand coordination, with 2:1 Lewis base adducts of halogallohydrides readily isolable.[45]

8 References for this chapter begin on pg. 14 Chapter One: General Introduction

Figure 1.3 - The solid-state thermal stabilities of tricyclohexylphosphine adducts of chlorogallanes[43]

The halides in group 13 halohydrides also provide a site for derivatisation through salt metathesis, a pathway not typically accessible to metallanes.[46] A large number of novel gallium hydride complexes have been synthesised in this manner.[44] Of significant note is the catalogue of single source precursors for the synthesis of industrially important III/V semiconductor materials, vide infra.

Synthetic protocols for haloalanes were first reported in the 1950s and 60s.[47] However, it wasn’t until recently that more general protocols were developed.[42b,48] Synthetic protocols for halogallanes were developed in 1965 by Greenwood[49] and Schmidbaur.[50] Thus far only two haloindanes have been reported.[42c,51] A comprehensive review of synthetic routes to group 13 halometallanes has been compiled.[44]

1.2.5 Anionic Donor Complexes of Group 13 Hydrides

Sterically demanding anionic donor ligands have been established as exceptional ligands for the stabilisation of reactive, typically thermodynamically unstable, d-, p- and f-block complexes.[52] Notable examples include the isolation of complexes containing a M-M quintuple bond,[53] where M is chromium[54] and molybdenum.[55]

Kinetic stabilisation of group 13 hydrides has been achieved by the coordination of bulky monoanionic N,Nʹ-ligands. These ligands sterically enshroud the metal centre, thus frustrating the M-H-M interactions that facilitate the decomposition of heavier metal hydrides, vide supra. For example, the incorporation of formamidinate ligands led to the isolation of thermally robust aluminium, gallium and indium hydride complexes (Figure 1.4, pg. 10).[56] Building upon this theme, previous research in our group employed sterically demanding triazenide ligands to prepare the most thermally stable aluminium hydride complex reported to date (Figure 1.5, pg. 10).[57]

9 References for this chapter begin on pg. 14 Chapter One: General Introduction

Figure 1.4 - Bis(formamidinate) group 13 hydride complexes[56]

Figure 1.5 - Bis(triazenide)aluminium hydride complex[57]

1.3 Industrial Applications of Group 13 Hydrides

1.3.1 Semiconductor Materials

Materials derived from group 13 and group 15 elements (III/V materials) are technologically important for semiconductor containing devices.[15] These materials can be found in solid-state optoelectronic devices such as light-emitting diodes (LEDs), liquid crystal displays (LCDs), lasers, and microwave circuits.[1,58] III/V materials extend the range of silicon semiconductor applications to microwave and optical devices, which cannot be accessed with silicon alone.[1] Gallium III/V semiconductor materials (e.g. GaN, GaP, GaAs) achieve a much higher electron drift velocity than silicon at specific temperatures, and therefore achieve faster electronic operational speeds, which makes these materials ideal for use in ultra-high frequency transistors. These materials are frequently prepared on an industrial scale from group 13 trialkyls and high stoichiometric excesses of the group 15 binary hydride (typically 2000:1) at high temperatures and pressures.[59] The trialkyl precursor, when handled at these high temperatures, often decomposes resulting in the final material’s electronic efficiency being limited by carbon contamination.[15] Owing to their reduced carbon content and

10 References for this chapter begin on pg. 14 Chapter One: General Introduction

low temperature of decomposition, group 13 metallanes have been extensively investigated as alternative precursors to trialkyls and, in most studies, found to be superior.[18,60] To date, this has not translated to their incorporation in industrial preparations of III/V materials.[59,61]

Recently, a very efficient synthesis of III/V materials has been developed utilising single source III/V precursors. These precursors contain both the group 13 and group 15 elements in a 1:1 ratio and directly bonded.[62] These precursors are (i) typically prepared through functionalisation of halometallanes, (ii) have greater aerobic stability than group 13 metal trialkyls and (iii) lower toxicity than group 13 metal trialkyls. The resultant materials are formed at significantly lower temperatures with lower carbon contamination.[15,63]

1.3.2 Organic Functional Group Reductions

Group 13 hydride complexes have a rich history as organic functional group reducing agents, the most common being sodium tetrahydridoborate, [NaBH4], and lithium [14,64] tetrahydridoaluminate, [LiAlH4]. These compounds inspired the next generation of

‘ate’ reducing agents, such as [LiAl(OEt)3H], which can deliver a high degree of selectivity and control to organic substrate reduction.[14,65] It is now commonly accepted that group 13 hydride complexes are an essential tool in the arsenal of organic chemists. The analogous reactivities of alane Lewis base adducts have been studied by Wyatt[66] and Park.[67] More recently Raston and Jones have extended these studies to gallane and indane respectively.[36b,68] Several intermediates were isolated during the course of these studies, and these have allowed the hydride transfer mechanism to be better understood.[36b]

The reactivities and selectivities of alane, gallane and indane Lewis base adducts vary quite widely. For example, [AlH3(NMe3)] reduces ethylbenzoate to benzyl alcohol, [36b,68] whilst [GaH3(NMe3)] and [InH3(PCy3)] do not react with esters. The reduction of 2,4’-dibromoacetophenone by group 13 metallane complexes affords mixtures of 1-(4-bromophenyl)-2-bromoethanol or 1-(4-bromophenyl)ethanol (Scheme 1.3, pg. 12),[36b,68] the selectivity of which may be rationalised on the grounds of the electronegativity of the metal and thus the polarity of the M-H bonds of group 13 trihydride adduct; Al > In > Ga (Table 1.1).

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Scheme 1.3 - Reduction of 2,4’-dibromoacetophenone by group 13 trihydride adducts[36b,68]

1.4 Low Oxidation State Group 13 Chemistry

1.4.1 Synthesis

In the 1950s and 60s it was reported that gallium and indium trihalides can be reduced [69] by the respective elemental metal to afford the corresponding MX2 species. Structural and raman spectroscopy studies later demonstrated that the binary dihalides of gallium + - [70] and indium were in fact ionic species of composition [M ][MX4] , and that the addition of either neutral or anionic donor ligands invariably afforded M(II) species [71] with a M-M bond. Similarly, the low oxidation state gallium halide Ga2I3 was found + 2- [72] + 3- to be [Ga ]2[Ga2I6] , whilst In2Cl3 and Tl2Cl3 were found to be [In ]3[InCl6] and + 3- [73] [Tl ]3[TlCl6] respectively.

The binary monohalides of indium, InX, can be synthesised by various routes; the reaction of indium metal with the appropriate elemental halogen or aqueous hydrogen halide,[74] transmetallation[75] or the reduction of a higher oxidation state indium halide.[76]

Early studies showed that gallium(I) halides (GaX) are not thermodynamically stable under standard conditions, disproportionating to gallium metal and gallium(III) halides.[77] To overcome this problem a specialised technique was developed by Schnöckel that enables the preparation of gram quantities of ‘metastable’ donor stabilised complexes of gallium monohalides; [{GaX(L)}n], where X = Cl, Br or I; and L = ether, amine or phosphine, and this was extended to their aluminium counterparts.[77a,78] This method relies on the fact that monovalent aluminium and gallium halides are thermodynamically stable at temperatures above 1000 °C and thus

12 References for this chapter begin on pg. 14 Chapter One: General Introduction

accessible when HX gas is passed over molten aluminium or gallium at 800-1000 °C in an evacuated reactor. The generated MIX is co-condensed on the reactor walls, which are cooled by liquid nitrogen, with a carrier arene solvent and the Lewis base. Upon melting of the frozen condensate, arene solutions of the metal(I) species can be isolated, and depending on the donor and the halide, these solutions can be stored for extended periods. Thus far, three of these “MIX(L)” systems have been crystallographically characterised.[79] It should be noted that the addition of some donor molecules results in partial disproportionation and the formation of metal(II) compounds.[80] Controlled disproportionations of these ‘metastable’ aluminium(I) and gallium(I) solutions have afforded a range of cluster compounds.[77b,81]

1.4.2 Chemistry

The contemporary development of synthetic routes to low oxidation state group 13 halides has ignited a substantial level of interest in the area, with particular focus on the development of stabilising ligands and complexes that exhibit multiple metal-metal bonding character.[82]

2,6-Terphenyl ligands represent just one of the many ligand varieties that have been employed. These have been used to isolate short Ga-Ga bonds (Figure 1.6, left)[83] and the first singly coordinated group 13 metal(I) complex (Figure 1.6, right).[84] This area has been highlighted recently by a number of excellent review articles.[85]

Figure 1.6 - Some representative terphenyl stabilised low oxidation state group 13 species[83-84]

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1.5 References

[1] Chemistry of Aluminium, Gallium, Indium and Thallium, Ed. Downs, A. J., 1993, Blackie Academic and Professional: Glasgow, UK. [2] The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, Eds. Downs, A. J.; Aldridge, S., 2011, John Wiley & Sons, Ltd: Chichester, UK. [3] The Elements, Emsley, J., 1991, Clarendon Press: Oxford, UK. [4] Periodicity and the s- and p-Block Elements, Norman, N. C., 1997, Oxford University Press: Oxford, UK. [5] Häuermann, U.; Lidin, S.; Simak, S. I.; Abrikosov, I. A., Chem. Eur. J. 1997, 3, 904-911. [6] Himmel, H.-J.; Gaertner, B., Chem. Eur. J. 2004, 10, 5936-5941. [7] Grimm, H. G.; Sommerfeld, A., Z. Phys. 1926, 36, 36-59. [8] The Electronic Theory of Valence, Sidgwick, N. V., 1927, Oxford University Press: Oxford, UK. [9] Drago, R. S., J. Phys. Chem. 1958, 62, 353-357. [10] Schwerdtfeger, P.; Heath, G. A.; Dolg, M.; Bennett, M. A., J. Am. Chem. Soc. 1992, 114, 7518-7527. [11] Cucinella, S.; Mazzei, A.; Marconi, W., Inorg. Chim. Acta Rev. 1970, 4, 51-71. [12] Stecher, O.; Wiberg, E., Ber. Dtsch. Chem. Ges. 1942, 75, 2003-2012. [13] Finholt, A. E.; Bond, A. C.; Schlesinger, H. I., J. Am. Chem. Soc. 1947, 69, 1199-1203. [14] Brown, H. C.; Yoon, N. M., J. Am. Chem. Soc. 1966, 88, 1464-1472. [15] Jegier, J. A.; Gladfelter, W. L., Coord. Chem. Rev. 2000, 206, 631-650. [16] (a) Downs, A. J.; Goode, M. J.; Pulham, C. R., J. Am. Chem. Soc. 1989, 111, 1936-1937; (b) Pulham, C. R.; Downs, A. J.; Goode, M. J.; Rankin, D. W. H.; Robertson, H. E., J. Am. Chem. Soc. 1991, 113, 5149-5162; (c) Souter, P. F.; Andrews, L.; Downs, A. J.; Greene, T. M.; Ma, B. Y.; Schaefer, H. F., J. Phys. Chem. 1994, 98, 12824-12827. [17] (a) Zakharkin, L. I.; Gavrilenko, V. V.; Karaksin, Y. N., Synth. React. Inorg. Met.-Org. Chem. 1971, 1, 37-43; (b) Shirk, A. E.; Shriver, D. F. In Inorganic Syntheses, Vol. 17, pp. 45-47, 1977, John Wiley & Sons, Inc.: New York, USA. [18] Gladfelter, W. L.; Boyd, D. C.; Jensen, K. F., Chem. Mater. 1989, 1, 339-343. 14

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[19] Wiberg, E.; Dittmann, O.; Noth, H.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 56-57. [20] Andrews, L.; Wang, X., Angew. Chem. Int. Ed. 2004, 43, 1706-1709. [21] Wiberg, E.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 54-55. [22] Kummel, C.; Meller, A.; Noltemeyer, M., Z. Naturforsch., Teil B 1996, 51, 209- 219. [23] (a) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P., J. Am. Chem. Soc. 2002, 124, 4448-4457; (b) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P., Angew. Chem. Int. Ed. 2002, 41, 796-799. [24] Wiberg, E.; Dittmann, O.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 60-61. [25] Kumar, N.; Sharma, R. K., J. Inorg. Nucl. Chem. 1974, 36, 2625-2626. [26] Downs, A. J.; Pulham, C. R., Chem. Soc. Rev. 1994, 23, 175-184. [27] Wang, X.; Andrews, L., J. Phys. Chem. A 2004, 108, 3396-3402. [28] Jones, C.; Koutsantonis, G. A.; Raston, C. L., Polyhedron 1993, 12, 1829-1848. [29] Hibbs, D. E.; Hursthouse, M. B.; Jones, C.; Smithies, N. A., Chem. Commun. 1998, 869-870. [30] Turley, J. W.; Rinn, H. W., Inorg. Chem. 1969, 8, 18-22. [31] Andrews, L.; Wang, X., Science 2003, 299, 2049-2052. [32] Boese, R.; Downs, A. J.; Greene, T. M.; Hall, A. W.; Morrison, C. A.; Parsons, S., Organometallics 2003, 22, 2450-2457. [33] Balasubramanian, K.; Tao, J. X., J. Chem. Phys. 1991, 94, 3000-3010. [34] Furfari, S. K., PhD Thesis, University of New South Wales, 2014. [35] (a) Ruff, J. K.; Hawthorne, M. F., J. Am. Chem. Soc. 1960, 82, 2141-2144; (b) Ruff, J. K., J. Am. Chem. Soc. 1961, 83, 1798-1800; (c) Ashby, E. C., J. Am. Chem. Soc. 1964, 86, 1882-1883; (d) Greenwood, N. N.; Storr, A.; Wallbridge, M. G. H., Inorg. Chem. 1963, 2, 1036-1039; (e) Greenwood, N. N.; Ross, E. J. F.; Storr, A., J. Chem. Soc. 1965, 1400-1406. [36] (a) Raston, C. L., J. Organomet. Chem. 1994, 475, 15-24; (b) Raston, C. L.; Siu, A. F. H.; Tranter, C. J.; Young, D. J., Tetrahedron Lett. 1994, 35, 5915-5918; (c) Gardiner, M. G.; Raston, C. L., Coord. Chem. Rev. 1997, 166, 1-34. [37] Jones, C., Chem. Commun. 2001, 2293-2298. [38] Atwood, J. L.; Bennett, F. R.; Elms, F. M.; Jones, C.; Raston, C. L.; Robinson, K. D., J. Am. Chem. Soc. 1991, 113, 8183-8185.

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[39] (a) Wiberg, E.; Graf, H.; Schmidt, M.; Lacal, R. U., Z. Naturforsch., Teil B 1952, 7, 578-579; (b) Peters, F. M., Can. J. Chem. 1964, 42, 1755-1758. [40] Cole, M. L.; Hibbs, D. E.; Jones, C.; Smithies, N. A., J. Chem. Soc., Dalton Trans. 2000, 545-550. [41] (a) N-Heterocyclic Carbenes in Synthesis, Ed. Nolan, S. P., 2006, Wiley-VCH: Weinheim, Germany; (b) de Fremont, P.; Marion, N.; Nolan, S. P., Coord. Chem. Rev. 2009, 253, 862-892; (c) Kirmse, W., Angew. Chem. Int. Ed. 2010, 49, 2-6; (d) N-Heterocyclic Carbenes in Transition Metal Catalysis, Glorius, F., 2007, Springer: New York, USA. [42] (a) Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F., J. Am. Chem. Soc. 1992, 114, 9724-9725; (b) Alexander, S. G.; Cole, M. L.; Forsyth, C. M., Chem. Eur. J. 2009, 15, 9201-9214; (c) Abernethy, C. D.; Cole, M. L.; Jones, C., Organometallics 2000, 19, 4852-4857. [43] (a) Atwood, J. L.; Robinson, K. D.; Bennett, F. R.; Elms, F. M.; Koutsantonis, G. A.; Raston, C. L.; Young, D. J., Inorg. Chem. 1992, 31, 2673-2674; (b) Elms, F. M.; Koutsantonis, G. A.; Raston, C. L., J. Chem. Soc., Chem. Commun. 1995, 1669-1670. [44] Alexander, S. G.; Cole, M. L., Eur. J. Inorg. Chem. 2008, 4493-4506. [45] Luo, B.; G. Young Jr, V.; L. Gladfelter, W., Chem. Commun. 1999, 123-124. [46] Luo, B.; Young, V. G.; Gladfelter, W. L., Inorg. Chem. 2000, 39, 1705-1709. [47] (a) Wiberg, E.; Lacal, R. U., Rev. Acad. Sci. Exact. Fis.-Quim. Nat. Zaragoza 1954, 9, 91-94; (b) Wiberg, E.; Lacal, R. U., Rev. Acad. Sci. Exact. Fis.-Quim. Nat. Zaragoza 1954, 9, 94-95; (c) Wiberg, E.; Lacal, R. U., Rev. Acad. Sci. Exact. Fis.-Quim. Nat. Zaragoza 1955, 10, 97-100; (d) Ashby, E. C.; Prather, J., J. Am. Chem. Soc. 1966, 88, 729-733; (e) Schmidt, D. L.; Flagg, E. E., Inorg. Chem. 1967, 6, 1262-1265. [48] Ganesamoorthy, C.; Loerke, S.; Gemel, C.; Jerabek, P.; Winter, M.; Frenking, G.; Fischer, R. A., Chem. Commun. 2013, 49, 2858-2860. [49] Greenwood, N. N.; Storr, A., J. Chem. Soc. 1965, 3426-3433. [50] Schmidbaur, H.; Findeiss, W.; Gast, E., Angew. Chem. Int. Ed. 1965, 4, 152- 152. [51] Cole, M. L.; Jones, C.; Kloth, M., Inorg. Chem. 2005, 44, 4909-4911.

16

Chapter One: General Introduction

[52] (a) Jones, C., Coord. Chem. Rev. 2010, 254, 1273-1289; (b) Fischer, R. C.; Power, P. P., Chem. Rev. 2010, 110, 3877-3923; (c) Tsai, Y.-C., Coord. Chem. Rev. 2012, 256, 722-758. [53] (a) Noor, A.; Kempe, R., Chem. Rec. 2010, 10, 413-416; (b) Wagner, F. R.; Noor, A.; Kempe, R., Nat. Chem. 2009, 1, 529-536. [54] (a) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P., Science 2005, 310, 844-847; (b) Hsu, C.-W.; Yu, J.-S. K.; Yen, C.-H.; Lee, G.-H.; Wang, Y.; Tsai, Y.-C., Angew. Chem. 2008, 120, 10081-10084; (c) Tsai, Y.-C.; Hsu, C.-W.; Yu, J.-S. K.; Lee, G.-H.; Wang, Y.; Kuo, T.-S., Angew. Chem. Int. Ed. 2008, 47, 7250-7253; (d) Kreisel, K. A.; Yap, G. P. A.; Dmitrenko, O.; Landis, C. R.; Theopold, K. H., J. Am. Chem. Soc. 2007, 129, 14162-14163; (e) Noor, A.; Wagner, F. R.; Kempe, R., Angew. Chem. Int. Ed. 2008, 47, 7246-7249. [55] Tsai, Y.-C.; Chen, H.-Z.; Chang, C.-C.; Yu, J.-S. K.; Lee, G.-H.; Wang, Y.; Kuo, T.-S., J. Am. Chem. Soc. 2009, 131, 12534-12535. [56] (a) Baker, R. J.; Jones, C.; Junk, P. C.; Kloth, M., Angew. Chem. Int. Ed. 2004, 43, 3852-3855; (b) Cole, M. L.; Jones, C.; Junk, P. C.; Kloth, M.; Stasch, A., Chem. Eur. J. 2005, 11, 4482-4491. [57] Alexander, S. G.; Cole, M. L.; Forsyth, C. M.; Furfari, S. K.; Konstas, K., Dalton Trans. 2009, 2326-2336. [58] (a) McKillop, A.; Hunt, J. D.; Taylor, E. C., J. Organomet. Chem. 1970, 24, 77- 88; (b) Chopra, K. L.; Major, S.; Pandya, D. K., Thin Solid Films 1983, 102, 1- 46. [59] Malik, M. A.; Afzaal, M.; O’Brien, P., Chem. Rev. 2010, 110, 4417-4446. [60] (a) Wee, A. T. S.; Murrell, A. J.; Singh, N. K.; O'Hare, D.; Foord, J. S., J. Chem. Soc., Chem. Commun. 1990, 11-13; (b) Dubois, L. H.; Zegarski, B. R.; Gross, M. E.; Nuzzo, R. G., Surf. Sci. 1991, 244, 89-95. [61] Malik, M. A.; O'Brien, P. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 612-653, 2011, John Wiley & Sons, Ltd: Chichester, UK. [62] Jones, A. C., Chem. Soc. Rev. 1997, 26, 101-110. [63] Cowley, A. H.; Jones, R. A., Polyhedron 1994, 13, 1149-1157.

17

Chapter One: General Introduction

[64] (a) Brown, H. C.; McFarlin, R. F., J. Am. Chem. Soc. 1958, 80, 5372-5376; (b) Brown, H. C.; Weissman, P. M.; Yoon, N. M., J. Am. Chem. Soc. 1966, 88, 1458-1463; (c) Yoon, N. M.; Brown, H. C., J. Am. Chem. Soc. 1968, 90, 2927- 2938. [65] Brown, H. C.; Weissman, P. M., J. Am. Chem. Soc. 1965, 87, 5614-5620. [66] Griffin, S.; Heath, L.; Wyatt, P., Tetrahedron Lett. 1998, 39, 4405-4406. [67] Marlett, E. M.; Park, W. S., J. Org. Chem. 1990, 55, 2968-2969. [68] Abernethy, C. D.; Cole, M. L.; Davies, A. J.; Jones, C., Tetrahedron Lett. 2000, 41, 7567-7570. [69] Klemm, W.; Tilk, W., Z. Anorg. Allg. Chem. 1932, 207, 161-174. [70] (a) Garton, G.; Powell, H. M., J. Inorg. Nucl. Chem. 1957, 4, 84-89; (b) Corbett, J. D.; Hershaft, A., J. Am. Chem. Soc. 1958, 80, 1530-1532; (c) McMullan, R. K.; Corbett, J. D., J. Am. Chem. Soc. 1958, 80, 4761-4764; (d) Woodward, L. A.; Greenwood, N. N.; Hall, J. R.; Worrall, I. J., J. Chem. Soc. 1958, 1505-1508; (e) Clark, R. J.; Griswold, E.; Kleinberg, J., J. Am. Chem. Soc. 1958, 80, 4764- 4767; (f) Carlston, R. C.; Griswold, E.; Kleinberg, J., J. Am. Chem. Soc. 1958, 80, 1532-1534. [71] (a) Beamish, J. C.; Small, R. W. H.; Worrall, I. J., Inorg. Chem. 1979, 18, 220- 223; (b) Wei, P.; Li, X.-W.; Robinson, G. H., Chem. Commun. 1999, 1287- 1288; (c) Nogai, S.; Schmidbaur, H., Inorg. Chem. 2002, 41, 4770-4774; (d) Ali, S. M.; Brewer, F. M.; Chadwick, J.; Garton, G., J. Inorg. Nucl. Chem. 1959, 9, 124-135. [72] Gerlach, G.; Honle, W.; Simon, A., Z. Anorg. Allg. Chem. 1982, 486, 7-21. [73] (a) Meyer, G., Z. Anorg. Allg. Chem. 1981, 478, 39-51; (b) Staffel, T.; Meyer, G., Naturwissenschaften 1987, 74, 491-492; (c) Boehme, R.; Rath, J.; Grunwald, B.; Thiele, G., Z. Naturforsch., Teil B 1980, 35, 1366-72; (d) Ackermann, R.; Hirschle, C.; Rotter, H. W.; Thiele, G., Z. Anorg. Allg. Chem. 2002, 628, 2675- 2682. [74] (a) Meyer, G.; Staffel, T., Z. Anorg. Allg. Chem. 1989, 574, 114-118; (b) Smith, F. J.; Barrow, R. F., Trans. Faraday Soc. 1955, 51, 1478-1480; (c) Dronskowski, R., Inorg. Chem. 1994, 33, 5960-5963. [75] Clark, R. J.; Griswold, E.; Kleinberg, J. In Inorganic Syntheses, Vol. 7, pp. 18- 21, 1963, John Wiley & Sons, Inc.: New York, USA.

18

Chapter One: General Introduction

[76] (a) Freeland, B. H.; Tuck, D. G., Inorg. Chem. 1976, 15, 475-476; (b) Goggin, P. L.; McColm, I. J., J. Inorg. Nucl. Chem. 1966, 28, 2501-2505. [77] (a) Dohmeier, C.; Loos, D.; Schnöckel, H., Angew. Chem. Int. Ed. Engl. 1996, 35, 129-149; (b) Schnöckel, H.; Schnepf, A. In Advances in Organometallic Chemistry, Vol. 47, pp. 235-281, 2001, Elsevier: Amsterdam, Netherlands. [78] (a) Ecker, A.; Schnöckel, H., Z. Anorg. Allg. Chem. 1996, 622, 149-152; (b) Ecker, A.; Schnöckel, H., Z. Anorg. Allg. Chem. 1998, 624, 813-816; (c) Tacke, M.; Schnöckel, H., Inorg. Chem. 1989, 28, 2895-2896. [79] (a) Doriat, C. U.; Friesen, M.; Baum, E.; Ecker, A.; Schnöckel, H., Angew. Chem. Int. Ed. 1997, 36, 1969-1971; (b) Duan, T.; Stößer, G.; Schnöckel, H., Angew. Chem. Int. Ed. 2005, 44, 2973-2975; (c) Mocker, M.; Robl, C.; Schnöckel, H., Angew. Chem. Int. Ed. Engl. 1994, 33, 1754-1755. [80] Mocker, M.; Robl, C.; Schnöckel, H., Angew. Chem. Int. Ed. Engl. 1994, 33, 862-863. [81] (a) Ecker, A.; Weckert, E.; Schnöckel, H., Nature 1997, 387, 379-381; (b) Schnepf, A.; Schnöckel, H., Angew. Chem. Int. Ed. 2001, 40, 712-715; (c) Klemp, C.; Bruns, M.; Gauss, J.; Haussermann, U.; Stosser, G.; van Wullen, L.; Jansen, M.; Schnöckel, H., J. Am. Chem. Soc. 2001, 123, 9099-9106; (d) Kohnlein, H.; Purath, A.; Klemp, C.; Baum, E.; Krossing, I.; Stosser, G.; Schnöckel, H., Inorg. Chem. 2001, 40, 4830-4838; (e) Loos, D.; Schnöckel, H.; Fenske, D., Angew. Chem. Int. Ed. Engl. 1993, 32, 1059-1060. [82] Murugavel, R.; Chandrasekhar, V., Angew. Chem. Int. Ed. 1999, 38, 1211-1215. [83] Su, J.; Li, X.-W.; Crittendon, R. C.; Robinson, G. H., J. Am. Chem. Soc. 1997, 119, 5471-5472. [84] Niemeyer, M.; Power, P. P., Angew. Chem. Int. Ed. 1998, 37, 1277-1279. [85] (a) Uhl, W.; Layh, M. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 246-284, 2011, John Wiley & Sons, Ltd: Chichester, UK; (b) Jones, C.; Stasch, A. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 285-341, 2011, John Wiley & Sons, Ltd: Chichester, UK; (c) Cooper, B. F. T.; Macdonald, C. L. B. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 342- 401, 2011, John Wiley & Sons, Ltd: Chichester, UK; (d) Schnöckel, H.;

19

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Schnepf, A. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 402-487, 2011, John Wiley & Sons, Ltd: Chichester, UK.

20

Chapter Two: Quantification of the Steric and Electronic Character of Monoanionic Bidentate N,Nʹ-Ligands

2.1 Introduction

The development of new ligands is an important and ongoing activity in academic and industrial chemistry. A key undertaking in ligand design is the ability to effect control of the ligand’s steric properties by means of careful tuning. To this end, the popularity of chelating monoanionic N,Nʹ-ligands has surged in the last decade.[1] The importance of these ligands has been realised through the development of applications in synthetic,[2] materials[3] and catalytic chemistry.[1] While there are numerous methods to quantify a ligand’s steric character such as cone angle,[4] solid angle[5] and molecular volume,[6] to date no global single steric measure has been developed to quantify the steric character of these bidentate ligands.

2.1.1 Cone Angle

The quantification of ligand sterics was first comprehensively examined by Tolman, who observed that the relative rate of substitution of many tertiary phosphine coordinated metal complexes, was dependent on the steric character of the included phosphine ligand(s).[4,7] Using this observation, Tolman developed the Cone Angle model to measure the steric profile of phosphines (Figure 2.1, pg. 22). For a phosphorus ligand, the cone angle θ is defined as the apex angle of a cylindrical cone, with origin

2.28 Å (the standard Ni-P bond length in [Ni(CO)3(L)] complexes) from the centre of the phosphorus atom and the lateral surface of the cone tangentially intersecting the van der Waals surfaces of the outermost atoms of the phosphine’s substituents. Tolman constructed space-filling (CPK) models of various phosphines and measured their cone angles by eye using a protractor. In cases where a variety of conformations of the groups bound to phosphorus were possible, the groups were folded back to give the smallest possible cone angle while still maintaining a nominal C3 symmetry about the Ni-P axis.

21 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.1 - Representation of the cone angle direct from Tolman’s report[8]

Subsequent determination of θ using X-ray crystal structures of related transition metal phosphine complexes led to θ values that correlated well with those obtained from the CPK model.[9] Due to the simplicity of Tolman’s concept it has been widely applied when quantifying the steric properties of ligands, such as phosphites,[8] arsines,[8] amines,[10] isonitriles,[11] η6-aryls,[12] η5-cyclopentadienyls[8,12-13] and alkyls.[14]

However, it is not generally applicable to ligands that lack C3 or higher symmetry, i.e. those ligands for which a “cone” is an inadequate representation.

2.1.2 Solid Angle

In the late 1970s, it was observed that for some ligands, e.g. PCy3, the cone angle can show significant variability upon rotation about the M-P axis (ϕ) (Figure 2.2, pg. 23).[9] These observations led to the development of the “ligand profile” concept which was independently reported by Mullica,[15] Oliver[16] and Stepaniak.[17] The ligand profile θ expresses the semicone angle ( /2) of a ligand as a function of rotation around the M-P bond (ϕ) (Figure 2.3, pg. 23). The ligand profile provides a more thorough description of the varied steric character of a ligand about the M-P axis rather than the single number by Tolman.

22 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.2 - Schematical representation of the semicone angle of a phosphine[18]

[9] Figure 2.3 - Representitive ligand profile of PCy3

Immirzi and Musco built upon the ligand profile concept by suggesting the steric bulk of an unsymmetrical phosphine could be quantified using a solid angle measurement.[5] The solid angle (Ω) of a ligand about a point can be most easily visualised by imagining a point light source at the centre of the metal atom, or point of interest, creating a shadow of the ligand on a sphere with its centre at the metal (Figure 2.4, pg. 24). The area of the shadow divided by the cube of the radius of the enveloping sphere gives the ligand’s solid angle, which is measured in steradians (Equation 2.1, pg. 24). Importantly, with reference to the molecular volumes method vide infra, the sphere used is sufficiently large to encompass the entire metal complex and the peripheral functional groups of the ligand. The advantage of this method of steric measurement is that it is more generally applicable than the cone angle and can be used to determine ligand-ligand overlap in terms of ligand intermeshing through overlapping solid angles.

23 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.4 - Schematic representation of the cone (θ) and solid (Ω) angles[19]

퐫̂ ∙ 푑푺 훺 = ∫ 3 푠 푟

Equation 2.1 - Definition of the solid angle

The Ω parameter can be used to calculate a ligand’s equivalent cone angle (훩̅) by constructing a circular spherical cap with the same overall solid angle (Equation 2.2). This enables Ω parameters to be compared to θ parameters.[5]

360 훺 훩̅ = 푐표푠−1 (1 − ) 휋 2휋

Equation 2.2 - Calculation of the equivalent cone angle

Over the years the methods for measuring Ω have evolved significantly, such to eliminate problems associated with substituent conformation, ligand meshing and ligand asymmetry, which have all plagued the simplistic cone angle model.[20] For the purpose of kinetic modelling, Hirota introduced the relative solid angle parameter, Ωs, which is [21] Ω divided by the total surface area of the sphere (Equation 2.3, pg. 25). The Ωs parameter is entropic in nature and measures the probability that an incoming nucleophile not be able to access the metal centre due to blocking by the ligand of interest. Owing to the general applicability of the relative solid angle methodology, and its use of non-steradian units, a ligand’s steric character is now more commonly represented as a Ωs parameter rather than a 훩̅ parameter. Indeed, Hirota has calculated

24 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Ωs parameters of various alkyl and aryl groups and has found an excellent correlation to [22] the Taft-Dubois steric parameter Es'.

훺 훺 = ≈ 0.0796훺 s 4휋

Equation 2.3 - Calculation of the relative solid angle

In developing Hirota’s relative solid angle parameter, Wendt and Guzei have proposed [23] that Ωs parameters be expressed as percentages, called G parameters. To facilitate [24] this, they developed the computer program Solid-G to calculate Ωs and G parameters from crystal structure and/or molecular modelling data. Solid-G calculations use zero [25] energy point atomic radii (Rz), and have since been used to quantify the steric profile of a number of monodentate anionic ligands.[26] It is noteworthy that Solid-G can calculate the coordination sphere shielded by more than one ligand (Gγ) and unfavourable overlaps cf. Chapter Seven. Allen has expanded upon this by developing a new solid angle algorithm from which Ωs parameters could be calculated using Rz or [20c,27] van der Waals radii (RvdW). This algorithm, named FindSolidAngle, is available in the form of a package[28] for the computational software program Mathematica.[29]

2.1.3 Molecular Volumes

Although the cone angle has been proven to be extremely effective in describing the steric properties of phosphines, it became evident that it was not as effective when describing the steric properties of the emerging N-heterocyclic carbene class of ligands

(NHCs). This is due to NHCs having a C2 or lesser symmetry about the M-CNHC bond. To address this, Cavallo introduced a new steric parameter; the percentage buried [6] volume, %VBur or V. This parameter is analogous to G (and Ωs) in that it measures the probability of an incoming nucleophile being blocked on approach to a metal centre. However, in contrast to G, Cavallo’s parameter is based on the volume of the metal’s [30] coordination sphere occupied by the ligand (Figure 2.5, pg. 26). According to %VBur, the metal’s coordination sphere is defined as a sphere, typically of radius 3.5 Å, centred at the metal, and the V parameter of a ligand is the percentage of the sphere’s volume 1 occupied by the ligand (Equation 2.4, pg. 26). %VBur calculations use scaled (1.17×)

1 Further details on the determination of a ligand’s %VBur value can be found in reference 30. 25 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

[30] Bondi radii (RsvdW) and do not typically include hydrogen atoms. Cavallo has developed the internet application SambVca[31] for V calculations and, like Solid-G, SambVca can use either computationally modelled or crystallographic data. In contrast to the solid angle programs of Wendt, Guzei and Allen, V parameters can also be calculated using the data available for the free ligand.

Figure 2.5 - Schematical representation of the V model[30]

푉 푉 = 100 ( Bur ) 푉Sphere

Equation 2.4 - Calculation of V

A linear correlation between V and θ parameters for various phosphines, but not phosphites, has been reported by Nolan.[32] In these studies the impact of the M-L bond length on the V calculated for phosphines and NHCs was also examined.[32-33] A study on the steric bulk of monodentate anionic donors found a linear correlation between V and G parameters for the ligands examined.[26] However, a study by Holland examining sterically induced rate enhancements in Suzuki-Miyaura coupling reactions using super bulky NHCs found that the calculated V parameter of the ligand did not correspond to the experimental results. A correlation was found, however, between the calculated G parameter of the ligand and the experimental results. This led Holland to suggest that V parameters do not effectively account for ligand bulk that is more distant from the metal due to coordination sphere size limitations and he recommended the use of G parameters which have no coordination sphere limitation in this regard.[34] This descent was recently echoed by Plenio.[35]

26 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.1.4 The Quantification of the Steric Character of High Denticity Ligands

Bidentate phosphine ligands became popular in organometallic catalysis in the 1970s.[36] This naturally placed importance on the determination of their steric profiles. To address this, Tolman proposed a method for extending the cone angle model to chelating diphosphine ligands, whereby the θ parameter for each phosphorous atom was calculated in isolation.[7] It should be noted, therefore, that this method does not quantify the steric profile of the “whole” ligand.

Although not directly pertinent to the determination of “whole” ligand steric profiles,

Casey and Whiteker examined the “ligand-preferred” P-M-P angle, or bite angle (βn), of chelating diphosphines ligands through computer modelling of their geometries (Figure [37] 2.6). The βn concept has enabled the design and evaluation of novel chelating bidentate ligands in silico. Indeed, the Xantphos family of ligands were discovered through this process.[38] With respect to the steric character of bidentate phosphines, the

βn concept can only be used to examine the steric influence of the diphosphine linker unit and not the donor atom substituents in entirety. In addition, there remains no widely accessible means of expanding the βn concept to higher denticity ligands.

Figure 2.6 - Schematic representation of βn

Returning to the Ωs and V methodologies, the steric characters of a limited number of neutral bidentate diamines[39] and diphosphines[20c,25,32,40] have been evaluated. With regards to monoanionic bidentate ligands, the steric characters of two β-diketiminates [41] have been evaluated by Ωs methods (Figure 2.7 left, pg. 28), whilst the steric character of a bulky guanidinate has been quantified using the V methodology (Figure 2.7 right, pg. 28).[42] These represent the only monoanionic bidentate N,N'-ligands to have had their steric bulk quantified. The steric characters of a small and disparate number of higher coordinate ligands, such as cyclopentadienides,[43] have been evaluated by Ωs methods, many of which without direct relevance to modern main group chemistry.

27 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.7 - Metal complexes containing monoanionic bidentate N,N'-ligands that have

been evaluated by Ωs (left) or V (right) methods

An overview of the Ωs and V methods used for the quantification of a ligand’s steric character are listed in Table 2.1.

Ωs (Solid-G) V (SambVca.)

X-ray and/or molecular X-ray and/or molecular Input modelling data modelling data

Mono-dentate ligands Yes Yes

Higher-dentate ligands Yes Noa

Hydrogen atoms included Yes Typically No

Metal needed Yes No

Atomic radii Rz RsvdW

Sphere radius not applicable Typically 3.5 Å

Multiple Ligands Yes No

Determination of ligand Yes No overlap and intermeshing

Table 2.1 - Comparison of Ωs and V methodologies a V parameters may be calculate for high-dentate ligands but this requires the .cif file to modified such that a dummy atom (‘X’) is introduced and the sphere centered at the dummy atom.

28 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.2 Project Outline

The development of new sterically demanding monoanionic bidentate N,N'-ligands has been at the forefront of contemporary coordination chemistry[2a] and remains an exceptional growth area in a number of sub-disciplines of synthetic inorganic chemistry. It is therefore surprising that there have been no attempts to comprehensively quantify the steric character of such ligands. The study described in this chapter will attempt to rectify this by identifying and developing a metal based probe that enables a ligand’s [44] steric character to be evaluated and compared using crystal structure data and Ωs and V[30] methodologies. It was noted earlier that Tolman used nickel tricarbonyl as a probe for cone angle calculation of neutral ligands, that system is clearly unsuitable for the study of monoanionic ligands. Correlations between βn, G and/or V parameters and the extension of the metal based probe to higher dentate ligand classes will also be investigated.

The research outlined in this chapter also seeks to develop a method to quantify the electronic character of the monoanionic bidentate N,N'-ligands studied. This is an area yet to be thoroughly explored.

In accomplishing the aim to develop a probe (or probes) with which to quantify the stereo-electronic character of monoanionic bidentate N,N'-ligands, this chapter will also expand upon the archive of monoanionic bidentate N,N'-ligands, with particular focus on the development of new “super” sterically demanding ligands.

29 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3 Results and Discussion

2.3.1 The Development of a Metal-Based Probe for the Quantification of Monoanionic Bidentate N,N'-Ligands’ Steric Character

At the outset of this project the comparison of the steric profiles of monoanionic bidentate N,N'-ligands was thought to be best achieved using X-ray crystal structure data for a series of [ML(L’)n] complexes where the M(L’)n cation represents a probe metal scaffold with a low steric profile. As per Tolman’s use of the sterically slight

“Ni(CO)3” probe (vide supra), this would serve to minimise any complications arising from ligand-ligand buttressing and enable meaningful cross-comparison of metal-ligand bond lengthening due to monoanionic bidentate N,N'-ligand steric bulk and electronics.

Thus, a number of potential metal-based models were surveyed using Ωs and V methodologies and available literature data. Of those assessed, the dimethylaluminium moiety was provisionally chosen as the benchmark system as monoanionic bidentate N,N'-ligand complexes of dimethylaluminium can be prepared by the simple addition of

HL to AlMe3, the ensuing complexes are predominately monomeric, four-coordinate and adopt a ‘tetrahedral’ geometry at aluminium in the solid-state and there are 209 literature examples of [AlMe2(L)] complexes document in the Cambridge Structural [45] Database (CSD). Indeed the methyl co-ligands of [AlMe2(L)] complexes act as very poor bridging ligands such that there are few cases of this complex type where the dimethylaluminium moiety bridges two ligands in preference to chelation by a single bidentate anionic donor. A survey of the Cambridge Structural Database reveals 19 examples,[45] all of which being derivatives of the structural motifs depicted in Figure 2.8.[46] These ligands feature a low number of atoms in the N,N'-linker (zero or one), include non-sterically demanding N-substituents, or present an N-linker-N angle that is predisposed to ligand bridging over N,N'-chelation.[47]

Figure 2.8 - Examples of dimeric dimethylaluminium complexes[46]

30 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Another feature of the dimethylaluminium moiety is that the methyl co-ligands are relatively small, which leads to minimal steric interaction with the ligand of interest.

2.3.1.1 Steric Measurements

[48] In the following discussion Ωs parameters were calculated using Solid-G applying the [44] Rz values recommended by Wendt and Guzei. The Ωs parameters are reported as G parameters, viz. section 2.1.2, to facilitate valid comparisons with V parameters.

Calculations of V were made using the method developed by Odom using SambVca,[26] whereby the ligand is evaluated in isolation of metal co-ligands. A sphere of radius 3.5

Å was used for these calculations along with both van der Waals radii (RvdW) and scaled 2 (1.17×) Bondi radii (RsvdW), as recommended by Cavallo. Hydrogen atoms were also included in V calculations, although it should be noted that this is not common practice in the literature.[30]

2.3.1.2 Evaluation of Aluminium as the Basis for a Steric Probe

To validate the use of the dimethylaluminium probe, the influence of the metal centre Dipp Dipp was investigated. nacnac complexes, [MLn( nacnac)] (Figure 2.9, pg. 32), were chosen to examine the role of the metal and its coordination number on G and V parameters because a considerable number of these complexes have been structurally characterised with a considerable range of metal coordination numbers and coordination geometries. To minimise the impact of co-ligands, complexes containing relatively small, typically methyl, co-ligands were chosen.

G, V and V* parameters for the Dippnacnac ligand in each of these complexes were calculated, these values are listed in Table 2.2 (pg. 33) and ranked by metal coordination number and escalating G parameter. The G parameters lie within a 15.83% range (45.40-61.23%), the V parameters lie within a 20.0% range (33.0-53.0%) and the V* parameters lie within a 22.6% range (42.0-64.6%). The means of the G, V and V* parameters are 52.93, 42.7 and 53.0% respectively, with standard deviations of 4.7, 5.9 and 6.6% respectively. For each of the steric parameters; it was noted that the parameter Dipp measured for [AlMe2( nacnac)], lies within a half standard deviation of the mean.

2 V parameters calculated using RvdW are labelled V, whilst parameters calculated using RsvdW are labelled V*. 31 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.9 - Solid angle representations of Dippnacnac ligand in a metal complex. Image generated using an 8 Å red sphere, Dippnacnac in blue.

The data in Table 2.2 (columns 3, 5 and 7) confirm that the coordination number and ionic radius of the metal contribute significantly to steric measurement. To remove the impact of the metal’s ionic radius, the steric measurements were recalculated by placing the metal a fixed distance from the centroid generated between the two coordinated nitrogen atoms, while ensuring the metal remained in the ligand’s five-membered chelate plane and is located diametrically opposite the N,Nʹ-linker methine (Figure

2.10). These parameters are denoted G1.29, V1.29 and V1.29* (Table 2.2, columns 4, 6 and 8 respectively). The fixed distance applied (1.29 Å) is the distance observed for the Dipp [49] aluminium position in [AlMe2( nacnac)]. The G1.29, V1.29 and V1.29* parameters lie within a significantly narrower range relative to the original parameters. This is reflected in the significant reduction in the standard deviation (Table 2.2). It is noteworthy that for each of the normalised steric parameters, the parameter calculated Dipp for [AlMe2( nacnac)] lies within a quarter standard deviation point of the mean. This validates the [AlMe2(L)] complex as a representative model compound for the metal Dippnacnac complexes examined and it is therefore a reliable choice for the quantification of anionic bidentate ligand steric character using the extensive library of monoanionic bidentate N,N'-ligands available.

Figure 2.10 - Representation of a Dippnacnac metal complex with a normalised metal-ligand centroid distance, in this instance 1.29 Å.

32 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Complex CN G G1.29 V V1.29 V* V1.29* Ref.

[YCl2(L)(thf)2] 6 45.40 50.91 33.0 42.8 42.0 52.9 [50]

[Ca(NH2·BH3)(L)(NH3)3] 6 46.90 53.39 34.5 47.1 44.0 57.9 [51]

[YbCl2(L)(dme)] 6 47.81 52.52 36.3 45.1 45.5 55.4 [52]

[Cr(L)(C≡N-2,6-Xy)4] 6 48.39 50.09 37.4 39.8 47.0 49.6 [53]

[Al(BH4)2(L)] 6 55.32 54.79 45.3 47.9 55.3 58.4 [54]

[ZrMe3(L)] 5 47.05 52.09 35.7 45.4 45.1 56.1 [55]

t [NbMe2(N Bu)(L)] 5 48.46 53.05 37.2 46.7 46.8 57.4 [56]

[ScMe2(L)(thf)] 5 48.96 52.72 37.8 46.1 47.4 56.7 [57]

[PtMe3(L)] 5 50.90 53.41 40.5 45.4 50.6 56.1 [58]

[CrMe2(L)(thf)] 5 51.58 53.78 41.1 47.2 50.9 57.6 [59]

[InMe2(L)] 4 51.25 54.65 40.6 48.6 50.7 59.5 [60]

[MgMe(L)(thf)] 4 52.38 53.89 42.1 47.0 52.1 57.8 [61]

[GaMe2(L)] 4 54.22 55.09 44.4 49.6 54.9 60.4 [60]

[AlMe2(L)] 4 54.94 54.95 45.2 48.8 55.5 59.6 [49]

[Li(L)(dme)] 4 55.09 54.84 44.7 46.8 54.9 57.4 [62]

[PbMe(L)] 3 49.47 54.81 37.9 49.0 47.5 59.6 [63]

[CdMe(L)] 3 52.30 55.48 42.6 49.1 53.5 60.3 [64]

[FeMe(L)] 3 59.69 59.69 51.1 51.7 62.4 63.1 [65]

[ZnMe(L)] 3 60.13 60.13 51.8 51.8 63.2 63.2 [66]

[Li(L)(thf)] 3 61.23 60.31 53.0 52.1 64.6 63.6 [67]

[Tl(L)] 2 51.74 58.33 41.3 50.0 52.1 61.1 [68]

[In(L)] 2 53.51 58.46 44.0 49.9 54.8 61.0 [69]

[Ga(L)] 2 57.89 60.32 49.5 51.9 60.6 63.2 [70]

[Li(L)] 2 58.99 57.89 50.4 49.1 61.8 60.5 [67]

[Al(L)] 2 59.65 60.88 50.9 52.2 62.0 63.4 [71]

Mean - 52.93 55.46 42.7 48.0 53.0 58.9 -

Std Dev. - 4.7 3.2 5.9 3.0 6.6 3.4 -

Table 2.2 - Steric measurements of Dippnacnac in various metal complexes, ordered by coordination number (CN) and subordered by G parameter.

33 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.1.3 Evaluation of Dimethylaluminium as a Steric Probe

To further validate the use of the dimethylaluminium probe, the influence of the Dipp Dipp co-ligands was investigated. nacnac complexes of aluminium, [AlLn( nacnac)], were chosen to examine the role of the co-ligands on G and V parameters. There are over 45 such complexes that have been structurally characterised.[45]

G and V parameters have been calculated for Dippnacnac as a function of co-ligands R1 and R2 in various [Al(R1)(R2)(Dippnacnac)] complexes (Table 2.3, pg. 35). The G parameters lie within a 7.67% range (51.76-59.43%), the V parameters lie within a 6.9% range (42.6-49.5%) and the V* parameters lie within an 8.0% range (52.4-60.4%). The mean G, V and V* parameters are 56.06, 46.3 and 56.6% respectively, with standard deviations of 2.0, 1.9 and 2.2% respectively. It is noted that all three parameters for Dipp [AlMe2( nacnac)] lie within half the standard deviation of the respective means by the three methods of determination and hence the methyl co-ligands are suitable general co-ligands for the probe.

34 References for this chapter begin on pg. 85

Co-ligands G V V* Ref. Co-ligands G V V* Ref. Co-ligands G V V* Ref.

Cl, Fp* 51.76 42.6 52.4 [72] SeH, SeH 55.19 45.1 55.3 [73] H, Si(H)(Me)Ph 57.11 47.6 58.0 [74]

H, η1-Cp* 52.39 44.0 53.7 [74] SH, SH 55.35 45.1 55.3 [75] OH, Me 57.12 46.9 57.3 [76]

κ2-O,O'- μ-S, μ-S 52.46 42.8 52.5 [77] μ-S3, μ-S3 55.63 45.2 55.4 [78] 57.58 46.9 57.5 [79] (OB(Ph)2)2O

N(H)Et, μ-Se, μ-Se 52.69 42.7 52.5 [77] 56.11 46.6 56.9 [80] H, Bpin 57.59 48.9 59.2 [74] N(H)Et

κ2-O,O'-(OB(m- μ-O, μ-O 52.98 44.9 54.7 [81] Et, OH 56.23 46.6 56.9 [82] 57.68 47.6 58.1 [83] tol)2)2O

2 μ-Te, μ-Te 53.29 43.3 53.1 [77] κ -(Me3SiC)2 56.29 46.7 56.9 [84] OH, OH 57.76 47.7 58.2 [85]

i t Cl, N Pr2 53.65 44.8 54.7 [86] OH, Ph 56.29 46.8 56.9 [87] H, N(H) Bu 57.76 48.3 58.6 [74]

2 Cl, N(SiMe3)2 53.68 43.0 52.9 [86] κ -P,P'-μ-P4 56.38 45.8 56.1 [88] OH, OSiMe3 58.03 48.1 58.4 [87]

2 κ -N,N'-((AdN)N)2 54.17 45.1 55.2 [89] Cl, Me 56.40 47.0 57.5 [90] F, Me 58.15 48.2 58.9 [90]

Me, η1-Cp 54.48 44.6 54.5 [82] Cl, Cl 56.44 46.2 56.7 [60] H, OiPr 58.30 48.3 58.9 [74]

2 κ -S,S'-(SSiMe2)2O 54.61 44.5 54.4 [91] H, PPh2 56.44 46.8 57.2 [74] OH, OEt 58.37 48.1 58.8 [87]

2 2 κ -O,O'-(OC(Ph)2)2 54.77 45.4 55.6 [84] Cl, I 56.68 47.3 57.9 [92] κ -(PhC)2 59.11 48.8 59.5 [84]

Me, Me 54.94 45.2 55.5 [49] Cl, NMe2 56.72 46.7 57.0 [86] H, H 59.33 49.4 60.2 [93]

N,N'-((Ph3SiN)N)2 55.15 44.6 54.9 [89] NH2, NH2 56.77 46.5 56.9 [94] F, F 59.42 49.3 60.1 [90]

2 κ -N,N'- 2 55.15 45.9 56.2 [95] H, N(H)Ph 56.96 46.9 57.4 [74] κ -(HC)2 59.43 49.5 60.4 [96] ((Me3SiN)N)2

Table 2.3 - Steric calculations of Dippnacnac in aluminium complexes, ordered by G parameter

Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.1.4 Ligand Intermeshing - A Menacnac Case Study

A significant limitation of the cone angle model is its inability to take into account the intermeshing of ligands. For the majority of complexes this is irrelevant, i.e. “meshing” or “gearing” of the ligand does not take place, however there are examples where meshing is evident and it is clear that with the development of super bulky ligands for main group applications, a means to quantify meshing would be valuable as an indicator of steric congestion. Intermeshing is where closer packing of the ligands is achieved relative to what the ligand’s steric parameter would allow.[17] For example, the complexes [Pd(PPh3)4] and [Pt(PCy3)3] would not be expected to exist on the basis of [97] combined θ parameters of PPh3 and PCy3 (145° and 170° respectively), yet both complexes are relatively stable and have been characterised by X-ray crystallography.[98] The existence of such complexes suggests either there is elongation of the M-L bonds, or there exists some level of ligand intermeshing. A similar example can be found for monoanionic bidentate N,N'-ligands: the G, V and V* measurements Me Me [99] for nacnac using the dimethylaluminium probe ([AlMe2( nacnac)] ) are 41.98, Me 33.0 and 42.1% respectively and yet [Al( nacnac)3] has been reported and [100] Me Me crystallographically characterised. A bis( nacnac) complex; [Al( nacnac)2][BPh4], has also been crystallographically characterised.[101]

To better understand the relationship between our steric measurements and the Al-L bond lengths, the measurements G, V and V* of Menacnac were reappraised in 0.05 Å Al-N bond increments across the range 1.845-2.059 Å which represents the range of Al-N bonds observed for the aforementioned three aluminium Menacnac complexes (Figure 2.11, pg. 37).

36 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

50.00 G

45.00 V V* Steric 40.00 Parameter (%) 35.00

30.00

25.00 1.75 1.85 1.95 2.05 2.15 Al-N Bond Length (Å)

Figure 2.11 - Correlation between steric parameter and Al-N bond length for Menacnac

Linear correlations were observed between the steric parameters and the Al-N bond distance over the observed range (R2 G; 0.98, V; 0.99, V*; 0.99). The G and V* Me [100] parameters obtained for the mean Al-N bond distance in [Al( nacnac)3] (2.03 Å, 36.34 and 38.3% respectively) indicate that ligand intermeshing must occur in this complex.

Guzei has developed several methods to evaluate ligand overlap in G calculations,[44] one such method evaluates the total overlap of ligand shadows in the complex. This is represented by Gγ (Equation 2.5).

푖 퐺훾(complex) = ∑ 퐺(L ) − 퐺(complex) 푖

Equation 2.5 - Calculation of ligand shadow overlap in solid angle assessments

It should be noted that Gγ does not differentiate between ligand shadow overlap and unfavourable ligand-ligand interactions. Unfavourable ligand-ligand interactions can be evaluated by examining the area of interpenetration of the atomic spheres from different ligands in three dimensional space. The sum of these areas is designated GU. It should be noted that Gγ ≥ GU. A problem with the form of the overlap between the two spheres is that it is anisotropic in shape and therefore the area of its projection on the reference sphere depends on the orientation of the interaction relative to the metal centre.[44] Thus an improved way to express these interactions is to use the volume of the conflicting

37 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

atoms in terms of interpenetration. The total volume of interpenetration for a complex is designated VG. Therefore a complex should ideally have a negligible value of VG. The [44] Gγ, GU and VG values of a complex can all be calculated using Solid-G.

Ligand intermeshing has not been investigated to date in V calculations because [30] calculations are typically made on a ligand in isolation. As per VG, but unlike Gγ (shadow overlap only), any ligand ‘atom sphere’ overlap in V calculations must arise from unfavourable inter-ligand interactions. Therefore, Vγ ≡ VU, hence, the degree of unfavourable inter-ligand interactions (VU) can be calculated in the same way as Gγ by substituting V(Li) for G(Li) (Equation 2.6). A complex will ideally have a negligible value of VU.

푖 푉U = ∑ 푉(L ) − 푉(complex) 푖

Equation 2.6 - Calculation of ligand overlap in molecular volume assessments

Returning to Menacnac intermeshing, to study ligand overlap in the dimethylaluminium Me [99] Me +[101] probe, these parameters were calculated for [AlMe2( nacnac)], [Al( nacnac)2] Me [100] and [Al( nacnac)3] (Table 2.4, pg. 39).

38 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Me [99] Me +[101] Me [100] [AlMe2( nacnac)] [Al( nacnac)2] [Al( nacnac)3]

G(complex) 79.83 88.59 98.71

V(complex) 58.1 67.8 88.4

V*(complex) 73.6 83.8 97.5

VC(complex)a 71.7 81.5 96.9

Gγ 0 0 9.42

GU 0 0 5.88

3 b VG (Å ) 0 0 0.40

VU 0.1 0 2.0

3 b VU (Å ) 0.2 0 3.5

VU* 3.2 1.8 16.1

3 b VU* (Å ) 5.7 3.2 28.9

C VU 3.2 1.8 15.4

C 3 ab VU (Å ) 5.7 3.2 27.7

Table 2.4 - Ligand overlap in Menacnac aluminium complexes a VC indicates the molecular volume calculation was made using the conditions recommended by [30] b Cavallo, i.e. employing RsvdW and the absence of hydrogen atoms. Calculation was made using a sphere of radius 3.5 Å, which has a volume of 179.6 Å3.

Me The VG, VU and VU* values calculated for the mono- and bis( nacnac) complexes revealed minimal (< 6.0 Å3) unfavourable inter-ligand interactions in these complexes. Me Similarly, both the VG and VU values for the tris( nacnac) complex are minimal (0.40 3 3 and 3.5 Å respectively), however, the VU* value was not (28.9 Å ). This highlights a flaw with the use of RsvdW values in V calculations, as they typically overestimate the ligand steric character even in the absence of hydrogen atoms (VC). Hence, the analysis of ligand sterics using the dimethylaluminium probe will herein be made using only G and V parameters derived from Rz and RvdW radii respectively with the inclusion of all hydrogen atoms.

39 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.2 The Preparation of Novel Super-Bulky Bidentate N,N'-Ligands and Evaluation of their Steric Character 2.3.2.1 The Synthesis of a 1,3-Bis(2,6-terphenyl)triazene

Having earlier established the dimethylaluminium model as a reliable probe with which to quantify the ligand steric character of monoanionic bidentate N,N'-ligands, the development of new super bulky ligands was undertaken. The new super bulky

1,3-bis(2,6-terphenyl)triazene, Dmp2N3H (1), was synthesised in good yield (69%) following the procedure used to synthesise the slightly smaller 1,3-bis(2,6- [102] terphenyl)triazene, (Me4Ter)2N3H (Scheme 2.1).

Scheme 2.1 - Preparation of the 1,3-bis(2,6-terphenyl)triazene (1)

Compound 1 exhibits an N-H stretch at 3264 cm-1 and a number of absorptions in the NNN stretch region of the IR spectrum (1300-1200 cm-1), which is consistent with -1 [103] DmpN3(H)Tph which exhibits stretches at 3264, 1283, 1224 and 1201 cm . In solution, 1 exists as a single isomer, as evidenced by singular terphenyl environments in 1 13 both its H and C NMR spectra (C6D6), with a single N-H proton resonance observed at 8.64 ppm in its 1H NMR spectrum. By contrast, smaller 1,3-bis(aryl)triazenes have been observed to exist as a number of geometric and conformational isomers in solution.[104] This demonstrates the influence of the N-2,6-terphenyl substituents on the isomerism of 1.

Single prismatic crystals of 1 suitable for X-ray structure determination were forthcoming during its purification by recrystallisation from acetone. The molecular structure of 1 is depicted in Figure 2.12 (pg. 41). Disorder of the near symmetrical N3H unit was modelled with partial hydrogen occupancies of 54:46% N(3)-H(1N):N(1)-H(2N). It should be noted that the N-N bonds in 1 are intermediate to single and double N-N bonds in their bond localised relatives ((Me4Ter)2N3H; N-N 1.3525(15) Å and N=N 1.2650(15) Å, 1; N-N: 1.2905(17) and 1.2954(18) Å).

40 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.12 - Molecular structure of 1 (50% thermal ellipsoids) normal to the N3 plane (left) and down the N(1)-N(3) vector (right). All hydrogen atoms excepting H(1N) omitted for clarity. Selected bond lengths (Å) and angles (°): N(1)-N(2) 1.2905(17), N(2)-N(3) 1.2954(18), N(3)-H(1N) 0.91(3), N(1)-H(2N) 0.92(4), C(1)-N(1)-N(2) 121.45(13), N(1)-N(2)-N(3) 109.78(12), N(2)-N(3)-C(25) 123.73(14).

[105] [106] As per (Me4Ter)2N3H, 1 exists solely as the E-anti isomer in the solid state. The N-N-N angle of 109.78(12)° is below the range observed for structurally characterised 1,3-bis(aryl)triazenes that display E-anti isomerism in the solid-state (111.74(10)-112.8(2)°).[104-105,107] This is likely due to steric interactions between the two 2,6-terphenyl moieties. The planes of the principal N-aryl groups are distorted away from being orthogonal to the N3-plane as indicated by the N3:ArC(1) and N3:ArC(25) torsion angles of 42.0° and 37.8° respectively. In fact, the planes of the aforementioned aryl groups relative to one another nears orthogonality ( ArC(1):ArC(25) 78.5°). This is larger than that reported for other 1,3-bis(aryl)triazenides that display E-anti isomerism in the solid-state: (C6F5)2N3H, Dipp2N3H and (Me4Ter)2N3H (21.2°, 49.7° and 68.0° respectively),[104-105,107] and is undoubtedly caused by the steric crowding of the

2,6-Mes2 substituents (Figure 2.12).

41 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.2.2 The Synthesis of C-2,6-terphenyl Substituted Amidine Ligands

The 2,6-terphenyl substituted amidines, DitopACyH (2) and DmpACyH (3) were prepared in an analogous manner to the 2,6-terphenyl substituted amidine, DmpAiPrH (Scheme 2.2).[108]

Scheme 2.2 - Preparation of 2,6-terphenyl substituted amidines

The IR spectra of 2 and 3 are in accord with their proposed formulations, with each exhibiting an N-H stretch (2; 3441 cm-1, 3; 3463 cm-1) and a C=N stretch (2; 1630 cm-1; 3; 1642 cm-1) in the expected region for an amidine.[109] In addition, the 1H and 13C

NMR spectra of 2 (C6D6) exhibit a single well-defined set of amidine resonances, as is consistent with the presence of a single isomer in solution. Amidines can potentially exist as four distinct isomers in the solid-state and in solution (Scheme 2.3, pg. 43). The amidine 2 was assigned as the E-syn or Z-anti isomeric form because these conformations minimise the steric interactions between the N-Cy and C-2,6-terphenyl substituents. Indeed, in the solid-state, 2 exhibits E-syn isomerism. The molecular structure of 2 can be found in the appendix and salient bond parameters can be found with those of 3 in Table 2.5 (pg. 45).

42 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Scheme 2.3 - Isomeric structures of amidines in solution[106]

1 The H NMR spectrum of 3 (C6D6) is significantly more complex. The presence of four broad multiplet resonances in the N-cyclohexyl methine/amine region of 2.50-4.00 ppm indicates at least two isomers present in solution (Figure 2.13).

NH NH

C=N-CH

NH-CH NH-CH

3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0 2.9 2.8 2.7 ppm

0.5 1.0 1.0 0.5 Figure 2.13 - Segment of the 1H NMR spectrum of 3 showing the NH and N-CH resonances 43 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

The N-H resonances at 3.51-3.55 ppm can be attributed to two overlapping doublets using a 1H-13C HSQC NMR experiment. The C(H)-NH resonances can be attributed to the multiplets at 2.85-2.97 and 3.71-3.81 ppm using a 1H-1H COSY NMR experiment. The C(H)-N=C resonances can be identified as the overlapping multiplet at 3.04-3.13 ppm using a 1H-1H COSY NMR experiment. The observation of two C(H)-NH resonances indicates there are two isomers in solution. The integrations from the 1H NMR spectrum indicate the two isomers exist in an approximate 1:1 ratio in solution at 1 ambient temperature. A variable temperature H NMR study (C7D8) indicates the aforementioned resonances do not coalesce up to the temperatures of 100 °C. Deconvolution of all the 1H NMR resonances into two independent sets of amidine peaks is enabled using a 1H-1H TOCSY NMR experiment. Inter-conversion between all of the C(H)-N resonances is observed in a 1H-1H NOESY NMR experiment (Figure 2.14).

C=N-CH NH-CH NH-CH

ppm

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 ppm Figure 2.14 - A segment of the 1H-1H NOESY NMR spectrum of 3 showing inter-conversion between the NH-CH of one isomer and the NH-CH of another, and the NH-CH of one isomer with the C=N-CH of another.

44 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Inter-conversion between the E-syn and Z-syn isomers of DmpAiPrH in solution has been reported previously.[108,110] It is plausible that inter-conversion between the E-syn and Z-anti isomers also accounts for the behaviour of 3 in solution, as indicated by the aforementioned 1H-1H NOESY experiment.

Like 2, 3 displays only E-syn isomerism in the solid-state (Figure 2.15). Important bond parameters for 2 and 3 are listed in Table 2.5.

Figure 2.15 - Molecular structure of 3 (50% thermal ellipsoids). All hydrogen atoms excepting H(1) omitted for clarity.

Bond Parameter 2 3

N(1)-H(1) 0.88(2) 0.91(3)

N(1)-C(1) 1.3730(17) 1.342(2)

N(2)-C(1) 1.2736(18) 1.296(3)

C(1)-C(2) 1.5141(17) 1.518(3)

N(1)-C(1)-N(2) 120.50(12) 119.48(17)

N(1)-C(1)-C(2) 111.26(11) 113.76(16)

N(2)-C(1)-C(2) 128.21(12) 126.77(17)

NCN:Ar 70.1 84.1

Table 2.5 - Selected bond lengths (Å), angles (°) and torsion angles (°) for the amidines 2 and 3

45 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

The metrical data for amidines 2 and 3 is consistent with bond localisation, whereby the N(2)-C(1) bonds have double bond character and the N(1)-C(1) bonds are representative of a C-N single bond. The N(1)-C(1)-N(2) angle in 3 is slightly smaller than that observed in 2, perhaps reflecting the increased steric congestion produced by the introduction of o-Me2 groups to the secondary aryls of the 2,6-terphenyl moiety in 3.

This effect can also be observed in the interplanar angle between the N2C plane and the plane of the principal arene ring (2 70.1°, 3 84.1°). Although the three angles about C(1) deviate from an idealised sp2 value of 120°, the sum of angles about C(1) for both amidines is 360.0°.

2.3.2.3 The Synthesis of Dimethylaluminium Complexes of 1-3 and Popular Ligands

To assess the sterics of the new 2,6-terphenyl substituted ligands, each respective protonated ligand (1-3) was treated with a slight excess of AlMe3 to afford Ditop Dmp [AlMe2(N3Dmp2)] (4), [AlMe2( ACy)] (5) and [AlMe2( ACy)] (6) respectively (Scheme 2.4). To provide for meaningful and literature relevant comparisons, Cy Dipp tBu Dipp tBu [AlMe2(N3Dipp2)] (7), [AlMe2( Giso)] (8) and [AlMe2( nacnac )] (9, nacnac t = {DippNC( Bu)}2CH) were prepared by an analogous procedure. The Me Me dimethylaluminium complex of Aiso, [AlMe2( Aiso)] (10) was prepared through treatment of N,N'-di(2,6-diisopropylphenyl)carbodiimide with AlMe3 (Scheme 2.4).

Scheme 2.4 - Preparation of the dimethylaluminium complexes 4-10 through protolysis or methyl migration

1 13 The H and C NMR spectra of 4-10 (C6D6) exhibit singular sets of ligand resonances with minimal resonance broadening. Sharp methyl resonances are also observed in the 1H and 13C NMR spectra of 4-10. The IR spectra of 4-10 are consistent with delocalised bonding across the ligand scaffolds.

46 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Single crystals of 4-10 suitable for X-ray diffraction studies were grown from concentrated hexane or toluene solutions. The molecular structure of the representative compound 4 is displayed in Figure 2.16. The molecular structures of 5-10 can be found in the appendix. Relevant metrical parameters for 4-10 as well as those of closely related reported dimethylaluminium complexes are listed in Table 2.6 (pg. 48).

Figure 2.16 - Molecular structure of 4 (50% thermal ellipsoids). All hydrogen atoms omitted and Mes groups depicted as wireframes for clarity.

47 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

[111] Ligand Mean Al-CMe (Å) Mean Al-N (Å) βn (°) τ4

DitopACy (5) 1.952 1.930 69.36(9) 0.85

DmpACy (6) 1.961 1.925 68.81(5) 0.88

MesPhACy[110] 1.947 1.939 68.5(2) 0.89

MeAiso (10) 1.949 1.942 68.59(11) 0.92

Fiso[112] 1.950 1.955 68.67(13) 0.87

tBuAiso[113] 1.954 1.938 68.15(7) 0.89

CyGiso (8) 1.959 1.929 69.03(5) 0.85

MeGiso[114] 1.953 1.934 69.25(6) 0.86

iPrGiso[115] 1.971 1.923 69.06(6) 0.86

N3Dipp2 (7) 1.943 1.952 65.16(6) 0.84

N3Dmp2 (4) 1.951 1.969 64.6(3) 0.83

DippnacnactBu (9) 1.974 1.931 99.04(7) 0.91

Dippnacnac[49a] 1.967 1.931 96.17(7) 0.91

Table 2.6 - Selected bond parameters of dimethylaluminium amidinate, guanidinate, triazenide and β-diketiminate complexes

The molecular structures of 4-10 show each complex to be monomeric with ligand geometries similar to those of analogous amidinate and β-diketiminate complexes in the literature.[46b,49a,116] In each complex the aluminium centre displays a distorted [111] tetrahedral geometry as evidenced by τ4 values in the range 0.83-0.92. The N-Al-N angle in the amidinate complexes lie in the range 68.15(7)-69.36(9)°, guandinates; 69.03(5)-69.25(6)°, triazenides; 64.6(3)-65.16(6)° and nacnacs; 96.17(7)-99.04(7). The

Al-CMe and Al-N bond lengths in each complex lie within the normal range (Table [45] 2.6). An examination of the NCN scaffold in 5, 6, 8, 10, the N3 scaffold in 4 and 7, and the N-C and C-C bond lengths in the ligand framework of 9 suggests a significant degree of delocalisation over each of the ligands’ backbone, whereby each measure is intermediate relative to localised N-C/N=C, N-N/N=N or C-C/N=C bonds (5,6,8,10: 1.326(3)-1.3726(18); 4,7: 1.3126(12)-1.339(7) and 9: 1.337(2)-1.407(2) Å respectively).

48 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.2.4 Steric Measurements of Anionic Bidentate N,N'-Ligands

Having earlier established the dimethylaluminium model as a reliable probe with which to quantify the ligand steric character of monoanionic bidentate N,N'-ligands (Section 2.3.1), G and V parameters were calculated for the ligands in complexes 4-10 (Table 2.7, pg. 51). Table 2.7 also includes the same steric measurements for a range of related monoanionic bidentate N,N'-ligands to facilitate a robust comparison of the data presented herein and the most recent literature studies (Figure 2.17, pg. 50). The steric parameters for each ligand were calculated using crystallographic data for the respective dimethylaluminium complex, for which the data was obtained in .cif and .xyz formats from the Cambridge Structural Database (CSD).

49 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.17 - Anionic bidentate N,N'-ligands for which the steric parameters have been calculated using the dimethylaluminium probe

50 References for this chapter begin on pg. 85

Ligand G V Mean Al-N (Å) βn (°) Ref. Ligand G V Mean Al-N (Å) βn (°) Ref.

MeACy 37.82 30.2 1.924 68.96 [116] iPrGiso 47.66 37.7 1.927 69.04 [115]

tBuACy 41.51 33.8 1.919 68.71 [116] tBuAiso 47.74 37.8 1.938 68.13 [113]

Me2pip N3Dipp2 (7) 41.91 31.6 1.952 65.16 - Giso 47.82 38.1 1.928 69.09 [114]

Menacnac 41.98 33.0 1.893 95.78 [99] C6F5nacnac 48.18 40.3 1.922 94.00 [117]

Fiso 42.29 32.8 1.950 68.58 [112] MeGiso 48.37 38.4 1.934 69.25 [114]

MesPhACy 43.13 34.1 1.917 68.55 [110] DippBIAN 48.86 38.9 1.950 86.26 [118]

MeAiso (10) 43.46 32.8 1.942 68.90 - CyGiso (8) 49.98 40.3 1.929 69.03 -

p-tolnacnac 43.70 36.7 1.907 94.68 [49b] Xynacnac 50.86 44.6 1.915 95.07 [119]

tBuAAd 44.36 36.8 1.916 69.05 [113] tBunacnac 51.09 43.8 1.933 101.86 [99]

DitopACy (5) 44.42 34.9 1.930 69.36 - Dippnacnac 54.94 45.2 1.931 96.13 [49]

tBuAtBu 44.72 37.2 1.907 68.69 [120] DippTAPDPh 55.41 45.3 1.931 93.05 [121]

Dmp ACy (6) 45.59 36.2 1.925 68.84 - P(NMes*)2 56.51 49.6 1.978 74.95 [122]

t PhAiso 46.49 36.0 1.938 68.59 [123] Dippnacnac Bu (9) 58.71 49.1 1.931 99.04 -

pipGiso 47.35 37.3 1.933 69.32 [114] DippBIPMPh 63.38 51.3 1.946 106.15 [124]

Cy Aiso 47.37 37.1 1.917 68.15 [123] N3Dmp2 (4) 64.60 45.0 1.969 64.60 -

Table 2.7 - Steric parameters of various monoanionic bidentate N,N'-ligands in complexes with the general formula [AlMe2(L)] ordered by G parameter.

Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

The dimethylaluminium steric probe was chosen based on the earlier appraisal of candidate MLn systems. As demonstrated in Table 2.7, this model exhibits little variation in Al-N bond length. Indeed, the mean Al-N bond lengths of all the dimethylaluminium complexes of the ligands in Table 2.7 lie within a relatively narrow range: 1.893-1.978 Å. It was also noted that zero values of VG were obtained for all complexes of the aforementioned complexes (Table 2.7) with the exception of 3 [AlMe2(P{NMes*}2)] (VG = 0.04 Å ). This emphasises the slight steric form of the methyl co-ligands.

A moderate linear correlation is observed (R2 = 0.86) between the G and V parameters for the ligands in Table 2.7 (Figure 2.18). It should be noted that the

1,3-bis(2,6-terphenyl)triazenide, N3Dmp2, is an outlier in this trend (G = 64.6%, V = 2 45.0%). Omission of N3Dmp2 affords an R value of 0.89. This disparity is consistent with Holland’s observation that V parameters do not effectively quantify the steric character of super bulky ligands, especially those with functions that likely extend beyond a 3.5 Å coordination sphere.[34]

70.00

65.00

60.00

55.00

G (%) 50.00

45.00 G = 1.240(V) R² = 0.86 40.00

35.00

30.00 25.0 30.0 35.0 40.0 45.0 50.0 55.0 V (%)

Figure 2.18 - Correlation between G and V parameters for various N,N'-ligands. V parameters calculated using a sphere of radius 3.5 Å.

52 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

An improved correlation (R2 = 0.90, Figure 2.19) was found when the V parameters were recalculated using a sphere of radius 4.0 Å (see appendix for recalculated V parameters). It is clear that sphere radius has a significant impact on V parameters. As sphere size is not required in Ωs calculations, the G parameter may be considered the primary descriptor of a super bulky ligand’s steric character, as per Table 2.7.

70.00

65.00

60.00

55.00

G (%) 50.00 G = 1.212(V) 45.00 R² = 0.90

40.00

35.00

30.00 25.0 30.0 35.0 40.0 45.0 50.0 55.0 V (%)

Figure 2.19 - Correlation between G and V parameters for various N,N'-ligands. V parameters calculated using a sphere of radius 4.0 Å.

A rough correlation between steric parameter and the number of atoms in the N,N'- linker is observed (Table 2.7, triazenides, guanidinates, amidinates < BIAN < nacnac, TAPD, BIMP). N-substituent steric effects in amidinates afforded the following general trend: Dipp > tBu > Ad > Cy. In β-diketiminates, a similar trend is observed: Dipp > t 2,6-Xy ≈ Bu > C6F5 > p-tolyl > Me, and in the triazenide and diazaphosphenide ligands the trend is: Dmp > Mes* > Dipp. The N-Dmp triazenide exhibits the largest G parameter (G = 64.6%) of the 30 ligands surveyed despite its single atom N,N'-linker which typically diminishes N-substituent steric impact (vide supra). P(NMes*)2 is also noteworthy in this regard.

The amidinate carbon substituents in the N-Cy systems display the following trend: t Dmp > Ditop > 2,4,6-Ph3C6H2 > Bu > Me. Whilst, for N-Dipp amidinates the following trend is observed: tBu > Cy > Ph > Me > H, likewise the N-Dipp guanidinates follow

53 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

i the trend: NCy2 > NMe2 > 2,6-Me2piperidine > N Pr2 > piperidine. There is no clear correlation between βn or N-C-N angle for that matter and G at the microscopic level when comparing the N-Cy amidinates, N-Dipp amidinates and N-Dipp guanidinates with one another.

The steric effect of the α-substituent in the N-Dipp β-diketiminate and t 1,3,5-triazapentadienyl derivatives affords the expected trend: PPh2 (BIPM) > C Bu > CPh (TAPD) > CMe.

From the work presented above; the dimethylaluminium model represents an excellent probe for quantifying the steric character of monoanionic bidentate N,N'-ligands thereby achieving objective (i) of this chapter (viz. Section 2.2). The following sections outline studies toward a similar probe for the quantification monoanionic bidentate N,N'-ligand electronic donicity.

2.3.3 The Development of a Metal-Based Probe to Quantify the Electronic Character of Monoanionic Bidentate N,N'-Ligands

Further to Tolman’s development of the cone angle model, he also established a metal-based probe for indirectly quantifying the σ-donicity of neutral monodentate [8] Lewis bases. Tolman defined the electronic parameter, ν, as the frequency of the A1 carbonyl stretching mode of [Ni(CO)3(L)] in as CH2Cl2 measured by IR spectroscopy

(Table 2.8, pg. 55). The sharpness of the A1 band permitted ν to be measured with a high degree of accuracy, however, the high toxicity and volatility of [Ni(CO)4], used as [125] a precursor to [Ni(CO)3(L)] complexes, motivated the search for other carbonyl complexes to be used as alternative electronic probes that can be used to determine ν by [126] linear regression. Contemporary alternatives to [Ni(CO)3(L)] are cis-[RhCl(CO)2(L)] [33,127] and cis-[IrCl(CO)2(L)]. The square planar geometry of the group 9 carbonyl complexes necessitates that the electronic parameter be redefined as the average of the frequencies of the symmetric and asymmetric carbonyl stretches, νav. The Tolman parameter ν can then be determined by back calculation using the aforementioned linear regression methods.

54 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Ligand ν (cm-1)

t P( Bu)3 2056.1

PMe3 2064.1

PPh3 2068.9

P(OPh)3 2085.3

PF3 2110.8

Table 2.8 - The electronic parameters of selected phosphine ligands obtained from their [8] [Ni(CO)3(L)] complexes

In principle, the replacement of the chloride atom of [RhCl(CO)2(L)] with a non-coordinating anion such as a tetraphenyl borate enables the electronic character of neutral bidentate ligands to be examined similarly.[128] Budzelaar has recently proposed that [Rh(L)(CO)2] complexes be employed as an electronic probe for the donicity of [129] monoanionic bidentate ligands. To this end, he has reported νav values for rhodium bis(carbonyl) fragments bound by various chelating monoanionic ligands determined by ab initio electronic structure calculations (Figure 2.20, pg. 56). Furthermore, linear correlations between experimentally determined νav values and Hammett σ values were observed in 1,5-substituted acetylacetonate (acac) complexes[130] and mono-substituted cyclopentadienyl complexes.[131]

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-1 Figure 2.20 - Calculated vav (cm ) for [Rh(L)(CO)2] complexes of a range of disparate bidentate monanionic ligands[129]

56 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.3.3.1 The Synthesis of Rhodium Bis(carbonyl) Complexes

To assess the electronic character of the new N-2,6-terphenyl triazenide, N3Dmp2, derived from 1, the preparation of [Rh(N3Dmp2)(CO)2] through salt metathesis was attempted. A THF solution of 1 was treated with one equivalent of nbutyllithium and the resultant mixture was then added to a THF solution of [{Rh(μ-Cl)(CO)2}2], this afforded [Rh(N3Dmp2)(CO)2] (11) as a yellow solid (Scheme 2.5). To provide useful tBu Cy comparisons the complexes [Rh( Aiso)(CO)2] (12), [Rh( Giso)(CO)2] (13) and Dipp tBu 1 [Rh( nacnac )(CO)2] (14) were also prepared by the same procedure. The H and 13C NMR spectra of 11-14 display resonances that are sharp and consistent with a high degree of symmetry in solution. The IR spectra of 11-14 each display a single symmetric and asymmetric carbonyl stretching frequency (ca. 2050 and 1990 cm-1), thereby confirming each complex is monomeric with cis-carbonyls and a square planar geometry about the rhodium centre.

Scheme 2.5 - The preparation of [Rh(L)(CO)2] complexes 11-14 through salt metathesis reaction

Attempts to prepare the analogous N-Dipp triazenide complex (15) afforded atypically dark orange crystals rather than the yellow solids observed for 11-14. A large number of rhodium bis(carbonyl) complexes featuring bridging triazenide or amidinate ligands have been reported.[132] Some of these maintain a square-planar geometry at the rhodium centre and cis-carbonyl placements (Figure 2.21). They are easily identified by the presence of three distinct carbonyl stretches in their IR spectra. The IR spectrum of -1 15 (CH2Cl2) displays two strong carbonyl stretches at 2020 and 1814 cm , which are inconsistent with the aforementioned dimeric bridging ligand form (Figure 2.21, pg. 58) and indicative of the presence of terminal (2020 cm-1) and bridging (1814 cm-1) [132h] carbonyl moieties. The IR spectrum of 15 (CH2Cl2) also exhibits an N3 stretch at

57 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

-1 -1 1364 cm , which is diagnostic of triazenide bridging (N3 stretch > 1300 cm ) rather -1 [133] than chelation (N3 stretch 1300-1200 cm ). The presence of a bridged triazenide ligand as well as the aforementioned carbonyl stretches are consistent with 15 exhibiting have a symmetrical structure like that shown in Figure 2.22.

Figure 2.21 - A possible triazenide bridged square planar cis-rhodium di(carbonyl) complex

Figure 2.22 - Proposed structure of 15

Attempts to prepare the analogous Fiso complex also afforded orange crystals (16), the

IR spectrum of these crystals (CH2Cl2) exhibit strong carbonyl stretches at 1864 and 1655 cm-1, both of which is inconsistent with those observed for 15 and 11-14. The frequencies of these stretches suggest the absence of a terminal carbonyl group. Assuming the former is generated by a bridging carbonyl, cf. IR spectrum of 15, the latter is consistent with an organic amide. In the present case this hints at the likely formation of an iminocarbamoyl moiety (Figure 2.23, pg. 59). Iminocarbamoyl moieties typically arise from CO insertion into a metal organoamide M-NR2 bond, in this instance this could be a Rh-N bond of the putative [Rh(Fiso)(CO)2] intermediate. Carbonyl insertion has previously been observed in Fe and Co amidinate complexes[134] and would explain the lack of a terminal CO stretch in the IR spectrum of 16 (cf. no CO stretch >1900 cm-1).

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Figure 2.23 - Metal iminocarbamoyl moiety

Given the failure to prepare monomeric rhodium carbonyl complexes of N3Dipp2 and Fiso via the route used to isolate 11-14, an alternate synthetic route was developed. A THF solution of FisoH was treated with nbutyllithium, and the resultant mixture added to a half equivalent of [{Rh(μ-Cl)(cod)}2] in THF to afford [Rh(Fiso)(cod)] (17) as a yellow crystalline solid (Scheme 2.6, left, pg. 60). The greater acidity of Dipp2N3H relative to FisoH enabled the analogous triazenide complex, [Rh(N3Dipp2)(cod)] (18), to be prepared through the reaction of [{Rh(μ-OEt)(cod)}2] with two equivalents of

Dipp2N3H (Scheme 2.6, right). Sparging solutions of 17 and 18 in CH2Cl2 with CO(g) leads to a colour change from yellow to red. The IR spectra (CH2Cl2) of the solutions immediately after carbonylation exhibit absorptions at; 17, 2077 and 2012 cm-1 and 18, 2083 and 2015 cm-1, which are consistent those of the cis-carbonyl complexes 11-14, thereby suggesting the formation of [Rh(Fiso)(CO)2] (19) and [Rh(N3Dipp2)(CO)2] (20) (Scheme 2.6). The IR spectra of the same solutions 10 minutes after carbonylation exhibit new broad absorptions at; 19, 2039, 1771 and 1651 cm-1 and 20, 2020 and 1814 cm-1. The former absorptions are inconsistent with those of 16 but do suggest the formation of products containing an iminocarbamoyl group with likely bridging and terminal carbonyls. The latter absorptions are consistent with complex 15.

59 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Scheme 2.6 - Preparation and carbonylation of the rhodium(I) 1,5-cyclooctadiene amidinate and triazenide complexes 17 and 18

2.3.3.2 Electronic Measurements for the Monoanionic Bidentate N,N'-Ligands Studied Herein

Using rhodium bis(carbonyl) as a metal based probe with which to quantify the electronic character of monoanionic bidentate N,N'-ligands, the νav values were calculated for the carbonyl stretches of in complexes 11-14, 19 and 20 (Table 2.9, pg. 61), these data have been compiled with those from for a range of related monoanionic and neutral bidentate ligands coordinated at rhodium bis(carbonyl). These data are also graphically represented Figure 2.24 (pg. 62).

60 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

-1 Ligand νav (cm ) C-Rh-C (°) Ref.

FcACy 2015a 89.7(2) [134a]

CyGiso (13) 2019b 89.37(9) -

Dippnacnac 2021a 85.78(10) [135]

DippnacnactBu (14) 2021b 83.16(12) -

p-tolBIPMPh 2022b - [136]

b N3Dmp2 (11) 2022 87.8(2) -

tBuAiso (12) 2028b 90.16(9) -

C6F5nacnac 2045c 85.98(11) [137]

Fiso (19) 2045b - -

bis(3,5-dimethylpyrazolyl)borate (Bp*) 2048b - [138]

DippnacnacCF3 2049a - [135]

acac 2050d 88.9(3) [130b,139]

bis(pyrazolyl)borate (Bp) 2052b - [138]

b N3Dipp2 (20) 2056 - -

1,2-bis(dicyclohexylphosphino)ethane 2057b - [140]

1,1,1-trifluoroacac 2061d - [130b]

bis(N-methylimidazol-2-yl)methane (bim) 2064e 90.91(11) [141]

2,2ʹ-bipyridine 2070e - [142]

1,1,1,5,5,5-hexafluoroacac 2072d - [130b]

1,2-bis(diphenylphosphino)ethane (DPPE) 2078b - [143]

f bis(3,5-di(trifluoromethyl)pyrazolyl)borate 2078 - [138]

bis(pyrazolyl)methane (bpm) 2081e - [141]

Table 2.9 - Selected structural data and mean IR carbonyl stretching frequencies of

[Rh(L)(CO)2] complexes of various bidentate ligands ranked by νav

a b c d e f Spectrum collected in: KBr. CH2Cl2. neat solid (ATR method). petroleum. Nujol. hexane.

61 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.24 - Visual representation of the νav carbonyl stretching frequencies of [Rh(L)(CO)2] complexes where L is a bidentate ligand

Comparison of the experimental data and the calculated data of Budzelaar reveals that the calculated νav values are typically shifted to a higher frequency relative to the experimental data, but the general trends with regards to ligand architecture is maintained. It is noteworthy, that the frequencies for N-Dipp β-diketiminates, amidinates, guanidinates and triazenides exhibit the following trend; CyGiso < Dipp tBu nacnac < Aiso < Fiso < N3Dipp2 (Figure 2.24), which is consistent with the

62 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

hypothesised poorer donor character of triazenides and in accord with the NPA values calculated for the chelating nitrogens of amidinates and triazenides.[103] This correlation also highlights that ligand “bite angle” βn has a minimal effect on the calculated νav Cy value. The νav value for the N-Dmp triazenide is similar to that of Giso which suggests the N-Dmp substituents distort the N3frame to invite better donation vis-à-vis N3Dipp2. The frequencies for the bis(pyrazolyl)borate and acac based ligands suggest that they are also poorer donors relative to other bidentate ligands such as β-diketiminates and guanidinates (Figure 2.24). Neutral N,Nʹ-ligands, such as 2,2ʹ-bipyridine, and diphosphines were found to have the poorest donicities of the ligands surveyed.

From the work presented above; the rhodium bis(carbonyl) model represents an excellent probe for quantifying the electronic character of neutral and monoanionic bidentate ligands thereby achieving objective (ii) of this chapter (viz. Section 2.2).

2.3.3.3 Structural Studies of Rhodium Complexes 11-18

Single crystals of 11-14 suitable for X-ray diffraction studies were grown from concentrated hexane solutions. The molecular structure of 11 is depicted in Figure 2.25. The molecular structures of 12-14 can be found in the appendix. Relevant metrical parameters for 11-14 are listed in Table 2.10 (pg. 64).

Figure 2.25 - Molecular structure of 11 (40% thermal ellipsoids). All hydrogen atoms omitted and mesityl rings depicted as wireframes for clarity.

63 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Mean Rh-N Mean Rh-C C-Rh-C Ligand β (°) τ [111] (Å) n (Å) (°) 4

N3Dmp2 (11) 2.063 60.99(13) 1.831 87.8(2) 0.21

tBuAiso (12) 2.053 63.11(6) 1.857 90.16(9) 0.19

CyGiso (13) 2.052 64.10(6) 1.854 89.37(9) 0.19

DippnacnactBu (14) 2.066 90.90(8) 1.868 83.16(12) 0.07

Dippnacnac[135,144] 2.051 89.75(8) 1.866 85.78(10) 0.07

Table 2.10 - Selected bonding parameters for rhodium bis(carbonyl) amidinate, guanidinate, triazenide and β-diketiminate complexes

Complexes 11-14 are expectedly monomeric in the solid-state. Each complex displays a distorted square planar geometry about the rhodium centre as evidenced by τ4 values in the range 0.07-0.21.[111] Although the influences of the relative steric bulk cannot be discounted, the Rh-N and Rh-C bond lengths in 11-14 suggest a weaker donor character for the triazenide (11) relative to the amidinate (12) and guanidinate (13) (Table 2.10). Complex 14 displays a longer mean Rh-N bond length and a more acute C-Rh-C bond Dipp [135,144] angle relative to the reported [Rh( nacnac)(CO)2] (Table 2.10). This likely arises from the increased steric crowding of the rhodium centre (cf. G parameters from the dimethylaluminium steric probe, Dippnacnac 54.94, DippnacnactBu 58.71).

Single crystals of 15 suitable for X-ray diffraction studies were grown from a concentrated hexane solution. Complex 15 crystallises in the triclinic space group P1̅ with two unique half molecules in the asymmetric unit. The molecular structure of molecule A is depicted in Figure 2.26 (pg. 65). The two crystallographically independent molecules are essentially identical. The corresponding structural parameters for A and B are presented side-by-side in Table 2.11 for ease of comparison (pg. 65).

64 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Figure 2.26 - Molecular structure of 15 (50% thermal ellipsoids). All hydrogen atoms omitted and Dipp groups depicted as wireframes for clarity. Symmetry operation used to generate # atoms: 1-x, 1-y, 1-z.

Bond Parameter Molecule A Molecule B

Rh(1)-Rh(1)# 2.5116(5) 2.5106(6)

Rh(1)-N(1) 2.051(3) 2.062(3)

Rh(1)-N(3) 2.057(3) 2.060(3)

Rh(1)-C(1) 1.922(4) 1.923(4)

Rh(1)-C(2) 2.082(4) 2.015(5)

Rh(1)#-C(2) 2.168(5) 2.234(7)

C(1)-O(1) 1.123(4) 1.129(5)

C(2)-O(2) 1.136(5) 1.163(5)

N(1)-N(2) 1.307(4) 1.294(4)

N(2)-N(3) 1.297(4) 1.293(4)

N(1)-N(2)-N(3) 117.2(3) 118.0(3)

Rh(1)-C(2)-Rh(1)# 72.43(15) 72.22(19)

Table 2.11 - Selected bond lengths (Å) and angles (°) of complex 15

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Each of the molecules in 15 possesses D2h symmetry, which is consistent with its simple IR spectrum vide supra. The distances between the rhodium atoms and terminal CO groups (mean 1.923 Å) are longer than those in 11-14 (Table 2.10). The μ-CO groups display a moderate degree of asymmetry in their Rh-C distances; this is most pronounced in molecule B. Furthermore, the C-O bond length for the μ-CO group in molecule B (1.163(5) Å) is considerably longer than that of molecule A (1.136(5) Å).

The D2h symmetrical Rh2(μ-CO)2 core in 15 is comparable to that in [145] [N(Me3)4]2[Rh12(CO)30]. The mean distance between the rhodium atoms and μ-CO groups in 15 (2.125 Å) is longer than that reported for [N(Me3)4]2[Rh12(CO)30] (2.00 Å),[145] whilst the mean C-O distance in the μ-CO groups in 15 (1.150 Å) is shorter than [145] that in [N(Me3)4]2[Rh12(CO)30] (1.17 Å). This demonstrates a lower degree of metal back bonding in 15 relative to [N(Me3)4]2[Rh12(CO)30], and is consistent with the higher frequency of the IR active μ-CO absorbance in 15 (1814 cm-1) relative to that of -1 [146] [N(Me3)4]2[Rh12(CO)30] (1771 cm ). The N-N distances in 15 are consistent with a high degree of delocalisation of electrons over each N3 donor set (vide supra).

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Single crystals of 16 suitable for X-ray diffraction study were grown by slow cooling of a concentrated hexane solution to -25 °C from ambient temperature. The molecular structure of 16 is depicted in Figure 2.27. Metrical data for 16 can be found in the appendix.

Figure 2.27 - Molecular structure of 16 (30% thermal ellipsoids). All hydrogen atoms omitted and Dipp groups depicted as wireframes for clarity (top), Dipp groups removed for clarity to show the cluster core (bottom).

The connectivity in the molecular structure of 16 confirms the suspected insertion of CO into the Rh-N bond identified by IR spectroscopy (vide infra). The molecular structure of 16 exhibits C3v symmetry and contains solely bridging and iminocarbamoyl CO groups, this is consistent with the two CO stretches in its IR spectrum. It was

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previously noted that the IR spectrum of 16 is different to that of the decomposition product of 19. This difference highlights the role of the salt metathesis by-product LiCl in templating the formation of the cluster from three Rh(LCO)(μ-CO) units. The formation of 16 indicates that the formamidinate Fiso exhibits some unique reactivity amongst the systems explored.

Single crystals of 17 and 18 suitable for X-ray diffraction studies were grown from concentrated hexane solutions. The molecular structure of 18 is depicted in Figure 2.28. The molecular structure of 17 can be found in the appendix. Relevant metrical parameters for both complexes are given in Table 2.12 (pg. 69).

Figure 2.28 - Molecular structure of 18 view down the Rh(2)···N(2) axis (30% thermal ellipsoids). All hydrogen atoms omitted for clarity

.

68 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

Bond Parameter 17 Bond Parameter 18

Rh(1)-N(1) 2.094(3) Rh(1)-N(1) 2.029(8)

Rh(1)-N(2) 2.107(3) Rh(1)-N(3) 2.102(8)

N(1)-C(13) 1.325(5) N(1)-N(2) 1.275(11)

N(2)-C(13) 1.303(4) N(2)-N(3) 1.329(10)

Rh(1)-cod alkene Rh(1)-cod 1.987 (mean) 1.977 (mean) centroid alkene centroid

N(1)-C(13)-N(2) 114.3(3) N(1)-N(2)-N(3) 106.8(3)

N(1)-Rh(1)-N(2) 63.40(12) N(1)-Rh(1)-N(3) 60.77(11)

Table 2.12 - Selected bond lengths (Å) and angles (°) of rhodium 1,5-cycloctadiene complexes 17 and 18

The molecular structures of 17 and 18 are similar to those of [Rh(PhAtBu)(cod)],[147] [Rh(PhAPh)(cod)][148] and [Rh(tBuAiso)(cod)].[149] The rhodium centre in each complex displays a distorted square planar geometry with Rh-C and Rh-N distances in the normal ranges (Table 2.12).[45] It is noteworthy that the binding of the triazenide to the rhodium centre in 18 is considerably more asymmetric than the analogous amidinate binding in 17. This manifests in the lesser degree of delocalisation across the chelate donor in 18 relative to 17 (Table 2.12).

2.3.4 The Development of a Second Generation Steric Probe

Earlier in this chapter, dimethylaluminium was identified as a reliable probe for the quantification of steric bulk of monoanionic bidentate N,N'-ligands because [AlMe2(L)] complexes are typically monomeric, four coordinate and tetrahedral about the aluminium. The solid-state structures of the rhodium bis(carbonyl) complexes 11-14 are likewise monomeric and four coordinate albethey square planar about the rhodium centre. As per Tolman’s use of nickel tricarbonyl, for both θ and νav, rhodium bis(carbonyl) may serve a secondary purpose as a probe for the steric quantification of monoanionic bidentate N,N'-ligands. To substantiate this, G and V parameters were calculated for 11-14 as well as a number of monoanionic bidentate N,N'-ligands for

69 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

which the crystallographic data was accessible from the CSD. This data is listed in Table 2.13.

3 a a Ligand GRh VG (Å ) GAl ΔG VRh VAl ΔV

Fiso 40.94b 0 42.29 1.35 32.4b 33.5 1.1

b b N3Dipp2 41.84 0 41.91 0.07 34.7 32.2 2.5

C6F5nacnac[137] 44.59 0.39 48.18 3.59 37.2 40.0 2.8

tBuAiso 47.93 0 47.74 0.19 41.8 40.0 1.8

CyGiso 48.84 0 49.98 1.14 41.6 42.1 0.5

Dippnacnac[135] 56.12 0.35 54.94 1.18 48.9 46.4 2.5

DippnacnactBu 59.11 0.60 58.71 0.40 51.7 50.3 1.4

N3Dmp2 62.99 0 64.60 1.61 48.8 49.1 0.3

Table 2.13 - Steric measurements of various monoanionic bidentate N,N'-ligands

derived from rhodium(I) complexes, ordered by GRh. a Calculated using a sphere of radius 4.0 Å. b Calculation was made on the complex which contained a cod co-ligand viz. 17 and 18.

Dipp It is noteworthy that the GRh parameter for nacnac ligand lays just outside of a half standard deviation of the mean of G parameter for Dippnacnac ligands listed in Table 2.2. For each ligand surveyed the G and V parameters from the rhodium bis(carbonyl) probe show excellent correlation with those measured from the dimethylaluminium probe (Δ range 0.07-3.59%, Table 2.13). It is noteworthy that zero values of VG were obtained for all complexes with the exception of those containing β-diketiminate ligands which 3 range 0.35-0.60 Å (Table 2.13). These non-zero values of VG contrast the zero values obtained for the same ligands using the dimethylaluminium probe (cf. Section 2.3.2.4), this disparity likely arises from the square planar geometry about the metal in the former relative to the tetrahedral geometry in the latter. It is also noteworthy that these 3 non-zero VG values lie well below the accepted threshold (< 6.0 Å , cf. Section 2.3.1.4), thereby demonstrating that the slight steric form of the carbonyl co-ligands. This shows that [Rh(L)(CO)2] complexes are also a useful probe for the quantification of steric properties of monoanionic bidentate N,N'-ligands. However, the relatively small number of structurally characterised [Rh(L)(CO)2] complexes of monoanionic bidentate

70 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

N,N'-ligands and their square planar geometry favour the use of the dimethylaluminium probe in the first instance.

One advantage of the rhodium bis(carbonyl) probe over the dimethylaluminium probe is that structurally characterised [Rh(L)(CO)2] complexes are known for other widely used classes of monoanionic ligands of such as cyclopentadienyl (Cp), tris(pyrazolyl)borate

(Tp) and monoanionic bidentate O,O'-ligands. These [Rh(L)(CO)2] complexes display the “common” binding modes observed for these ligands, for instance η5-Cp and κ3-Tp, 2 2 [150] by contrast η -Cp and κ -Tp were observed in the respective [AlMe2(L)] complexes. To an extent this curtails the wider applicability of the dimethylaluminium probe for ligands with denticity > 2. It is also conceivable that the rhodium bis(carbonyl) probe could be extended to evaluate the steric character of neutral polydentate ligands by employing a non-coordinating anion (cf. Section 2.3.3). G and V parameters were calculated for a range of common ligands coordinated to rhodium(I). These data are listed in Table 2.14.

3 a Ligand G VG (Å ) V Ref.

κ2-O,O'-acac 31.02 0 18.7 [139]

η5-Cpbc 34.93 0 23.0 [151]

η5-Cp* 38.54 0 36.6 [152]

κ3-Tpc 42.46 0.01 33.7-33.8 [153]

η5-CpPh5 45.37 0 43.4 [154]

κ3-Tp*d 50.04 0 40.4-40.5 [155]

κ3-4-tBuTp* 50.74 0 41.1-41.2 [156]

κ3-3-(p-tol),4-tBuTp 62.99 0 46.8-46.9 [157]

Table 2.14 - Steric measurements of various multidentate ligands derived from Rh(I) complexes, ordered by G. a Calculated using a sphere of radius 4.0 Å. The calculation of V for boron containing ligands is not possible using SambVca, V parameters were therefore calculated by replacing boron with bromine to represent the lower range of steric bulk and with iodine to estimate the upper range of steric bulk. The van der Waals radii of boron, bromine and iodine are 1.92 Å, 1.83 Å and 1.98 Å respectively.[158] b Hydrogen atom locations were not reported in the crystallographic data for this complex, therefore the values of G and V reflect the steric character of the ligand in the absence of hydrogen atoms. c Calculation was made on the [Rh(L)(cod)] complex. d Calculation was made on the [Rh(Tp*)(nbd)] complex.

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The rhodium bis(carbonyl) template enables the steric profiles of a diverse range of monoanionic ligand architectures to be compared (Figure 2.29). This data further highlights the remarkable steric bulk of the new 1,3-bis(2,6-terphenyl)triazenide, based on 1, which is comparable to the most sterically demanding Tp ligands studied.

Figure 2.29 - Steric characters of monoanionic ligands ranked by G

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2.4 Conclusions

The dimethylaluminium probe has been established as a reliable method for the quantification of the steric character of monoanionic bidentate N,Nʹ-ligands. A range of metal centres and geometries were examined using the Dippnacnac donor, from which aluminium was found to be a good representative metal. A range of co-ligands at Al(Dippnacnac) were also evaluated. These confirmed that methyl groups act as sterically slight and representative co-ligands. Two methods for the quantification of steric character were explored; (i) solid angle (Ω) and (ii) molecular volume (V). A case study revealed the use of RsvdW in V calculations leads to considerable inter-ligand overlap.

This led to RvdW being adopted for V calculations. The steric bulk of 30 monoanionic bidentate N,Nʹ-ligands bound to dimethylaluminium were evaluated by Ωs and V methodologies. This data enabled the comparison of the steric character of a diverse range of ligand architectures, such as amidinates, guanidinates, β-diketiminates and triazenides. N-substituents aside, a general correlation between the number of atoms in the N,Nʹ-linker and steric bulk was found. This data also enabled a comprehensive study of substituent steric effects in amidinates, guanidinates, β-diketiminates and triazenides.

A probe for the quantification of ligand donicity for monoanionic bidentate N,Nʹ-ligands was developed beyond the early theoretical proposals of Budzelaar. In achieving this goal a number of novel rhodium complexes (11-20) were prepared. Calculation of the mean νCO (νav) in the IR spectra of [Rh(L)(CO)2] complexes enabled the donicities of a diverse range of monoanionic bidentate N,Nʹ-ligands to be quantified. Monoanionic bidentate N,Nʹ-ligands were generally found to have greater donicities compared to neutral bidentate ligands. The following trend for donicity was found: guanidinate > β-diketiminate > amidinate > formamidinate > triazenide. This is in accord with calculated NPA values and the hypothesised poorer donor character of triazenides.

Rhodium bis(carbonyl) was found to be comparable to dimethylaluminium as a probe for the quantification of ligand steric character. The use of rhodium bis(carbonyl) enables the comparison of a significantly more diverse catalogue of ligand architectures to be addressed with the potential to expand beyond the dimethylaluminium probe scaffold.

This Chapter also describes the syntheses of a new super bulky 1,3-bis(2,6-terphenyl)triazene (1) and two C-2,6-terphenyl substituted amidines (2 and

73 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

3). Dimethylaluminium complexes of these and several other bidentate N,Nʹ-ligands were prepared and crystallographically characterised (4-10). The steric character of these ligands was assessed and compared to those in the literature. It is noteworthy that the aforementioned super bulky ligand, based on 1, was found to be superior in bulk to all other ligands. Furthermore the bulk of this ligand highlights a flaw in V calculations owing to coordination sphere size limitations. Such a flaw is not encountered in Ωs calculations; therefore the G parameter may be considered the primary descriptor of a ligand’s steric character.

74 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

2.5 Future Directions

The development of probes for the quantification of ligand steric and electronic character, as per the study herein can used to optimise catalyst design in a range of processes. Immediate examples include rhodium and iridium catalysed hydroamination.[141,159]

Studies have shown that sterically bulky ligands can kinetically stabilise low oxidation state s-, p-, d- and f-block metal complexes by preventing disproportionation processes and/or other decomposition pathways.[47] The probes developed in this chapter have the potential to deconvolute the decision making process when choosing ligands for the stabilisation of labile species such as magnesium(I),[160] aluminium(I)[71] and zinc(I).[161] Similarly, these probes can be applied to the stabilisation of heavy group 13 metal hydride complexes, which typically necessitate steric shielding of the frail M-H functions.

Recently monomeric trigonal planar dimethylaluminium complexes of bulky aryl ligands have been reported.[162] It is conceivable that the dimethylaluminium probe can be employed to quantify the steric character of “super bulky” monoanionic monodentate ligands like these 2,6-terphenyls,[163] carbazoles[164] and amides.[165]

Finally, given the problems incurred when using the molecular volume technique to quantify the steric character of super bulky ligands, it would be prudent for the steric character of super bulky NHC ligands to be requantified by solid angle, e.g. G methods, to determine their primary steric descriptors.

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2.6 Experimental

2.6.1 General Synthetic Procedures

[166] [167] [168] [104,169] [170] Cy [171] DmpI, DmpN3, DitopI, Dipp2N3H, (DippN)2C, GisoH, Dipp tBu [172] [173] [174] nacnac H, [{Rh(μ-Cl)(CO)2}2], [{Rh(μ-Cl)(cod)}2], [159] [175] [{Rh(μ-OEt)(cod)}2] and FisoH were synthesised by literature procedures. N,N'-dicyclohexylcarbodiimide was purified by distillation prior to use.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

2.6.2 Synthesis of Dmp2N3H (1) nBuLi (1.6 M in hexanes, 7.6 mL, 12.2 mmol) was added dropwise at 0 °C to a slurry of DmpI (5.28 g, 12.0 mmol) in diethyl ether (150 mL) and stirring was continued for 2 h.

DmpN3 (4.30 g, 12.1 mmol) in diethyl ether (100 mL) was then added dropwise. After warming to ambient temperature and stirring for an additional 12 h, the red-brown solution was quenched with water (100 mL). The aqueous phase was separated and extracted with diethyl ether (3×50 mL) and dried over anhydrous MgSO4. Solvent removal in vacuo followed by recrystallisation from acetone afforded pale yellow prisms suitable for X-ray diffraction structure determination (5.53 g, 68%); m.p. 1 163-164 °C. H NMR (500 MHz, C6D6) δ 1.87 (s, 24H, o-CH3), 2.17 (s, 12H, p-CH3), AAB 6.78-6.80 (m, 12H, m-ArH and m-Ar’H), 6.86 (t, JHH = 7.3 Hz, 2H, p-ArH), 8.64 (br 13 s, 1H, NH). C NMR (100 MHz, C6D6) δ 21.0, 21.2 (CH3), 125.0, 128.5, 130.1 (ArCH), 132.2, 136.0, 136.2, 136.5, 137.6 (ArC). IR (Nujol, cm-1) 3264 (w, N-H), 1612 (w, N=N), 1496 w, 1262 (w, N-N), 1231 (w, N-N), 1202 (w), 1141 (br w), 1092 (w),

850 (m), 799 (w), 766 (w), 753 (w), 740 (w). Anal. Calc. for C48H51N3: C, 86.05; H, 7.67; N, 6.27. Found: C, 85.98; H, 7.81; N, 6.35%.

2.6.3 Synthesis of DitopACyH (2) nBuLi (1.6 M in hexanes, 5.25 mL, 8.40 mmol) was added to a solution of DitopI (3.22 g, 8.38 mmol) in diethyl ether (60 mL) at 0°C. The resulting yellow solution was gradually warmed to ambient temperature and stirred for a further 4 h whereupon a solution of N,N'-dicyclohexylcarbodiimide (1.75 g, 8.48 mmol) in diethyl ether (30 mL) was added dropwise. After 12 h the reaction was quenched with water (50 mL). The 76 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

aqueous phase was separated and extracted with dichloromethane (3×40 mL) and dried over anhydrous MgSO4. Solvent removal in vacuo afforded a viscous pale yellow oil, addition of hexane (30 mL) induced precipitation of a colourless solid. Recrystallisation from hexane afforded colourless hexagonal elongated plates suitable for X-ray diffraction structure determination (2.74 g, 70%); m.p. 124-125 °C. 1H NMR (400

MHz, C6D6) δ 0.77-1.82 (m, 20H, CH2), 2.15 (s, 6H, CH3), 3.02 (br m, 1H, NCH), 3.29 AABB (br s, 1H, NH), 3.89 (br m, 1H, NCH), 7.10 (d, JHH = 7.9 Hz, 4H, o- or m-Ar’H), AAB AAB 7.21 (t, JHH = 7.6 Hz, 1H, p-ArCH), 7.34 (d, JHH = 7.6 Hz, 2H, m-ArCH), 7.58 AABB 13 (d, JHH = 7.9 Hz, 4H, o- or m-Ar’H). C NMR (100 MHz, C6D6) δ 21.7 (CH3),

25.9, 26.2, 27.1, 27.2, 33.7, 35.9 (CH2), 49.6, 59.5 (NCH), 129.4, 129.6, 130.0, 134.8 (ArCH), 137.7, 139.7, 142.1, 152.3 (ArC), 159.5 (NCN). IR (Nujol, cm-1) 3441 (sh m, N-H), 1630 (s, N=C), 1577 (w), 1514 (w), 1299 (m), 1273 (w), 1252 (w), 1238 (w), 1183 (w), 1151 (m), 1103 (w), 1019 (w), 964 (w), 888 (w), 831 (w), 805 (s), 771 (m),

756 (w). Anal. Calc. for C33H40N2: C, 85.30; H, 8.68; N, 6.03. Found: C, 85.00; H, 8.79; N, 5.99%.

2.6.4 Synthesis of DmpACyH (3)

A solution of DmpLi (995 mg, 3.11 mmol) in diethyl ether (30 mL) was treated dropwise with a solution of N,N'-dicyclohexylcarbodiimide (700 mg, 3.39 mmol) in diethyl ether (30 mL). After 12 h the reaction was quenched with water (50 mL). The aqueous phase was separated and extracted with dichloromethane (3×40 mL) and dried over anhydrous MgSO4. Solvent removal in vacuo afforded a viscous pale yellow oil, addition of hexane (30 mL) induced precipitation of a colourless solid. Recrystallisation from hexane afforded colourless prisms suitable for X-ray diffraction structure 1 determination (940 mg, 58%); m.p. 172-173 °C. H NMR (400 MHz, C6D6) δ (isomer

1) 0.28-0.43 (br m, 2H, CH2), 0.80-1.77 (br m, 18H, CH2), 2.12-2.22 (m, 12H, o-CH3),

2.31 (s, 6H, p-CH3), 2.89-2.96 (br m, 1H, N(H)CH), 3.09 (br s, 1H, N=NCH), 3.51-3.59 (br m, 1H, NH), 6.88 (s, 4H, m-Ar’H), 6.95-7.00 (m, 3H, m- and p-ArH); (isomer 2)

0.71-0.76 (br m, 2H, CH2), 0.80-1.77 (br m, 16H, CH2), 1.91-1.95 (br m, 2H, CH2),

2.12-2.22 (m, 12H, o-CH3), 2.31 (s, 6H, p-CH3), 3.09 (br s, 1H, N=NCH), 3.51-3.59 (br m, 1H, NH), 3.71-3.80 (br m, 1H, N(H)CH), 6.82-6.85 (m, 4H, m-Ar’H), 7.12-7.20 (m, 13 3H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 21.1, 21.2, 21.6 (o-CH3), 21.7, 22.2

(p-CH3), 25.5, 25.7, 25.8, 26.6, 26.7, 32.7, 34.3, 34.8, 36.3 (CH2), 49.6, 52.9, 56.3, 57.8

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(NCH), 128.1, 128.1, 128.3, 128.5, 128.6, 129.2, 130.4 (ArCH), 135.7, 136.3, 136.6, 136.8, 137.4, 138.4, 138.9, 139.3, 140.7, 141.6 (ArC), 148.3, 149.3 (NCN). IR (Nujol, cm-1) 3463 (m, N-H), 1642 (s, N=C), 1625 (s, N=C), 1332 (w), 1311 (w), 1297 (w), 1266 (w), 1253 (w), 1231 (w), 1183 (w), 1159 (w), 1144 (m), 1107 (m), 1087 (w), 1072 (w), 1029 (m), 978 (m), 886 (s), 858 (m), 850 (s), 813 (m), 794 (w), 767 (s), 740 (m),

687 (w), 665 (w), 621 (w), 585 (w). Anal. Calc. for C37H48N2: C, 85.33; H, 9.29; N, 5.38. Found: C, 85.54; H, 9.20; N, 5.28%.

2.6.5 General Procedure for the Preparation of Dimethylaluminium Complexes

A solution of protonated ligand (1.0 equiv.) in toluene (20 mL mmol-1) was treated with

AlMe3 (2.0 M in toluene, 1.1 equiv.) at ambient temperature. Gas evolution was immediately observed. The resultant solution was stirred for 2 h followed by the removal of the solvent and excess AlMe3 in vacuo. The resultant solid was recrystallised from the minimum amount of hexane (4, 7-9) or toluene (5, 6) at -25 °C over 24 h.

[AlMe2(N3Dmp2)] (4). Yellow tabular plates suitable for X-ray diffraction structure 1 determination (428 mg, 97%); m.p. 202-203 °C. H NMR (250 MHz, C6D6) δ -1.27 (s, AAB 6H, Al-CH3), 1.95 (s, 24H, o-CH3), 2.19 (s, 12H, p-CH3), 6.72 (d, JHH = 7.3 Hz, 4H, AAB 13 m-ArH), 6.84 (t, JHH = 7.3 Hz, 2H, p-ArH), 6.84 (s, 8H, m-Ar’H). C NMR (50

MHz, C6D6) δ -10.1 (Al-C), 21.2 (p-CH3), 21.7 (o-CH3), 125.9, 129.0, 131.0 (ArCH), 134.3, 136.2, 136.7, 137.2, 140.3 (ArC). IR (Nujol, cm-1) 2731 (m), 1936 (w), 1875 (w), 1759 (w), 1727 (w), 1611 (s), 1573 (w), 1487 (m), 1291 (w), 1262 (s, N=N), 1231 (m), 1179 (s), 1093 (w), 1032 (m), 880 (w), 848 (s), 804 (w), 780 (m), 766 (m), 759 (m), 743

(w), 720 (w), 695 (s), 682 (w), 660 (w), 610 (m), 590 (w). Anal. Calc. for C50H56AlN3: C, 82.72; H, 7.77; N, 5.79. Found: C, 81.79; H, 7.67; N, 5.68%.

Ditop [AlMe2( ACy)] (5). Colourless plates suitable for X-ray diffraction structure 1 determination (450 mg, 86%); m.p. 190-192 °C (dec.). H NMR (400 MHz, C6D6)

δ -0.20 (s, 6H, Al-CH3), 0.80-1.79 (m, 20H, CH2), 2.13 (s, 6H, p-CH3), 2.81 (br m, 2H, AABB AAB NCH), 7.15 (d, JHH = 7.9 Hz, 4H, o- or m-Ar’H), 7.17 (t, JHH = 7.6 Hz, 1H, AAB AABB p-ArH), 7.31 (d, JHH = 7.6 Hz, 2H, m-ArH), 7.64 (d, JHH = 7.9 Hz, 4H, o- or 13 m-Ar’H). C NMR (100 MHz, C6D6) δ -9.4 (Al-C), 21.3 (CH3), 25.7, 25.8, 35.8 (CH2), 53.9 (NCH), 129.4, 129.5, 129.8, 130.1 (ArCH), 137.9, 138.1, 141.4 (ArC), 171.0

78 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

(NCN) (one ArC not observed). IR (Nujol, cm-1) 1906 (w), 1631 (s, N=C), 1614 (w), 1586 (w), 1515 (s), 1365 (s), 1344 (m), 1312 (w), 1299 (w), 1271 (w), 1257 (w), 1237 (m), 1215 (w), 1185 (m), 1178 (m), 1151 (w), 1110 (w), 1081 (w), 1065 (w), 1020 (w), 991 (m), 899 (w), 887 (s), 844 (w), 830 (w), 819 (s), 793 (s), 769 (s), 707 (s), 670 (s),

611 (w), 546 (w). Anal. Calc. for C35H45AlN2: C, 80.73; H, 8.71; N, 5.38. Found: C, 81.05; H, 8.97; N, 5.27%.

Dmp [AlMe2( ACy)] (6). Colourless octahedra suitable for X-ray diffraction structure 1 determination (450 mg, 97%); m.p. 158-160 °C (dec.). H NMR (400 MHz, C6D6)

δ -0.31 (s, 6H, Al-CH3), 0.91-1.98 (m, 20H, CH2), 2.14 (s, 6H, p-CH3), 2.23 (s, 12H, AAB o-CH3), 2.82 (br s, 2H, NCH), 6.84 (s, 4H, m-Ar’H), 6.95 (d, JHH = 7.7 Hz, 2H, AAB 13 m-ArH), 7.04 (t, JHH = 7.7 Hz, 1H, p-ArH). C NMR (100 MHz, C6D6) δ -8.7

(Al-C), 20.9, 23.1 (CH(CH3)2), 26.0, 26.2, 36.8 (CH2), 53.1 (NCH), 128.3, 129.2 (ArCH), 131.0 (ArC), 133.2 (ArCH), 136.4, 137.1, 138.9, 141.5 (ArC), 169.0 (NCN). IR (Nujol, cm-1) 1960 (w), 1900 (w), 1745 (w), 1643 (w), 1614 (m, N=C), 1572 (m), 1411 (br s), 1360 (s), 1342 (s), 1306 (w), 1295 (w), 1262 (m), 1236 (w), 1180 (s), 1150 (w), 1121 (w), 1062 (m), 1040 (w), 991 (m), 893 (w), 883 (m), 857 (s), 815 (m), 760

(w), 776 (s), 700 (w), 661 (m). Anal. Calc. for C39H53AlN2: C, 81.20; H, 9.26; N, 4.86. Found: C, 81.52; H, 9.40; N, 4.75%.

[AlMe2(N3Dipp2)] (7). Colourless blocks suitable for X-ray diffraction structure 1 determination (190 mg, 33%); m.p. 82-84 °C. H NMR (400 MHz, C6D6) δ -0.17 (s, 6H, 3 3 Al-CH3), 1.22 (d, JHH = 6.9 Hz, 24H, CH(CH3)2), 3.49 (sept, JHH = 6.9 Hz, 4H, 13 CH(CH3)2), 7.05-7.20 (m, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ -10.1

(Al-C), 24.3 (CH(CH3)2), 28.7 (CH(CH3)2), 124.0, 128.1 (ArCH), 139.7, 144.9 (ArC). IR (Nujol, cm-1) 1929 (w), 1863 (w), 1587 (w), 1515 (w), 1383 (m), 1362 (m), 1329 (w), 1300 (w), 1276 (s, N=N), 1190 (m), 1103 (m), 1058 (m), 957 (w), 935 (s), 901 (w), 884 (w), 854 (w), 821 (w), 800 (s), 771 (m), 755 (m), 696 (br s). Anal. Calc. for

C26H40AlN3: C, 74.07; H, 9.56; N, 9.97. Found: C, 73.64; H, 10.04; N, 9.75%.

Cy [AlMe2( Giso)] (8). Colourless blocks suitable for X-ray diffraction structure 1 determination (455 mg, 66%); m.p. 286-288 °C (dec.). H NMR (400 MHz, C6D6) 3 δ -0.12 (s, 6H, Al-CH3), 0.62-0.77 (m, 6H, CH2), 1.08-1.45 (m, 6H, CH2), 1.28 (d, JHH 3 = 6.8 Hz, 12H, CH(CH3)2), 1.39 (d, JHH = 6.8 Hz, 12H, CH(CH3)2), 1.40-1.68 (m, 8H, 3 CH2), 3.57 (br s, 2H, NCH), 3.76 (sept, JHH = 6.8 Hz, 4H, CH(CH3)2), 7.11-7.13 (m,

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13 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ -6.8 (Al-C), 23.2 (CH(CH3)2), 25.6,

27.1 (CH2), 28.0 (CH(CH3)2), 28.4 (CH(CH3)2), 34.7 (CH2), 59.1 (NCH), 124.1, 125.5 -1 (ArCH), 139.8, 145.0 (ArC), 164.9 (CN3). IR (Nujol, cm ) 1919 (m), 1862 (m), 1798 (w), 1695 (w), 1678 (w), 1610 (s, N=C), 1581 (s, N=C), 1251 (s), 1189 (s), 1162 (m), 1119 (w), 1105 (m), 1050 (w), 1019 (m), 972 (s), 954 (w), 930 (s), 894 (s), 868 (s), 847 (w), 829 (w), 818 (w), 799 (s), 770 (w), 754 (w), 728 (w), 652 (w), 625 (w), 566 (w).

Anal. Calc. for C39H62AlN3: C, 78.08; H, 10.42; N, 7.00. Found: C, 78.22; H, 10.65; N, 7.10%.

Dipp tBu [AlMe2( nacnac )] (9). Colourless blocks suitable for X-ray diffraction structure 1 determination (100 mg, 18%); m.p. 140-141 °C. H NMR (400 MHz, C6D6) δ -0.45 (s, 3 6H, Al-CH3), 1.10 (s, 18H, C(CH3)3), 1.30 (d, JHH = 6.8 Hz, 12H, CH(CH3)2), 1.31 (d, 3 3 JHH = 6.8 Hz, 12H, CH(CH3)2), 3.49 (sept, JHH = 6.8 Hz, 4H, CH(CH3)2), 5.85 (s, 1H, 13 β-CH), 7.02-7.15 (m, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ -9.7 (Al-C),

24.6, 26.7 (CH(CH3)2), 28.4 (CH(CH3)2), 32.4 (C(CH3)3), 43.2 (C(CH3)3), 101.1 (β-C), 124.4, 126.6 (ArCH), 142.9, 144.5 (ArC), 179.1 (α-C). IR (Nujol, cm-1) 1933 (m), 1867 (m), 1802 (w), 1601 (m), 1310 (w), 1254 (w), 1230 (s br), 1135 (w), 1103 (m), 1056 (w), 1022 (w), 1009 (w), 952 (w), 933 (w), 893 (w), 860 (w), 844 (w), 830 (w), 820 (w),

787 (s), 756 (s), 731 (w), 699 (s), 661 (m), 616 (w). Anal. Calc. for C37H59AlN2: C, 79.52; H, 10.64; N, 5.01. Found: C, 80.14; H, 11.08; N, 4.86%.

Me 2.6.6 Synthesis of [AlMe2( Aiso)] (10)

An excess of AlMe3 (2.0 M in toluene, 1.2 mL, 2.4 mmol) was added dropwise to a solution of (DippN)2C (369 mg, 1.0 mmol) in toluene (20 mL) at ambient temperature. The resultant colourless solution was stirred for 12 h, followed by the removal of volatiles in vacuo. The resultant colourless residue was extracted with hexane (40 mL), concentrated to insipient crystallisation and cooled to -25 °C overnight to afford colourless parallelepipeds suitable for X-ray diffraction structure determination (270 1 mg, 60%); m.p. 170-172 °C (dec.). H NMR (400 MHz, C6D6) δ -0.15 (s, 6H, Al-CH3), 3 3 1.18 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 1.23 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 1.28 3 (s, 3H, CCH3), 3.49 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 7.09-7.17 (m, 6H, m- and 13 p-ArH). C NMR (100 MHz, C6D6) δ -9.4 (Al-C), 14.0 (CCH3), 24.0, 24.7 (CH(CH3)2),

28.5 (CH(CH3)2), 124.0, 126.6 (ArCH), 138.3, 144.9 (ArC), 176.3 (NCN). IR (Nujol,

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cm-1) 1930 (m), 1868 (m), 1807 (w), 1705 (w), 1641 (s, N=C), 1584 (m), 1281 (w), 1255 (m), 1224 (w), 1188 (br s), 1101 (s), 1056 (s), 992 (m), 936 (s), 860 (s), 795 (s),

773 (m), 750 (w), 684 (br w), 586 (w). Anal. Calc. for C28H43AlN2: C, 77.37; H, 9.97; N, 6.45. Found: C, 77.14; H, 9.96; N, 6.71%.

2.6.7 General Procedure for the Preparation of Rhodium Carbonyl Complexes

A solution of protonated ligand (1.0 equiv.) in THF (30 mL mmol-1) was treated with nBuLi (1.6 M in hexane, 1.0 equiv.) at ambient temperature. The resultant solution was stirred for a further 2 h then added to a bright yellow solution of [{Rh(μ-Cl)(CO)2}2] (0.5 equiv.) at ambient temperature. The resultant mixture was stirred for 12 h, followed by the removal of volatiles in vacuo. The resultant solid was extracted with hexane (11, 12, 15, 16) or toluene (13, 14), concentrated to insipient crystallisation and cooled to -25 °C overnight.

[Rh(N3Dmp2)(CO)2] (11). Orange elongated plates suitable for X-ray diffraction structure determination (125 mg, 26%); m.p. 127-130 °C (dec.). 1H NMR (400 MHz,

C6D6) δ 1.97 (s, 24H, o-CH3), 2.20 (s, 12H, p-CH3), 6.78-6.84 (m, 6H, m- and p-ArH), -1 6.92 (s, 8H, m-Ar’H). IR (CH2Cl2, cm ) 2054 (sh s, CO), 1990 (sh s, CO).

tBu [Rh( Aiso)(CO)2] (12). Yellow plates suitable for X-ray diffraction structure 1 determination (77 mg, 27%); 156-157 °C (dec.). H NMR (400 MHz, C6D6) δ 0.82 (s, 3 3 9H, C(CH3)3), 1.35 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 1.51 (d, JHH = 6.9 Hz, 12H, 3 CH(CH3)2), 3.89 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 7.02-7.08 (m, 6H, m- and 13 p-ArH). C NMR (100 MHz, C6D6) δ 22.4, 24.7 (CH(CH3)2), 28.9 (CH(CH3)2), 28.9 3 (C(CH3)3), 44.4 (d, JRhC = 2.4 Hz, C(CH3)3), 123.7, 126.2 (ArCH), 142.9, 144.9 (ArC), 1 2 -1 186.6 (d, JRhC = 69.0 Hz, CO), 188.8 (d, JRhC = 5.3 Hz, NCN). IR (Nujol, cm ) 2064 -1 (sh s, CO), 1996 (sh s, CO); (CH2Cl2, cm ) 2063 (sh s, CO), 1992 (sh s, CO). Anal.

Calc. for C31H43RhO2N2·0.5(C6H14): C, 65.69; H, 8.11; N, 4.51. Found: C, 65.84; H, 8.43; N, 5.10%.

Cy [Rh( Giso)(CO)2] (13). Yellow prisms suitable for X-ray diffraction structure 1 determination (241 mg, 69%); m.p. 194-198 °C (dec.). H NMR (400 MHz, C6D6) δ 3 0.65-0.80 (m, 6H, CH2), 1.20-1.58 (m, 14H, CH2), 1.42 (d, JHH = 6.8 Hz, 12H, 3 CH(CH3)2), 1.69 (d, JHH = 6.8 Hz, 12H, CH(CH3)2), 3.52 (br t, 2H, NCH), 3.87 (sept, 3 13 JHH = 6.8 Hz, 4H, CH(CH3)2), 7.06-7.13 (m, 6H, m- and p-ArH). C NMR (100 MHz,

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C6D6) δ 22.9, 25.0 (CH(CH3)2), 25.8, 26.9 (CH2), 28.6 (CH(CH3)2), 35.4 (CH2), 57.5 2 (NCH), 124.0, 125.2 (ArCH), 142.9, 146.1 (ArC), 172.1 (d, JRhC = 5.9 Hz, CN3), 187.5 1 -1 (d, JRhC = 69.2 Hz, CO). IR (Nujol, cm ) 2050 (sh s, CO), 1979 (sh s, CO); (CH2Cl2, -1 cm ) 2055 (sh s, CO), 1983 (sh s, CO). Anal. Calc. for C39H56RhO2N3: C, 66.75; H, 8.04; N, 5.99. Found: C, 67.07; H, 8.26; N, 6.01%.

Dipp tBu [Rh( nacnac )(CO)2] (14). Yellow blocks suitable for X-ray diffraction structure 1 determination (150 mg, 45%); m.p. 140-142 °C (dec.). H NMR (400 MHz, C6D6) δ 3 3 1.18 (s, 18H, C(CH3)3), 1.29 (d, JHH = 6.8 Hz, 12H, CH(CH3)2), 1.69 (d, JHH = 6.8 Hz, 3 12H, CH(CH3)2), 3.51 (sept, JHH = 6.8 Hz, 4H, CH(CH3)2), 5.63 (s, 1H, β-CH), 13 6.98-7.15 (m, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 23.7, 24.8 (CH(CH3)2), 3 3 28.3 (CH(CH3)2), 33.9 (C(CH3)3), 43.5 (d, JRhC = 1.2 Hz, C(CH3)3), 98.2 (d, JRhC = 2.9 1 Hz, β-C), 123.2, 126.4 (ArCH), 140.4, 160.0 (ArC), 168.0 (br s, α-C), 181.4 (d, JRhC = -1 -1 66.5 Hz, CO). IR (Nujol, cm ) 2052 (sh s, CO), 1989 (sh s, CO); (CH2Cl2, cm ) 2054

(sh s, CO), 1988 (sh s, CO). Calc. for C37H53RhN2O2: C, 67.26; H, 8.09; N, 4.24. Found: C, 67.15; H, 8.09; N, 4.23%.

[{Rh(μ-N3Dipp2)(μ-CO)(CO)}2] (15). Orange blocks suitable for X-ray diffraction 1 3 structure determination (182 mg, 70%). H NMR (400 MHz, C6D6) δ 1.25 (d, JHH = 6.9 3 3 Hz, 12H, CH(CH3)2), 1.32 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 3.96 (sept, JHH = 6.9 -1 Hz, 4H, CH(CH3)2), 7.04-7.08 (m, 6H, m- and p-ArH). IR (CH2Cl2, cm ) 2020 m, 1840 sh s. Calc. for C52H64Rh2N6O4: C, 59.89; H, 6.19; N, 8.06. Found: C, 60.81; H, 6.58; N, 8.17%.

[Li{Rh(FisoCO)(μ-CO)}3Cl] (16). Yellow rhombohedrons suitable for X-ray -1 diffraction structure determination (95 mg, 49%). IR (CH2Cl2, cm ) 1864 (sh s, μ-CO), 1655 (sh s, NCO).

2.6.8 Synthesis of [Rh(Fiso)(cod)] (17)

A solution of FisoH (182 mg, 0.50 mmol) in THF (20 mL) was treated with nBuLi (1.19 M in hexane, 0.45 mL, 0.50 mmol) at ambient temperature. The resultant colourless solution was stirred at ambient temperature for 12 h, then added to a yellow solution of

[{Rh(μ-Cl)(cod)}2] (125 mg, 0.25 mmol) in THF (20 mL). The resultant mixture was stirred for a further 16 h, over which time the colour of solution changed from yellow to gold. The solvent was removed in vacuo and the residue was extracted with hexane (60

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mL). Concentration to insipient crystallisation (ca. 25 mL) followed by cooling to -25 °C afforded golden yellow prisms suitable for X-ray diffraction structure determination 1 3 (227 mg, 79%); 186-187 °C. H NMR (400 MHz, C6D6) δ 1.30 (d, JHH = 6.9 Hz, 12H, 3 CH(CH3)2), 1.46 (br m, 4H, CH2-cod), 1.47 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 2.26 (br 3 m, 4H, CH2-cod), 3.81 (br m, 4H, CH-cod), 4.09 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 3 1 7.00-7.13 (m, 6H, m- and p-ArH), 8.00 (d, JRhH = 2.3 Hz, 1H, NCH). H NMR (400 3 3 MHz, THF-d8) δ 1.20 (d, JHH = 6.9 Hz, 12H, CH(CH3)2), 1.39 (d, JHH = 6.9 Hz, 12H,

CH(CH3)2), 1.67-1.74 (br m, 4H, CH2-cod), 2.35-2.44 (br m, 4H, CH2-cod), 3.71 (br s, 3 4H, CH-cod), 3.94 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 6.96-7.03 (m, 6H, m- and 3 13 p-ArH), 8.09 (d, JRhH = 2.3 Hz, 1H, NCH). C NMR (100 MHz, C6D6) δ 23.4, 25.7 1 (CH(CH3)2), 28.2 (CH(CH3)2), 31.1 (CH2-cod), 78.7 (d, JRhC = 13.1 Hz, =CH), 123.3, 2 13 125.3 (ArCH), 142.0, 144.6 (ArC), 169.9 (d, JRhC = 5.1 Hz, NCN). C NMR (100

MHz, THF-d8) δ 23.3, 25.7 (CH(CH3)2), 28.4 (CH(CH3)2), 31.3 (CH2-cod), 79.0 (d, 1 2 JRhC = 13.0 Hz, =CH), 123.3, 125.2 (ArCH), 142.3, 144.9 (ArC), 170.9 (d, JRhC = 5.2 Hz, NCN). IR (Nujol, cm-1) 1531 (br s, N=C), 1360 (m), 1321 (s), 1260 (s), 1193 (s), 1152 (w), 1100 (m), 1077 (w), 1057 (m), 1045 (w), 993 (w), 976 (w), 952 (s), 935 (w), 899 (w), 885 (w), 865 (m), 831 (w), 802 (sh s), 758 (s), 723 (w), 666 (w). Anal. Calc. for C33H47RhN2: C, 68.97; H, 8.24; N, 4.87. Found: C, 69.14; H, 8.53; N, 4.74%.

2.6.9 Synthesis of [Rh(N3Dipp2)(cod)] (18)

A solution of [{Rh(μ-OEt)(cod)}2] (80 mg, 0.17 mmol) in toluene (20 mL) was treated with a solution of Dipp2N3H (109 mg, 0.30 mmol) in toluene (10 mL) at ambient temperature. After 10 min, the colour of the mixture had changed from yellow to orange. After 4 h the solvent was removed in vacuo and the residue was extracted with hexane (40 mL). Concentration to insipient crystallisation, followed by cooling to -25 °C afforded red prisms suitable for X-ray diffraction structure determination (80 mg, 1 3 46%); m.p. 190-192 °C (dec.). H NMR (400 MHz, C6D6) δ 1.24 (d, JHH = 6.9 Hz,

24H, CH(CH3)2), 1.64 (br m, 4H, CH2-cod), 2.19 (br m, 4H, CH2-cod), 3.86 (br s, 4H, 3 CH-cod), 4.21 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 7.12-7.15 (m, 6H, m- and p-ArH). 13 C NMR (100 MHz, C6D6) δ 24.4 (CH(CH3)2), 28.2 (CH(CH3)2), 30.8 (CH2-cod), 81.9 1 -1 (d, JRhC = 12.3 Hz, =CH), 123.4, 127.0 (ArCH), 143.0, 144.6 (ArC). IR (Nujol, cm ) 1926 (w), 1860 (w), 1584 (w), 1356 (w), 1320 (w), 1253 (s, N=N), 1234 (w), 1176 (w), 1154 (w), 1104 (w), 1057 (w), 994 (w), 966 (w), 955 (m), 933 (w), 920 (w), 864 (w),

83 References for this chapter begin on pg. 85 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

797 (s), 766 (w), 752 (s), 726 (w). Anal. Calc. for C32H46RhN3: C, 66.77; H, 8.05; N, 7.30. Found: C, 67.36; H, 8.25; N, 7.51%.

2.6.10 General Procedure for the Carbonylation of Rhodium 1,5-cod Complexes

A solution of [Rh(L)(cod)] (ca. 0.10 mmol) in dichloromethane (2.0 mL) was sparged with CO(g) for 5 min. The colour of the solution changed from pale orange to dark red. The reaction mixture was then evaluated as soon as practicable (< 5 min) by IR spectroscopy.

-1 [Rh(Fiso)(CO)2] (19). IR (CH2Cl2, cm ) 2077 (sh s, CO), 2012 (sh s, CO).

New Carbonyl stretches 10 minutes later: 2039, 1771 and 1651 cm-1.

-1 [Rh(N3Dipp2)(CO)2] (20). IR (CH2Cl2, cm ) 2083 (sh s, CO), 2015 (sh s, CO).

New Carbonyl stretches 10 minutes later: 2020 and 1814 cm-1

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2.7 References

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[21] Komatsuzaki, T.; Sakakibara, K.; Hirota, M., Tetrahedron Lett. 1989, 30, 3309- 3312. [22] Hirota, M.; Sakakibara, K.; Komatsuzaki, T.; Akai, I., Comput. Chem. 1991, 15, 241-248. [23] Radzewich, C. E.; Guzei, I. A.; Jordan, R. F., J. Am. Chem. Soc. 1999, 121, 8673-8674. [24] Guzei, I. A.; http://xray.chem.wisc.edu/Resources.html#solidg. [25] Landis, C. R.; Nelson, R. C.; Jin, W.; Bowman, A. C., Organometallics 2006, 25, 1377-1391. [26] DiFranco, S. A.; Maciulis, N. A.; Staples, R. J.; Batrice, R. J.; Odom, A. L., Inorg. Chem. 2011, 51, 1187-1200. [27] Bilbrey, J. A.; Kazez, A. H.; Locklin, J.; Allen, W. D., J. Comput. Chem. 2013, 34, 1189-1197. [28] Allen, W. D.; http://www.ccqc.uga.edu/references/software.php. [29] Mathematica 10.0.2, Wolfram Research, Inc.: Champaign, IL, USA, 2014. [30] Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano, V.; Cavallo, L., Eur. J. Inorg. Chem. 2009, 1759-1766. [31] Cavallo, L.; https://www.molnac.unisa.it/OMtools/sambvca.php. [32] Clavier, H.; Nolan, S. P., Chem. Commun. 2010, 46, 841-861. [33] Kelly III, R. A.; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens, E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P., Organometallics 2008, 27, 202-210. [34] Dible, B. R.; Cowley, R. E.; Holland, P. L., Organometallics 2011, 30, 5123- 5132. [35] Savka, R.; Plenio, H., Eur. J. Inorg. Chem. 2014, 6246-6253. [36] Birkholz, M.-N.; Freixa, Z.; van Leeuwen, P. W. N. M., Chem. Soc. Rev. 2009, 38, 1099-1118. [37] Casey, C. P.; Whiteker, G. T., Israel J. Chem. 1990, 30, 299-304. [38] Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J., Organometallics 1995, 14, 3081-3089. [39] Holló-Sitkei, E.; Tárkányi, G.; Párkányi, L.; Megyes, T.; Besenyei, G., Eur. J. Inorg. Chem. 2008, 1573-1583.

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[156] Blake, A. J.; George, M. W.; Hall, M. B.; McMaster, J.; Portius, P.; Sun, X. Z.; Towrie, M.; Webster, C. E.; Wilson, C.; Zarić, S. D., Organometallics 2008, 27, 189-201. [157] Rheingold, A. L.; Liable-Sands, L. M.; Golan, J. A.; Trofimenko, S., Eur. J. Inorg. Chem. 2003, 2767-2773. [158] Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G., J. Phys. Chem. A 2009, 113, 5806-5812. [159] Burling, S.; Field, L. D.; Li, H. L.; Messerle, B. A.; Turner, P., Eur. J. Inorg. Chem. 2003, 3179-3184. [160] (a) Green, S. P.; Jones, C.; Stasch, A., Science 2007, 318, 1754-1757; (b) Bonyhady, S. J.; Jones, C.; Nembenna, S.; Stasch, A.; Edwards, A. J.; McIntyre, G. J., Chem. Eur. J. 2010, 16, 938-955; (c) Stasch, A., Angew. Chem. Int. Ed. 2014, 53, 10200-10203. [161] (a) Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A., Science 2004, 305, 1136-1138; (b) Wang, Y.; Quillian, B.; Wei, P.; Wang, H.; Yang, X.-J.; Xie, Y.; King, R. B.; Schleyer, P. v. R.; Schaefer, H. F.; Robinson, G. H., J. Am. Chem. Soc. 2005, 127, 11944-11945; (c) Zhu, Z.; Brynda, M.; Wright, R. J.; Fischer, R. C.; Merrill, W. A.; Rivard, E.; Wolf, R.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P., J. Am. Chem. Soc. 2007, 129, 10847-10857; (d) Schulz, S.; Schuchmann, D.; Krossing, I.; Himmel, D.; Bläser, D.; Boese, R., Angew. Chem. Int. Ed. 2009, 48, 5748-5751; (e) Jones, C.; Furness, L.; Nembenna, S.; Rose, R. P.; Aldridge, S.; Stasch, A., Dalton Trans. 2010, 39, 8788-8795; (f) Schmidt, S.; Schulz, S.; Bläser, D.; Boese, R.; Bolte, M., Organometallics 2010, 29, 6097- 6103; (g) Stasch, A., Chem. Eur. J. 2012, 18, 15105-15112. [162] (a) Erickson, J. D.; Fettinger, J. C.; Power, P. P., Inorg. Chem. 2015, 54, 1940- 1948; (b) Schädle, C.; Maichle-Mössmer, C.; Törnroos, K. W.; Anwander, R., Organometallics, In press, DOI: 10.1021/acs.organomet.5b00013. [163] (a) Zhu, Z.; Fischer, R. C.; Ellis, B. D.; Rivard, E.; Merrill, W. A.; Olmstead, M. M.; Power, P. P.; Guo, J. D.; Nagase, S.; Pu, L., Chem. Eur. J. 2009, 15, 5263- 5272; (b) Wilfling, P.; Schittelkopf, K.; Flock, M.; Herber, R. H.; Power, P. P.; Fischer, R. C., Organometallics, In Press, DOI: 10.1021/om500946e.

95 Chapter Two: Quantification of Steric and Electronic Character of Bidentate Ligands

[164] (a) Coombs, N. D.; Stasch, A.; Cowley, A.; Thompson, A. L.; Aldridge, S., Dalton Trans. 2008, 332-337; (b) Ortu, F.; Moxey, G. J.; Blake, A. J.; Lewis, W.; Kays, D. L., Chem. Eur. J., In press, DOI: 10.1002/chem.201406490. [165] (a) Dange, D.; Li, J.; Schenk, C.; Schnöckel, H.; Jones, C., Inorg. Chem. 2012, 51, 13050-13059; (b) Wright, R. J.; Brynda, M.; Power, P. P., Inorg. Chem. 2005, 44, 3368-3370; (c) Wright, R. J.; Brynda, M.; Fettinger, J. C.; Betzer, A. R.; Power, P. P., J. Am. Chem. Soc. 2006, 128, 12498-12509. [166] (a) Du, C. J. F.; Hart, H.; Ng, K. K. D., J. Org. Chem. 1986, 51, 3162-3165; (b) Akbar, S.; Hart, H., Synthesis 1996, 28, 1455-1458. [167] Gavenonis, J.; Tilley, T. D., Organometallics 2002, 21, 5549-5563. [168] Sattler, A.; Parkin, G., J. Am. Chem. Soc. 2012, 134, 2355-2366. [169] Nimitsiriwat, N.; Gibson, V. C.; Marshall, E. L.; Takolpuckdee, P.; Tomov, A. K.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.; Dale, S. H., Inorg. Chem. 2007, 46, 9988-9997. [170] Findlater, M.; Hill, N. J.; Cowley, A. H., Dalton Trans. 2008, 4419-4423. [171] Jin, G.; Jones, C.; Junk, P. C.; Lippert, K.-A.; Rose, R. P.; Stasch, A., New J. Chem. 2009, 33, 64-75. [172] Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G., Eur. J. Inorg. Chem. 1998, 1485-1494. [173] Krafft, M. E.; Wilson, L. J.; Onan, K. D., Organometallics 1988, 7, 2528-2534. [174] Giordano, G.; Crabtree, R. H.; Heintz, R. M.; Forster, D.; Morris, D. E. In Inorganic Syntheses, Vol. 28, pp. 88-90, 1990, John Wiley & Sons, Inc.: New York, USA. [175] Kolychev, E. L.; Portnyagin, I. A.; Shuntikov, V. V.; Khrustalev, V. N.; Nechaev, M. S., J. Organomet. Chem. 2009, 694, 2454-2462.

96

Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

3.1 Introduction

The quest for alternatives to cyclopentadienyl ligands has led to the development of a number of novel ligand systems.[1] Foremost among these are the organoamides, N(R1)R2.[2] In particular, the N,Nʹ-chelating organoamides subclasses such amidinates and β-diketiminates have surged due to their relative ease of synthesis and their facility for steric and electronic variation.[3] Indeed, the application of this class of ligand has led to the discovery of many exciting and unique coordination chemistries (vide infra), particularly in the specialised fields of main group[4] and lanthanide chemistry.[5]

Organoamide ligands may be accessed by protolysis of the protonated ligand,[3] as per cyclopentadienes, using suitably functionalised p- or f-block precursors.[4-5] However, such complexes are typically accessed through their alkali metal complexes, which act as metathesis transfer agents.[6] This chapter focuses on the development of alkali metal complexes of the sterically demanding monoanionic bidentate N,N'-chelating ligands based on 1-3 reported in Chapter Two. A major theme of this work is the impact of ligand sterics on the ensuing alkali metal coordination chemistry.

3.1.1 β-Diketiminate Complexes

Alkali metal β-diketiminates are widely used as transmetallation reagents for the synthesis of new metal β-diketiminate complexes.[6] These complexes are easily synthesised by deprotonation of the parent β-diketimine with alkali metal alkyls, amides and tbutylalkoxides or simply by direct reduction with the alkali metal. The solid-state structure of these complexes is dependent on the steric bulk of the β-diketiminate and the identity of the alkali metal (Figure 3.1, pg. 97).[7] Metal···π-arene interactions increasingly influence bonding (upon descent of the group) eventually usurping M-N bonding (Figure 3.1).[8]

96 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.1 - Examples of the nuclearity and ligand binding in homoleptic alkali metal β-diketiminate complexes[7-8]

In the presence of an auxiliary donor such as an ether or an amine, monomeric complexes of the lighter alkali metals (Li, Na) are typically obtained (Figure 3.2).[9]

Figure 3.2 - Examples of THF solvated alkali metal β-diketiminate complexes[9]

3.1.2 Amidinate, Guanidinate and Triazenide Complexes

A number of donor free alkali metal amidinate and guanidinate complexes have been structurally characterised.[10] In these structures there exists a strong correlation between the steric bulk of the ligand and the nuclearity of the complex in the solid-state (Figure 3.3, pg. 98). The recent development of an N-2,6-bis(diphenylmethyl)-4-tBuphenyl (Dippʹ) guanidine ligand has led to the first examples of donor free monomeric lithium and potassium guanidinate complexes (Figure 3.3).[11] 97 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.3 - Examples of donor free lithium guanidinate complexes demonstrating the impact of the ligands steric profile on the nuclearity of the complex

Amidinates and guanidinates exhibit a tremendously diverse range of binding modes. These often result in aggregation even in the presence of an auxiliary donor.[12] The mode of ligand binding is primarily dependent on the steric profile of the ligand and the provision of pendant arene donors (Figure 3.4). More sterically demanding ligands usually afford monomeric complexes (Figure 3.4).[13]

Figure 3.4 - The impact of the ligand’s steric profile and available N-arene groups on complex nuclearity and ligand binding mode[14]

Highly sterically congested ligands may only permit κ1-N-binding (Figure 3.5, pg. 99). Thus, the formation of an alkali metal complex of a ligand may result in the ligand undergoing isomerisation to minimise congestion at the metal centre (Figure 3.5).[14]

98 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.5 - Differing lithium coordination modes in sterically demanding amidinate complexes[15]

The choice of auxiliary donor can also have a significant impact on the ligand binding mode and therefore the nuclearity of the complex. Strongly coordinating chelating donors often afford lower nuclearity complexes (Figure 3.6).[13c,16]

Figure 3.6 - Dependence of complex nuclearity and amidinate binding mode on the nature of the auxiliary donor (all examples contain Li(FDep))

As with β-diketiminate complexes, higher coordination numbers are observed for the heavier alkali metals, and arene coordination becomes increasingly important when descending the group (Figure 3.7, pg. 100).[13c,17]

99 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.7 - Varying metal coordination modes in DME and THF coordinated complexes of FDep[13c,17]

The alkali metal chemistry of triazenides has featured less prominently in the literature relative those of β-diketiminates, amidinates and guanidinates. The coordination chemistry of small 1,3-bis(aryl)triazenides largely mimics that of the amidinates.[18] Interestingly, alkali metal complexes of a bulky 1,3-bis(2-biaryl)triazenide display inverse aggregation behaviour upon descent of the group (Figure 3.8), wherein the heavier metals exhibit lower nuclearities than their lighter counterparts.[19] This serves to highlight the increasing influence of alkali metal π-arene interactions on triazenide coordination down the group.

Figure 3.8 - Inverse aggreagation behavior of alkali metal complexes of a 1,3-bis(2-biaryl)triazenide 100 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

3.2 Project Outline

The development of new chelating anionic N,Nʹ-ligands has been essential to some of the advancements made in the coordination chemistries of s-, p-, d- and f-block metals.[20] These ligands have facilitated the isolation of a bounty of complexes that feature low oxidation state main group metals, such as magnesium(I)[21] and aluminium(I).[22] The development of complexes that feature extraordinarily short metal-metal bonding interactions can also be attributed to these ligands.[23] In addition, monoanionic bidentate N,Nʹ-ligands have been used as auxiliary ligands in a range of catalytic processes such as the hydroamination of aminoalkenes and olefin polymerisation.[6] The continued development of this ligand class therefore remains a hotbed of activity worldwide.

Alkali metal complexes of monoanionic bidentate nitrogen donor ligands are primarily used as metathesis transfer reagents in inorganic coordination chemistry.[6] Herein, this chapter aims to develop the alkali metal chemistry of the novel 2,6-terphenyl substituted N,Nʹ-ligands 1-3 that were introduced in Chapter Two. This work will provide a platform for later studies. It is also hoped that the steric bulk of these ligands will lead to the isolation of rare alkali metal coordination modes and monomeric solvent free species. As a complement to the study of 1, this chapter will also explore the alkali - metal chemistry of the smaller 1,3-bis(aryl)triazenide ligand; N3Dipp2 . All four amidinate and triazenide ligands are used prodigiously in Chapters Four through Six.

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3.3 Results and Discussion

3.3.1 The Synthesis of Ether Solvated Lithium Amidinate Complexes

The addition of one equivalent of nbutyllithium to THF solutions of amidines 2 and 3 affords the respective bis(thf) solvated lithium amidinate complexes, Ditop Dmp [Li( ACy)(thf)2] (21) and [Li( ACy)(thf)2] (22) in good yields (Scheme 3.1).

Scheme 3.1 - Preparation of the lithium amidinate complexes 21 and 22

1 13 The H and C NMR spectra of 21 (C6D6) exhibit a single NCH resonance, which is indicative of symmetrical amidinate coordination and therefore the likely N,N'-chelation 1 13 of a lithium centre by the amidinate. The H and C NMR spectra of 22 (C6D6) are broad and significantly more complex than those of 21. Two different cyclohexyl methine resonances are observed in its 1H NMR spectrum. This could indicate a monodentate or asymmetrically coordinated amidinate. The former mode of binding is rare and has only been observed in one instance in the presence of monodentate auxiliary donors (cf. Figure 3.5).[14c]

Compounds 21-22 were characterised by X-ray crystallography and their monomeric molecular structures and salient bonding parameters are provided in Figures 3.9 (pg. 103) and 3.10 (pg. 104) respectively.

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Figure 3.9 - Molecular structure of 21 (50% thermal ellipsoids). All hydrogen atoms omitted and cyclohexyl groups depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Li(1)-O(1) 1.896(9), Li(1)-O(2) 1.929(9), Li(1)-N(1) 1.976(9), Li(1)-N(2) 1.984(9), N(1)-C(1) 1.302(5), C(1)-N(2) 1.299(5),

N(1)-C(1)-N(2) 117.8(5), O(1)-Li(1)-O(2) 100.0(4), N(1)-Li(1)-N(2) 68.5(3), NCN:LiO2 83.5, NCN:Ar 80.3.

The amidinate in complex 21 displays E-anti isomerism, with the lithium ion coordinated in the conventional κ2 chelating binding mode and sitting in the plane of the NCN donor unit (Li(1) 0.067 Å out of the NCN plane). The N-C bond lengths within the NCN moiety are statistically identical and representative of electron delocalisation across the diazaallyl unit. An expectedly distorted tetrahedral geometry (τ4 = 0.77, see

Chapter Two) is observed about the lithium principally due to the βn of 68.5(3)°. The Li-N bond lengths (Li(1)-N(1) 1.976(9) Å, Li(1)-N(2) 1.984(9) Å) and amidinate N-C- N angle (117.8(5)°) are similar to those observed in the monomeric κ2-amidinate complex [Li(Ditop*AiPr)(tmeda)] (Li(1)-N(1) 1.995(9) Å, Li(1)-N(2) 1.998(9) Å, N-C-N 116.4(4)°).[14b]

103 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.10 - Molecular structure of 22 (50% thermal ellipsoids). Lowest occupancy disordered atoms (O1THF and N2Cy) omitted, all hydrogen atoms omitted and 2,6-mesityl rings depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Li(1)-O(1A) 1.835(12), Li(1)-O(2) 1.962(4), Li(1)-N(1) 1.923(4), N(1)-C(1) 1.333(2), C(1)-N(2) 1.302(3), N(1)-C(1)-N(2) 126.79(17), O(1A)-Li(1)-N(1) 119.3(4), O(2)-Li(1)-N(1) 134.5(2), O(1A)-Li(1)-O(2) 102.4(3), NCN:Ar 85.1.

Complex 22 is also monomeric in the solid-state, however, in contrast to 21, its amidinate displays Z-anti isomerism and is coordinated in a κ1 mode to the lithium ion, which resides in a distorted trigonal planar environment (Σ angles = 356.2(9)°) made up of one N-donor and two THF donors. The lithium coordination environment is comparable to those in the closely related complexes [Li(κ1-DmpAiPr)(tmeda)] (Σ angles = 358.4(3)°) and [Li(κ1-TrippAiPr)(tmeda)] (Σ angles = 360.0(7)°) (Figure 3.5).[14a,b] A degree of C-N and C=N bond localisation is evident in the amidinate scaffold, with C-N bond lengths of 1.333(2) Å and 1.302(3) Å. The amidinate Li-N bond length in 22 (1.923(4) Å) is shorter than those observed for related lithium κ1-amidinate complexes ([Li(κ1-DmpAiPr)(tmeda)] 1.942(6) Å and [Li(κ1-TrippAiPr)(tmeda)] 1.978(8) Å).[14a,b] Complex 22 exhibits one very short Li-O bond length (Li(1)-O(1A) 1.835(12) Å), which is the shortest of all bis(THF) solvated lithium amide complexes reported in the [24] literature. By means of comparison; [Li(N{PPh2}Dipp)(thf)2] contains a Li-O bond [25] of length 1.881(3) Å, which is the Li-OTHF contact in [Li(L)(thf)2] complexes deposited in the CSD. The mean Li-O bond length in 22 (1.899(13) Å) is in accord with

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[25-26] reported Li-OTHF bond lengths at three coordinate lithium ions (1.888-1.945 Å). The N-C-N angle of 22 (126.79(17)°) is more obtuse than that of the parent amidine 3 (119.48(17)°) and that in [Li(κ1-TrippAiPr)(tmeda)] (123.6(4)°), and within error of that in [Li(κ1-DmpAiPr)(tmeda)] (126.5(3)°).[14a-c]

Surprisingly, the coordinated THF ligands in 22 exhibit considerable lability upon dissolution in non-polar solvents. For instance, recrystallisation of 22 from the minimum volume of toluene affords the mixed coordination species [{Li(DmpACy)}{Li(DmpACy)(thf)}] (23). The lability of the THF donors in 22 contrasts those of 21 which display no signs of lability in toluene. The molecular structure of 23 and salient bonding parameters are given in Figure 3.11.

Figure 3.11 - Molecular structure of 23 (30% thermal ellipsoids). All hydrogen atoms omitted and mesityl groups depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Li(1)-N(2) 1.970(8), Li(1)-N(3) 1.908(8), Li(2)-N(1) 1.908(9), Li(2)-O(1) 1.863(9), Li(2)-C(2) 2.464(10), N(1)-C(1) 1.335(5), C(1)-N(2) 1.318(5), N(3)-C(38) 1.339(5), C(38)-N(4) 1.323(5), N(2)-Li(1)-N(3)

157.3(4), N(1)-C(1)-N(2) 127.3(4), N(3)-C(38)-N(4) 127.1(4), NCN:ArC(2) 77.2, NCN:ArC(39) 75.6.

Complex 23 contains two amidinate ligands that exhibit κ1-Z-anti isomerism about a single lithium ion. The apparent two coordinate lithium centre is further supported by two intramolecular Li···H-Calkyl interactions to the methine carbons of the pendant cyclohexyl groups attached at N(1) and N(4). The lengths of these contacts

(Li···H-Calkyl, 2.201 and 2.401 Å) lie within the range of recognised Li···H-Calkyl n t [27] interactions in the complex [{ BuLi·LiO Bu}4] (1.97-2.80 Å). One amidinate is 105 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

further coordinated to a Li(thf) unit via NCy coordination and arene donation (principal arene of Dmp, η1 bound). Similar binding of a second lithium ion was observed in the Ph [28] crystal structure of [Li( Aiso)(thf)2]. It is apparent that the substitution of the secondary arene o-hydrogen substituents in the terphenyl moiety of amidine 2 with methyl groups in amidine 3 has a significant impact on the resulting coordination motif and amidinate isomerism in their THF solvated lithium complexes 21-23.

3.3.2 The Synthesis of Ether Solvated Lithium Triazenide Complexes

The solvated lithium triazenide complexes, [Li(N3Dipp2)(thf)2] (24) and

[Li(N3Dmp2)(thf)2] (25) were prepared in an analogous fashion to their amidinate counterparts 21 and 22 (Scheme 3.1). Conducting these reactions in diethyl ether instead of THF resulted in the isolation of the diethyl ether solvated lithium triazenides

[Li(N3Dipp2)(OEt2)2] (26) and [Li(N3Dmp2)(OEt2)] (27).

1 13 The H and C NMR spectra of 24-27 (C6D6) exhibit single sets of defined triazenide N-arene resonances, that are indicative of symmetrical triazenide coordination in each complex. Coordinated solvent resonances were observed in their 1H NMR spectra, with relative integrals consistent with two (24-26) or one molecule (27) of coordinated solvent, the latter presumably due to steric congestion. The chemical shift of the α-diethyl ether proton resonance in the 1H NMR spectrum of 27 lies significantly upfield (0.56 ppm) of those for 26. A similar but less pronounced upfield shift (0.22 ppm) is also observed for the α-THF proton resonance in the 1H NMR spectrum of 25 relative to that observed for 24. The upfield shifts likely arise from arene ring current effects, suggesting that the flanking aryl moieties in the N-2,6-terphenyltriazenide lie in close proximity to the α-hydrogens of the coordinated solvent(s) and are therefore proximate to the metal centre. The IR spectra of 24-27 show strong N3 absorptions in the range 1262-1229 cm-1, which are indicative of triazenide ligands chelating the lithium in each complex.[29]

Complexes 24-27 were characterised by X-ray crystallography and the representative molecular structure of 25 is depicted in Figure 3.12 (pg. 107). The molecular structures of 24, 26 and 27 can be found in the appendix. Relevant metrical parameters for 24-27 are given in Table 2.6 (pg. 108).

106 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.12 - Molecular structure of 25 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Li(1)-O(1) 1.951(4), Li(1)-O(2) 1.966(4), Li(1)-N(1) 2.064(4), Li(1)-N(3) 2.068(4), N(1)-N(2) 1.315(2), N(2)-N(3) 1.319(2), N(1)-N(2)-N(3) 108.72(15), O(1)-Li(1)-O(2)

102.58(17), N(1)-Li(1)-N(3) 62.40(12), N3:ArC(1) 39.0, N3:ArC(25) 38.8, ArC(1):ArC(25) 76.7, N3:LiO2 70.7.

Structurally characterised solvated lithium triazenide complexes are scarce with only a single example in the literature.[18a] This lone triazenide complex features N-tolyl substituents and is dimeric through μ-κ1 binding to each lithium ion by the triazenide. The coordination of each lithium ion is completed by a single diethyl ether molecule. By contrast, complexes 24-27 are monomeric in the solid-state with each lithium ion bound by the triazenide through chelation. The mononuclearity of 24-27 reflects the increased steric bulk of the N-aryl substituents relative to the aforementioned literature example.[18a] The N-N bond lengths in 24-27 (24, 1.326(6) and 1.301(5) Å; 25, 1.315(2) and 1.319(2) Å; 26, 1.313(5) and 1.307(4) Å; 27, 1.323(3) and 1.312(3) Å) suggest near or complete delocalisation of electrons across each of the triazenide N3 donor sets.

Complexes 25 and 27 exhibit comparable interplanar angles between the planes of their principal aryl rings (76.7° and 71.7° respectively) to that exhibited by the parent triazene, 1 (78.5°).

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Mean Li- Mean Li- N-Li-N Complex G (L) Ref. N (Å) O (Å) (°) Al

[Li(N3Dipp2)(thf)2] (24) 2.038(12) 1.917(13) 63.6(2) 41.91 -

[Li(N3Dmp2)(thf)2] (25) 2.066(6) 1.969(6) 62.39(11) 64.60 -

Ditop [Li( ACy)(thf)2] (21) 1.980(13) 1.913(13) 68.5(3) 44.42 -

[Li({DippNC(H)}2CPh)(thf)2] 1.991(5) 1.962(6) 94.76(15) - [30]

[Li(N3Dipp2)(OEt2)2] (26) 2.070(11) 1.961(9) 63.3(2) 41.91 -

[{Li(N3p-tol2)(OEt2)}2] 2.126(24) 1.911(6) 61.8(5) - [18a]

[Li(N3Dmp2)(OEt2)] (27) 2.021(7) 1.870(5) 63.53(15) 64.60 -

[Li(Ph3CNPNMes*)(OEt2)] 1.98(3) 1.95(2) 77.5(5) - [31]

[Li({DmpN}2As)(OEt2)] 1.973(8) 1.876(6) 81.7(2) - [32]

Dipp [Li( nacnac)(OEt2)] 1.915(6) 1.911(4) 99.9(2) 54.94 [7b]

Dipp Ph [Li( nacnac )(OEt2)] 1.922(6) 1.928(4) 98.32(16) - [33]

Dipp tBu [Li( nacnac )(OEt2)] 1.929(4) 1.949(3) 98.97(12) 58.71 [34]

Table 3.1 - Selected bond parameters of ether solvated lithium amidinate, β-diketiminate and triazenide complexes

The mean Li-N bond lengths observed for the bis(thf) solvated complexes 24 and 25 are significantly longer than those of the related amidinate complex 21 and β-diketiminate complex [Li({DippNC(H)}2CPh)(thf)2] (Table 2.6). Taking account of the proven smaller sterics the of triazenides versus near identical amidinate counterparts (Section 2.3.2.4) and thus, elimination of a steric argument for Li-N bond expansion, the extension of Li-N bonds in 24 versus 21 must be driven by the poor donation of triazenides relative to amidinates and β-diketiminates. The mean Li-N bond length in 25 is slightly longer than that of 24 (Table 2.6) presumably due to N-Dmp steric effects. This is also reflected in the mean Li-O bond lengths observed for 24 and 25 (Table 2.6).

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3.3.3 Donor-Free Monomeric Alkali Metal Triazenide Complexes and a Less Hindered Aggregate

n Treatment of Dipp2N3H with butyllithium or lithium bis(trimethylsilyl)amide in toluene or hexane results in the immediate precipitation of a cream coloured solid, which is thought to be a polymeric form of the solvent donor free lithium triazenide;

[{Li(N3Dipp2)}x] (28). The analogous reaction of Dipp2N3H and potassium bis(trimethylsilyl)amide in toluene affords an off white precipitate that is thought to be

[{K(N3Dipp2)}x] (29). Complexes 28 and 29 are insoluble in all non-polar hydrocarbon solvents. Treatment of 28 with THF or diethyl ether affords 24 and 26 respectively. The -1 IR spectrum of 28 exhibits strong N3 absorptions at 1276 and 1244 cm , whilst that of -1 -1 29 exhibits a single N3 absorption at 1276 cm . These absorptions (< 1300 cm ) are indicative of the triazenide binding the metal through an N,Nʹ-chelating mode, which, together with the aforementioned poor solubilities, indicates the likely presence of μn-κ2-chelating motifs in the solid-state structure of 28 and 29.

The reaction of nbuthyllithium with the larger triazene, 1, in toluene, affords a golden yellow solution without precipitation. Upon cooling to -25 °C yellow prisms of the rare monomeric lithium triazenide [Li(N3Dmp2)] (30) deposited (Scheme 3.2, pg. 110). Analogous reactions with nbutylsodium or sodium bis(trimethylsilyl)amide in hexane also affords golden yellow solutions from which yellow octahedra of [Na(N3Dmp2)]

(31) could be isolated. Yellow blocks of [K(N3Dmp2)] (32b) were similarly isolated from the reaction of potassium bis(trimethylsilyl)amide with 1 in hexane. The reaction of 1 with elemental potassium in toluene at 80 °C affords yellow octahedra of

[K(N3Dmp2)] (32a) from the concentrated toluene mother liquor at -25 °C. Golden yellow prisms of [Rb(N3Dmp2)] (33) and [Cs(N3Dmp2)] (34) were isolated from analogous reactions of 1 with elemental rubidium and caesium respectively in hexane at ambient temperature. Complexes 30-34 display excellent solubilities in non-polar solvents, indicating that the N-Dmp substituents sufficiently prevent aggregation and the formation of strongly bonded aggregates or polymers like those for N3Dipp2 in 28 and 29. Complexes 30-34 represent the first time that non-solvated complexes of a monoanionic bidentate N,Nʹ-ligand have been prepared for the complete synthetically accessible alkali metal series.

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Scheme 3.2 - The preparation of the donor-free alkali metal triazenide complexes 30-34

-1 The IR spectra of 30-34 exhibit strong N3 absorptions in the range 1262-1229 cm , which are consistent with N,Nʹ-chelation in the solid-state.[29] The 1H and 13C NMR spectra of 30-34 (C6D6) display a single set of well defined triazenide resonances for each complex indicating highly symmetrical coordination in solution without broadening or obvious signs of fluxionality. This is consistent with each complex maintaining N,Nʹ-chelation in solution as per the IR data.

Single crystals of 30-34 suitable for single crystal X-ray diffraction studies were grown direct from the mother liquor or fresh hexane or toluene at -25 °C. Different morphologies of [K(N3Dmp2)] 32 were obtained when single crystals were grown from either toluene (32a) or hexane (32b). The representative molecular structure of 30 is depicted in Figure 3.13 (pg. 112). The molecular structures of 31-34 can be found in the appendix. Relevant metrical parameters are listed in Table 3.2 (pg. 111).

110 References for this chapter begin on pg. 133

Bond Parameter 30 31 32a 32b 32·C6H14 33 34

M-N(1) 1.976(5) 2.3574(16) 2.7114(16) 2.676(4) 2.655(9) 2.867(4) 3.024(4) M-N(3) 2.030(5) 2.3685(15) 2.6917(16) 2.683(4) 2.687(8) 2.841(4) 2.995(4) N(1)-M-N(3) 62.55(14) 52.98(5) 46.04(5) 46.56(10) 47.0(2) 44.10(11) 41.68(11) N(1)-N(2)-N(3) 105.57(15) 107.16(13) 107.44(15) 107.6(3) 108.0(7) 108.7(4) 109.2(4)

M···C 3.302(11) 6.186(3) 3.509(3) 3.304(2) 5.282(3) 3.931(6) 3.806(5) (intermolecular) 3.326(12)

[35] RvdW(M···C) 3.900 4.275 4.540 4.540 4.540 4.848 5.190

M···CAr 2.661(5)- 2.823(2)- 2.999(2)- 3.092(5)- 3.219(11)- 3.366(5)- 3.459(5)- (intramolecular) 3.629(7) 3.491(3) 3.322(2) 3.597(7) 4.430(11) 3.680(5) 3.825(6) ηm/ηn η5/η0 η3/η6 η5/η5 η4/η4 η1/η1 η5/η5 η4/η6

a M···Xm (M···X6) 2.472 (2.501) 2.763 (2.866) 2.828 (2.850) 2.977 (3.008) 3.239 (3.443) 3.218 (3.241) 3.327 (3.370)

a M···Xn (M···X6') (3.024) 2.761 2.887 (2.895) 2.985 (3.059) 3.218 (3.613) 3.270 (3.274) 3.370 Representative M···X 2.558-2.661b 2.497-2.501c 2.994-3.095d 2.994-3.095d 3.224e 3.156-3.213f 3.367-3.430g (lit.)

N3:ArC(1) 25.4 8.6 8.0 30.2 34.2 30.6 33.9

N3:ArC(25) 38.7 39.8 39.6 31.7 42.8 39.3 38.5

ArC(1):ArC(25) 58.7 47.6 47.2 60.0 76.8 66.1 68.0

Table 3.2 - Selected bond distances (Å), angles (°) and interplanar angles (°) for complexes 30-34

Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

a b t [11] c Centroids of the C(7)→C(12) (X6) and C(31)→C(36) (X6') rings. [Li({DippʹN}2C{N=C Bu2})]. [36] Dipp [37] d [19] [18b] [Na(2,4,6-Ph3C6H2)(thf)3] and [{Na( BIAN)}2]. [K(N3Tph2)], [K(N3{Dmp}Mph)] and [18b] e [18b] f [38] g [19] [K(N3{Dmp}Tph)]. [{K(N3{Me4Ter}2)}2]. [{Rb(S{2,6-Trip2C6H3})}2]. [Cs(N3Tph2)].

Complex 30 crystallises in the monoclinic space group P21/c with a single monomer in the asymmetric unit. The closest Li···C intermolecular contact is 6.186 Å, which lies well outside the combined van der Waals radii of the elements (Table 3.2). There have been two reports of a monomeric solvent donor free lithium complex with a monoanionic bidentate N,Nʹ-ligand; [Li(TbtNC{Me}CHC{Me}NMes)][7c,d] (Figure 3.1) t [11] and [Li({DippʹN}2C{N=C Bu2})] (Figure 3.3). The donor-free lithium complexes of Cy Dipp Giso (GAl = 49.98%, GRh = 48.84%, Chapter Two) and nacnac (GAl = 54.94%, GRh = 56.12%, Chapter Two) are dimeric in the solid-state.[7b,10c] Indeed, the mononuclearity of 30 in the solid-state relative to CyGiso and Dippnacnac is consistent with the greater sterics of N3Dmp2 (GAl = 64.60%, GRh = 62.99%), which further validates the steric model introduced in Chapter Two.

Figure 3.13 - Molecular structure of 30 (40% thermal ellipsoids). All hydrogen atoms omitted for clarity. Salient bond parameters are listed in Table 3.2.

The mean Li-N bond length in 30 (2.003(7) Å) is shorter than those observed in the analogous ether solvated complexes (25: 2.066(6) Å, 27: 2.021(7) Å). However, unlike the ether solvated complexes there is a significant difference between the Li-N(1) and

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Li-N(3) bond lengths (Table 3.2). This arises from distortions in the ligand scaffold due to coordination of the ArC(7) mesityl ring to the lithium centre (Figure 3.13). The

Li···CAr contact distances range from 2.661(5)-3.042(7) Å, which may be assigned as 5 an η interaction based on the Li-Xn distance (d) and the angle (α) formed by the Li-Xn vector and the mesityl plane (Figure 3.14, further details can be found in the [39] appendix). The shortest Li···CAr contact to the ArC(31) aryl ring is 2.994(6) Å. Although this lies within the combined van der Waals radii of lithium and carbon (Table [24] 3.2), it is longer than Li···CAr contacts reported in the literature. For instance, the Dipp 1 analogous nacnac complex dimerises through an η Li···CAr contact that is 2.834(7)

Å long, hence, the second Li···CAr interaction in 30 must be considered extremely weak by comparison.

Xn d (Å) α (°)

X6 2.501 99.2

X5 2.472 92.9

X4 2.478 86.5

X3 2.522 78.0

Figure 3.14 - Determination of hapicity of Li-π-arene interaction in 30

The lithium arene interaction in 30 leads to a significant reduction in the N3:ArC(1) interplanar angle (25.4°) relative to the N3:ArC(25) interplanar angle (38.7°) and those of the aforementioned ether solvated complexes (25: 39.0°, 38.9°; 27: 38.0°, 39.2°). This leads to a smaller interplanar angle between the principal N-aryl groups in 30 (58.7°) relative to the ether solvated complexes (25: 76.7°; 27: 71.7°) and demonstrates the influence of the Li-π-arene interaction on the geometry of the triazenide.

Complexes 31 and 32a crystallise in the monoclinic space group P21/n with a single monomer in the asymmetric unit and are isomorphous. Complexes 31 and 32a are weakly dimeric through intermolecular M···CMe interactions between the metal ion of one complex and an o-Me substituent of an adjacent complex (Figure 3.15, pg. 114).

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Figure 3.15 - Solid-state aggregation of 31 (35% thermal ellipsoids). All hydrogen atoms omitted and Dmp groups depicted as wireframes for clarity. Symmetry operation used to generate # atoms: -x, -y, 2-z. Na(1)-C(48)# 3.509(3) Å.

The length of the Na···CMe contact in 31 (3.509(3) Å) is considerably longer than the accepted intermolecular Na···CMe interactions in [{Na(Si{SiMe3}3)}2(C6H6)] (2.758-3.142 Å),[40] but does lie within the combined van der Waals radii of the elements (Table 3.2). The analogous contact in 32a is significantly shorter (3.304(2) Å) [40] and lies within the range of K···CMe contacts observed for [{K(Si{SiMe3}3)}2]

(2.25-3.33 Å). It is considerably shorter than the two K···CMe interactions observed in [18b] the similar triazenide complex [K(N3{Dmp}Tph)] (3.872 Å and 3.907 Å). It is noteworthy that the comparable potassium N-2,6-terphenyl triazenide complex,

[{K(N3{Me4Ter}2)}2], in which the ligand represents 1 with N-2,6-(3,5-Me2Ph)2Ph groups rather than N-2,6-(2,4,6-Me3Ph)2Ph groups, exists as a dimer in the solid-state, however in that instance the smaller arene groups permit dimerisation via μ-κ2-binding [18b] of the triazenide rather than supramolecular K···CMe contacts.

Complexes 31 and 32a display symmetric κ2-chelation to the triazenide (Table 3.2) which contrasts the binding in 30 where the Li-N bond length associated with the π- arene interaction is significantly shorter than its non π-coordinated counterpart (vide supra). The mean Na-N bond length in 31 (2.3630(21) Å) is shorter than those observed in the related formamidinate and triazenide complexes, which all include auxiliary

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[13c] [13c] donors, e.g. [Na(Fiso)(thf)3] 2.432(3) Å, [Na(Fiso)(dme)2] 2.426(1) Å and [41] [Na(N3Ph2)(15-crown-5)] 2.48(1) Å. The mean K-N bond length in 32a (2.7016(23) Å) is near identical to those of other donor-free potassium κ2-triazenide complexes, e.g. [19] [K(N3Tph2)] 2.7163(20) Å. The coordination spheres of the metal ions in 31 and 32a are further furnished by π-arene interactions to one mesityl from each Dmp group; 3 6 5 5 ArC(7) and ArC(31) rings (31: η /η ; 32a: η /η ), which further contrasts 30 (Table 3.2).

The distances of the sodium ion from the arene centroids (Xn) in 31 are considerably longer than accepted Na to π-arene contacts in literature examples (Table 3.2). However, it should be noted that there are no literature N-bi- or terphenyl triazenides with which to compare 31, or for that matter 2-biphenyl substituted amides.[24] The potassium ion in 32a lies closer to the arene centroids relative to the aforementioned donor-free potassium κ2-triazenide complexes (Table 3.2).[18b] This intimates that, contrary to the sodium in 31, the similar length of the K-N bonds in 32a to other potassium triazenides (viz. short Na-N contacts in 31) permit close to optimum M-π-arene interactions. This is also reflected in the significant deviation of the planes of the principal N-aryl groups away from orthogonality relative to one another vide supra

(Table 3.2). The higher overall hapticity interactions of the metal ion with the ArC(7) and 5 5 3 6 ArC(31) rings in 32a (η , η ) versus those in 31 (η , η ) are typical of the transition to a larger more charge diffuse metal. This also decreases the length of the observed intermolecular M···CMe interaction in 32a relative to that in 31 (32a 3.304(2) Å, 31 3.509(3) Å).

Crystallisation of 32 from hexane at -25 °C rather than toluene (32a) affords a different polymorph of 32 (32b). Polymorph 32b crystallises in the monoclinic space group P21. The molecular structure of 32b is depicted in Figure 3.16 (pg. 116).

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Figure 3.16 - Molecular structure of 32b (50% thermal ellipsoids). All hydrogen atoms removed for clarity.

Complex 32b is a rare example of a donor-free monomeric potassium complex with a monoanionic ligand (Figure 3.16). The absence of short intermolecular K···C contacts (K···C > 5.2 Å) supports this assignment viz. 32a. The aforementioned complexes [19] t [11] [K(N3Tph2)] and [K({DippʹN}2C{N=C Bu2})] are the only other reported examples. The mean K-N bond length in 32b (2.680(6) Å) is shorter than that observed for 32a (2.7016(23) Å). The hapticities of the intramolecular K···Ar interactions of 32b (η4, η4) are lower relative to those in 32a (η5, η5). This indicates weaker intramolecular arene interactions in 32b relative to 32a and is likely due to the shorter K-N interactions although crystal packing effects likely contribute also. The aforementioned [K(N3Tph2)] i 6 5 (cf. Tph = 2-(2,4,6- Pr3Ph)Ph) features an intramolecular η and η interaction of the potassium ion with the pendant Trip rings. Herein, a similar conformation is seemingly prevented by intramolecular Mes:Mes buttressing between the two non-coordinated mesityl groups of the N-2,6-terphenyls (vide supra). This also manifests in the larger interplanar angle between the N-aryl planes in 32b (60.0°) relative to that in 32a (47.2°).

Surprisingly crystallisation of 32 from hexane afforded a third crystal variant which includes lattice solvent. This form crystallises in the non-centrosymmetric orthorhombic

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space group Pca21 with a full molecule and a molecule of hexane in the asymmetric unit

(32·C6H14).

Figure 3.17 - Solid-state aggregation in 32·C6H14 (30% thermal ellipsoids). All hydrogen atoms omitted and Dmp groups depicted as wireframes for clarity. Symmetry operation used to generate # atoms: ½+x, 1-y, z. K(1)-C(4)# 3.326(12) Å and K(1)-C(5)# 3.302(11) Å.

Complex 32·C6H14 is polymeric in the solid-state, with aggregation occurring via a relatively long intermolecular K-η2(Ar) interaction with the principal N-Dmp arene of an adjacent molecule (Figure 3.17). The distances involved in this interaction are

3.302(11) Å and 3.326(12) Å (K···X2 3.240 Å). These distances lie within the range of recognised K···CAr contacts in 32a and 32b (2.999(2)-3.407(6) Å).

The mean K-N bond length in 32·C6H14 (2.671(12) Å) is shorter than that observed for 32a (2.7016(23) Å) and within error of that for 32b (2.680(6) Å). The increased intermolecular interactions in 32·C6H14 vis-à-vis 32a and 32b diminishes the hapticities of its intramolecular K···Ar interactions relative to 32a and 32b (Table 3.2). The weakening of the intramolecular arene interactions confers greater rotational freedom at the biaryl axes permitting the planes of the principal N-aryls of 32·C6H14 to approach orthogonality to a far greater extent than those of 32a and 32b (Table 3.2).

Complexes 33 and 34 crystallise in the monoclinic space group P21 with a single molecule in the asymmetric unit and are isomorphous. 117 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

Figure 3.18 - Solid-state aggregation of 34 (50% thermal ellipsoids). All hydrogen atoms omitted and Dmp groups depicted as wireframes for clarity. Symmetry operation used to generate # atoms: -x, ½-y, -z.

Complexes 33 and 34 form 1D polymers via weak η1 contacts to a secondary N-Dmp arene group of an adjacent unit (Figure 3.18). This mode of aggregation contrasts that of

32·C6H14 which binds to the principal N-aryl group of an adjacent molecule. The length of the contact in 33 (3.931(6) Å) is considerably longer than recognised Rb···CAr [42] [38] contacts in the literature (3.11-3.70 Å), like those in [{Rb(S{2,6-Trip2C6H3})}2], but does lie within the combined van der Waals radii of the rubidium and carbon (Table 3.2). The analogous contact in 34 is shorter (3.806(5) Å) and lies within the range of

Cs···CAr contacts observed for [Cs(C{SiMe3}3)(C6H6)3.5] and [Cs(Si{SiMe3}3)(C7H8)1.5] (3.51-4.11 Å).[43]

The mean M-N bond lengths in 33 (2.854(6) Å) and 34 (3.010(6) Å) are significantly shorter than those of [Rb(2-phenylamidopyridine)(18-crown-6)] (2.99 Å)[44] and [19] [Cs(N3Tph2)] (3.07 Å). The metal ions in 33 and 34 are further coordinated to the 5 5 4 6 ArC(7) and ArC(31) rings by high hapticity π-arene interactions (33: η /η ; 34: η /η ). The typically higher hapticities of the M-π-arene interactions in 33 and 34 relative to their hexane crystallised potassium counterparts (32b and 32·C6H14, Table 3.2) prevent closer intermolecular M···CMe contacts like that in 32a or higher hapticity intermolecular π-arene interactions. The higher hapticity interaction of the metal ion 6 5 with the ArC(31) ring in 34 (η ) relative to 33 (η ), offsets a lower hapticity interaction of

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4 5 the metal ion with the ArC(7) ring in 34 (η ) relative to 33 (η ). The shorter intermolecular M···CAr interaction of 34 (vide supra) versus that of the isomorphous 33 despite an increase in van der Waals radii (Table 3.2) is reminiscent of the transition from sodium (31) to its isomorphous potassium cousin (32a) and the contract M···CMe contact of the latter (Table 3.2). It is also noteworthy that the large covalent radii of rubidium and caesium (2.20 and 2.44 Å respectively)[45] relative to those of the lighter group 1 elements (Li 1.28 Å; Na 1.66 Å; K 2.03 Å)[45] permit the formation of two high hapticity π-arene interactions with the pendant mesityl groups whilst the planes of the principal N-aryl rings to achieve larger interplanar angles (Table 3.2).

The solid-state structures of 30-34 display the expected trend with regards to aggregation in that a greater tendency to aggregate is observed upon descent of the group. Interestingly, the reverse was observed in the series [M(N3Tph2)] (M = Li, K, Cs), whereby the lithium complex is dimeric in the solid-state, whilst the potassium and caesium complexes exist as discrete monomers in the solid-state.[19] The series of thiolate complexes [{M(S{2,6-Trip2C6H3})}2] (M = Li, Na, K, Rb, Cs), remains the only series of alkali metal species where the same degree of aggregation is observed for all of the metals the group.[38]

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3.3.4 Bimetallic Triazenide Complexes

A small number of yellow plates were isolated from the toluene mother liquor of 32a (yellow octahedra). X-ray crystallographic study revealed the plates to be 2 [K2(μ-κ -N3Dmp2)(μ-N{H}Dmp)] (35). The molecular structure of 35 is depicted in

Figure 3.19. It should be noted that the Dipp2N3H triazene thermally decomposes to [46] DippNH2 and “DippN2” in the solid-state. Complex 35 likely arises from the analogous partial decomposition of Dmp2N3H at high temperature in the presence of potassium (cf. conditions 80 °C in toluene), whereby the DmpNH2 decomposition product is reduced to “KN(H)Dmp” followed by addition to an equivalent of 32 to afford 35.

Figure 3.19 - Molecular structure of 35 (30% thermal ellipsoids) normal to the

K2Nanilide plane (left) and down the K(1)-K(2) vector (right). All hydrogen atoms excepting H(1) omitted and Dmp groups depicted as wireframes for clarity. Selected bond lengths (Å) and angles (°): K(1)-N(1) 2.775(3), K(1)-N(3) 3.004(3), K(1)-N(4) 2.738(3), K(2)-N(1) 2.917(3), K(2)-N(3) 2.728(3), K(2)-N(4) 2.966(4), K(1)···K(2) 3.806(1), N(1)-N(2) 1.312(4), N(2)-N(3) 1.323(4), N(1)-N(2)-N(3) 112.23(15).

Complex 35 is monomeric in the solid-state, with the shortest intermolecular K···C distance being > 6.00 Å. Like 30-34, complex 35 features an N,Nʹ-(chelating) triazenide moiety, however in contrast 30-34, the triazenide μ-κ2-chelates two metal centres in a [18b] similar manner to that observed in [{K(N3{Me4Ter}2)}2] and [18a] [{K(N3p-tol2)(μ-dme)2}∞]. The K-Ntriaz bond lengths in 35 (2.775(3)-3.004(3) Å) are considerably longer than those observed in all three variants of 32 (2.655(9)-2.7114(16)

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Å), and significant asymmetry is observed in the μ-κ2-binding of the triazenide, whereby each potassium ion possesses one short and one long K-Ntriaz contact. The two potassium ions are further bridged by an N(H)Dmp anilide moiety. The K(1)-Nanilide bond length (2.738(3) Å) lies at the lower end of the range observed for

[K(N{H}Tripp)(OEt2)2], [{K2(μ-N{H}Dipp)(μ-N{SiMe3}2)(dme)}2], [47] [{K2(μ-N{H}Dipp)2(μ-thf)}∞] and [{K2(μ-N{H}Dipp)2(tmeda)2}∞] (2.611-2.916 Å).

By contrast the K(2)-Nanilide bond length (2.966(4) Å) lies well above the aforementioned range. The K(1) ion is further coordinated to the triazenide’s ArC(7) ring 1 5 in an η fashion and to the anilide’s ArC(55) ring in an η fashion. A K···CMe interaction (3.536(5) Å) with the other arm of the triazenide was also observed. The K(2) ion is 1 further coordinated to the ArC(16) ring of the triazenide in an η fashion and the ArC(40) 3 ring in an η fashion. A K···CMe interaction (3.407(5) Å) with the pendant mesityl group of the anilide completes the coordination environment of K(2).

The μ-κ2-chelating mode of the triazenide in 35 is similar to the μ-κ1 mode observed for the triazenide upon treatment of 30 with an equivalent of nbutyllithium in hexane. This n reaction affords the heteroleptic complex [Li2(N3Dmp2)( Bu)] (36) as yellow prisms and was intentionally repeated after the isolation of 36 in some crops of 30 when prepared in hexane.

-1 The IR spectrum of 36 exhibits a number of strong N3 absorption at 1280-1200 cm , this is inconsistent with μ-κ1-binding modes reported in the literature. For example, the 1 -1 [48] 1 N3 IR absorption of [{Cu(μ-κ -N3TPh2)}2] is located at 1334 cm . The The H

NMR spectrum of 36 (C6D6) exhibits sharp triazenide Dmp resonances which are consistent with a high degree of symmetry and low fluxionality in solution. Typically broad resonances attributable to the nbutyl ligand (-1.46, 1.10-1.20 and 1.34-1.42 ppm) are also observed in the 1H NMR spectrum of 36 owing to its considerable degrees of freedom.

Complex 36 crystallises in the monoclinic space group P21/n with a single monomer in the asymmetric unit (Figure 3.20, pg. 122).

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Figure 3.20 - Molecular structure of 36 (40% thermal ellipsoids) normal to the Li-N3-Li plane (left) and down the Li(1)-Li(2) vector (right). Lowest occupancy disorder nBu atoms and all hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): Li(1)-N(1) 2.006(4), Li(2)-N(3) 2.004(4), Li(1)-C(1A) 2.091(5), Li(2)-C(1A) 2.093(5), Li(1)···Li(2) 2.508(5), Li(1)-C(7) 2.361(4), Li(1)-C(8) 2.629(4), Li(1)-C(12) 2.609(4), Li(2)-C(31) 2.352(4), Li(2)-C(32) 2.553(4), Li(2)-C(36) 2.716(4), N(1)-N(2) 1.314(2), N(2)-N(3) 1.311(2), Li(1)-C(1A)-Li(2) 73.64(18), N(1)-N(2)-N(3) 110.73(14).

Complex 36 exhibits a non-chelating bridging μ-κ1-triazenide that contrasts that the κ2-chelating forms in the monolithium complexes 25, 27 and 30 and the dipotassium complex 35 (μ-κ2-chelating). This binding mode is been common in lithium formamidinate complexes which also exhibit larger N-X-N angles across the ligand donor set relative to C-substituted amidinates like DitopACy.[12] The Li-N bond lengths in 36 (Li(1)-N(1) 2.006(4) Å and Li(2)-N(3) 2.004(4) Å) are shorter than the ranges [13c,49] observed in [{Li(μ-FMes)(dme)}2] and [{Li(μ-FDep)(dme)}2] (2.033-2.050 Å). The two lithium ions of 36 are further bridged by a disordered nbutyl group which was modelled over two sites with occupancies of 66:34% C(1A)-C(4A):C(1B)-C(4B). Each lithium ion is further coordinated to a pendant mesityl group by an η3 interaction. The distance to the arene ring centroids (Xn) of the interactions in 36 (n = 3, 2.310 and 2.319 Å) are shorter than that for 30 (n = 5, 2.472 Å). This is likely the cause of the upfield shift of the 7Li NMR resonance in 36 vis-à-vis that of 30 (vide supra).

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3.4 Conclusions

This Chapter describes the preparation of alkali metal complexes of the novel bulky monoanionic bidentate N,Nʹ-ligands based on the amidines (2 and 3) and triazene (1).

Addition of nbutyllithium to DitopACyH (2) affords the monomeric bis(thf) solvated complex 21. The amidinate ligand in 21 displays E-anti isomerism with the lithium ion coordinated in the conventional κ2 binding mode. By contrast the lithium bis(thf) complex of the bulkier amidinate DmpACy (22) adopts a Z-anti conformation which leads to κ1 binding of the lithium ion. Recrystallisation of this complex from toluene affords a partially desolvated dilithium complex (23), which exhibits a unique lithium bis(amidinate) binding motif that features two κ1-bound Z-anti amidinates. The coordination sphere of the apparent two coordinate lithium centre is supplemented by intramolecular Li···H-CAlkyl interactions.

Ether (THF and diethyl ether) solvated lithium complexes of some bulky triazenides were also prepared. Four complexes were structurally characterised; [Li(N3Dipp2)(L)2]

(L = THF (24), diethyl ether (26)) and [Li(N3Dmp2)(L)n] (L = THF, n = 2 (25); L = diethyl ether, n = 1 (27)). Each complex features κ2 binding of the triazenide to the lithium ion. The steric bulk of the triazenide based on 1 enables only a single molecule of diethyl ether to coordinate the lithium ion in 27. In the analogous N-Dipp complex (26) two diethyl ether molecules are coordinated to the lithium ion. The coordinated ethers in each of the molecules display no lability unlike the aforementioned bulky amidinate system (22).

Unsolvated alkali metal complexes of the triazenide based on 1 were also prepared (30-34). This is the first time that non-solvated complexes of a monoanionic bidentate N,Nʹ-ligand have been prepared for the complete alkali metal series.

The lithium complex (30) is monomeric in the solid-state and is only the third example of a monomeric lithium complexes of a monoanionic bidentate N,Nʹ-ligand reported to date. In the solid-state the analogous sodium complex (31) is weakly dimeric through intermolecular Na···CMe interactions. Three different polymorphic or lattice solvent included molecular structures of the potassium analogue (32) have been characterised. The first (32a) is isomorphous with the sodium complex 31. The second (32b) is monomeric in the solid-state with higher hapticity intramolecular π-arene contacts

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2 versus 32a. The third (32·C6H14) is polymeric through extended K-η (Ar) interactions. The analogous rubidium (33) and caesium (34) complexes are also with weak intermolecular M-η1(Ar) interactions that lead to weakly bonded 1D-polymers.

The coordination spheres of the alkali metal ions in 30-34 are completed by π-arene interactions to the pendant mesityl rings of the triazenide. Higher hapticity interactions of the metal ion with the pendant mesityl rings were observed upon descent of the alkali metal series

Small quantities of the heteroleptic dipotassium complex (35) were isolated from one preparation of the potassium triazenide complex (32a). This complex consists of two potassium ions bridged by an N-Dmp triazenide and an N-Dmp anilide and is believed to have been generated by the partial decomposition of 1 in the presence of potassium at elevated temperatures in toluene.

The addition of two equivalents of nbutyllithium to 1 affords the heteroleptic dilithium complex 36. This species exhibits two lithium ions bridged by a triazenide and an nbutyl group. The triazenide binds via a non-chelating bridging mode (μ-κ1) that contrasts those observed in 25, 27 and 30 (κ2-chelating) and that in 35 (μ-κ2-chelating).

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3.5 Future Directions

This chapter has demonstrated the significant steric character of the 1,3-bis(2,6-terphenyl)triazenide base on 1 through the preparation of a rare monomeric monoanionic N,Nʹ-ligand complex of lithium. The steric encapsulation afforded by the triazenide based on 1, may be useful in the kinetic stabilisation of low oxidation state group 13 metals. It is noteworthy that the smaller (cf. Chapter Two) β-diketiminate

t ligands Dippnacnac and Dippnacnac Bu have been used prodigiously in this field.[22,50] Triazenide ligands are weaker donors than β-diketiminate, amidinate and guanidinate ligands (cf. Chapter Two) which may be considered advantageous when designing systems to support low oxidation state group 13 metal centres. The lithium complex 30 represents a good candidate metathesis reagent in this regard owing to its lesser haptic π-arene bonding and is to be used in the low oxidation state group 13 chemistry described in Chapter Four.

The steric encumbrance of the triazenide based on 1 (cf. Chapter Two, GAl 62.99%, GRh 64.60%) lends it to the kinetic stabilisation of other highly unstable and reactive systems. For example hydride complexes of the heavy group 13 metals, which are thought to decompose though the formation of intermolecular M-H-M bridges (see Section 1.2.2) could benefit considerably from the steric protection afforded by the triazenide derived from 1. This is one of the hypotheses explored in the group 13 hydride studies described in Chapter Six.

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3.6 Experimental

3.6.1 General Synthetic Procedures

[46,51] Dipp2N3H was prepared using the literature procedure. NaN(SiMe3)2 was sublimed prior to use. KN(SiMe3)2 was recrystallised from toluene and vacuum dried prior to use.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

3.6.2 General Synthetic Procedure for the Preparation of Lithium Amidinate Complexes nBuLi (1.6 M in hexane, 1.0 equiv.) was added dropwise to a solution of amidine (1.0 equiv.) in THF (30 mL mmol-1) at ambient temperature. After 3 h, the reaction volatiles were removed in vacuo. The resultant solid was extracted with toluene (21, 23) or THF (22), concentrated to insipient crystallisation and cooled to -25 °C overnight to afford a crystalline solid.

Ditop [Li( ACy)(thf)2] (21). Colourless plates suitable for X-ray diffraction structure 1 determination (178 mg, 42%); m.p. 206-207 °C. H NMR (400 MHz, C6D6) δ 0.76-1.56

(m, 28H, Cy-CH2 and β-CH2 thf), 2.06 (s, 6H, p-CH3), 2.97 (br s, 2H, NCH), 3.58 (br AAB AABB m, 8H, α-CH2 thf), 7.05 (t, JHH = 7.6 Hz, 1H, p-ArH), 7.14 (d, JHH = 7.9 Hz, 4H, AAB AABB o- or m-Ar’H), 7.28 (d, JHH = 7.6 Hz, 2H, m-ArH), 7.44 (d, JHH = 7.9 Hz, 4H, 13 o- or m-Ar’H). C NMR (400 MHz, C6D6) δ 20.6 (CH3), 26.9 (β-CH2 thf), 31.3, 34.5,

38.2 (CH2), 59.7 (NCH), 65.6 (α-CH2 thf), 125.3, 128.2, 128.7, 130.2 (ArCH), 137.5, 140.9, 145.2, 148.9 (ArC), 169.6 (NCN). IR (Nujol, cm-1) 1632 (m, N=C), 1514 (m), 1301 (m), 1255 (m), 1152 (w), 1019 (br m), 889 (w), 817 (m), 804 (m), 771 (m), 655 (sh w).

1 Dmp [Li(κ - ACy)(thf)2] (22). Colourless blocks suitable for X-ray diffraction structure 1 determination (480 mg, 42%); m.p. 234-237 °C. H NMR (400 MHz, C6D6) δ 0.31-1.82

(br m, 28H, CH2-Cy and β-CH2 thf), 2.17 (s, 6H, p-CH3), 2.68 (br s, 14H, o-CH3 and AAB NCH), 3.21 (br s, 8H, α-CH2 thf), 6.89 (s, 4H, m-Ar’H), 7.08 (d, JHH = 7.4 Hz, 2H, AAB 13 m-ArH), 7.24 (t, JHH = 7.4 Hz, 1H, p-ArH). C NMR (100 MHz, C6D6) δ 21.3, 22.3

(CH3), 25.4 (β-CH2 thf), 27.1, 27.5 (CH2), 57.1 (NCH), 68.3 (α-CH2 thf), 125.4, 127.7, 128.4, 129.4 (ArCH), 135.0, 140.8, 141.3 (ArC), 162.5 (NCN). IR (Nujol, cm-1) 1526

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(s, N=N), 1367 (s), 1311 (w), 1289 (w), 1270 (w), 1148 (w), 1131 (w), 1102 (w), 1039 (m), 1019 (w), 976 (w), 946 (w), 855 (w), 793 (w), 758 (w). Anal. Calc. for

C45H63LiN2O2: C, 80.56; H, 9.46; N, 4.18. Found: C, 80.50; H, 9.54; N, 4.13%.

3.6.3 General Synthetic Procedure for the Preparation of Ether Solvated Lithium Triazenide Complexes nBuLi (1.6 M in hexane, 1.0 equiv.) was added dropwise to a solution of triazene (1.0 equiv.) in THF (30 mL mmol-1, 24, 25) or diethyl ether (30 mL mmol-1, 26, 27) at ambient temperature. After 3 h, the reaction volatiles were removed in vacuo. The resultant solid was extracted with THF (24, 25) or hexane (26, 27), concentrated to insipient crystallisation and cooled to -25 °C overnight to afford a crystalline solid.

[Li(N3Dipp2)(thf)2] (24). Pale yellow square slabs suitable for X-ray diffraction structure determination (330 mg, 72%); m.p. 94-96 °C (dec.). 1H NMR (400 MHz, 3 C6D6) δ 1.20 (m, 8H, β-CH2 thf), 1.23 (d, JHH = 6.7 Hz, 24H, CH(CH3)2), 3.41 (m, 8H, 3 α-CH2 thf), 3.62 (sept, JHH = 6.7 Hz, 4H, CH(CH3)2), 7.05-7.17 (m, 6H, m- and 1 3 p-ArH). H NMR (250 MHz, THF-d8) δ 1.12 (d, JHH = 6.9 Hz, 24H, CH(CH3)2), 3.51 3 AAB (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 6.83 (t, JHH = 7.6 Hz, 2H, p-ArH), 6.98 (d, AAB 13 JHH = 7.6 Hz, 4H, m-ArH). C NMR (100 MHz, C6D6) δ 24.6 (CH(CH3)2), 25.4

(β-CH2 thf), 28.3 (CH(CH3)2), 68.4 (α-CH2 thf), 123.3, 123.5 (ArCH), 142.2, 148.9 13 (ArC). C NMR (63 MHz, THF-d8) δ 24.6 (CH(CH3)2), 28.4 (CH(CH3)2), 122.8, 123.0 (ArCH), 142.4, 150.0 (ArC). IR (Nujol, cm-1) 1587 (w), 1515 (w), 1361 (w), 1256 (br s, N=N), 1098 (m), 1044 (s), 971 (w), 935 (w), 894 (w), 837 (w), 799 (s), 770 (s), 755 (s), 723 (w), 666 (w). Samples of 24 repeatedly gave microanalyses low in carbon and hydrogen. This presumably results from incomplete combustion. Example analysis:

Anal. Calc. for C37H52N3LiO2: C, 74.53; H, 9.77; N, 8.15. Found: C, 72.66; H, 8.78; N, 10.18%.

[Li(N3Dmp2)(thf)2] (25). Yellow prisms suitable for X-ray diffraction structure 1 determination (260 mg, 38%); m.p. 176-177 °C. H NMR (500 MHz, C6D6) δ 1.34 (m,

8H, β-CH2 thf), 1.99 (s, 24H, o-CH3), 2.18 (s, 12H, p-CH3), 3.19 (m, 8H, α-CH2 thf), 13 6.80 (s, 8H, m-Ar’H), 6.85 (s, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 21.2

(p-CH3), 21.7 (o-CH3), 25.6 (β-CH2 thf), 67.9 (α-CH2 thf), 121.9, 128.1, 130.1 (ArCH), 7 132.9, 134.5, 135.9, 140.5, 147.4 (ArC). Li NMR (156 MHz, C6D6) δ 0.44 (s). IR

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(Nujol, cm-1) 1612 (w), 1261 (m, N=N), 1201 (w), 1149 (br w), 1075 (w), 1031 (br w),

974 (w), 845 (w), 799 (w), 766 (w), 753 (w). Anal. Calc. for C56H66N3LiO2: C, 82.02; H, 8.11; N, 5.12. Found: C, 81.90; H, 7.88; N, 5.60%.

[Li(N3Dipp2)(OEt2)2] (26). Colourless prisms suitable for X-ray diffraction structure 1 determination (223 mg, 65%); m.p. 98-99 °C (dec.). H NMR (400 MHz, C6D6) δ 0.95

(br s, 12H, CH2CH3), 1.33 (br s, 24H, CH(CH3)2), 3.26 (br s, 8H, OCH2), 3.67 (br s, 4H, 13 CH(CH3)2), 7.15-7.24 (m, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 14.6

(CH2CH3), 24.7 (CH(CH3)2), 28.1 (CH(CH3)2), 65.6 (OCH2), 123.2, 123.8 (ArCH), 142.6, 148.5 (ArC). IR (Nujol, cm-1) 1589 (w), 1518 (m), 1416 (m), 1362 (w), 1328 (w), 1256 (s, N=N), 1218 (s), 1189 (s), 1097 (w), 1058 (s), 934 (w), 838 (w), 799 (s), 770 (m), 751 (s), 721 (w). Samples of 26 repeatedly gave microanalyses low in carbon and hydrogen. This presumably results from incomplete combustion. Example analysis:

Anal. Calc. for C37H54N3LiO2: C, 73.95; H, 10.47; N, 8.08. Found: C, 72.64; H, 9.44; N, 10.68%.

[Li(N3Dmp2)(OEt2)] (27). Yellow prisms suitable for X-ray diffraction structure 1 determination (260 mg, 38%); m.p. 170-171 °C (dec.). H NMR (400 MHz, C6D6) δ 3 0.43 (t, JHH = 7.0 Hz, 6H, CH2CH3), 1.99 (s, 24H, o-CH3), 2.18 (s, 12H, p-CH3), 2.69 3 (q, JHH = 7.0 Hz, 4H, OCH2), 6.81 (s, 8H, m-Ar’H), 6.85-6.86 (m, 6H, m-ArH and 13 p-ArH). C NMR (100 MHz, C6D6) δ 12.6 (CH2CH3), 21.2 (p-CH3), 21.8 (o-CH3), 67.0 7 (OCH2), 122.0, 128.2, 130.2 (ArCH), 132.8, 134.6, 135.8, 140.4, 147.0 (ArC). Li NMR -1 (156 MHz, C6D6) δ 0.56 (s). IR (Nujol, cm ) 2730 (w), 1912 (w), 1715 (w), 1611 (m), 1579 (m), 1486 (m), 1412 (m), 1386 (m), 1355 (w), 1279 (s, N=N), 1255 (s, N=N), 1158 (m), 1083 (s), 1044 (w), 1030 (m), 1013 (m), 972 (w), 932 (m), 861 (w), 849 (s),

805 (m), 770 (m), 762 (s), 743 (m), 665 (m), 651 (w). Anal. Calc. for C53H60N3LiO: C, 83.27; H, 8.06; N, 5.60. Found: C, 83.21; H, 7.85; N, 5.89%.

3.6.4 Synthesis of [{Li(N3Dipp2)}x] (28)

A solution of LiN(SiMe3)2 (460 mg, 2.75 mmol) in toluene (10 mL) was added to a solution of Dipp2N3H (1.00 g, 2.74 mmol) at ambient temperature. A colourless precipitate was immediately observed. The slurry was stirred for a further 12 h, whereupon the solvent was decanted and the precipitate washed with pentane (5×5 mL). Drying in vacuo afforded a pale brown powder (895 mg, 88%); m.p. > 360 °C. IR

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(ATR, cm-1) 3036 (w), 2937 (s), 2845 (w), 1447 (m), 1422 (m), 1371 (m), 1350 (m), 1315 (w), 1276 (s, N=N), 1244 (s, N=N), 1173 (m), 1150 (w), 1087 (w), 1050 (w), 1032 (w), 964 (w), 927 (w), 794 (m), 768 (m), 751 (s), 723 (w), 680 (w), 591 (w), 548 (w), 529 (m), 449 (w), 422 (m).

3.6.5 Synthesis of [{K(N3Dipp2)}x] (29)

KN(SiMe3)2 (0.5 M in toluene, 1.1 mL, 0.55 mmol) was added to a solution of

Dipp2N3H (194 mg, 0.53 mmol) in toluene (10 mL) at ambient temperature. A colourless precipitate was immediately observed. The slurry was stirred for a further 2 h, whereupon the solvent was decanted and the precipitate washed with toluene (3×5 mL). Drying in vacuo afforded a pale pink powder (197 mg, 92%); m.p. > 360 °C. IR (ATR, cm-1) 3029 (w), 2932 (s), 2840 (w), 2146 (w), 1450 (m), 1419 (m), 1369 (m), 1346 (m), 1307 (w), 1276 (s, N=N), 1239 (w), 1226 (w), 1215 (w), 1179 (m), 1149 (w), 1090 (w), 1049 (w), 1030 (w), 961 (w), 947 (w), 926 (w), 794 (m), 773 (m), 747 (s), 722 (w), 675 (w), 640 (w), 599 (w), 513 (w), 467 (w), 448 (m), 427 (w).

3.6.6 Synthesis of [Li(N3Dmp2)] (30) nBuLi (1.6 M in hexanes, 0.34 mL, 0.54 mmol,) was added dropwise to a solution of 1 (360 mg, 0.54 mmol) in toluene (30 mL), the solution immediately changed colour from pale yellow to golden yellow. Stirring was continued for ca. 3 h followed by solvent removal in vacuo. The resultant yellow solid was extracted with hexane (60 mL), concentrated to insipient crystallisation and cooled to -25 °C overnight afforded bright yellow prisms suitable for X-ray diffraction structure determination (130 mg, 36%); 1 m.p. 174-176 °C. H NMR (400 MHz, C6D6) δ 1.90 (s, 24H, o-CH3), 2.17 (s, 12H, 13 p-CH3), 6.73 (s, 8H, m-Ar’H), 6.78 (s, 2H, p-ArH), 6.90 (s, 4H, m-ArH). C NMR (100

MHz, C6D6) δ 21.1 (p-CH3), 21.2 (o-CH3), 122.0, 128.8, 129.5 (ArCH), 132.5, 135.9, 7 -1 136.0, 140.2, 145.8 (ArC). Li NMR (156 MHz, C6D6) δ 0.48 (s). IR (Nujol, cm ) 1611 (w), 1495 (w), 1401 (w), 1277 (w), 1260 (m, N=N), 1227 (w), 1093 (w), 1031 (w), 849 (m), 801 (w), 765 (w), 754 (w), 735 (w). Samples of 30 repeatedly gave microanalyses low in carbon. This presumably results from high air/moisture sensitivity of the complex. Example analysis: Anal. Calc. for C48H50N3Li: C, 85.30; H, 7.46; N, 6.22. Found: C, 81.98; H, 7.61; N, 6.11%.

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3.6.7 Synthesis of [Na(N3Dmp2)] (31)

Method A: Hexane (20 mL) was added to a mixture of 1 (268 mg, 0.40 mmol) and nBuNa (40 mg, 0.50 mmol). Gas evolution was immediately observed, with the formation of a bright yellow solid and a dark orange solution. The resultant mixture was stirred for 16 h. Filtration followed by concentration to insipient crystallisation in vacuo and cooling to -25 °C overnight afforded bright yellow octahedra. Further concentration in vacuo afforded two additional crops. Yield of combined crops (270 mg, 97%).

Method B: Toluene (40 mL) was added to a mixture of 1 (340 mg, 0.50 mmol) and

NaN(SiMe3)2 (93 mg, 0.50 mmol). The resultant golden solution was stirred at ambient temperature for a further 8 h. The solvent was then removed in vacuo. The resultant yellow solid was extracted with hexane (50 mL), concentrated to insipient crystallisation and cooling to -25 °C overnight afforded bright yellow octahedra (155 1 mg, 45%); m.p. 170 °C. H NMR (400 MHz, C6D6) δ 1.93 (s, 24H, o-CH3), 2.15 (s, 13 12H, p-CH3), 6.70 (s, 8H, m-Ar’H), 6.87-6.90 (m, 6H, m- and p-ArH). C NMR (100

MHz, C6D6) δ 21.1 (p-CH3), 21.3 (o-CH3), 121.1, 127.7, 129.6 (ArCH), 132.0, 134.8, 136.2, 141.3, 147.6 (ArC). IR (Nujol, cm-1) 1612 (m), 1496 (s), 1463 (s), 1414 (w), 1261 (s, N=N), 1230 (w), 1202 (w), 1142 (m), 1092 (w), 1076 (w), 1013 (w), 849 (s), 899 (s), 766 (s), 754 (w), 741 (w), 665 (w). Samples of 31 repeatedly gave microanalyses low in carbon. This presumably results from high air/moisture sensitivity of the complex. Anal. Calc. for C48H50N3Na: C, 83.32; H, 7.28; N, 6.07. Found: C, 78.26; H, 7.22; N, 5.74%.

3.6.8 Synthesis of [K(N3Dmp2)] (32)

Method A: A solution of 1 (1.05 g, 1.57 mmol) in toluene (50 mL), was added to a potassium mirror (250 mg, 6.39 mmol). The resultant mixture was stirred for 24 h at 80 °C, during this period the colour changed from pale yellow to gold. Filtration followed by solvent removal in vacuo afforded a golden yellow powder. Extraction with fresh toluene, concentration to insipient crystallisation and cooling to -25 °C overnight afforded bright yellow octahedra suitable for X-ray diffraction structure determination (902 mg, 81%).

Method B: Toluene (30 mL) was added to a mixture of 1 (340 mg, 0.50 mmol) and

KN(SiMe3)2 (100 mg, 0.50 mmol). The resultant golden solution was stirred at ambient

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temperature for a further 8 h, followed by solvent removal in vacuo. The resultant yellow residue was then extracted with hexane (50 mL), concentrated to insipient crystallisation and cooling to -25 °C overnight to afford bright yellow prisms suitable for X-ray diffraction structure determination (202 mg, 58%), m.p. 226-230 °C (dec.). 1H

NMR (400 MHz, C6D6) δ 1.97 (s, 24H, o-CH3), 2.15 (s, 12H, p-CH3), 6.72 (s, 8H, 13 m-Ar’H), 6.75-6.88 (m, 6H, m-ArH and p-ArH). C NMR (100 MHz, C6D6) δ 21.2

(p-CH3), 21.6 (o-CH3), 120.7, 127.9, 129.8 (ArCH), 132.0, 134.4, 136.1, 141.8, 149.6 (ArC). IR (Nujol, cm-1) 2728 (w), 1607 (w), 1580 (m), 1486 (m), 1398 (s), 1277 (s, N=N), 1260 (s, N=N), 1240 (w), 1213 (br s), 1192 (s), 1073 (w), 1031 (w), 1015 (w), 952 (w), 858 (m), 850 (s), 801 (w), 784 (m), 761 (s), 740 (s), 660 (w). Samples of 32 repeatedly gave microanalyses low in carbon. This presumably results from high air/moisture sensitivity of the complex. Anal. Calc. for C48H50N3K: C, 81.43; H, 7.18; N, 5.93. Found: C, 80.08; H, 7.30; N, 5.88%.

3.6.9 Synthesis of [Rb(N3Dmp2)] (33)

A solution of 1 (340 mg, 0.50 mmol) in hexane (60 mL), was added to a rubidium mirror (150 mg, 1.76 mmol). The resultant mixture was stirred for 4 h at ambient temperature, during this period the colour changed from pale yellow to gold. Filtration followed by concentration to insipient crystallisation and cooling to -25 °C overnight afforded golden yellow prisms (247 mg, 65%); m.p. 218-220 °C (dec.). 1H NMR (400

MHz, C6D6) δ 1.98 (s, 24H, o-CH3), 2.15 (s, 12H, p-CH3), 6.75 (s, 8H, m-Ar’H), 13 6.81-6.89 (m, 6H, m-ArH and p-ArH). C NMR (100 MHz, C6D6) δ 21.2 (p-CH3), 21.7

(o-CH3), 120.4, 127.9, 129.8 (ArCH), 131.7, 134.3, 136.1, 142.0, 149.7 (ArC). IR (Nujol, cm-1) 2729 (m), 2028 (m), 1723 (w), 1603 (m), 1574 (w), 1276 (m, N=N), 1259 (m, N=N), 1195 (w), 1156 (w), 1074 (w), 1013 (m), 849 (s), 800 (m), 780 (w), 763 (w),

739 (w), 722 (m), 665 (w). Anal. Calc. for C48H50N3Rb: C, 76.42; H, 6.68; N, 5.57. Found: C, 76.61; H, 6.82; N, 5.60%.

3.6.10 Synthesis of [Cs(N3Dmp2)] (34)

A solution of 1 (170 mg, 0.25 mmol) in hexane (50 mL), was added to a caesium mirror (150 mg, 1.13 mmol). The resultant mixture was stirred for 2 h at ambient temperature, during this period the colour changed from pale yellow to gold. Filtration followed by concentration to insipient crystallisation and cooling to -25 °C overnight afforded

131 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

golden yellow prisms suitable for X-ray diffraction structure determination (100 mg, 1 50%); 244-246 °C (dec.). H NMR (400 MHz, C6D6) δ 2.00 (s, 24H, o-CH3), 2.16 (s,

12H, p-CH3), 6.76 (s, 8H, m-Ar’H), 6.79-6.83 (m, 2H, p-ArH), 6.87-6.89 (m, 4H, 13 m-ArH). C NMR (100 MHz, C6D6) δ 21.2 (p-CH3), 21.9 (o-CH3), 120.2, 128.1, 129.8 (ArCH), 131.4, 134.2, 136.2, 142.2, 150.0 (ArC). IR (Nujol, cm-1) 2724 (w), 1780 (w), 1744 (w), 1607 (w), 1579 (m), 1485 (w), 1398 (s), 1276 (s, N=N), 1257 (s, N=N), 1208 (br s), 1075 (m), 1027 (w), 1014 (w), 960 (w), 851 (s), 833 (w), 801 (w), 781 (m), 763 (s), 754 (s), 740 (m), 665 (w). Samples of 34 repeatedly gave microanalyses low in carbon. This presumably results from high air/moisture sensitivity of the complex. Anal.

Calc. for C48H50N3Cs: C, 71.90; H, 6.29; N, 5.25. Found: C, 70.56; H, 6.22; N, 5.18%.

1 n 3.6.11 Synthesis of [Li2(μ-κ -N3Dmp2)(μ- Bu)] (36) nBuLi (1.6 M in hexanes, 0.65 mL, 1.0 mmol,) was added dropwise to a solution of 1 (338 mg, 0.50 mmol) in hexane (60 mL) at ambient temperature. The colour of the solution immediately changed from pale yellow to golden yellow. Stirring was continued for a further 12 h. Concentration to ca. 20 mL in vacuo, followed by cooling to -25 °C overnight afforded bright yellow prisms suitable for X-ray diffraction 1 3 structure determination (244 mg, 66%). H NMR (400 MHz, C6D6) δ -1.46 (br t, JHH =

8.2 Hz, Li-CH2), 1.10-1.20 (br m, 5H, Li-CH2CH2 and CH2CH3), 1.34-1.42 (br m, 2H,

CH2CH3), 1.96 (s, 24H, o-CH3), 2.15 (s, 12H, p-CH3), 6.75-7.82 (m, 8H, m- and p- ArH), 6.78 (s, 2H, p-ArH), 6.86 (s, 4H, m-Ar’H). IR (Nujol, cm-1) 1609 (w), 1582 (w), 1484 (w), 1413 (w), 1277 (m), 1257 (s), 1226 (s), 1078 (w), 1032 (w), 854 (w), 802 (w),

783 (w), 764 (w), 744 (w). Anal. Calc. for C52H59N3Li2: C, 84.41; H, 8.04; N, 5.68. Found: C, 84.44; H, 8.13; N, 5.74%.

132 References for this chapter begin on pg. 133 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

3.7 References

[1] Edelmann, F. T., Angew. Chem. Int. Ed. 1995, 34, 2466-2488. [2] Piers, W. E.; Emslie, D. J. H., Coord. Chem. Rev. 2002, 233–234, 131-155. [3] (a) Edelmann, F. T., Adv. Organomet. Chem. 2008, 57, 183-352; (b) Bourget- Merle, L.; Lappert, M. F.; Severn, J. R., Chem. Rev. 2002, 102, 3031-3066. [4] Asay, M.; Jones, C.; Driess, M., Chem. Rev. 2010, 111, 354-396. [5] Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H., Chem. Rev. 2002, 102, 1851-1896. [6] Tsai, Y.-C., Coord. Chem. Rev. 2012, 256, 722-758. [7] (a) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S., J. Chem. Soc., Chem. Commun. 1994, 1699-1700; (b) Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.; Olmstead, M. M.; Roesky, H. W.; Power, P. P., J. Chem. Soc., Dalton Trans. 2001, 3465-3469; (c) Takeda, N.; Hamaki, H.; Tokitoh, N., Chem. Lett. 2004, 33, 134-135; (d) Hamaki, H.; Takeda, N.; Yamasaki, T.; Sasamori, T.; Tokitoh, N., J. Organomet. Chem. 2007, 692, 44-54; (e) Clegg, W.; Cope, E. K.; Edwards, A. J.; Mair, F. S., Inorg. Chem. 1998, 37, 2317-2319. [8] Wooles, A. J.; Lewis, W.; Blake, A. J.; Liddle, S. T., Organometallics 2013, 32, 5058-5070. [9] (a) Hitchcock, P. B.; Lappert, M. F.; Layh, M.; Liu, D.-S.; Sablong, R.; Shun, T., J. Chem. Soc., Dalton Trans. 2000, 2301-2312; (b) Cheng, Y.; Hitchcock, P. B.; Lappert, M. F.; Zhou, M., Chem. Commun. 2005, 752-754; (c) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S.; Sablong, R., Chem. Commun. 2002, 1920-1921. [10] (a) Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B., Dalton Trans. 2006, 2052- 2054; (b) Willcocks, A. M.; Robinson, T. P.; Roche, C.; Pugh, T.; Richards, S. P.; Kingsley, A. J.; Lowe, J. P.; Johnson, A. L., Inorg. Chem. 2011, 51, 246-257; (c) Jin, G.; Jones, C.; Junk, P. C.; Lippert, K.-A.; Rose, R. P.; Stasch, A., New J. Chem. 2009, 33, 64-75; (d) Luo, Y.-J.; Zhang, Y.; Shen, Q., Chinese J. Chem. 2007, 25, 562-565; (e) Giesbrecht, G. R.; Shafir, A.; Arnold, J., J. Chem. Soc., Dalton Trans. 1999, 3601-3604; (f) Jones, C.; Bonyhady, S. J.; Holzmann, N.; Frenking, G.; Stasch, A., Inorg. Chem. 2011, 50, 12315-12325; (g) Benndorf, P.; Preuß, C.; Roesky, P. W., J. Organomet. Chem. 2011, 696, 1150-1155; (h) Hitchcock, P. B.; Lappert, M. F.; Layh, M., J. Chem. Soc., Dalton Trans. 1998,

133

Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

3113-3118; (i) Yao, S.; Chan, H.-S.; Lam, C.-K.; Lee, H. K., Inorg. Chem. 2009, 48, 9936-9946. [11] Maity, A. K.; Fortier, S.; Griego, L.; Metta-Magaña, A. J., Inorg. Chem. 2014, 53, 8155-8164. [12] Junk, P. C.; Cole, M. L., Chem. Commun. 2007, 1579-1590. [13] (a) Villiers, C.; Thuéry, P.; Ephritikhine, M., Eur. J. Inorg. Chem. 2004, 4624- 4632; (b) Cole, M. L.; Junk, P. C.; Louis, L. M., J. Chem. Soc., Dalton Trans. 2002, 3906-3914; (c) Cole, M. L.; Davies, A. J.; Jones, C.; Junk, P. C., J. Organomet. Chem. 2004, 689, 3093-3107; (d) Loh, C.; Seupel, S.; Görls, H.; Krieck, S.; Westerhausen, M., Eur. J. Inorg. Chem. 2014, 1312-1321. [14] (a) Schmidt, J. A. R.; Arnold, J., Chem. Commun. 1999, 2149-2150; (b) Schmidt, J. A. R.; Arnold, J., J. Chem. Soc., Dalton Trans. 2002, 2890-2899; (c) Baker, R. J.; Jones, C., J. Organomet. Chem. 2006, 691, 65-71; (d) Chlupatý, T.; Padělková, Z.; Lyčka, A.; Růžička, A., J. Organomet. Chem. 2011, 696, 2346- 2354. [15] Häfelinger, G.; Kuske, K. H. In The Chemistry of the Amidines and Imidates, 2nd ed.; pp. 1-100, Eds. Patai, S.; Rappoport, Z., 1991, Wiley: Chichester, UK. [16] (a) Cole, M. L.; Davies, A. J.; Jones, C.; Junk, P. C., Z. Anorg. Allg. Chem. 2011, 637, 50-55; (b) Cole, M. L.; Davies, A. J.; Jones, C.; Junk, P. C., New J. Chem. 2005, 29, 1404-1408. [17] Cole, M. L.; Davies, A. J.; Jones, C.; Junk, P. C., J. Organomet. Chem. 2007, 692, 2508-2518. [18] (a) Gantzel, P.; Walsh, P. J., Inorg. Chem. 1998, 37, 3450-3451; (b) Lee, H. S.; Hauber, S.-O.; Vinduš, D.; Niemeyer, M., Inorg. Chem. 2008, 47, 4401-4412. [19] Lee, H. S.; Niemeyer, M., Inorg. Chem. 2006, 45, 6126-6128. [20] Advanced Inorganic Chemistry, 6th Ed., Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M., 1999, John Wiley & Sons, Inc.: New York, USA. [21] (a) Green, S. P.; Jones, C.; Stasch, A., Science 2007, 318, 1754-1757; (b) Bonyhady, S. J.; Green, S. P.; Jones, C.; Nembenna, S.; Stasch, A., Angew. Chem. Int. Ed. 2009, 48, 2973-2977. [22] Cui, C. M.; Roesky, H. W.; Schmidt, H. G.; Noltemeyer, M.; Hao, H. J.; Cimpoesu, F., Angew. Chem. Int. Ed. 2000, 39, 4274-4276.

134 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

[23] (a) Hsu, C.-W.; Yu, J.-S. K.; Yen, C.-H.; Lee, G.-H.; Wang, Y.; Tsai, Y.-C., Angew. Chem. 2008, 120, 10081-10084; (b) Tsai, Y.-C.; Hsu, C.-W.; Yu, J.-S. K.; Lee, G.-H.; Wang, Y.; Kuo, T.-S., Angew. Chem. Int. Ed. 2008, 47, 7250- 7253; (c) Tsai, Y.-C.; Chen, H.-Z.; Chang, C.-C.; Yu, J.-S. K.; Lee, G.-H.; Wang, Y.; Kuo, T.-S., J. Am. Chem. Soc. 2009, 131, 12534-12535; (d) Noor, A.; Wagner, F. R.; Kempe, R., Angew. Chem. Int. Ed. 2008, 47, 7246-7249; (e) Wagner, F. R.; Noor, A.; Kempe, R., Nat. Chem. 2009, 1, 529-536; (f) Noor, A.; Kempe, R., Chem. Rec. 2010, 10, 413-416; (g) Noor, A.; Bauer, T.; Todorova, T. K.; Weber, B.; Gagliardi, L.; Kempe, R., Chem. Eur. J. 2013, 19, 9825-9832. [24] As determined by a survey of the Cambridge Structural Database v. 5.36 with updates for November 2014. [25] Stasch, A., Angew. Chem. Int. Ed. 2012, 51, 1930-1933. [26] (a) Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M. M.; Power, P. P., J. Am. Chem. Soc. 1989, 111, 4338-4345; (b) Westerhausen, M.; Wieneke, M.; Nöth, H.; Seifert, T.; Pfitzner, A.; Schwarz, W.; Schwarz, O.; Weidlein, J., Eur. J. Inorg. Chem. 1998, 1998, 1175-1182; (c) Moorhouse, R. S.; Moxey, G. J.; Ortu, F.; Reade, T. J.; Lewis, W.; Blake, A. J.; Kays, D. L., Inorg. Chem. 2013, 52, 2678-2683; (d) Rabe, G. W.; Sommer, R. D.; Rheingold, A. L., Organometallics 2000, 19, 5537-5540. [27] Marsch, M.; Harms, K.; Lochmann, L.; Boche, G., Angew. Chem. Int. Ed. 1990, 29, 308-309. [28] Hong, J.; Zhang, L.; Wang, K.; Chen, Z.; Wu, L.; Zhou, X., Organometallics 2013, 32, 7312-7322. [29] Moore, D. S.; Robinson, S. D., Adv. Inorg. Chem. 1986, 30, 1-68. [30] Cheng, Y.; Doyle, D. J.; Hitchcock, P. B.; Lappert, M. F., Dalton Trans. 2006, 4449-4460. [31] Detsch, R.; Niecke, E.; Nieger, M.; Schoeller, W. W., Chem. Ber. 1992, 125, 1119-1124. [32] Demeshko, S.; Godemann, C.; Kuzora, R.; Schulz, A.; Villinger, A., Angew. Chem. Int. Ed. 2013, 52, 2105-2108. [33] Arrowsmith, M.; Crimmin, M. R.; Hill, M. S.; Kociok-Kohn, G., Dalton Trans. 2013, 42, 9720-9726.

135 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

[34] Woodul, W. D.; Richards, A. F.; Stasch, A.; Driess, M.; Jones, C., Organometallics 2010, 29, 3655-3660. [35] Guzei, I. A.; Wendt, M., Dalton Trans. 2006, 3991-3999. [36] Krieck, S.; Görls, H.; Westerhausen, M., Organometallics 2010, 29, 6790-6800. [37] Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K., Angew. Chem. Int. Ed. 2003, 42, 3294-3298. [38] Niemeyer, M.; Power, P. P., Inorg. Chem. 1996, 35, 7264-7272. [39] Hauber, S. O.; Lissner, F.; Deacon, G. B.; Niemeyer, M., Angew. Chem. Int. Ed. 2005, 44, 5871-5875. [40] Klinkhammer, K. W., Chem. Eur. J. 1997, 3, 1418-1431. [41] Lego, C.; Neumueller, B., Z. Anorg. Allg. Chem. 2011, 637, 1784-1789. [42] Hoffmann, D.; Bauer, W.; Schleyer, P. v. R.; Pieper, U.; Stalke, D., Organometallics 1993, 12, 1193-1200. [43] (a) Klinkhammer, K. W.; Schwarz, W., Z. Anorg. Allg. Chem. 1993, 619, 1777- 1789; (b) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Smith, J. D., Angew. Chem. Int. Ed. 1995, 34, 687-688. [44] Liddle, S. T.; Clegg, W.; Morrison, C. A., Dalton Trans. 2004, 2514-2525. [45] Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S., Dalton Trans. 2008, 2832-2838. [46] Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou, P. A., Inorg. Chem. 2008, 47, 7366-7376. [47] (a) Arnold, P. L.; Liddle, S. T., C. R. Chimie 2008, 11, 603-611; (b) Glock, C.; Younis, F. M.; Ziemann, S.; Görls, H.; Imhof, W.; Krieck, S.; Westerhausen, M., Organometallics 2013, 32, 2649-2660. [48] Lee, H. S.; Niemeyer, M., Inorg. Chim. Acta 2011, 374, 163-170. [49] Baldamus, J.; Berghof, C.; Cole, M. L.; Hey-Hawkins, E.; Junk, P. C.; Louis, L. M., Eur. J. Inorg. Chem. 2002, 2878-2884. [50] (a) Hardman, N. J.; Eichler, B. E.; Power, P. P., J. Chem. Soc., Chem. Commun. 2000, 1991-1992; (b) Hill, M. S.; Hitchcock, P. B., Chem. Commun. 2004, 1818- 1819; (c) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R., Dalton Trans. 2005, 273-277; (d) Li, X.; Cheng, X.; Song, H.; Cui, C., Organometallics 2007, 26, 1039-1043; (e) Choong, S. L.; Woodul, W. D.; Stasch, A.; Schenk, C.; Jones, C., Aust. J. Chem. 2011, 64, 1173-1176.

136 Chapter Three: Alkali Metal Complexes of Bulky Bidentate N,N'-Ligands

[51] Nimitsiriwat, N.; Gibson, V. C.; Marshall, E. L.; Takolpuckdee, P.; Tomov, A. K.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.; Dale, S. H., Inorg. Chem. 2007, 46, 9988-9997.

137

Chapter Four: Stabilisation of Low Oxidation State Group 13 Complexes by Kinetic Control

4.1 Introduction

Since the early 1990s, there has been a significant resurgence in the air and moisture chemistries of the main group metals, particularly those of group 13.[1] This renewed interest has been fuelled by the isolation of novel sub-valent clusters,[2] low oxidation state complexes[3] and a multitude of metal-metal bonded species,[4] and has been underpinned by tremendous advances in diffraction structure determination. The primary focus of this chapter is the synthesis and chemistry of +1 oxidation state metal complexes supported by the ligands introduced in earlier chapters (MIL, M = Al, Ga, In and Tl, L = sterically demanding monoanionic bidentate N,Nʹ-ligand). Generally speaking, the isolation of such complexes is made possible through the development of sterically demanding ligands. These serve to kinetically stabilise otherwise unstable metal oxidation states.

4.1.1 Halides

The stabilities of the binary monohalides of group 13 increase upon descent of the group, such that monohalide compounds of indium and thallium are commercially available. By contrast, aluminium and gallium monohalides are only thermodynamically stable at elevated temperatures and low pressures.[5] In the late 1980’s, Schnöckel [5-6] reported a method to prepare metastable solutions of AlCl·xEt2O, wherein AlCl is prepared by heating aluminium and hydrogen chloride at 1200 K in vacuo. Subsequent condensation in the presence of diethyl ether and toluene at 77 K affords a deep red solution that can be stored at 196 K indefinitely.[5-6] The analogous bromide,[7] iodide,[8] as well as gallium monohalides,[9] have since been prepared by this method.

A number of research groups have attempted to prepare GaI by heating the elements [10] under vacuum. However, only mixtures of subhalides such Ga2I3 (later found to be [11] [12] [Ga]2[Ga2I6], in the solid state) were isolated. In 1990, Green reported the isolation of an insoluble green powder that displayed reactivity akin to a monovalent gallium system.[13] This material, tentatively labelled “GaI”, was prepared by the sonication of 138 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

liquid gallium in the presence of half of an equivalent of diiodine in toluene at 50 °C. Subsequently, the reactivity of “GaI” in salt metathesis reactions has been studied extensively,[14] demonstrating the value of a readily accessible low oxidation state gallium feedstock.[15] Despite its widespread usage, “GaI” remains poorly characterised. On the basis of solid-state NMR and Raman spectroscopy data, “GaI” is currently [16] thought to consist of a mixture of subhalides with the overall formula [Ga]4[Ga2I6].

The aforementioned commercially available indium and thallium monohalides and “GaI” display exceptionally poor solubility in common organic solvents. Recently poorly coordinating pseudo-halides such as triflate,[17] or charge delocalised weakly F [18] t F [19] coordinating anions such as [BAr 4] and [Al(O Bu )4], have been employed as a means of providing soluble sources of gallium(I), indium(I) and thallium(I).

4.1.2 Alkyl, Amide, Cyclopentadienyl and Silyl Clusters

A large number of thermally stable low oxidation state group 13 complexes of bulky alkyls, silyls, amides and cyclopentadienyls have been reported. These complexes, which were generally accessed via salt metathesis reactions with an alkali metal reagent,[20] exist as oligomeric, typically tetrameric, clusters in the solid-state (Figure 4.1).[21]

Figure 4.1 - Tetrameric clusters of low oxidation state group 13 complexes

The tetrameric composition of many of these clusters arises from the linear combination of the highest occupied molecular σ-orbital of each of the four monomeric fragments, which gives one bonding (a1) and three degenerate, effectively non-bonding, orbitals

(t2). The latter can interact with the eight empty π-type orbitals of the cluster derived from the two degenerate e(π) lowest unoccupied molecular orbitals of each monomeric fragment. This lowers the energy of the t2 orbitals, making them weakly bonding and making eight electrons available for cluster formation (Figure 4.2, pg. 140).[22] The

139 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

weaker M···M interactions observed upon descending the group can be attributed to the inert pair effect, which results in an increased energy difference between the occupied t2 orbitals and the vacant π-type orbitals.[3]

Figure 4.2 - Molecular orbital scheme of tetrahedral clusters[22]

Alkali metal reductions of suitably substituted metal dihalides, typically diiodides, has also been applied successfully to the preparation of similar MIL complexes,[23] as has reductive ligand elimination.[24] An overview of the synthetic protocols used to access low oxidation state metal tetrahedral clusters is featured in Scheme 4.1.

Scheme 4.1 - Syntheses of tetrahedral clusters

140 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

4.1.3 Bulky Aryl and Amide Complexes

The development of the sterically encumbrant 2,6-terphenyl ligand, principally by the groups of Power and Robinson, has led to the preparation of a number of low oxidation state group 13 aryl complexes.[25] As outlined in Figure 4.3 for gallium, complexes featuring “smaller” terphenyl moieties generate dimers in the solid-state and increased steric bulk can drive the formation of monomeric arylgalliums.[26]

Figure 4.3 - Nuclearity of gallium(I) terphenyl complexes[26d]

The complexes in Figure 4.3 were prepared through either a salt metathesis reaction or alkali metal reduction (cf. Scheme 4.1).[27] Interestingly, dimeric aluminium(I) and gallium(I) terphenyls may be further reduced, even to a formally zero oxidation state, by alkali metals.[26b,27e,28] This was famously reported by Robinson in 1996, wherein he interpreted a short Ga-Ga bond in [Na]2[Ga2Ar2] (Ar = 2,6-bis(2,4,6- triisopropylphenyl)phenyl) as an indication of its triple bond “gallyne” character (Figure 4.4, pg. 142).[29] The grandiosity of this statement triggered numerous experimental and computational investigations,[26b,30] with the general consensus being that whilst this bond displays multiple bond character, it is better described as a weak double bond.[4a,27e] Sodium and potassium reductions of less bulky terphenyl complexes have afforded a number of planar Al3, Ga3 and Ga4 rings that owing to apparent electron delocalisation, led Robinson to coin the term “metalloaromaticity”.[28a,b] Once again these claims have been hotly and robustly debated.[31]

141 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

Figure 4.4 - Robinson’s so-called Gallyne, image taken directly from reference 29

The incorporation of steric bulk in amide MIL complexes (cf. Figure 4.1) has enable the isolation of a number of amide stabilised monomeric complexes of the group 13 metals in the +1 oxidation state (Figure 4.5).[32]

Figure 4.5 - Monomeric gallium(I) and indium(I) amide complexes[32a]

4.1.4 Anionic Polydentate N-Donor Ligands

Sterically demanding monoanionic bidentate N,Nʹ-ligands have been used to stabilise low oxidation state group 13 metals.[3] Due to their similar electronic structure and strong σ-donor ability, several of these, particularly for the lighter elements of group 13, have been described as NHC analogues (Figure 4.6, pg. 143).[33]

142 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

Figure 4.6 - An isolobal group 13 metal(I) heterocycle and NHC

Dippnacnac complexes of all the group 13 metals in the +1 oxidation state have been reported, however, the indium and thallium complexes display considerable light sensitivity.[34] Analogous guanidinate (cf. Scheme 4.2, left, pg. 144)[35] and Tp[36] complexes have also been reported for gallium, indium and thallium, and a number of thallium(I) triazenide complexes have been reported.[37] Anionic gallium(I) heterocyclic species have also been reported (Figure 4.7).[38] The coordination chemistry of these compounds has been well documented.[33,39] Attempts to prepare analogous anionic aluminium and indium complexes were not successful,[38a,40] however, boron analogues have recently been reported.[41] As per the aforementioned aryl complexes, these species are typically prepared through a metathesis reaction or alkali metal reduction (Scheme 4.1).

Figure 4.7 - Gallium(I) heterocyclic anions

143 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

Insufficient N-donor ligand bulk can lead to disproportionation reactions that afford complexes with the group 13 metal in a higher oxidation state (Scheme 4.2, right).[35,42]

Scheme 4.2 - Attempted preparation of low oxidation state indium amidinate and guanidinate complexes using indium(I) chloride

Decreasing the ligand steric demand of the β-diketiminate ligand has led to the isolation of a number of aggregated indium(I) and thallium(I) complexes (Figure 4.8),[43] with analogies to the monomeric and di- or trimeric aryl and amide complexes discussed earlier (Figures 4.3 and 4.5).

Figure 4.8 - Aggregation observed in indium(I) β-diketiminate complexes

4.1.5 The Oxidative Chemistry of MIL Species

Aluminium(I), gallium(I) and indium(I) complexes can be oxidised through reactions with elemental pnictogens[44] and chalcogens.[23a,45] Similarly, aluminium(I) and gallium(I) complexes can be oxidised through the reaction with organoazides to afford aluminium(III) and gallium(III) imide complexes (Scheme 4.3, pg. 145).[32c,46]

144 Reference for this chapter begin on pg. 171 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

Scheme 4.3 - Oxidation of a group 13 metal(I) complex by an organoazide[46b]

A number of studies have shown that group 13 metal(I) complexes can insert into M-X (M = d- or p-block metal, X = halogen)[47] and R-X (R = alkyl) bonds.[48] Additionally, aluminium(I)[49] and gallium(I)[50] complexes have been shown to readily insert into H-H, C-H, Si-H, Sn-H, N-H, P-H and O-H bonds.

4.1.6 The Coordination Chemistry of MIL Species

DFT calculations on MIL species indicate that the ground state of each species is a singlet state and that regardless of the substituent R the singlet-triplet energy gap tends to increase with atomic number (cf. Figure 4.2, left).[51] Thus, it can be stated that MIL monomers formally possess a lone pair of electrons located in a σ-orbital (HOMO). The directionality of the lone pair decreases with atomic number. Whilst these species formally possess two degenerate unoccupied π-orbitals (cf. Figure 4.2, left), the nature of the LUMO is dependent upon the conjugative ability of the L substituent. Hence, MIL species are in some cases considered isolobal with CO and, by extension, some [52] PR3 ligands (Figure 4.9).

Figure 4.9 - Isolobality of MIL species with CO[52]

To this end, there are a number of examples where the electron pair of a MIL species

2 interacts with a formally dz orbital of a transition metal, resulting in strong σ-donation (Figure 4.10, pg. 146).[52] In principle, the vacant π-orbitals in MIL species afford it π acidity (Figure 4.10), however, experimental and theoretical studies have shown that

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metal π-back-donation only becomes significant in homoleptic complexes, due to decreased competition with stronger π-acids such as CO.[53]

Figure 4.10 - Orbital interactions in LMI-Mʹ complexes[52]

The donation of electron density from pendant fluorine atoms in a π-acidic ligand to the vacant π-orbitals of the MIL species has been observed.[54] It should be noted that shorter MI···F contacts are observed when the L substituent is a poor π-donor relative to when L is a strong π-donor (Figure 4.11).[55] This Lewis amphoteric behaviour has led to some MIL species being called Janus-type ligands.[54a]

Figure 4.11 - Lewis amphoteric behaviour of two aluminium(I) species coordinated by a highly Lewis acidic borane[54a,56]

Quantifying the σ-donor strength of MIL species has proven to be difficult. One method, I developed by Berke, requires the B(C6F5)3 adduct of the M L species to be crystallographically characterised (Figure 4.12, pg. 147).[57] From this data, the σ-donor strength of the MIL species is believed to be proportional to the deviation of the geometry at boron from trigonal planar towards tetrahedral, as denoted by the sum of the CC6F5-B-CC6F5 angles about the coordinated boron (∑ = 360° = no σ-donation, ∑ = [58] I 328.5° = full σ-donation). Data for various M L complexes of B(C6F5)3 are compiled in Table 4.1 (pg. 147). A similar method has been developed by Schulz which uses t [59] Al Bu3 instead of B(C6F5)3.

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Figure 4.12 - Tris(perfluorophenyl)borane complex of MIL

Metal Tp* Dippnacnac Ar* TmAd TmtBu Cp* Cp

Al - 330.3[54a] - - 339.8[56] -

Ga 333.5[60] 333.6[61] 337.5[30m] 340.7[62] 342.2[63] 342.2[61] 344.4[64]

In - - 339.3[26a] 345.5[62] 347.9[65] - -

Tl - - 341.0[26c] - - -

I Table 4.1 - Sum of CC6F5-B-CC6F5 angles for various LM -B(C6F5)3 complexes

The data in Table 4.1 demonstrates σ-donor strength gradually diminishes upon descent of the group, due the loss of directionality of the lone electron pair. This data also shows that the electronic nature of the MIL support ligand, i.e. L, also has a significant impact on σ-donor strength. In view of the limited data available for quantitative measurement of MIL donicity, Cowley has recommended that MIL species be further examined through theoretical calculations and competition experiments.[66]

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4.2 Project Outline

This chapter seeks to expand the coordination chemistry of triazenide ligands, such as that derived from 1, through attempts to stabilise +1 oxidation state group 13 metals.

The steric profile of 2,6-terphenyl triazenides such as N3Dmp2 (Chapter Two) lends them to such applications and downstream applications in coordination chemistry. In addition, the poor electron donor properties of triazenides relative to other monoanionic bidentate N,Nʹ-ligands (electronic analyses in Chapter Two) indicate that triazenides have potential as ligands for low oxidation state group 13 metals. In the event of successful syntheses, the σ-donor capability of these complexes will be assessed using the Berke “B(C6F5)3” method (Table 4.1). The reactivity of the ensuing complexes with coordinatively unsaturated d-block metal complexes will be explored.

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4.3 Results and Discussion

4.3.1 Attempted Stabilisation of Low Oxidation State Group 13 Metals using a 1,3-Bis(aryl)triazenide

The preparation of [Ga(N3Dipp2)] was attempted by treating “GaI” with an equimolar amount of [{K(N3Dipp2)}x] (29) in toluene at -78 °C. Slow warming of the reaction mixture to room temperature overnight afforded a pale yellow solution with grey suspended solids. Concentration of the filtered reaction mixture afforded a colourless crystalline solid upon standing that characterised as the gallium(III) complex,

[GaI(N3Dipp2)2] (37) by single crystal XRD structure determination. Repeating the reaction using two equivalents of “GaI” also resulted in disproportionation, however in this instance the gallium(II) dimer [{GaI(N3Dipp2)}2] (38) was isolated (Scheme 4.4). These results are akin to those observed for the sterically similar formamidinate Fiso.[42a,c] Attempts to prepare the chloro analogue of 38 through the reaction of

Ga[GaCl4] with two equivalents of 28 in toluene at -78 °C, resulted in gallium metal deposition and the isolation of the chloro analogue of 37; [GaCl(N3Dipp2)2] (39).

Scheme 4.4 - Preparation of gallium(II) and gallium(III) triazenide complexes

Attempts to prepare [In(N3Dipp2)] through the stoichiometric addition of

[{Li(N3Dipp2)}x] (28) or 29 to indium(I) chloride or iodide in toluene at -78 °C resulted in the isolation of the disproportionation products [InCl(N3Dipp2)2] (40) and

[InI(N3Dipp2)2] (41) (Scheme 4.5, pg. 150). These outcomes are similar to those involving the sterically similar formamidinate Fiso.[42a] It should be noted that disproportionation products were isolated during initial attempts to prepare [In(Dippnacnac)] by similar methods.[67] The eventual synthesis of [In(Dippnacnac)] was subsequently reported by Hill using a one pot procedure with equimolar amounts of InI,

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Dipp [34c] KN(SiMe3)2 and nacnacH in THF at -78 °C. A closely modelled one pot Dipp procedure using Dipp2N3H instead of nacnacH afforded indium metal and 41 once again. Attempts to prepare an indium(II) analogue of 38 using In[InCl4] also afforded 40 (Scheme 4.5).

Scheme 4.5 - Preparation of bis(triazenide)indium halide complexes

Having failed to prepare [In(N3Dipp2)] via salt metathesis with indium monohalides, alternate routes were investigated. Roesky has reported the metallation of [68] tris(trifluoromethyl)phenol with InCp through protoylsis. The reaction of Dipp2N3H with InCp was therefore investigated. Equimolar amounts of InCp and Dipp2N3H were added to a J. Youngs valved NMR tube followed by heating in C6D6 at 80 °C for 12 h. 1H NMR spectra collected on the resultant mixture reveal the formation of a number of products, none of which corresponding to cyclopentadiene, its Diels-Alder coupled product, or cis-2,2',6,6'-tetrakisisopropyldiazobenzene, a known thermal decomposition [69] product of Dipp2N3H. An attempt to metallate Dipp2N3H with the more basic [70] pentamethylcyclopentadienyl derivative InCp* (pKa CpH 18.0, Cp*H 26.1), was also unsuccessful.

Niemeyer has reported the preparation of thallium(I) triazenide complexes through [37c] metallation with thallium ethoxide. Following this procedure, [{Tl(N3Dipp2)}2] (42) was isolated as a deep red, highly crystalline, solid in high yield (Scheme 4.6, pg. 151). Crystalline 42 displays no evidence of photo-induced decomposition, as has been reported for the related β-diketiminate complexes.[43d]

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Scheme 4.6 - Reaction of Dipp2N3H with heavy group 13 metal(I) bases

Compounds 37-42 have been full characterised and their molecular structures determined by single crystal X-ray diffraction studies. The IR spectra of 37-42 show -1 strong N3 absorptions in the range 1279-1228 cm , which is indicative of the triazenide ligands acting as N,Nʹ-chelate donors in each complex.[71] The 1H NMR spectra of 37-41

(C6D6) exhibit two sets of methyl doublet resonances, by contrast the spectrum of 42

(C6D6) exhibits a single methyl doublet resonance. The former is likely due to impedance of free rotation about the isopropyl to arene bond thereby locking one methyl above the arene plane and one below. The isopropyl methine resonances in the 1H NMR spectra of 38 and 42 (3.74 and 3.56 ppm respectively) lie downfield relative to those observed in the 1H NMR spectra of metal(III) complexes 37 and 39-41, which lie in the range 3.40-3.46 ppm. Thus the chemical shift of the isopropyl methine resonances appears to be diagnostic of metal oxidation state, which presents a useful handle when assessing crude reaction mixtures.

Colourless single crystals of 37-41 suitable for X-ray crystallographic study were grown by the slow cooling of saturated hexane solutions to -25 °C. Complexes 37 and 39-41 crystallise in the space group P21/c and are isomorphous with the known [MX(Fiso)2] formamidinate complexes.[42a] The representative molecular structure of 40 is depicted in Figure 4.13 (pg. 152). The molecular structures of 37, 39 and 41 can be found in the appendix. Salient metrical parameters for these complexes are listed in Table 4.2 (pg. 153).

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Figure 4.13 - Molecular structure of 40 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. See Table 4.2 for metrical parameters for 37 and 39-41.

Each metal centre is five coordinate with two chelating triazenide units and one halide atom, giving a heavily distorted trigonal bipyramidal coordination geometry about the metal centre, with N(3) and N(6) in the apical positions. These N-atoms are significantly more distant from the metal centre than the equatorial N(1) and N(4) donors. The N-N distances in the triazenide scaffolds of each complex show close to complete bond delocalisation despite the noted disparity in the M-N bond lengths (axial vs equatorial). The degree of steric congestion in the bis(triazenide) complexes can be seen in the non-orthogonal placement of the arene ring planes to the N3 donor planes as would be expected in the ideal geometry.

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Bond Parameter 37 39 40 41

M-X 2.5020(13) 2.1618(10) 2.3530(5) 2.6931(11)

M-N(1) 1.974(7) 1.966(3) 2.1772(15) 2.192(9)

M-N(3) 2.143(7) 2.110(3) 2.2662(14) 2.253(7)

M-N(4) 1.991(7) 1.976(3) 2.1917(15) 2.191(9)

M-N(6) 2.163(7) 2.105(2) 2.2568(15) 2.196(7)

N(1)-N(2) 1.324(9) 1.310(3) 1.301(2) 1.331(9)

N(2)-N(3) 1.277(9) 1.294(3) 1.294(2) 1.263(11)

N(4)-N(5) 1.306(9) 1.313(3) 1.305(2) 1.270(10)

N(5)-N(6) 1.272(10) 1.289(4) 1.295(2) 1.282(11)

N(1)-M-N(3) 61.1(3) 61.87(10) 56.90(5) 56.8(3)

N(4)-M-N(6) 60.6(3) 61.62(10) 56.92(5) 57.2(3)

N(1)-N(2)-N(3) 107.5(6) 107.4(3) 109.45(14) 109.1(8)

N(4)-N(5)-N(6) 109.2(7) 107.2(2) 109.30(14) 110.7(8)

N3:ArC(1) 68.5 70.2 62.5 62.2

N3:ArC(13) 89.0 88.8 85.4 89.0

N3:ArC(25) 68.8 68.9 65.0 65.0

N3:ArC(37) 77.2 80.5 83.0 77.2

ArC(1):ArC(13) 54.1 52.9 52.2 57.8

ArC(25):ArC(37) 56.8 53.4 55.5 58.8

Table 4.2 - Selected bond lengths (Å), angles (°) and torsion angles (°) for 37 and 39-41

The molecular structure of 38 is depicted in Figure 4.14 (pg. 154). Complex 38 crystallises in space group P1̅ with a half dimer in the asymmetric unit. The unique gallium forms a planar four membered ring with the chelating triazenide unit (mean Ga-

N: 2.004(13) Å, βn: 62.7(4) °). The N-N bond lengths in the triazenide are near identical (1.298(11) and 1.299(13) Å) which is consistent with complete delocalisation over the

N3 scaffold. The gallium is further coordinated by an iodine atom with a bond length of

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2.5227(19) Å, which is expectedly longer (GaII versus GaIII) than that for 38 (2.5020(13) Å). The distorted tetrahedral geometry of the gallium centre is completed by a Ga-Ga bond with a contact distance of 2.427(3) Å, which is longer than those of i Me i [42b] similar N- Pr guanidinate and amidinate complexes ([{GaI( G Pr)}2] 2.3952(9) Å, tBu i [42d] [{GaI( A Pr)}2] 2.406(1) Å ) but consistent with those observed for N-Dipp [42a] Me amidinate complexes ([{GaI(Fiso)}2] 2.4303(10) Å, [{GaI( Aiso)}2] 2.430(1) [42c] tBu [42a] Å, [{GaI( Aiso)}2] 2.4521(9) Å). The steric congestion in this dimer is increased relative to 37 as determined by the increased perturbation of the arene rings away from orthogonal to the N3 donor plane (∑Ar:N3 37, 303.5°; 38, 290.6°).

Figure 4.14 - Molecular structure of 38 (50% thermal ellipsoids). All hydrogen atoms omitted and Dipp groups depicted as wireframes for clarity. Symmetry operation used to generate # atoms: -x, -y, -z. Selected bond lengths (Å), angles (°) and torsion angles (°): Ga(1)-Ga(1)# 2.427(3), Ga(1)-I(1) 2.5227(19), Ga(1)-N(1) 2.000(9), Ga(1)-N(3) 2.007(9), N(1)-N(2) 1.298(11), N(2)-N(3) 1.299(13), N(1)-Ga(1)-N(3) 62.7(4),

Ga(1A)-Ga(1)-I(1) 121.55(8), N(1)-N(2)-N(3) 106.7(9), N3:ArC(1) 83.0, N3:ArC(13) 62.3, ArC(1):ArC(13) 47.7.

Orange single crystals of 42 suitable for X-ray crystallographic study were grown by the slow cooling of a saturated hexane solution to -25 °C. Compound 42 crystallises in the orthorhombic space group P212121 with two unique dimer molecules in the asymmetric unit. The two distinct molecules (42a and 42b) exhibit comparable bonding parameters. The molecular structure and salient bond parameters of 42a are given in Figure 4.15 (pg. 155).

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Figure 4.15 - Molecular structure of 42a (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Tl(1A)-N(1A) 2.642(7), Tl(1A)-N(3A) 2.759(7), Tl(1A)-N(4A) 2.692(7), Tl(1A)-N(6A) 2.745(7), Tl(2A)-N(1A) 2.756(7), Tl(2A)-N(3A) 2.645(7), Tl(2A)-N(4A) 2.731(6), Tl(2A)-N(6A) 2.724(7), T1(1A)···Tl(2A) 3.4610(5), N(1A)-N(2A) 1.299(9), N(2A)-N(3A) 1.320(9), N(4A)-N(5A) 1.319(9), N(5A)-N(6A) 1.318(9), N(1A)-Tl(1A)-N(3A) 46.9(2), N(4A)-Tl(1A)-N(6A) 47.0(2), N(1A)-Tl(2A)-N(3A) 46.9(2), N(4A)-Tl(2A)-N(6A) 46.9(2),

N(1A)-N(2A)-N(3A) 110.4(7), N(4A)-N(5A)-N(6A) 110.7(6), N3:ArC(1A) 58.1, N3:ArC(13A) 49.5, N3:ArC(25A) 66.9, N3:ArC(37A) 56.7, ArC(1A):ArC(13A) 84.8, ArC(1A):ArC(13A) 74.6.

Complex 42 is dimeric in the solid-state, though it lacks the two-fold axis observed for [37c] the thallium triazenide [{Tl(N3{Me4Ter}2)}2]. Each thallium atom is coordinated by the four nitrogen atoms of the bridging triazenide ligands with two short and two long Tl-N bonds. The mean Tl-N bond length in 42 (2.71 Å) is significantly shorter than that [37c] of [{Tl(N3{Me4Ter}2)}2] (2.84 Å), which is consistent with decreased steric crowding. The mean Tl···Tl' contact in 42 (3.464 Å) is slightly shorter than that of [37c] [{Tl(N3{Me4Ter}2)}2] (3.489 Å) and significantly shorter than that of [37a] [37b] [{Tl(N3Ph2)}2] (3.641 Å) and [{Tl(N3{C6H4NO2}2)}2] (3.846 Å). In fact, the average Tl···Tl' contact in 42 closely approximates the sum of the metallic radii (3.408 [72] Å). The N-N bond lengths in the N3 triazenide donor units are consistent with full electron delocalisation. The steric congestion in the dimers prevents the planes of the aryl rings and the N3 units from being orthogonal, however, unlike 37, 39-41 this

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congestion is clearly inadequate for locking of the Dipp Ar-CiPr bonds to occur in solution (cf. single Me doublet resonance by 1H NMR).

The thallium centres in each dimeric unit of 42 maintain long intermolecular Tl···CAr contacts to adjacent dimers. The lengths of these contacts (4.093-5.099 Å) are [37a] intermediate between those in [{Tl(N3Ph2)}2] (3.470-3.601 Å), which is defined as 6 an η π-arene interaction and those of [{Tl(N3{Me4Ter}2)}2] for which all intermolecular Tl···C contacts are greater than 6.8 Å.[37c] By way of further comparison, the closest intermolecular Tl···C in the monomeric singly coordinated arylthallium(I) complex [Tl(Tripp)] is 4.19 Å.[25b] This suggests that the aforementioned intermolecular

Tl···CAr contacts in 42 should be considered as very weak by comparison to that in

[{Tl(N3Ph2)}2].

4.3.2 Kinetic Stabilisation of Low Oxidation State Group 13 Metals using a 1,3-Bis(2,6-terphenyl)triazenide

To capitalise on the successful demonstration of substantial steric bulk for the N-Dmp triazenide derived from 1, as reported in Chapters Two and Three (GAl 62.99%, GRh 64.60%), it was applied to group 13 metals in the +1 oxidation state.

The gallium and indium complexes; [Ga(N3Dmp2)] (43) and [In(N3Dmp2)] (44), were successfully isolated as dark orange solids from the salt metathesis reaction of in situ prepared 30 with “GaI” and InCl respectively (Scheme 4.7). The thallium analogue;

[Tl(N3Dmp2)] (45), was isolated as a dark orange solid in high yield from the same procedure used to prepare the N-Dipp analogue 42 (Scheme 4.7).

Scheme 4.7 - Preparations of group 13 metal(I) N-triazenide complexes

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Complexes 43-45 were characterised by IR and NMR spectroscopies, melting point and

C, H, N elemental analyses. Their IR spectra display strong N3 absorptions in the range 1279-1228 cm-1, which is indicative of the triazenide group acting as an N,N'-chelating [71] 1 ligand in each complex. Similarly, the H NMR spectra of 43-45 (C6D6) exhibit single sets of sharp triazenide N-Dmp resonances, which is also indicative of symmetrical N,N'-donation as per chelation.

Orange single crystals of 43-45 suitable for X-ray crystallographic study were grown by cooling saturated toluene (43 and 44) or hexane (45) solutions to -25 °C. Complexes 43-45 crystallise in the space group P1̅. Complexes 43 and 44 are isomorphous and crystallise with a disordered half molecule of toluene in the asymmetric unit. The thallium complex 45 crystallises with a molecule of hexane in its asymmetric unit. The molecular structure of 43 is depicted in Figure 4.16 whilst the molecular structures of 44 and 45 are depicted in Figure 4.17 (pg. 158). Salient metrical parameters for 43-45 are listed in Table 4.3 (pg. 159).

Figure 4.16 - Molecular structure of 43 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Salient metrical parameters for 43 are listed in Table 4.3.

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Figure 4.17 - Molecular structures of 44 (top, 50% thermal ellipsoids) and 45 (bottom, 50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Salient metrical parameters for 44-45 are listed in Table 4.3.

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Bond Parameter 43 44 45

M-N(1) 2.113(6) 2.372(5) 2.482(4)

M-N(3) 2.172(5) 2.403(5) 2.529(4)

N(1)-N(2) 1.321(6) 1.301(6) 1.303(6)

N(2)-N(3) 1.337(7) 1.307(6) 1.324(6)

M···C(7) 3.331(8) 3.539(6) 3.424(7)

M···C(8) 3.266(9) 3.372(8) 3.351(7)

M···C(31) 3.320(9) 3.300(8) 3.377(8)

M···C(32) 3.280(10) 3.257(8) 3.299(8)

[73] RvdW(M···C) 4.150 4.278 4.866

ηm/ηn η0/η0 η0/η0 η2/η2

N(1)-M-N(3) 60.19(19) 52.40(15) 50.11(13)

N(1)-N(2)-N(3) 107.9(5) 107.9(4) 107.8(4)

M out of N3 plane 0.03 0.16 0.09

N3:ArC(1) 40.5 41.1 39.1

N3:ArC(25) 33.3 30.6 30.0

ArC(1):ArC(25) 72.9 71.0 68.3

Table 4.3 - Selected bond lengths (Å), angles (°) and torsion angles (°) for 43-45

Complexes 43-45 are monomeric in the solid-state with each metal cation being two coordinate through N,N'-chelation by the triazenide. The similar N-N bond lengths within 43-45 demonstrate delocalisation over the N3 donor set for each complex (Table 4.3) as per their N-Dipp congeners. The mean M-N bond lengths in 43-45 (43, 2.143 Å; 44, 2.388 Å; 45, 2.506 Å) are significantly longer than those for the related guanidinate and β-diketiminate complexes ([Ga(CyGiso)] mean 2.091 Å,[35a] [In(CyGiso)] mean 2.298 Å,[35a] [Tl(Dippnacnac)] mean 2.416 Å).[34d] The longer mean M-N distance likely demonstrates the decreased donor ability of the triazenide (GAl 62.99%, GRh 64.60%) relative to the guanidinate (GAl 48.84%, GRh 48.18%) and β-diketiminate (GAl 59.11%,

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GRh 58.71%) ligands (Chapter Two), as well as the increased steric bulk of the N3Dmp2 ligand vis-à-vis the guandinates and β-diketiminates studied (Chapter Two). Despite apparent N3 charge delocalisation, the M-N bonding in 43-45 consistently displays a degree of asymmetry, with M-N(1) shorter than M-N(3) (Table 4.3). The thallium of 45 displays π-arene contacts to the flanking mesityl groups of the triazenide. The analogous intramolecular metal-arene distances in 43 and 44 are too long to be considered bonding interactions. The thallium cation interacts with one Mes ring from each terphenyl substituent in an η2 fashion (viz. Chapter Three) with Tl···C distances in the range 3.299-3.424 Å to one ipso and one ortho carbon of each mesityl ring (other distances > 3.5 Å). The lengths of these contacts lie well within the combined van der Waals radii of the thallium and carbon (4.866 Å)[73] and are similar to those reported for other 1,3-bis(2-biaryl/2,6-terphenyl)triazenide complexes.[37c] They are, however, significantly longer than the thallium···π-Mes contacts observed for [Tl(N{Dmp}Me)] [32b] [74] (Tl···Cipso 2.980 Å) and [Tl(N{C(C3F7)N(Mes)}2)] (Tl···Cipso 3.022 Å), suggesting the interactions herein are weak. This is also reflected in the lower hapticity of the interactions in 45 relative to other monomeric thallium 1,3-bis(2-biaryl)triazenide complexes, where η4 and η5 π-arene interactions are observed.[37c] As previously discussed in Chapter Three, this likely originates from buttressing of the non-coordinating Dmp mesityl groups which stymies better π-coordination. These interactions also prevent near orthogonal arrangement of the N3 donor plane and principal arene planes (all Ar:N3 < 45°, Table 4.3).

4.3.3 The Chemistry of Group 13 Metal(I) Triazenide Complexes

Having successfully isolated several four-membered group 13 metal(I) complexes, an investigation into their coordination chemistry was undertaken in light of the. MIL NHC isolobal analogy (Figure 4.6). It should be noted that the coordination chemistry of group 13 metal(I) guanidinates has been studied extensively.[75] Unfortunately attempts to probe the σ-donor strength of 43-45 through preparation of their B(C6F5)3 donor- acceptor complexes (cf. Section 4.1.6) were unsuccessful. In each case near quantitative recovery of starting materials was observed as determined by 1H, 11B and 19F NMR spectroscopies. The failure to prepare donor-acceptor complexes of 43-45 is surprising as there are a significant number of analogous complexes, especially those of gallium(I), reported (Table 4.1). This could indicate 43-45 are very poor σ-donors and/or that the

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sterically demanding N-Dmp groups prevent the approach of the borane to the MI donor. The less sterically demanding thallium complex, 42 also displays no reactivity 1 11 19 with B(C6F5)3 as evidenced by in situ monitoring using H, B and F NMR spectroscopies. This is less surprising as, despite smaller sterics it is probable that thallium(I) triazenide complexes 42 and 45 are very poor σ-donors, due to the high s-character of the lone pair, which arises from the ‘inert pair effect’.

Group 13 metal(I) β-diketiminate complexes have been reported to form stable coordination complexes with coordinatively unsaturated group 10 complexes, such as [76] [Ni(cdt)] and [Pd2(dvds)3]. These acceptor molecules are significantly less sterically demanding with respect to B(C6F5)3. Thus, the syntheses of [(Dmp2N3)In{Ni(cdt)}] and

[(Dmp2N3)In{Pd(dvds)}] were attempted using 44 (Scheme 4.8). These reactions resulted in immediate metal deposition and the isolation of 1 as sole Dmp containing product. These results suggest 44 to be a weaker σ-donor relative to group 13 metal(I) β-diketiminate complexes.

Scheme 4.8 - Attempted preparation of coordination complexes of 44

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4.4 Conclusions

In summary, this chapter describes a number of attempts to prepare group 13 metal(I) triazenide complexes. The stabilisation of such complexes was found to be kinetic in origin, with the sterically demanding N-Dmp triazenide based on 1 successfully stabilising gallium(I) and indium(I) species (43 and 44 respectively). By comparison, only disproportionation products are isolated (37-41) when the less sterically demanding N-Dipp triazenide is employed.

A dimeric gallium(II) complex (38) was isolated as one of the disproportion products when attempting to prepare [Ga(N3Dipp2)]. Attempts to deliberately prepare analogous indium complexes lead to disproportion to afford the respective trivalent metal complex and indium metal.

Thallium(I) complexes of both the N-Dipp and N-Dmp triazenide (42 and 45 respectively) were successfully prepared and crystallographically characterised. The N-Dipp complex is dimeric in the solid-state and displays a relative short contact between the thallium centres. By contrast, the N-Dmp complex is monomeric in solid-state. The analogous gallium(I) and indium(I) complexes of the N-Dmp triazenide are also monomeric in the solid-state.

Attempts to quantify the σ-donor strengths of these species proved unsuccessful, with no evidence of reaction between B(C6F5)3 and 43-45 observed. In addition to the possible poor σ-donicity, the failed reactions suggest steric congestion prohibits formation of an acid-base adduct.

This chapter details a considerable expansion in the triazenide chemistry of the group 13 metals. In particular, it should be noted that this research significantly increases the number of gallium triazenide complexes, as only six (two gallium(II) and four gallium(III)) have been reported previously.[77]

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4.5 Future Directions

Given the poor stability of [Ga(N3Dipp2)] and [In(N3Dipp2)] towards disproportionation, the use of a trapping agent could be investigated. Other low [64] Ad [62] Ad [62] oxidation complexes, such as [{GaCp}x], [{Ga(Tm )}x] and [{In(Tm )}x] have been reported to decompose via disproportionation when attempts were made to isolate them. However, the inclusion of an equivalent of the strong Lewis acid B(C6F5)3 I [62,64] during their preparation led to the isolation of the LM -B(C6F5)3 adducts. Thus, repeating the preparations of [Ga(N3Dipp2)] and [In(N3Dipp2)] in the presence of

B(C6F5)3 may enable the isolation of these species as their borane adducts. This would enable the σ-donor strength of the group 13 metal(I) triazenides to be evaluated relative to other group 13 metal(I) Lewis bases (Table 4.1).

Roesky has reported the only monomeric aluminium(I) complex to date; [Al(Dippnacnac)][34a] which was prepared by potassium reduction of its trivalent diiodo relative. This route removes the need for a “metastable” aluminium(I) halide solution.[5] It is conceivable that an analogous route employing triazene 1 may afford

[Al(N3Dmp2)], thus completing the series of group 13 metal(I) stabilised by the N-Dmp triazenide. It is also likely that the reaction of [AlMe2(N3Dmp2)] (9) (viz. Chapters Two and Five) or [AlH2(N3Dmp2)] (viz. Chapter Six) with iodine would afford

[AlI2(N3Dmp2)] as a precursor for potassium reduction.

[Al(N3Dmp2)] and 43 are superior candidates for coordination and oxidative insertion chemistries relative to 44 and 45 on account of their lighter group 13 metals and presumed superior σ-donicity (Section 4.1.6). An investigation of the coordination chemistries of such compounds is presently missing, making it difficult to compare and Dipp contrast different ligand frameworks (e.g. nacnac versus N3Dmp2).

In view of the substantial steric bulk of [M(N3Dmp2)] the reaction of these species with elemental chalcogens presents a unique opportunity to isolate complexes that may feature terminal metal chalcogen bonds about a three coordinate group 13 metal. The reaction of [M(Dippnacnac)] (M = Al and Ga) with elemental chalcogens affords chalcogen bridged dimeric complexes.[78] Analogous reactions with gallium and indium TptBu complexes lead to the first structurally authenticated examples of terminal Ga=S,[79] Ga=Se,[80] Ga=Te[80] and In=Se[81] bonds. It is conceivable that the enhanced

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Dipp steric bulk of N3Dmp2 relative to nacnac (viz. Chapter Two) may enable the isolation of the first examples of Al=O and Ga=O bonds too.

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4.6 Experimental

4.6.1 General Synthetic Procedures

[13] [82] [20b] [69,83] [84] [85] “GaI”, [{InCp}x], [{InCp*}6], Dipp2N3H, [Pd2(dvds)3] and [Ni(cdt)] were synthesised by literature procedures. NaN(SiMe3)2 was sublimed prior to use. TlOEt was decanted into a foil wrapped J. Youngs tapped flask under argon and stored at 4 °C in the dark.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

4.6.2 Synthesis of [GaI(N3Dipp2)2] (37)

Cold (-78 °C) toluene (30 mL) was added to a mixture of 29 (200 mg, 0.50 mmol) and “GaI” (120 mg, 0.61 mmol). The resultant light brown slurry was allowed to warm to ambient temperature over 4 h leading to the formation of a black precipitate. After a further 4 h, the mixture was filtered and the filtrate dried in vacuo. The resultant brown solid was recrystallised from the minimum amount of hexane at -25 °C, which afforded pale yellow blocks suitable for X-ray diffraction structure determination (88 mg, 48%); 1 3 m.p. 188-192 °C (dec.). H NMR (300 MHz, C6D6) δ 1.06 (d, JHH = 6.7 Hz, 24H, 3 3 CH(CH3)2), 1.13 (d, JHH = 6.7 Hz, 24H, CH(CH3)2), 3.40 (sept, JHH = 6.7 Hz, 8H, 13 CH(CH3)2), 7.03-7.11 (m, 12H, m- and p-ArH). C NMR (76 MHz, C6D6) δ 23.7, 24.3

(CH(CH3)2), 29.2 (CH(CH3)2), 123.9, 124.2 (ArCH), 144.6, 145.6 (ArC). Anal. Calc. for C48H68GaIN6: C, 62.28; H, 7.40; N, 9.08. Found: C, 62.69; H, 7.53; N, 8.99%.

4.6.3 Synthesis of [{GaI(N3Dipp2)}2] (38)

Cold (-78 °C) toluene (30 mL) was added to a mixture of 29 (300 mg, 0.75 mmol) and “GaI” (300 mg, 1.53 mmol). The resultant light brown slurry was allowed to warm to ambient temperature over 4 h leading to the formation of a black precipitate. After a further 4 h, the mixture was filtered and the filtrate dried in vacuo. The resultant pale yellow solid was recrystallised from the minimum amount of hexane at -25 °C, which afforded colourless prisms suitable for X-ray diffraction structure determination (180 1 3 mg, 42%); m.p. 176-182 °C (dec.). H NMR (300 MHz, C6D6) δ 1.14 (d, JHH = 6.7 Hz, 3 3 24H, CH(CH3)2), 1.29 (d, JHH = 6.7 Hz, 24H, CH(CH3)2), 3.74 (sept, JHH = 6.7 Hz, 13 8H, CH(CH3)2), 7.03-7.11 (m, 12H, m- and p-ArH). C NMR (76 MHz, C6D6) δ 24.6,

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25.3 (CH(CH3)2), 29.2 (CH(CH3)2), 124.2, 128.7 (ArCH), 138.8, 145.5 (ArC). Anal.

Calc. for C48H68Ga2I2N6·2C6H14: C, 55.66; H, 7.47; N, 6.49. Found: C, 54.79; H, 7.42; N, 6.71%.

4.6.4 Synthesis of [GaCl(N3Dipp2)2] (39)

Cold (-78 °C) toluene (20 mL) was added to a mixture of 28 (180 mg, 0.50 mmol) and

Ga[GaCl4] (70 mg, 0.25 mmol). The resultant light brown slurry was allowed to warm to ambient temperature over 8 h leading to the formation of a black precipitate. The mixture was filtered and the filtrate dried in vacuo. The resultant pale yellow solid was then extracted with hexane (40 mL), concentrated to ca. 10 mL, placement at -25 °C overnight afforded a crop of colourless crystals suitable for X-ray diffraction structure 1 3 determination (55 mg, 26%). H NMR (400 MHz, C6D6) δ 1.04 (d, JHH = 6.7 Hz, 24H, 3 3 CH(CH3)2), 1.13 (d, JHH = 6.7 Hz, 24H, CH(CH3)2), 3.46 (sept, JHH = 6.7 Hz, 8H, 13 CH(CH3)2), 7.04-7.12 (m, 12H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 23.8, 24.4

(CH(CH3)2), 28.9 (CH(CH3)2), 124.1, 128.5 (ArCH), 139.3, 145.4 (ArC). Anal. Calc. for C48H68GaClN6: C, 69.10; H, 8.22; N, 10.07. Found: C, 68.99; H, 8.23; N, 10.06%.

4.6.5 Synthesis of [InCl(N3Dipp2)2] (40)

Method A: Cold (-78 °C) toluene (30 mL) was added to a mixture of 28 (296 mg, 0.81 mmol) and InCl (122 mg, 0.81 mmol). The resultant slurry was allowed to warm to ambient temperature overnight. The colourless supernant solution was then isolated from a large amount of grey precipitate by filtration. The solvent was removed in vacuo and the colourless residue was extracted with hexane (80 mL). The volume of the solution was reduced to ca. 40 mL in vacuo, and the obtained precipitate was redissolved by slight warming. Storage at ambient temperature overnight afforded large colourless cubes over two crops (207 mg, 42%).

Method B: Cold (-78 °C) toluene (20 mL) was added to a mixture of 28 (180 mg, 0.50 mmol) and In[InCl4] (90 mg, 0.25 mmol). The resultant light brown slurry was allowed to warm to ambient temperature over 8 h leading to the formation of a black precipitate. The mixture was then filtered and the toluene removed in vacuo. The resultant pale yellow powder was then extracted with hexane (40 mL), concentrated to ca. 10 mL, placement at -25 °C afforded a crop of colourless cubes suitable for X-ray diffraction

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structure determination (78 mg, 35%); m.p. 103-105 °C (dec.). 1H NMR (400 MHz, 3 3 C6D6) δ 1.06 (br d, JHH = 6.7 Hz, 24H, CH(CH3)2), 1.15 (br d, JHH = 6.7 Hz, 24H, 3 CH(CH3)2), 3.43 (sept, JHH = 6.7 Hz, 8H, CH(CH3)2), 7.01-7.12 (m, 12H, m- and 13 p-ArH). C NMR (100 MHz, C6D6) δ 23.6, 24.3 (CH(CH3)2), 28.9 (CH(CH3)2), 124.0, 128.2 (ArCH), 139.8, 144.9 (ArC). IR (ATR, cm-1) 3112 (w), 3038 (w), 2936 (s), 2903 (m), 2844 (m), 1608 (w), 1576 (w), 1503 (m), 1447 (s), 1427 (m), 1404 (s), 1371 (m), 1350 (m), 1320 (m), 1245 (s, N=N), 1207 (s), 1175 (s), 1087 (m), 1050 (w), 1037 (w), 927 (m), 828 (w), 792 (s), 746 (s), 712 (w), 610 (w), 531 (w), 499 (w), 425 (w), 402

(w). Anal. Calc. for C48H68InClN6: C, 65.56; H, 7.89; N, 9.56. Found: C, 63.91; H, 8.09; N, 8.51%.

4.6.6 Synthesis of [InI(N3Dipp2)2] (41)

Cold (-78 °C) THF (25 mL) was added to a mixture of Dipp2N3H (366 mg, 1.0 mmol),

[NaN(SiMe3)2] (184 mg, 1.0 mmol) and InI (240 mg, 1.0 mmol). The resultant slurry was allowed to warm to ambient temperature overnight. The colourless supernant was then filtered to remove a large amount of grey precipitate. The solvent was removed in vacuo and the colourless residue was extracted with hexane (40 mL). The volume of the solution was reduced to ca. 20 mL under vacuum, and the obtained precipitate was redissolved by slight warming. Storage at ambient temperature overnight afforded large colourless cubes suitable for X-ray diffraction structure determination (48 mg, 13%), 1 3 m.p. 206-210 °C (dec.). H NMR (250 MHz, C6D6) δ 1.06 (d, JHH = 6.7 Hz, 24H, 3 3 CH(CH3)2), 1.16 (d, JHH = 6.7 Hz, 24H, CH(CH3)2), 3.43 (sept, JHH = 6.7 Hz, 8H, 13 CH(CH3)2), 7.03-7.14 (m, 12H, m- and p-ArH). C NMR (63 MHz, C6D6) δ 23.7, 24.8

(CH(CH3)2), 29.1 (CH(CH3)2), 124.0, 128.2 (ArCH), 140.2, 144.9 (ArC). IR (ATR, cm-1) 3040 (w), 2937 (s), 2903 (w), 2844 (m), 1573 (w), 1491 (s), 1451 (s), 1429 (m), 1404 (s), 1371 (m), 1350 (m), 1333 (w), 1289 (w), 1246 (s, N=N), 1203 (s), 1170 (m), 1089 (m), 1048 (m), 984 (w), 962 (w), 928 (m), 878 (w), 832 (w), 793 (s), 765 (s), 747 (s), 723 (w), 678 (w), 624 (w), 607 (w), 587 (w), 532 (w), 506 (w), 464 (w), 445 (w).

Anal. Calc. for C48H68InIN6: C, 59.38; H, 7.06; N, 8.66. Found: C, 59.60; H, 7.18; N, 8.55%.

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4.6.7 The Reaction of InCp with Dipp2N3H

A solution of Dipp2N3H (70 mg, 0.11 mmol) in C6D6 (0.4 mL) was added to a solution of InCp (20 mg, 0.11 mmol) in C6D6 (0.4 mL) at ambient temperature. The resultant mixture was left to stand at ambient temperature for 48 h, followed by standing at 80 °C for 12 h. The sample was then evaluated by 1H NMR spectroscopy.

4.6.8 Synthesis of [{Tl(N3Dipp2)}2] (42)

TlOEt (255 μL, 3.70 mmol) was added dropwise with stirring, to a solution of

Dipp2N3H (1.30 g, 3.60 mmol) in toluene (20 mL) at -20 °C with immediate colour change from pale yellow to deep red. With the exclusion of light, the mixture was allowed to warm to ambient temperature and stirred for a further 24 h. The solvent was removed in vacuo and the red residue was extracted into hexane (60 mL). Concentration of the solution to ca. 15 mL in vacuo and standing at ambient temperature after light warming to dissolve precipitated solids afforded large red plates suitable for X-ray diffraction structure determination (604 mg, 29%); m.p. 203-205 °C (dec.). 1H NMR 3 3 (300 MHz, C6D6) δ 1.23 (d, JHH = 6.9 Hz, 48H, CH(CH3)2), 3.56 (sept, JHH = 6.9 Hz, AAB AAB 8H, CH(CH3)2), 7.07 (t, JHH = 7.4 Hz, 4H, p-ArH), 7.17 (d, JHH = 7.4 Hz, 8H, 13 m-ArH). C NMR (76 MHz, C6D6) δ 24.8 (CH(CH3)2), 29.1 (CH(CH3)2), 123.4, 125.5 (ArCH), 142.7, 148.7 (ArC). IR (Nujol, cm-1) 1588 (m), 1361 (m), 1322 (w), 1256 (m, N=N), 1236 (w), 1202 (w), 1178 (w), 1163 (w), 1109 (s), 1059 9s), 939 (w), 917 (s), 887 (w), 802 (s), 786 (s), 751 (s), 732 (s), 591 (w), 575 (w), 559 (w). Anal. Cal. for

C24H34N3Tl: C 50.67, H 6.02, N 7.39. Found: C, 49.73; H, 6.06; N, 7.25%.

4.6.9 Synthesis of [Ga(N3Dmp2)] (43)

A cool (-78 °C) solution of 30 (204 mg, 0.44 mmol) in toluene (15 mL) was added dropwise to a stirred slurry of “GaI” (120 mg, 0.61 mmol) in toluene (10 mL) at -78 °C. The resultant slurry was stirred at -78 °C for 1 h followed by warming to ambient temperature overnight, which afforded a red solution and dark grey precipitate. Filtration and followed by concentration in vacuo (ca. 5 mL) and standing at ambient temperature after light warming to dissolve precipitated solids afforded a crop of dark orange prisms suitable for X-ray diffraction structure determination. The supernant was decanted and slowly cooled to -25 °C overnight to afford a second crop of orange

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prisms. Yield of combined crops (203 mg, 62%); m.p. 202-206 °C (dec.). Anal. Calc. for C48H50N3Ga: C, 78.05; H, 6.82; N, 5.69. Found: C, 78.26; H, 7.22; N, 5.72%.

4.6.10 Synthesis of [In(N3Dmp2)] (44)

A cool (-78 °C) solution of 30 (330 mg, 0.44 mmol) in toluene (15 mL) was added dropwise to a stirred slurry of InCl (75 mg, 0.50 mmol) in toluene (10 mL) at -78 °C. The resultant slurry was stirred at -78 °C for 1 h, then allowed to warm to ambient temperature overnight, which afforded a red solution and dark grey precipitate. Filtration and followed by concentration in vacuo (ca. 5 mL) and standing at ambient temperature after light warming to dissolve precipitated solids afforded a crop of dark orange prisms suitable for X-ray diffraction structure determination. The supernant was decanted and slowly cooled to -25 °C overnight to afford a second crop of orange prisms. Yield of combined crops (203 mg, 59%); m.p. 223-229 °C (dec.). 1H NMR (250

MHz, C6D6) δ 1.97 (s, 24H, o-CH3), 2.13 (s, 12H, p-CH3), 6.78-6.83 (m, 6H, m- and 13 p-ArH), 6.86 (s, 8H, m-Ar’H). C NMR (50 MHz, C6D6) δ 21.1 (p-CH3), 21.6 (o-CH3), 122.9, 129.0, 130.0 (ArCH), 133.1, 135.9, 136.0, 139.0 (ArC). IR (Nujol, cm-1) 1612 (w), 1278 (w), 1262 (m, N=N), 1230 (w), 1077 (br w), 1030 (br w), 854 (w), 845 (w),

801 (w), 784 (w), 764 (w), 756 (w), 737 (w). Anal. Calc. for C48H50N3In·C7H8: C, 75.42; H, 6.67; N, 4.79. Found: C, 75.71; H, 7.21; N, 5.12%.

4.6.11 Synthesis of [Tl(N3Dmp2)] (45)

TlOEt (24 μL, 0.34 mmol) was added dropwise to a solution of 1 (221 mg, 0.33 mmol) in toluene (30 mL) at -20 °C with immediate colour change from pale yellow to deep red. With the exclusion of light, the mixture was allowed to warm to ambient temperature and stirred for a further 24 h, during which a small amount of metal deposition was observed. The solvent was removed in vacuo and the red residue was extracted into hexane (60 mL). Concentration of the solution to ca. 10 mL in vacuo and standing at ambient temperature after light warming to dissolve precipitated solids afforded large red blocks suitable for X-ray diffraction structure determination (175 mg, 1 58%); m.p. 243-250 °C (dec.). H NMR (500 MHz, C6D6) δ 1.97 (s, 24H, o-CH3), 2.13 AAB (s, 12H, p-CH3), 6.78 (t, JHH = 7.4 Hz, 2H, p-ArH), 6.84 (m, 12H, m-ArH and 13 m-Ar’H). C NMR (100 MHz, C6D6) δ 21.1 (p-CH3), 23.1 (o-CH3), 122.9, 128.7, 129.9 (ArCH), 133.1, 135.6, 136.1, 139.6 (ArC). IR (Nujol, cm-1) 1610 (w), 1278 (w), 1262

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(m, N=N), 1230 (w), 1077 (br w), 1030 (br w), 854 (w), 845 (w), 801 (w), 784 (w), 764

(w), 756 (w), 737 (w). Anal. Calc. for C48H50TlN3·0.5C6H14: C, 66.84; H, 6.27; N, 4.58. Found: C, 66.78; H, 6.35; N, 4.38%.

4.6.12 Attempted Preparation of B(C6F5)3 Adducts of 42-45

A cool (-78 °C) solution of B(C6F5)3 (100 mg, 0.20 mmol) in toluene (20 mL) was added dropwise to a solution of [M(N3Dmp2)] (ca. 0.20 mmol) in toluene (20 mL) at -78 °C. The resultant orange solution was stirred at -78 °C for 1 h followed by warming to ambient temperature overnight. Filtration and followed by solvent removal in vacuo afforded an orange residue that was examined as soon as practicable by 1H, 11B 19 and F NMR spectroscopies (C6D6 solution). In all cases no reaction was observed.

4.6.13 The Reaction of [Ni(cdt)] with 44

Cold (-78 °C) toluene (20 mL) was added to a mixture of [Ni(cdt)] (32 mg, 0.14 mmol) and 44 (109 mg, 0.14 mmol). Immediately the formation of a grey precipitate was observed. The resultant slurry was allowed to warm to ambient temperature overnight. Filtration, followed by solvent removal in vacuo, afforded a yellow powder that characterises as 1 by 1H NMR spectroscopy.

4.6.14 The Reaction of [Pd2(dvds)3] with 44

Cold (-78 °C) toluene (20 mL) was added to a mixture of [Pd2(dvds)3] (109 mg, 0.14 mmol) and 44 (109 mg, 0.14 mmol). Immediately the formation of a grey precipitate was observed. The resultant slurry was allowed to warm to ambient temperature overnight. Filtration, followed by solvent removal in vacuo, afforded a yellow powder that characterises as 1 by 1H NMR spectroscopy.

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4.7 References

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Inorg. Chem. 2010, 4415-4418; (j) Prabusankar, G.; Gemel, C.; Winter, M.; Seidel, R. W.; Fischer, R. A., Chem. Eur. J. 2010, 16, 6041-6047; (k) Bollermann, T.; Prabusankar, G.; Gemel, C.; Seidel, R. W.; Winter, M.; Fischer, R. A., Chem. Eur. J. 2010, 16, 8846-8853; (l) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R., Dalton Trans. 2008, 2854-2860. [48] (a) Ganesamoorthy, C.; Blaser, D.; Wolper, C.; Schulz, S., Chem. Commun. 2014, 50, 12382-12384; (b) Ganesamoorthy, C.; Bläser, D.; Wölper, C.; Schulz, S., Angew. Chem. Int. Ed. 2014, 53, 11587-11591; (c) Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer, M., Angew. Chem. Int. Ed. 2000, 39, 1815-1817; (d) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R., Inorg. Chem. 2007, 46, 3783-3788. [49] Chu, T.; Korobkov, I.; Nikonov, G. I., J. Am. Chem. Soc. 2014, 136, 9195-9202. [50] (a) Seifert, A.; Scheid, D.; Linti, G.; Zessin, T., Chem. Eur. J. 2009, 15, 12114- 12120; (b) Zhu, Z.; Wang, X.; Peng, Y.; Lei, H.; Fettinger, J. C.; Rivard, E.; Power, P. P., Angew. Chem., Int. Ed. 2009, 48, 2031-2034. [51] Macdonald, C. L. B.; Cowley, A. H., J. Am. Chem. Soc. 1999, 121, 12113- 12126. [52] González-Gallardo, S.; Bollermann, T.; Fischer, R. A.; Murugavel, R., Chem. Rev. 2012, 112, 3136-3170. [53] (a) Uhl, W.; Benter, M.; Melle, S.; Saak, W.; Frenking, G.; Uddin, J., Organometallics 1999, 18, 3778-3780; (b) Uddin, J.; Frenking, G., J. Am. Chem. Soc. 2001, 123, 1683-1693. [54] (a) Yang, Z.; Ma, X.; Oswald, R. B.; Roesky, H. W.; Zhu, H.; Schulzke, C.; Starke, K.; Baldus, M.; Schmidt, H.-G.; Noltemeyer, M., Angew. Chem. Int. Ed. 2005, 44, 7072-7074; (b) Moxey, G. J.; Jones, C.; Stasch, A.; Junk, P. C.; Deacon, G. B.; Woodul, W. D.; Drago, P. R., Dalton Trans. 2009, 2630-2636. [55] Uddin, J.; Boehme, C.; Frenking, G., Organometallics 2000, 19, 571-582. [56] Gorden, J. D.; Voigt, A.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H., J. Am. Chem. Soc. 2000, 122, 950-951. [57] Jacobsen, H.; Berke, H.; Döring, S.; Kehr, G.; Erker, G.; Fröhlich, R.; Meyer, O., Organometallics 1999, 18, 1724-1735. [58] It should be noted that the ligand steric character also contibute to this deviation, though this influence is believed to be dwarfed by electronic influences.

178 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

[59] (a) Kuczkowski, A.; Schulz, S.; Nieger, M.; Schreiner, P. R., Organometallics 2002, 21, 1408-1419; (b) Schulz, S.; Kuczkowski, A.; Schuchmann, D.; Flörke, U.; Nieger, M., Organometallics 2006, 25, 5487-5491. [60] Yurkerwich, K.; Parkin, G., J. Clust. Sci. 2010, 21, 225-234. [61] Hardman, N. J.; Power, P. P.; Gorden, J. D.; Macdonald, C. L. B.; Cowley, A. H., Chem. Commun. 2001, 1866-1867. [62] Yurkerwich, K.; Yurkerwich, M.; Parkin, G., Inorg. Chem. 2011, 50, 12284- 12295. [63] Yurkerwich, K.; Buccella, D.; Melnick, J. G.; Parkin, G., Chem. Sci. 2010, 1, 210-214. [64] Schenk, C.; Köppe, R.; Schnöckel, H.; Schnepf, A., Eur. J. Inorg. Chem. 2011, 3681-3685. [65] Yurkerwich, K.; Buccella, D.; Melnick, J. G.; Parkin, G., Chem. Commun. 2008, 3305-3307. [66] Cowley, A. H., Chem. Commun. 2004, 2369-2375. [67] Stender, M.; Power, P. P., Polyhedron 2002, 21, 525-529. [68] Scholz, M.; Noltemeyer, M.; Roesky, H. W., Angew. Chem. Int. Ed. 1989, 28, 1383-1384. [69] Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou, P. A., Inorg. Chem. 2008, 47, 7366-7376. [70] Kreindlin, A. Z.; Rybinskaya, M. I., Russ. Chem. Rev. 2004, 73, 417-432. [71] Moore, D. S.; Robinson, S. D., Adv. Inorg. Chem. 1986, 30, 1-68. [72] Chemistry of Aluminium, Gallium, Indium and Thallium, Ed. Downs, A. J., 1993, Blackie Academic and Professional: Glasgow, UK. [73] Guzei, I. A.; Wendt, M., Dalton Trans. 2006, 3991-3999. [74] Dias, H. V. R.; Singh, S.; Cundari, T. R., Angew. Chem. Int. Ed. 2005, 44, 4907- 4910. [75] (a) Green, S. P.; Jones, C.; Stasch, A., Inorg. Chem. 2007, 46, 11-13; (b) Jones, C.; Stasch, A.; Moxey, G. J.; Junk, P. C.; Deacon, G. B., Eur. J. Inorg. Chem. 2009, 3593-3599. [76] (a) Kempter, A.; Gemel, C.; Cadenbach, T.; Fischer, R. A., Organometallics 2007, 26, 4257-4264; (b) Kempter, A.; Gemel, C.; Fischer, R. A., Chem. Eur. J. 2007, 13, 2990-3000.

179 Chapter Four: Low Oxidation State Group 13 Complexes by Kinetic Control

[77] (a) Uhl, W.; Hann, I.; Wartchow, R., Chem. Ber. 1997, 130, 417-420; (b) Uhl, W.; Spies, T.; Koch, R., J. Chem. Soc., Dalton Trans. 1999, 2385-2392; (c) Uhl, W.; El-Hamdan, A.; Lawerenz, A., Eur. J. Inorg. Chem. 2005, 1056-1062; (d) Alexander, S. G.; Cole, M. L.; Forsyth, C. M.; Furfari, S. K.; Konstas, K., Dalton Trans. 2009, 2326-2336. [78] (a) Hardman, N. J.; Power, P. P., Inorg. Chem. 2001, 40, 2474-2475; (b) Jancik, V.; Moya Cabrera, M. M.; Roesky, H. W.; Herbst-Irmer, R.; Neculai, D.; Neculai, A. M.; Noltemeyer, M.; Schmidt, H.-G., Eur. J. Inorg. Chem. 2004, 3508-3512; (c) Zhu, H.; Chai, J.; Jancik, V.; Roesky, H. W.; Merrill, W. A.; Power, P. P., J. Am. Chem. Soc. 2005, 127, 10170-10171. [79] Kuchta, M. C.; Parkin, G., J. Chem. Soc., Dalton Trans. 1998, 2279-2280. [80] Kuchta, M. C.; Parkin, G., Inorg. Chem. 1997, 36, 2492-2493. [81] Kuchta, M. C.; Parkin, G., J. Am. Chem. Soc. 1995, 117, 12651-12652. [82] Beachley, O. T.; Pazik, J. C.; Glassman, T. E.; Churchill, M. R.; Fettinger, J. C.; Blom, R., Organometallics 1988, 7, 1051-1059. [83] Nimitsiriwat, N.; Gibson, V. C.; Marshall, E. L.; Takolpuckdee, P.; Tomov, A. K.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.; Dale, S. H., Inorg. Chem. 2007, 46, 9988-9997. [84] Krause, J.; Cestaric, G.; Haack, K.-J.; Seevogel, K.; Storm, W.; Pörschke, K.-R., J. Am. Chem. Soc. 1999, 121, 9807-9823. [85] Bogdanović, B.; Kröner, M.; Wilke, G., Liebigs Ann. Chem. 1966, 699, 1-23.

180

Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.1 Introduction

Group 13 compounds incorporating monoanionic chelating N,N'-ligands have been studied intensively in recent years.[1] These complexes are of potential interest as single source precursors to III/V semiconductor materials and as Lewis acids in selective syntheses and catalysis.[2] Anionic N,N'-ligands are also useful ligands for the fundamental study of the relationship between ligand structure and metal coordination geometry, simply because their steric and electronic properties can be readily modified, viz. Chapter Two.

5.1.1 β-Diketiminate Complexes

Dihalo aluminium, gallium and indium β-diketiminate complexes have been prepared through the salt metathesis of group 13 trihalides with many alkali metal β-diketiminates (e.g. Scheme 5.1).[3] Difluoro species have been prepared by treatment of dihydrido, dichloro or diiodo complexes with fluorinating agents such as boron trifluoride diethyl etherate and fluorotrimethylstannane (Scheme 5.1).[3b]

Scheme 5.1 - Preparation of methyl and halo Dippnacnac complexes of +3 oxidation state group 13 metals

180 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Dimethyl complexes have been prepared through the treatment of the β-diketimine with

MMe3 or through the treatment of suitable dihalo complexes with a methylating agent such as methyllithium and methylmagnesium iodide (Scheme 5.1).[3a,4] Monoalkyl halo complexes have been prepared through the insertion of low oxidation state group 13 metal β-diketiminates into C-X bonds.[5] Cationic aluminium variants of composition [AlMe(L)]+ have been prepared through methyl abstraction using trityl tetrakis(pentafluorophenyl)borate (Scheme 5.1).[6] These β-diketiminate complexes are monomeric in the solid state, wherein the significant steric bulk of the β-diketiminate ligand prevents the formation of bis(β-diketiminate) complexes viz. Chapter Two. Of note, it has been demonstrated that treatment of monoalkyl halide β-diketiminate complexes that incorporate methyl groups as the 1- and 5-positions of the β-diketiminate, for example [AlCl(Me)(Dippnacnac)], with a strong base leads to deprotonation at the methyl and the formation of a dianionic chelating N,N'-ligand (Scheme 5.2).[5c,7]

Scheme 5.2 - Further reactivity of [AlCl(Me)(Dippnacnac)] with a base

5.1.2 Amidinate Complexes

Alkyl and halo amidinate complexes of the group 13 metals may be synthesised in the same manner to β-diketiminate complexes.[8] Dialkyl acetamidinate complexes may additionally be prepared by the reaction of a group 13 metal trialkyl with a carbodiimide Me [8-9] (Scheme 5.3, pg. 182, cf. [AlMe2( Aiso)] (10), Chapter Two). The use of non- sterically demanding amidinates permits the formation of bis- or even tris(amidinate) complexes,[10] and ligand redistribution reactions have been observed when bis- or tris(amidinate)aluminium complexes are treated with stoichiometric quantities of trialkylaluminium (Scheme 5.4, pg. 182).[10c,11]

181 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Scheme 5.3 - Preparation of dialkylaluminium and gallium amidinates

Scheme 5.4 - Ligand redistribution reactions

Amidinates with small substituents at the NCN carbon have been shown to bind the metal centre via either a κ2-chelating or a μ-κ1-bridging motif (Chapter Three). The transition from a chelating to a bridging motif depends on a fine balance in the ligand steric profile and the availability of a suitably large NCN angle for bridging (Figure [12] tBu 5.1). Herein we have observed the changed metal binding from [Rh( Aiso)(CO)2] Cy and [Rh( Giso)(CO)2] versus [Rh(Fiso)(CO)2] and [Rh(N3Dipp2)(CO)2] which can be rationalised on steric character and the availability of a larger NCN/N3 angle (Chapter Two).

Figure 5.1 - Steric frustration of the bridging motif

182 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.1.3 1,3-Triazenide Complexes

Only a small number of group 13 metal(III) triazenide complexes have been reported.[13] Overall, the coordination chemistry mirrors that of amidinate complexes with very little bulk bonded at the NCN carbon, although only the κ2-chelating motif has been observed to date.[13] It should be noted that attempts to prepare monoalkyl and dialkylaluminium complexes of small N-aryl triazenides led to the formation of the tris(triazenide) complexes as the sole triazenide products (Scheme 5.5).[13a] This may be interpreted as an outcome of aluminium’s preference to have coordination numbers greater than four. Indeed, Barron has shown that the addition of 3,5-dimethylpyridine stymies [13b] tris(triazenide) formation to afford [AlMe(N3Ph2)2(3,5-Me2py)] (Scheme 5.5). Employing more sterically demanding triazenes or bulkier trialkyls can result in four-coordinate aluminium triazenide complexes being isolated (viz. Chapter Two).[13d,h] A small number of +3 oxidation state gallium and indium triazenide complexes have been reported.[13c] The metal centres in these complexes generally exhibit a coordination number of six. Like aluminium, sub- tris(triazenide) complexes may be obtained through the addition of a donor or through employing bulky alkyl groups at the metal.[13e-g] A number of thallium tris(triazenide) complexes have also been reported.[14]

Scheme 5.5 - Preparation of aluminium 1,3-triazenide complexes

Attempts to prepare low oxidation state aluminium triazenide complexes through the reduction of the tris(triazenide) complex [Al(N3Ph2)3] with sodium afforded the paramagnetic ionic complex [Na(thf)4][Al(N3Ph2)3], which features a reduced dianionic [15] triazenyl ligand. Electrochemical studies of [Al(N3Ph2)3] show three successive reduction waves (-1.50, -1.84 and -2.16 V), which Barron and co-workers proposed to be successive reductions of each triazenide to yield three triazenyl radical ligands (Scheme 5.6, pg. 184).[15] A subsequent electrochemical study has confirmed the formation of triazenyl radicals.[16]

183 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Scheme 5.6 - The Reduction of triazenide ligands to afford triazenyl radicals[15]

5.1.4 Reactivity

Group 13 metal(III) amidinate complexes have been observed to act as precursors to MIL “ligands” in transition metal chemistry (see Chapter Four, Section 4.1.6). These complexes were prepared through a two-step protocol involving salt metathesis between

[MX2(L)] and Na[FeCp(CO)2] followed by halide abstraction using the salt of a weakly coordinating anion (Scheme 5.7).[17]

Scheme 5.7 - Preparation of group 13 iron complexes

184 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.2 Project Outline

In recent years a number of main group metal complexes containing monoanionic bidentate N,Nʹ-ligands have been reported. Those containing triazenides and group 13 metals are predominately 3:1 complexes (ligand:metal), with a sparing number of aluminium, gallium and indium complexes that display a 1:1 metal to ligand ratio. There are no analogous thallium(III) complexes (i.e. all thallium(II) triazenides are homoleptic and of the form TlL3).

The aim of this chapter is to address the scarcity of group 13 trivalent metal mono(triazenide) complexes by employing the sterically demanding N-Dmp triazenide derived from 1 (viz. Chapter Two), and to build on the low oxidation state studies conducted in Chapter Four. Principally this will comprise a systematic study of both dihalo- and dimethyl- complexes of the group 13 metals, concentrating on their preparation, reactivity and solid-state structure.

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5.3 Results and Discussion

5.3.1 Triazenide Complexes of the Dihalo Group 13 Metals

The dichloroaluminium triazenide complex [AlCl2(N3Dmp2)] (46) was prepared by treatment of 1 with an equimolar quantity of methylaluminium dichloride at ambient temperature (Scheme 5.8).

Scheme 5.8 - Preparation of a dichloroaluminium triazenide complex by protolysis

Triazenide complexes of the heavier group 13 metal dihalides, [GaCl2(N3Dmp2)] (47) and [InBr2(N3Dmp2)] (48), were prepared by salt metathesis reactions of in situ prepared 27 and the respective metal trihalide (Scheme 5.9).

Scheme 5.9 - Preparation of dihalogallium and -indium triazenide complexes

-1 The IR spectra of 46-48 display strong N3 absorptions in the range 1228-1279 cm that are indicative of each triazenide acting as a κ2-chelating ligand (viz. Chapter Three, 1 13 Section 3.3.2). The H and C spectra of 46-48 (C6D6) display single sets of triazenide Dmp resonances, which is similarly indicative of a high degree of symmetry in solution and consistent with κ2-chelation.

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The synthesis of the thallium analogue [TlX2(N3Dmp2)] through the salt metathesis reactions of [Li(N3Dmp2)(thf)2] (25) with TlCl3 or TlBr3 proved unsuccessful (Scheme 5.10), with near quantitative recovery of triazene 1. Dehnicke has reported the Ph [18] successful preparation of the dichlorothallium amidinate complex [TlCl2( ASiMe3)], however, the complex was characterised by solely IR spectroscopy and elemental analysis and not NMR spectroscopy or diffraction based structure determination [18] Ph techniques. As [TlCl2( ASiMe3)] was prepared by a chlorosilane metathesis reaction using an N-trimethylsilyl amidinate rather than a lithium amidinate, the use of

[SiMe3(N3Dmp2)] (49) as a triazenide transfer reagent was investigated. Complex 49 was isolated as a pale yellow powder from the reaction of 25 with a slight excess of chlorotrimethylsilane and has been characterised by 1H NMR spectroscopy.

Unfortunately, the reaction of TlCl3 with an equimolar quantity of 49 did not afford the desired dichlorothallium triazenide complex, instead yielding triazene 1 (Scheme 5.10).

Scheme 5.10 - Attempted preparation of [TlX2(N3Dmp2)] via salt metathesis reactions

As an alternative approach to the synthesis of [TlX2(N3Dmp2)], attempts were made to oxidatively add halogens and halogen sources to the thallium(I) analogue [Tl(N3Dmp2)]

(45) (Chapter Four). This synthetic approach is successful for the preparations of TlCl3 [19] and TlBr3 from their respective monohalides and, perhaps more significantly [20] [TlCl2(Dmp)] from in situ prepared “Tl(Dmp)”.

Treatment of 45 with sulfuryl chloride in C6D6 at ambient temperature results in the immediate loss of the orange colour of 45 (Scheme 5.11, pg. 188). Contrary to expectation, a 1H NMR spectrum of a reaction aliquot collected five minutes after addition displays multiple sets of triazenide Dmp resonances, cf. single sharp resonances for 46-48. Attempts to isolate one or more products from the crude reaction

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mixture lead to brown intractable mixtures. The same outcome is encountered when 45 is treated with Br2.

β-Diketiminate complexes of the lighter group 13 metal dihalides have been prepared through the reaction of elemental halogens with the respective dimethyl β-diketiminate complex.[21] Unfortunately, the addition of boron trifluoride diethyl etherate, sulfuryl chloride, Br2 or I2 to [TlMe2(N3Dmp2)] (vide infra) afforded intractable mixtures of decomposition products (Scheme 5.11).

Scheme 5.11 - Attempted preparation of [TlX2(N3Dmp2)]

Single crystals of 46-48 were grown from saturated hexane (46), pentane (47) or diethyl ether (48) solutions at -25 °C. Complexes 46-48 crystallise in the space group P1̅ with molecules of solvent in the asymmetric unit (46, 0.5 C6H14; 47; 1.5 C5H12; 48, 0.5

Et2O). The molecular structure of 48 is depicted in Figure 5.2. The molecular structures of 46 and 47 can be found in the appendix. Salient metrical parameters are listed in Table 5.1 (pg. 190).

188 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Figure 5.2 - Molecular structure of 48 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Salient bond parameters are listed in Table 5.1.

189 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Bond Parameter 46 47 43 (GaI) 48 44 (InI)

M-X(1) 2.043(2) 2.132(3) - 2.4473(4) -

M-X(2) 2.0993(16) 2.137(3) - 2.4540(4) -

M-N(1) 1.945(3) 1.987(6) 2.113(6) 2.210(2) 2.372(5)

M-N(3) 1.936(3) 1.993(6) 2.172(5) 2.200(2) 2.403(5)

N(1)-N(2) 1.319(4) 1.328(8) 1.321(6) 1.303(3) 1.301(6)

N(2)-N(3) 1.321(4) 1.327(8) 1.337(7) 1.305(3) 1.307(6)

X(1)-M-X(2) 116.53(8) 113.93(11) - 115.340(15) -

N(1)-M-N(3) 64.98(12) 63.6(2) 60.19(19) 56.94(8) 52.40(15)

N(1)-N(2)-N(3) 104.3(3) 104.3(6) 107.9(5) 107.4(2) 107.9(4)

[22] τ4 0.80 0.78 - 0.74 -

M out of N3 plane 0.06 0.02 0.03 0.00 0.16

MX2:N3 75.7 75.7 - 68.4 -

N3:ArC(1) 40.9 44.4 40.5 43.4 41.1

N3:ArC(25) 37.6 43.7 33.3 37.8 30.6

ArC(1):ArC(25) 77.9 87.7 72.9 78.9 71.0

N2C(1):N2C(25) 15.2 16.1 10.5 10.5 10.6

Table 5.1 - Selected bond distances (Å), angles (°) and torsion angles (°) for triazenide complexes 43, 44 and 46-48

The mean Al-N bond distance in 46 is 1.941 Å and the βn angle is 64.98(12)°. As per the trend observed in Chapter Two, the Al-N bond lengths in the N3Dmp2 complex are considerably longer than those observed for analogous four coordinate dichloroaluminium N-alkyl amidinate,[8,23] guanidinate,[23b,24] bis(imino)phosphinide[25] and bis(imino)phosphonamide complexes.[26] This may reflect the increased steric bulk of the ligand herein, however, the Al-N bond lengths in 46 are also considerably longer than those observed for four coordinate aluminium complexes that employ highly sterically demanding N-aryl ligands such as DippBIAN,[27] bis(phosphinimino)methanides[28] and β-diketiminates (see Chapter Two for discussion

190 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

of steric bulk of these ligand classes).[3a,4,29] It is therefore reasonable to conclude that the extended Al-N bonds of 46 demonstrates the poorer donor properties of triazenides relative to most other monoanionic bidentate N,Nʹ-ligands (Chapters Two through

Four). The aluminium of 46 lies in the plane of the N3 unit unlike the analogous Dippnacnac complex.[3a] Beyond the metallacyclic framework, the aluminium chlorine bond lengths in 46 (mean 2.071 Å) are considerably shorter than those observed for the aforementioned complexes (2.103-2.150 Å). Presumably, this emanates from the increased positive charge on the aluminium that arises from the relatively poorly donating triazenide. As described in Table 5.1, delocalised bonding is observed across the triazenide N3 donor set. The Cl(1)-Al-Cl(2) and N(1)-Al-N(2) angles (116.53(8)° and 64.98(12)° respectively) highlight the distortion of the underlying aluminium [22] tetrahedral geometry (τ4 = 0.80, cf. Chapter Two). The steric congestion about the metal centre prevents the orthogonal placement of the AlCl2 plane to the metallacyclic

AlN3 plane (Table 5.1) and also leads to some unconventional distortion in the ipso-N-Dmp carbons, which sit out of the N3 plane. This leads to non-zero

C(1)N2:N2C(25) torsion angles of 10.5-16.1°.

Like 46, the mean M-N bond lengths in 47 (1.990 Å) and 48 (2.005 Å) are also considerably longer than those of other popular monoanionic bidentate N,Nʹ-ligands [3a,d,30] coordinated to the same MX2 unit. They are, however, considerably shorter than those of the group 13 metal(I) N-Dmp triazenide complexes 43 and 44 (2.143 Å and 2.388 Å respectively, Table 5.1, MI versus MIII radius). The mean In-N bond length in 48 is also shorter than those of more sterically congested six coordinate indium monotriazenides which range from 2.267-2.328 Å.[13c] The increased steric congestion in 47 relative to 43, manifests in a near orthogonal arrangement of the principal N-aryl planes of the triazenide to one another (47, 87.7°; 43, 72.9°) and the greater loss of planarity across the C-N3-C unit of the triazenide (47, 15.2°; 43, 10.5°). Delocalised bonding is also observed over the triazenide donor sets in 47 and 48 (Table 5.1). The M-X bond lengths in 47 (mean 2.135 Å) and 48 (mean 2.451 Å) are short relative to related [MX2(L)] complexes, L = monoanionic bidentate N,Nʹ-ligand, due to the aforementioned increased positive charge at the metal cf. 46 and poor triazenide donicity (Chapter Two).[3a,d,30]

191 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.3.2 Triazenide Complexes of the Dimethyl Group 13 Metals

As detailed in Chapter Two, dimethylaluminium triazenide 4 was prepared by treating 1 with AlMe3 in hexane. Analogous complexes of the heavier group 13 metals;

[GaMe2(N3Dmp2)] (50) and [InMe2(N3Dmp2)] (51), were prepared through the addition of two equivalents of methyllithium to 47 and 48 respectively (Scheme 5.12). This route was favoured over that used to prepare 4 due to the relative expense of GaMe3 and

InMe3.

Scheme 5.12 - Preparation of dimethylgallium and -indium triazenide complexes

Due to the lack of a [TlX2(N3Dmp2)] precursor, [TlMe2(N3Dmp2)] (52) was prepared by the reaction of a slight excess of Me2TlCl with 25 (Scheme 5.13). The synthesis of 52 is noteworthy as it is the first neutral heteroleptic trivalent thallium complex that features a monoanionic bidentate N,N'-ligand. As discussed earlier in this thesis, thallium has a well-known preference for the +1 oxidation state (viz. Chapters One and Four).

Scheme 5.13 - Preparation of dimethylthallium triazenide complex 52

The 1H and 13C NMR spectra of 50-52 display single sharp sets of triazenide Dmp resonances that are similar to those observed for their aluminium counterpart 4. Sharp methyl ligand singlet resonances are also observed in the 1H and 13C NMR spectra of 4, 1 2 50 and 51 (Table 5.2, pg. 193). Broad doublets are observed in the H ( JTlH = 364 Hz) 13 1 and C ( JTlC = 1771 Hz) NMR spectra of 52, wherein the resonance multiplicities arise

192 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

from coupling of the methyls to the spin active thallium centres (203Tl, 29.5%, I = ½; 205Tl, 70.5%, I = ½).3 The aforementioned coupling constants are consistent with Tl-Me moieties previously reported.[32]

Interestingly, there appears to be a correlation between the period of the metals in 4 and 50-52 and the degree of shielding experienced at the methyl ligands (1H and 13C NMR spectroscopy, Table 5.2). It should be noted that this trend does not extend to the related

Lewis adduct series [MMe3(dmap)] (M = Al, Ga, In and Tl, dmap = 4-dimethylaminopyridine).[32a]

Complex δ (1H) ppm δ (13C) ppm

[AlMe2(N3Dmp2)] 4 -1.27 -10.1

[GaMe2(N3Dmp2)] 50 -0.82 -4.5

[InMe2(N3Dmp2)] 51 -0.62 -3.1

[TlMe2(N3Dmp2)] 52 0.13 23.2

Table 5.2 - Chemical shifts (ppm) of the methyl resonances in [MMe2(N3Dmp2)] complexes 4 and 50-52

Single crystals of 4 and 50-52 were grown by cooling room temperature saturated hexane solutions to -25 °C. A second morphology of 52 was grown from toluene at -25 °C (52b). Complexes 4 and 50 are isomorphous and crystallise in the space group P1̅ with a half molecule of hexane in the asymmetric unit. Complexes 51 and 52a are isomorphous and crystallise in the space group P21/n, with two unique molecules in the asymmetric unit. The second morphology of 52 (52b) crystallises in the orthorhombic space group Pbna with half a molecule and half a molecule of toluene in the asymmetric unit. The molecular structure of 51 is depicted in Figure 5.3 (pg. 194). The molecular structures of 4, 50, 52a and 52b can be found in the appendix. Relevant metrical parameters are listed in Table 5.3 (pg. 195).

3 Due to their similar magnetogyric ratios (203Tl = 1.5436×108 rad s-1 T-1, 205Tl = 1.5589×108 rad s-1 T-1) resonances which arise due to 203Tl and 205Tl coupling are rarely resolvable.[31] 193 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Figure 5.3 - Molecular structure of 51 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Salient bond parameters are listed in Table 5.3.

The mean M-N bond distances in 4, 50 and 51 (1.969 Å, 2.053 Å and 2.284 Å respectively) are longer than those in their respective dihalo analogues (46, 1.941 Å; 47, 1.990 Å; 48, 2.205 Å). These variations may be due to the increased steric congestion that results from substituting a chloride or bromide with a methyl group and its shorter contact distance to the metal. The increased steric congestion does not lead to a loss of Dipp planarity of the MN3 unit, which was observed in the analogous nacnac complexes, Dipp e.g. the aluminium sits 0.72 Å out of the nacnac plane in [AlMe2( nacnac)] versus [4] 0.12 Å out of the N3 plane in 4. The mean M-C bond lengths in 4, 50 and 51 (1.951 Å, 1.951 Å and 2.143 Å respectively) lie at the low end of the range observed for N-aryl amidinate, guanidinate and β-diketiminate complexes (Al, 1.935-1.985 Å; Ga, 1.950- 2.010 Å; In, 2.157-2.168 Å).[33] This is analogous to the shorter M-X contacts observed for 46-48 vis-à-vis those for amidinate, guanidinate and β-diketiminate complexes. This trend almost certainly arises due to the poorer donicity of triazenides relative to these “other” ligand architectures and the greater ML electropositivity that ensues (viz. Chapter Two).

194 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

Bond Parameter 4 50 51 52a 52b

2.133(4) 2.160(8) M-C(1) 1.952(8) 1.947(3) 2.159(7) {2.147(5)} {2.160(9)}

2.146(4) 2.172(8) M-C(2) 1.949(7) 1.954(3) - {2.146(4)} {2.160(9)}

2.297(3) 2.457(5) M-N(1) 1.965(6) 2.0633(19) 2.445(5) {2.271(3)} {2.432(5)}

2.265(3) 2.412(5) M-N(3) 1.973(7) 2.0428(19) - {2.303(3)} {2.451(5)}

1.303(4) 1.314(7) N(1)-N(2) 1.321(8) 1.309(3) 1.305(6) {1.320(4)} {1.306(7)}

1.302(4) 1.290(7) N(2)-N(3) 1.339(7) 1.311(3) - {1.309(4)} {1.304(7)}

126.00(17) 143.8(3) C(1)-M-C(2) 118.5(4) 123.72(14) 148.2(4) {129.98(18)} {150.9(4)}

54.90(9) 51.59(17) N(1)-M-N(3) 64.6(3) 61.10(7) 51.1(2) {55.03(10)} {51.12(18)}

107.7(3) 108.9(5) N(1)-N(2)-N(3) 104.6(6) 105.59(18) 107.8(6) {107.0(3)} {107.7(5)}

[22] τ4 0.83 0.83 0.79 {0.78} 0.72 {0.70} 0.71

M out of N3 plane 0.12 0.12 0.05 {0.14} 0.04 {0.21} 0.00

N3:MC2 78.7 80.4 74.1 {75.9} 74.1 {75.4} 74.7

N3:ArC(3) 38.6 44.6 40.3 {31.8} 40.2 {33.7} 34.6

N3:ArC(27) 41.6 35.7 38.6 {37.9} 38.5 {35.4} -

ArC(3):ArC(27) 79.2 79.3 77.1 {68.4} 76.7 {68.9} 69.1

N2C(3):N2C(27) 15.5 16.5 14.2 {16.1} 13.0 {16.9} 18.9

Table 5.3 - Selected bond lengths (Å), angles (°) and torsion angles (°) for complexes 4 and 50-52. Values for the second unique molecule in 51 and 52a are given in braces.

Complex 52 represents the first structurally characterised monoanionic bidentate N,Nʹ-ligand complex of thallium(III).[33] The increased mean M-N bond length in 52 (52a, 2.438 Å; 52b, 2.445 Å) relative to 51 (2.284 Å) is consistent with the increased

195 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

ionic radius of thallium relative to indium (In3+ 0.800 Å, Tl3+ 0.880 Å).[34] The thallium lies in the plane of the N3 units of both 52a and 52b. Symmetrical coordination of to the methyl moieties is observed in both 52a and 52b, with the mean Tl-C bond lengths being 2.163 Å and 2.159 Å respectively. These values are consistent with the mean Tl-C [35] bond length of [TlMe2(acac)] (2.12 Å). The larger metallic radius of thallium means the N(1)-Tl-N(3) and C(1)-Tl-C(2) angles of 52a and 52b describe distortion of the tetrahedral geometry about the metal centre to a greater extent than 4, 50 and 51 (viz. τ4 in the range 0.70-0.72).[22] However, the C(1)-Tl-C(2) angles of 52a and 52b (147.4°4 and 148.4(2)° respectively) are smaller than that observed for [TlMe2(acac)] (170.0(20)°).[35]

4 Mean of the two molecules. 196 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.4 Conclusions

A series of group 13 metal complexes featuring the sterically demanding triazenide ligand N3Dmp2 based on 1, have been prepared and characterised spectroscopically and structurally. The halide derivatives [MX2(N3Dmp2)] (M = Al (46), Ga (47), In (48)) were isolated in good yield through the reaction of 1 with one equivalent of methylaluminium dichloride (46) or one equivalent of in situ prepared 27 and the respective metal trihalides (47 and 48). A number of routes were explored in several attempts to prepare a thallium analogue of 46-48, all of which proved unsuccessful.

The methyl derivatives [MMe2(N3Dmp2)] (M = Al (4), Ga (50), In (51), Tl (52)), were synthesised through the reaction of trimethylaluminium with 1 (4), through the reaction of the halide derivatives 47 and 48 with two equivalents of methyllithium (50 and 51), or through the reaction of the 25 with one equivalent of dimethylthallium chloride (52).

The complexes 4, 46-48, 50-52 exist as bright yellow crystalline solids. The relatively long M-N distances in the aforementioned complexes are consistent with the poorer donor character of triazenides vis-à-vis amidinates, guanidinates and β-diketiminates (Chapter Two). In general, this leads to relatively short M-X or M-C bond versus literature precedent. All complexes were also characterized by IR, 1H and 13C NMR spectroscopies. The chemical shifts of the M-Me resonances in the 1H and 13C NMR spectra of 4 and 50-52 are consistent with an increase in shielding of the M-Me bonds upon descent of the group.

197 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.5 Future Directions

The reaction of halide complexes (46-48) with [K2Fe(CO)4] may afford, via a redox reaction, [(Dmp2N3)M{Fe(CO)4}] complexes (Scheme 5.14). Given our failure to measure the σ-donor strength of the low oxidation state complexes 43-45 using

B(C6F5)3, the frequency of the trans CO IR stretch represents a means of indirectly evaluating the σ-donor strength of these complexes cf. Tolman’s electronic parameter (see Chapter Two, Section 2.3.3). A number of analogous halide,[36] terphenyl,[37] tris(pyrazolyl)borate,[38] cyclopentadienide,[36,39] β-diketiminate[40] and guanidinate[41] complexes have been reported, providing a significant basis upon which to investigate the σ-donor strength of the new MIL species.

Scheme 5.14 - Proposed preparation of group 13 metal(I) iron tetracarbonyl complexes

The dihalide complexes (46-48) could provide facile access to their dihydride counterparts through halo-hydride exchange reactions. This route has literature Dipp Dipp precedence in the synthesis of [GaH2( nacnac)] from [GaX2( nacnac)] (X = Cl, I).[3b,42]

198 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

5.6 Experimental

5.6.1 General Synthetic Procedures

[43] Me2TlCl was synthesised by the literature procedure. SO2Cl2 was distilled from phosphorus pentoxide and stored under argon. MeAlCl2 (1.0 M in hexane) and MeLi (1.0 M in diethyl ether) were purchased from Sigma-Aldrich and decanted into J. Youngs tapped flasks under argon. The preparation of 4 is reported in Chapter Two.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

5.6.2 Synthesis of [AlCl2(N3Dmp2)] (46)

A solution of MeAlCl2 (1.0 M hexane solution, 0.60 mL, 0.60 mmol) was added to a solution of 1 (374 mg, 0.56 mmol) in hexane (50 mL) at ambient temperature. Gas evolution was immediately observed and the colour changed from pale yellow to bright yellow. The resultant solution was stirred for a further 12 h, followed by the removal of volatiles in vacuo. Extraction with hexane (50 mL), concentration (ca. 15 mL) and cooling to -25 °C afforded yellow prisms suitable for X-ray diffraction structure 1 determination (152 mg, 35%); m.p. 184-185 °C (dec.). H NMR (400 MHz, C6D6) δ AAB 1.99 (s, 24H, o-CH3), 2.19 (s, 12H, p-CH3), 6.82 (d, JHH = 7.6 Hz, 4H, m-ArH), 6.89 AAB 13 (s, 8H, m-Ar’H), 6.94 (t, JHH = 7.6 Hz, 2H, p-ArH). C NMR (100 MHz, C6D6) δ

20.6 (p-CH3), 21.1 (o-CH3), 126.3, 130.1, 130.4 (ArCH), 132.5, 133.0, 133.8, 136.1, 138.9 (ArC). IR (Nujol, cm-1) 2731 (m), 1612 (s), 1570 (w), 1285 (m), 1264 (s, N=N), 1191 (m), 1168 (s), 1093 (w), 1031 (m), 1013 (m), 849 (s), 803 (s), 780 (s), 763 (s), 742

(s), 723 (w), 676 (br s), 567 (w), 528 (w). Anal. Calc. for C48H50AlCl2N3·0.5(C6H14): C, 75.63; H, 7.09; N, 5.19. Found: C, 76.46; H, 7.87; N, 5.91%.

5.6.3 Synthesis of [GaCl2(N3Dmp2)] (47)

An in situ prepared solution of 27 (ca. 1.00 mmol) in diethyl ether (50 mL) was added dropwise to a solution of GaCl3 (180 mg, 1.00 mmol) in diethyl ether (30 mL) at ambient temperature. The resultant bright yellow solution was stirred for a further 12 h, followed by the removal of volatiles in vacuo. Extraction with pentane (60 mL), concentration (ca. 25 mL) and cooling to -25 °C afforded yellow prisms suitable for X-ray diffraction structure determination (615 mg, 72%), m.p. 162-164 °C (dec.). 1H

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AAB NMR (400 MHz, C6D6) δ 1.96 (s, 24H, o-CH3), 2.20 (s, 12H, p-CH3), 6.69 (d, JHH = AAB 13 7.6 Hz, 4H, m-ArH), 6.83 (t, JHH = 7.6 Hz, 2H, p-ArH), 6.87 (s, 8H, m-Ar’H). C

NMR (100 MHz, C6D6) δ 21.2 (p-CH3), 21.6 (o-CH3), 127.2, 129.5, 130.9 (ArCH), 135.1, 135.6, 136.1, 137.6 (ArC). IR (Nujol, cm-1) 2732 (w), 1941 (w), 1727 (w), 1613 (s), 1573 (w), 1485 (w), 1414 (m), 1290 (s), 1270 (s, N=N), 1246 (w), 1236 (w), 1192 (w), 1171 (s), 1104 (w), 1032 (m), 882 (w), 848 (s), 803 (s), 782 (s), 763 (s), 744 (w),

685 (m), 665 (w), 607 (w), 587 (w). Anal. Cal. for C48H50GaCl2N3: C, 71.21; H, 6.23; N, 5.19. Found: C, 70.93; H, 6.60; N, 4.41%.

5.6.4 Synthesis of [InBr2(N3Dmp2)] (48)

An in situ prepared solution of 27 (ca. 0.29 mmol) in diethyl ether (30 mL) was added dropwise to a solution of InBr3 (102 mg, 0.29 mmol) in diethyl ether (30 mL) at ambient temperature. The resultant bright yellow solution was stirred for a further 2 h, followed by the removal of volatiles in vacuo. Extraction with diethyl ether (40 mL), concentration (ca. 20 mL) and cooling to -25 °C afforded yellow prisms suitable for X-ray diffraction structure determination (190 mg, 69%); m.p. 145-146 °C (dec.). 1H AAB NMR (500 MHz, C6D6) δ 1.97 (s, 24H, o-CH3), 2.20 (s, 12H, p-CH3), 6.69 (d, JHH = AAB 13 7.6 Hz, 4H, m-ArH), 6.82 (t, JHH = 7.6 Hz, 2H, p-ArH), 6.87 (s, 8H, m-Ar’H). C

NMR (100 MHz, C6D6) δ 21.3 (o-CH3), 22.1 (o-CH3), 126.6, 129.9, 130.8 (ArCH), 134.7, 135.6, 136.0, 138.0, 138.2 (ArC). IR (Nujol, cm-1) 2732 (w), 1941 (w), 1728 (w), 1612 (s), 1572 (w), 1486 (w), 1411 (m), 1294 (s), 1271 (s, N=N), 1248 (w), 1236 (w), 1192 (m), 1177 (m), 1104 (w), 1032 (m), 852 (s), 804 (s), 782 (s), 764 (s), 742 (w), 677

(m), 608 (w), 585 (w). Anal. Calc. for C48H50InBr2N3·0.5(OC4H14): C, 61.11; H, 5.84; N, 4.27. Found: C, 60.49; H, 5.72; N, 3.84%.

5.6.5 Synthesis of [SiMe3(N3Dmp2)] (49)

Me3SiCl (0.20 mL, 1.6 mmol) was added to a solution of 25 (210 mg, 0.25 mmol) in THF (20 mL) at ambient temperature. A colourless precipitate formed immediately. The resultant slurry was stirred for a further 12 h, followed by removal of volatiles in vacuo to afford 49 as bright yellow powder. Extraction with hexane (20 mL), concentration to 10 mL and gradual cooling to -25 °C afforded a yellow microcrytstalline powder (151 1 mg, 81%). H NMR (400 MHz, C6D6) δ -0.02 (br s, 9H, Si-CH3), 1.94 (s, 24H, o-CH3),

200 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Trivalent Group 13 Metal Halides and Alkyls

AAB 2.20 (s, 12H, p-CH3), 6.72 (d, JHH = 7.4 Hz, 4H, m-ArH), 6.80-6.84 (m, 10H, p-ArH and m-Ar’H).

5.6.6 Attempted Synthesis of [TlX2(N3Dmp2)] (X = halide)

Method A: A solution of 25 (200 mg, 0.25 mmol) in THF (20 mL) was added dropwise to a solution of TlCl3 (90 mg 0.29 mmol) in THF (40 mL) at ambient temperature. The resultant orange solution was stirred for a further 8 h, during which time a colourless precipitate formed. Filtration followed by solvent removal in vacuo afforded a yellow residue. Extraction into hexane (60 mL) followed by solvent removal in vacuo afforded 1 a pale yellow powder that characterises as per 1 by H NMR spectroscopy (C6D6).

Method B: A solution of 49 (200 mg, 0.25 mmol) in THF (20 mL) was added dropwise to a solution of TlCl3 (80 mg 0.26 mmol) in THF (20 mL) at ambient temperature. The resultant orange solution was stirred for a further 12 h, during which time a colourless precipitate formed. Filtration followed by solvent removal in vacuo afforded a yellow residue. Extraction into hexane (60 mL) followed by solvent removal in vacuo afforded 1 a pale yellow powder that characterises as per 1 by H NMR spectroscopy (C6D6).

Method C: A solution of SO2Cl2 (0.03 mL, 0.37 mmol) in toluene (10 mL) was added to a solution of 45 (220 mg, 0.25 mmol) in toluene (5 mL) at ambient temperature. The reaction mixture immediately darkened and was stirred for a further 12 h at ambient temperature during which time a colourless precipitate formed. Filtration followed by 1 the removal of volatiles in vacuo afforded a yellow solid. The H NMR spectrum (C6D6) of this solid exhibits o- and p-CH3 resonances at a number of chemical shifts: 1.73, 1.78, 1.84, 1.91, 1.95, 1.98, 2.02, 2.04, 2.12, 2.13, 2.29, 2.32 ppm.

Method D: A solution of 52 (70 mg, 0.077 mmol) in C6D6 (2.0 mL) was added to a solution of I2 (39 mg, 0.153 mmol) in C6D6 (1.0 mL) at ambient temperature. The resultant orange solution was stirred for a further 12 h, during which time a colourless precipitate formed. A yellow solution was isolated by filtration which characterises as 1 per 1 by H NMR spectroscopy (C6D6).

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5.6.7 Synthesis of [GaMe2(N3Dmp2)] (50)

A solution of MeLi (1.0 M in diethyl ether, 0.45 mL, 0.45 mmol) was added dropwise to a pale yellow solution of 47 (170 mg, 0.21 mmol) in diethyl ether (20 mL) at ambient temperature. Gas evolution was immediately observed and the colour changed from pale yellow to bright yellow. The resultant solution was stirred for a further 12 h followed by removal of volatiles in vacuo to yield 50 as a bright yellow powder. Extraction with hexane (40 mL), concentration (ca. 10 mL) and cooling to -25 °C afforded yellow plates suitable for X-ray diffraction structure determination (138 mg, 85%); m.p. 172-174 °C 1 (dec.). H NMR (400 MHz, C6D6) δ -0.82 (s, 6H, Ga-CH3), 1.94 (s, 24H, o-CH3), 2.20 AAB (s, 12H, p-CH3), 6.72 (d, JHH = 7.4 Hz, 4H, m-ArH), 6.80-6.84 (m, 10H, p-ArH and 13 m-Ar’H). C NMR (100 MHz, C6D6) δ -4.5 (Ga-C), 21.2 (p-CH3), 21.7 (o-CH3), 125.2, 128.9, 130.9 (ArCH), 134.1, 136.1, 136.4, 137.7, 141.1 (ArC). IR (Nujol, cm-1) 1262 (s, N=N), 1231 (m), 1194 (m), 1154 (w), 1093 (w), 1030 (m), 965 (w), 849 (s), 802 (s),

765 (m), 754 (w), 741 (w), 723 (w), 666 (s). Anal. Calc. for C50H56GaN3: C, 78.12; H, 7.34; N, 5.46. Found: C, 78.22; H, 7.57; N, 5.50%.

5.6.8 Synthesis of [InMe2(N3Dmp2)] (51)

A solution of MeLi (1.0 M in diethyl ether, 0.38 mL, 0.38 mmol) was added dropwise to a pale yellow solution of 48 (170 mg, 0.18 mmol) in diethyl ether (10 mL) at ambient temperature. Gas evolution was immediately observed and the colour changed from pale yellow to bright yellow. The resultant solution was stirred for a further 12 h followed by removal of volatiles in vacuo to yield 51 as a bright yellow powder. Extraction with hexane (40 mL), concentration (ca. 10 mL) and cooling to -25 °C afforded yellow prisms suitable for X-ray diffraction structure determination (95 mg, 65%); m.p. 1 172-174 °C (dec.). H NMR (400 MHz, C6D6) δ -0.63 (s, 6H, In-CH3), 1.95 (s, 24H, AAB o-CH3), 2.19 (s, 12H, p-CH3), 6.73 (d, JHH = 7.6 Hz, 4H, m-ArH), 6.80-6.84 (m, 13 10H, p-ArH and m-Ar’H). C NMR (100 MHz, C6D6) δ -3.1 (In-C), 21.2 (p-CH3), 21.7

(o-CH3), 124.5, 129.0, 130.7 (ArCH), 133.5, 135.8, 136.4, 137.8, 138.2 (ArC). IR (Nujol, cm-1) 2730 (w), 1610 (m), 1410 (m), 1280 (m), 1265 (s, N=N), 1246 (w), 1231 (m, N=N), 1195 (w), 1181 (w), 1092 (w), 1029 (m), 849 (s), 803 (m), 782 (w), 763 (m),

742 (w), 722 (w), 675 (w). Anal. Calc. for C50H56InN3: C, 73.79; H, 6.94; N, 5.16. Found: C, 73.13; H, 6.98; N, 5.15%.

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5.6.9 Synthesis of [TlMe2(N3Dmp2)] (52)

A solution of 25 (200 mg, 0.24 mmol) in THF (20 mL) was added to a stirred slurry of

Me2TlCl (100 mg, 0.37 mmol) in THF (10 mL) at ambient temperature. A colourless precipitate formed immediately and the slurry was stirred for 1 hour. Volatiles were removed in vacuo to yield a yellow solid. Extraction with hexane (50 mL), concentration (ca. 10 mL) and cooling to -25 °C afforded yellow prisms suitable for X-ray diffraction structure determination (195 mg, 89%); m.p. 192-193 °C (dec.). 1H 2 NMR (400 MHz, C6D6) δ 0.13 (br d, JTlH = 364 Hz, 6H, Tl-CH3), 1.96 (s, 24H, o-CH3), AAB 2.20 (s, 12H, p-CH3), 6.75 (d, JHH = 7.4 Hz, 4H, m-ArH), 6.81 (s, 8H, m-Ar’H), 6.83 AAB 13 (t, JHH = 7.4 Hz, 2H, p-ArH). C NMR (100 MHz, C6D6) δ 21.1 (p-CH3), 21.8 1 (o-CH3), 23.2 (d, JTlC = 1771 Hz, Tl-C), 123.4, 128.8, 130.6 (ArCH), 133.2, 135.8, 139.0 (ArC). IR (ATR, cm-1) 2924 (w), 2891 (w), 2830 (w), 2708 (w), 1597 (m), 1565 (w), 1473 (w), 1428 (m), 1392 (m), 1365 (m), 1269 (w), 1249 (s, N=N), 1234 (w), 1216 (m), 1185 (w), 1073 (w), 1019 (m), 940 (w), 841 (m), 794 (m), 775 (m), 756 (m), 736 (s), 662 (w), 607 (w), 580 (w), 555 (w), 528 (w), 503 (m), 459 (w), 429 (w). Anal. Calc. for C50H56TlN3: C, 66.48; H, 6.25; N, 4.65. Found: C, 66.11; H, 6.25; N, 4.63%.

203 References for this chapter begin on pg. 204. Chapter Five: Triazenide Complexes of Group 13 Metal Halides and Alkyls

5.7 References

[1] Brothers, P. J.; Ruggiero, C. E. In The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, pp. 519-611, 2011, John Wiley & Sons, Ltd: Chichester, UK. [2] (a) Barry, S. T., Coord. Chem. Rev. 2013, 257, 3192-3201; (b) Duchateau, R.; Meetsma, A.; Teuben, J. H., Chem. Commun. 1996, 223-224. [3] (a) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust, J.; Noltemeyer, M.; Roesky, H. W., Inorg. Chem. 2001, 40, 2794-2799; (b) Singh, S.; Ahn, H.-J.; Stasch, A.; Jancik, V.; Roesky, H. W.; Pal, A.; Biadene, M.; Herbst-Irmer, R.; Noltemeyer, M.; Schmidt, H.-G., Inorg. Chem. 2006, 45, 1853-1860; (c) Cheng, Y.; Doyle, D. J.; Hitchcock, P. B.; Lappert, M. F., Dalton Trans. 2006, 4449-4460; (d) Chisholm, M. H.; Navarro-Llobet, D.; Gallucci, J., Inorg. Chem. 2001, 40, 6506-6508. [4] Qian, B.; Ward, D. L.; Smith, M. R., Organometallics 1998, 17, 3070-3076. [5] (a) Kempter, A.; Gemel, C.; Fischer, R. A., Inorg. Chem. 2008, 47, 7279-7285; (b) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R., Inorg. Chem. 2007, 46, 3783-3788; (c) Abdalla, J. A. B.; Riddlestone, I. M.; Tirfoin, R.; Aldridge, S., Angew. Chem. Int. Ed., In press, DOI: 10.1002/anie.201500570. [6] Radzewich, C. E.; Guzei, I. A.; Jordan, R. F., J. Am. Chem. Soc. 1999, 121, 8673-8674. [7] (a) Sarish, S. P.; Roesky, H. W.; John, M.; Ringe, A.; Magull, J., Chem. Commun. 2009, 2390-2392; (b) Sarish, S. P.; Nekoueishahraki, B.; Jana, A.; Roesky, H. W.; Schulz, T.; Stalke, D., Chem. Eur. J. 2011, 17, 890-894. [8] Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Organometallics 1997, 16, 5183-5194. [9] Hausen, H. D.; Gerstner, F.; Schwarz, W., J. Organomet. Chem. 1978, 145, 277- 284. [10] (a) Davies, R. P.; Linton, D. J.; Schooler, P.; Snaith, R.; Wheatley, A. E. H., Eur. J. Inorg. Chem. 2001, 619-622; (b) Barry, S. T.; Gordon, P. G.; Ward, M. J.; Heikkila, M. J.; Monillas, W. H.; Yap, G. P. A.; Ritala, M.; Leskela, M., Dalton Trans. 2011, 40, 9425-9430; (c) Kenney, A. P.; Yap, G. P. A.; Richeson, D. S.; Barry, S. T., Inorg. Chem. 2005, 44, 2926-2933; (d) Pallister, P. J.;

204 Chapter Five: Triazenide Complexes of Group 13 Metal Halides and Alkyls

Buttera, S. C.; Barry, S. T., J. Phys. Chem. C 2014, 118, 1618-1627; (e) Barker, J.; Blacker, N. C.; Phillips, P. R.; Alcock, N. W.; Errington, W.; Wallbridge, M. G. H., J. Chem. Soc., Dalton Trans. 1996, 431-437. [11] Brazeau, A. L.; DiLabio, G. A.; Kreisel, K. A.; Monillas, W.; Yap, G. P. A.; Barry, S. T., Dalton Trans. 2007, 3297-3304. [12] (a) Zhou, Y.; Richeson, D. S., Inorg. Chem. 1996, 35, 1423-1424; (b) Zhou, Y.; Richeson, D. S., Inorg. Chem. 1996, 35, 2448-2451. [13] (a) Leman, J. T.; Barron, A. R.; Ziller, J. W.; Kren, R. M., Polyhedron 1989, 8, 1909-1912; (b) Leman, J. T.; Barron, A. R., Organometallics 1989, 8, 1828- 1829; (c) Leman, J. T.; Roman, H. A.; Barron, A. R., J. Chem. Soc., Dalton Trans. 1992, 2183-2191; (d) Leman, J. T.; Braddock-Wilking, J.; Coolong, A. J.; Barron, A. R., Inorg. Chem. 1993, 32, 4324-4336; (e) Leman, J. T.; Roman, H. A.; Barron, A. R., Organometallics 1993, 12, 2986-2990; (f) Uhl, W.; Hann, I.; Wartchow, R., Chem. Ber. 1997, 130, 417-420; (g) Uhl, W.; El-Hamdan, A.; Lawerenz, A., Eur. J. Inorg. Chem. 2005, 1056-1062; (h) Litlabo, R.; Lee, H. S.; Niemeyer, M.; Toernroos, K. W.; Anwander, R., Dalton Trans. 2010, 39, 6815- 6825. [14] (a) Hörner, M.; Fenner, H.; Beck, J.; Hiller, W., Z. Anorg. Allg. Chem. 1989, 571, 69-74; (b) Hörner, M.; de Oliveira, A. B.; Beck, J., Z. Anorg. Allg. Chem. 1997, 623, 65-68. [15] Braddock-Wilking, J.; Leman, J. T.; Farrar, C. T.; Cosgrove-Larsen, S. A.; Singel, D. J.; Barron, A. R., J. Am. Chem. Soc. 1995, 117, 1736-1745. [16] Ehret, F.; Bubrin, M.; Záliš, S.; Kaim, W., Angew. Chem. Int. Ed. 2013, 52, 4673-4675. [17] Jones, C.; Aldridge, S.; Gans-Eichler, T.; Stasch, A., Dalton Trans. 2006, 5357- 5361. [18] Borgholte, H.; Dehnicke, K.; Goesmann, H.; Fenske, D., Z. Anorg. Allg. Chem. 1991, 600, 7-14. [19] Asadi, H. R.; Maliarik, M.; Ilyukhin, A.; Murashova, E., Inorg. Chim. Acta 2009, 362, 2293-2298. [20] Ahmad, S. U.; Beckmann, J., Organometallics 2009, 28, 6893-6901. [21] Cui, C. M.; Roesky, H. W.; Schmidt, H. G.; Noltemeyer, M.; Hao, H. J.; Cimpoesu, F., Angew. Chem. Int. Ed. 2000, 39, 4274-4276.

205 Chapter Five: Triazenide Complexes of Group 13 Metal Halides and Alkyls

[22] Yang, L.; Powell, D. R.; Houser, R. P., Dalton Trans. 2007, 955-964. [23] (a) Schmidt, J. A. R.; Arnold, J., Organometallics 2002, 21, 2306-2313; (b) Riddlestone, I. M.; Urbano, J.; Phillips, N.; Kelly, M. J.; Vidovic, D.; Bates, J. I.; Taylor, R.; Aldridge, S., Dalton Trans. 2013, 42, 249-258. [24] (a) Aeilts, S. L.; Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Organometallics 1998, 17, 3265-3270; (b) Chang, C.-C.; Hsiung, C.-S.; Su, H.- L.; Srinivas, B.; Chiang, M. Y.; Lee, G.-H.; Wang, Y., Organometallics 1998, 17, 1595-1601. [25] (a) Pohl, S., Chem. Ber. 1979, 112, 3159-3165; (b) Burford, N.; Losier, P.; Bakshi, P. K.; Cameron, T. S., Chem. Commun. 1996, 307-308. [26] Nekoueishahraki, B.; Roesky, H. W.; Schwab, G.; Stern, D.; Stalke, D., Inorg. Chem. 2009, 48, 9174-9179. [27] Lukoyanov, A. N.; Fedushkin, I. L.; Hummert, M.; Schumann, H., Russ. Chem. Bull. 2006, 55, 422-428. [28] Hill, M. S.; Hitchcock, P. B.; Karagouni, S. M. A., J. Organomet. Chem. 2004, 689, 722-730. [29] Vidovic, D.; Moore, J. A.; Jones, J. N.; Cowley, A. H., J. Am. Chem. Soc. 2005, 127, 4566-4567. [30] (a) Delpech, F.; Guzei, I. A.; Jordan, R. F., Organometallics 2002, 21, 1167- 1176; (b) Saur, I.; Garcia Alonso, S.; Gornitzka, H.; Lemierre, V.; Chrostowska, A.; Barrau, J., Organometallics 2005, 24, 2988-2996; (c) Ong, C. M.; McKarns, P.; Stephan, D. W., Organometallics 1999, 18, 4197-4204; (d) Dagorne, S.; Jordan, R. F.; Young, V. G., Organometallics 1999, 18, 4619-4623; (e) Kuhn, N.; Fahl, J.; Fuchs, S.; Steimann, M.; Henkel, G.; Maulitz, A. H., Z. Anorg. Allg. Chem. 1999, 625, 2108-2114; (f) Liu, Y.; Li, S.; Yang, X.-J.; Li, Q.-S.; Xie, Y.; Schaefer, H. F.; Wu, B., J. Organomet. Chem. 2011, 696, 1450-1455. [31] Hinton, J. F. In Encyclopedia of Magnetic Resonance, 2007, John Wiley & Sons, Inc.: New York, USA. [32] (a) Thomas, F.; Bauer, T.; Schulz, S.; Nieger, M., Z. Anorg. Allg. Chem. 2003, 629, 2018-2027; (b) Yurkerwich, K.; Coleman, F.; Parkin, G., Dalton Trans. 2010, 39, 6939-6942. [33] As determined by a survey of the Cambridge Structural Database v. 5.36 with updates for November 2014.

206 Chapter Five: Triazenide Complexes of Group 13 Metal Halides and Alkyls

[34] The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, Eds. Downs, A. J.; Aldridge, S., 2011, John Wiley & Sons, Ltd: Chichester, UK. [35] Chow, Y. M.; Britton, D., Acta Crystallogr., Sect. B 1975, 31, 1929-1934. [36] Weiss, J.; Stetzkamp, D.; Nuber, B.; Fischer, R. A.; Boehme, C.; Frenking, G., Angew. Chem. Int. Ed. 1997, 36, 70-72. [37] Su, J.; Li, X.-W.; Crittendon, R. C.; Campana, C. F.; Robinson, G. H., Organometallics 1997, 16, 4511-4513. [38] (a) Reger, D. L.; Garza, D. G.; Rheingold, A. L.; Yap, G. P. A., Organometallics 1998, 17, 3624-3626; (b) Reger, D. L.; Mason, S. S.; Rheingold, A. L.; Haggerty, B. S.; Arnold, F. P., Organometallics 1994, 13, 5049-5053. [39] (a) Cowley, A. H.; Lomelí, V.; Voigt, A., J. Am. Chem. Soc. 1998, 120, 6401- 6402; (b) Macdonald, C. L. B.; Cowley, A. H., J. Am. Chem. Soc. 1999, 121, 12113-12126; (c) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H. G., Organometallics 1998, 17, 1305-1314. [40] Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P., J. Am. Chem. Soc. 2003, 125, 2667-2679. [41] Jones, C.; Stasch, A.; Moxey, G. J.; Junk, P. C.; Deacon, G. B., Eur. J. Inorg. Chem. 2009, 3593-3599. [42] Turner, J.; Abdalla, J. A. B.; Bates, J. I.; Tirfoin, R.; Kelly, M. J.; Phillips, N.; Aldridge, S., Chem. Sci. 2013, 4, 4245-4250. [43] Marko, I. E.; Southern, J. M., J. Org. Chem. 1990, 55, 3368-3370.

207

Chapter Six: Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.1 Introduction

Aluminium and gallium hydride chemistry is well developed and complexes that incorporate Al-H and Ga-H bonds have found a wide variety of applications in organic transformations, inorganic synthesis, and materials chemistry.[1] Until recently, it was generally accepted that the relative weakness of the In-H bond lead to inherent thermal instability, and that the development of synthetic and materials applications would be extremely unlikely.

In the early 1990s, Downs and co-workers highlighted that the calculated enthalpy of the In-H bond is greater than those of known In-C bonds and, given the well-established thermal stability of trialkylindiums,[2] the instability of indium hydride compounds must be due to a distinct decomposition path that is likely kinetically controlled.[3] To this end, Downs suggested that indium hydride instability is derived from the propensity of group 13 metal hydrides to associate through M-H-M bridges, and that these in effect lower the barrier to homolytic decomposition processes that reductively eliminate dihydrogen.[4] This proposal is consistent with thermal stability studies on indane, which decomposes above -90 °C,[5] whilst the use of sterically bulky ligands that frustrate In-H-In bridges has led to the isolation of a number of indium hydride complexes with thermal stabilities in excess of 100 °C.[6] The following sections provide an overview of the application of monoanionic bidentate N,Nʹ-ligands, principally β-diketiminates, amidinates, bicyclic guanidinates and triazenides, to group 13 metal hydride chemistry.

6.1.1 β-diketiminate Complexes

Several β-diketiminate supported group 13 hydride species have been prepared in recent years. The first, which were reported by Kuhn and co-workers in 2000, were prepared through the treatment of [AlH3(NMe3)] with a number of sterically slight β-diketimines (RnacnacH, R = Me, iPr and Ph). In the specific case of iPrnacnacH, addition of excess hydride reagent results in imine reduction and the isolation of an unusual

208 References for this chapter begin on pg. 247 Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

tetraaluminium compound (Scheme 6.1, pg. 209).[7] In the presence of excess Me Me nacnacH, [AlH2( nacnac)], reacts to afford the tris(β-diketiminate) complex Me [8] [Al( nacnac)3].

Scheme 6.1 - Reduction of β-diketimines with [AlH3(NMe3)]

A number of analogous N-aryl complexes β-diketiminate complexes have been prepared by treatment of the parent β-diketimine with [AlH3(NMe3)] or [LiAlH4] (Scheme 6.2), Xy [9] Mes [10] Dipp [11] e.g. [AlH2( nacnac)], [AlH2( nacnac)] and [AlH2( nacnac)]. Dipp [AlH2( nacnac)] was also prepared by ligand transmetallation from Dipp [12] [BiCl2( nacnac)] to [LiAlH4], and by the oxidative addition of H2 to Dipp [13] Dipp [Al( nacnac)]. Interestingly when equimolar amounts of [AlH2( nacnac)] and Dipp [Al( nacnac)] were dissolved in C6D6, an enthalpic equilibrium between these Dipp complexes and the aluminium(II) hydride [{AlH( nacnac)}2] was formed (Scheme 6.3), whereby formation of the comproportionation species was favoured at low temperatures.[13]

Scheme 6.2 - Preparation of N-aryl β-diketiminate complexes of aluminium dihydride

Scheme 6.3 - Enthalpic comproportionation equilibrium

209 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Two dihydridogallium β-diketiminate complexes have been reported. Mes Mes [GaH2( nacnac)] was prepared by treating the galloxane [{GaCl( nacnac)}2(μ-O)] [14] Dipp with [AlH3(NMe3)]. [GaH2( nacnac)] was prepared by treatment of a [15] Dipp dihalogallium precursor with [LiBEt3H] and by treatment of [Ga( nacnac)] with H2 (Scheme 6.4).[16] There have been no reported attempts to prepare these same complexes by treatment of the β-diketimine with [GaH3(L)] or [LiGaH4], as per the aluminium complexes. The analogous dihydridoindium complexes have not been reported.

Dipp Scheme 6.4 - Synthesis of [GaH2( nacnac)]

According to X-ray diffraction structure determination studies, the aforementioned N-aryl β-diketiminate complexes are monomeric in the solid-state, which suggests excellent potential for the kinetic stabilisation of heavy group 13 hydrides. This can also be seen in the enhanced thermal stability of the β-diketiminate complexes relative to those of the naked metallanes (Figure 6.1).[10,14,17]

Figure 6.1 - Decomposition temperatures of Mesnacnac complexes of group 13 metal dihydrides and group 13 metallanes[10,14,17b,c]

6.1.2 Amidinate and Guanidinate Complexes

Amidinate and guanidinate ligands have also been employed to stabilise group 13 hydrides. Aluminium complexes were prepared by treating [AlH3(NMe3)] with one [18] equivalent of amidine (Scheme 6.5, pg. 211). Repeating the reaction with [LiAlH4] [18a] instead of [AlH3(NMe3)] resulted in retention of LiH in the ensuing metallohydride. As N-aryl amidinate ligands are on the whole less sterically demanding than N-aryl

210 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

β-diketiminates (Chapter Two), the amidinate complexes of dihydridoaluminium and its LiH inclusion complexes tend to be dimeric in the solid-state, wherein the mode of dimerisation dependents on the bite angle ‘βn’ of the amidinate (Scheme 6.5).

Scheme 6.5 - Preparation of mono(amidinate) complexes of aluminium hydrides

Very few mono(amidinate) or mono(guanidinate) complexes of the heavier group 13 metal hydrides have been reported (Scheme 6.6, pg. 212).[18a,19] This is likely due to the failure of the amidinate framework to provide sufficient bulk to prevent bridging hydride moieties, viz. aluminium complexes (Scheme 6.5). As aforementioned, these bridging interactions are believed to be responsible for the poor thermal stabilities of gallium and indium hydride complexes in general (Scheme 6.6).[18a,19] Of the known mono(amidinate) or mono(guanidinate) gallium and indium hydrides, which have been prepared using similar protocols to those used in Scheme 6.5, the greatest stabilities emerge when the dihydridometal function is sterically shielded by the ligand, electronically masked by LiH inclusion, or M-H-M bridging is impeded by the constrained geometry of the stabilising ligand.

211 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Scheme 6.6 - Preparation of mono(amidinate) complexes of gallium and indium hydrides

The decreased steric bulk of amidinates relative to β-diketiminates (Chapter Two) does however permit the preparation of bis(amidinate) complexes. Such complexes can be prepared using two equivalents of amidine (Scheme 6.7, pg. 213).[18a,19a] Alternatively, Ph the bis(amidinate)aluminium hydride complex [AlH( ASiMe3)2] was prepared through Ph [20] treatment of [AlCl( ASiMe3)2] with [KBEt3H] (Scheme 6.7), and a bis(guanidinate)aluminium hydride was prepared by ligand redistribution between alane [21] [(AlH3)∞] and an aluminium tris(guanidinate) (Scheme 6.7). It is important to note that attempts to prepare bis(amidinate) complexes of the sterically larger amidinate tBu Aiso using [LiAlH4] proved unsuccessful, instead yielding a mono(amidinate) complex.[18a] This suggests the steric threshold for the formation of bis(amidinate)aluminium complexes is ca. GAl < 47.5% (viz. Section 2.3.2.4).

212 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Scheme 6.7 - Preparation of bis(amidinate) complexes of group 13 metal hydrides

Bis(amidinate) complexes of the heavier group 13 metal hydrides exhibit considerably enhanced thermal stability relative to their mono(amidinate) cousins. From X-ray crystal structures it is clear that the two amidinates enshroud the metal hydride and thereby sterically frustrate further hydride interactions.[18a,19a] These complexes possess some of the highest thermal stabilities on record for molecular group 13 hydrides (Figure 6.2).[18a,19a]

Figure 6.2 - Thermal stability of bis(formamidinate) complexes of the group 13 metal hydrides

6.1.3 Triazenide Complexes

Due to their similarity to amidinates, triazenides have also been used to stabilise group 13 metal hydrides. Niemeyer’s preparations of sterically demanding 1,3-bis(2,6-terphenyl)triazenes, reported in 2005,[22] made this class of ligand potentially superior to amidinates for the kinetic stabilisation of group 13 metal hydrides. This theme was explored by Cole and co-workers, who employed unsymmetrically substituted N-aryl, Nʹ-2,6-terphenyltriazenides to stabilise aluminium and gallium hydride moieties (Scheme 6.8, pg. 214).[23]

213 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Scheme 6.8 - Preparation of triazenide complexes of group 13 hydrides

The reaction of equimolar quantities of [LiAlH4] with DitopN3(H)p-tol afforded a LiH inclusion dimer analogous to the aforementioned amidinate complexes.[23] Whilst the reaction of equimolar quantities of [LiAlH4] and the larger triazenes DitopN3(H)Mes and DmpN3(H)p-tol afforded the respective bis(triazenide) complexes. The reaction of equimolar quantities of [LiAlH4] and largest triazene studied; DmpN3(H)Mes, afforded the mono(triazenide) complex [AlH2(DmpN3Mes)(thf)]. Treatment of two large triazenes with [LiGaH4] afforded the respective monomeric LiH inclusion products. The products obtained from these 1:1 reactions are heavily dependent on the steric character of the triazene employed and the coordination preference of the metal (Scheme 6.8).

The thermal stability of the bis(triazenide) complex [AlH(DitopN3Mes)2] (dec. 258 °C) exceeds that of the amidinate and β-diketiminate complexes reported to date, making it the most thermally stable aluminium hydride species at this time.[23]

214 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.1.4 The Reactivity of Group 13 Hydride Complexes

R Controlled hydrolysis of [MH2( nacnac)] (M = Al and Ga, R = Mes or Dipp) affords alumoxane and galloxane complexes.[9-10] These complexes have been employed to study the mechanism of ‘single-site’ olefin polymerisation catalysis at zirconium and hafnium centres.[14] β-diketiminate complexes of aluminium hydride have been employed as reductants in the zirconocene catalysed hydrodefluorination of fluoroarenes.[24] Recently, Aldridge has reported the formation of σ-complexes between low oxidation state mid-transition metal carbonyls and β-diketiminate, amidinate and guanidinate complexes of aluminium hydrides (Figure 6.3).[25]

Figure 6.3 - σ-alane complexes of transition metals

Attempts to prepare analogous σ-complexes with gallium hydrides resulted in reductive dehydrogenation and the formation of donor/acceptor complexes featuring [Ga(Dippnacnac)] (Scheme 6.9).[17a] The differing reactivity of the aluminium and gallium hydride complexes was rationalised by the authors on the basis of the weaker M-H bonds in the gallium complex.[26]

Scheme 6.9 - Reductive dehydrogenation of dihydridogallium β-diketiminate complexes

215 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.2 Project Outline

The recent development of sterically demanding monoanionic bidentate N,Nʹ-ligands has enabled the coordination chemistries and the reactivities of the group 13 metal hydrides to be explored in a number of areas (viz. Section 6.1.4). The use of triazenides to stabilise group 13 metal hydride bonds is limited to one study that focused primarily on aluminium.[23] Indeed, the use of monoanionic bidentate N,Nʹ-ligands to stabilise the heavier group 13 metal (M = Ga, In) hydrides is sparse.

Herein, this chapter aims to utilise the novel 2,6-terphenyl substituted monoanionic bidentate N,Nʹ-ligands based on 1-2 that were introduced in Chapter Two for the stabilisation of heavy group 13 metal hydrides. It is intended that these sterically encumbrant ligands will kinetically stabilise the hydride moieties by preventing the formation of M-H-M bridging. As a complement to the study of 1, this chapter will also explore the alkali metal chemistry of the smaller 1,3-bis(aryl)triazenide ligand; based on

Dipp2N3H.

The initial phase of the research presented in this chapter will be to carry out a systematic study of monoanionic bidentate N,Nʹ-ligand complexes of the lighter group 13 metals hydrides, concentrating on the thermal stability imparted by the monoanionic bidentate N,Nʹ-ligand and the solid-state structures. These species will be used to highlight candidate ligands for the preparation of stable Tl-H hydrides, which are presently unknown.

216 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.3 Results and Discussion

6.3.1 The Stabilisation of M-H Bonds with C-2,6-Terphenyl Substituted Amidinate Ligands

As previously discussed, a number of mono(amidinate), mono(guanidinate) and mono(triazenide) complexes of aluminium hydrides have been prepared through the 1:1 reaction of [LiAlH4] or [AlH3(NMe3)] and an amidine, guanidine or triazene. It was thought that the analogous 1:1 reaction of [LiAlH4] and amidine 2 would yield Ditop Ditop [{AlH2( ACy)}2] or [{LiAlH3( ACy)}n] owing to ligand sterics (GAl = 44.4%), Ditop however, the bis(amidinate) complex [AlH( ACy)2] (53) was obtained as the sole amidinate containing product, as evidenced by single crystal X-ray diffraction studies and a single Al-H containing species by IR spectroscopy vide infra (Scheme 6.10).5 The

1:2 reaction of [LiAlH4] and 2 also affords 53. Attempts to prepare the analogous gallium and indium complexes through the same method resulted in metal deposition and near quantitative recovery of 2. These differing outcomes can be rationalised by considering the relative polarities of M-H bonds in [LiMH4] compounds; M = Al > In > Ga[18a] and the decreasing M-H bond enthalpies observed upon descent of the group.

Scheme 6.10 - The preparation of the bis(amidinate) aluminohydride 53

The IR spectrum of 53 exhibits a sharp Al-H absorption at 1823 cm-1. Generally speaking the frequency of the Al-H stretching absorption can be used to identify bridging (< ~1800 cm-1) and terminal (> 1800 cm-1) Al-H bonds, and to evaluate the

5 Complex 53 was prepared collaboratively with Ms Sze Ping Clara Ng as part of an Honours degree project. 217 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

relative donation of the ligands, whereby greater ligand donation leads to weakening of the Al-H bond due to greater alleviation of aluminium electropositivity by the co-ligand(s). In the specific case of 53, the location of the Al-H absorption peak compares well with that of the analogous formamidinate complex [AlH(Fiso)2] (1823 cm-1). Thus, the donor character of DitopACy may be presumed to be similar to Fiso -1 (Table 6.1) and greater than those of the triazenides DitopN3Mes (1889 cm ) and -1 Ph -1 DmpN3p-tol (1893 cm ) but significantly poorer than that of ASiMe3 (1773 cm ).

1H NMR δ M-H Complex IR ν M-H (cm-1) Reference (ppm)

53 1823 4.23 This work

[AlH(Fiso)2] 1823 not observed [18a]

Ph [AlH( ASiMe3})2] 1773 1.11 (C6D6) [20]

[AlH(DitopN3Mes)2] 1889 not observed [23]

[AlH(DmpN3p-tol)2] 1893 not observed [23]

Table 6.1 - Selected spectroscopic data for bis(N,N'-ligand)aluminium hydride complexes

1 13 The H and C NMR spectra of 53 (C6D6) display single sets of amidinate resonances without substantial broadening of the resonances for the Ditop group. This is indicative of the amidinates’ relatively unhindered bonding to aluminium without significant inter-ligand overlap or clashing. A very broad hydride resonance is also observed at 4.23 ppm in its 1H NMR spectrum. The broadness of this resonance results from the quadrupolar moment of the naturally abundant aluminium isotope (27Al, 100%, I = 5 [27] 1 /2), which often frustrates the observation of hydride H NMR resonances (Table 6.1).[23] The chemical shift of the hydride resonance of 53 lies considerably downfield Ph of that observed for [AlH( ASiMe3)2] (1.11 ppm) but is consistent with that reported for the dimeric mono(formamidinate)aluminium hydride complex [{AlH2(Fiso)}2] (4.60 ppm).[18a] The downfield shift of the hydride resonance of 53 relative to that for Ph Ditop [AlH( ASiMe3)2] (Table 6.1) demonstrates the poorer donicity of ACy relative to Ph [20] ASiMe3.

218 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Complex 53 exhibits excellent thermal stability, decompositing in the solid-state at 264

°C. The decomposition temperature of 53 exceeds that of [AlH(Fiso)2] (dec. 233 °C) and approximates that of [AlH(DitopN3Mes)2] (dec. 258 °C) which is the most thermally stable molecular aluminium hydride complex reported to date.[23] It is thought that the thermal stability of hydride 53, and the stabilities of the related compounds in Table 6.1, are likely proportional to the co-ligands ability to kinetically shield the hydride and frustrate bridging interactions. The thermal stability of 53 is therefore not surprising given that DitopACy has been shown to be slightly more sterically demanding than Fiso (GAl = 44.4 and 42.3% respectively, Chapter Two). To this end, the combined steric influence of the monoanionic bidentate N,Nʹ-ligands in each of the aforementioned bis(N,N'-ligand)aluminium hydride complexes have been calculated using their molecular structures. These values (GAl(2L)), along with the thermal stabilities of these complexes, are listed in Table 6.2.

Ligand ([AlHL2]) GAl(2L) Dec. (°C) Reference

DitopACy (53) 86.26 264 This work

MeGiPr 74.42 < 150 [21]

Fiso 82.75 233 [18a]

DitopN3Mes 88.80 258 [23]

DmpN3p-tol 90.00 170 [23]

Table 6.2 - Impact of ligand sterics on the thermal stabilities of [AlL2H]

The data listed in Table 6.2 shows that the thermal stability of a bis(N,N-ligand)aluminium hydride complex is “generally” proportional to the ability of the two ligands to sterically protect the metal hydride. It should be noted that the thermal stability of [AlH(DmpN3p-tol)2] (dec. 170 °C, GAl(2L) = 90.0%) represents an outlier in this regard. This may be because the decomposition of [AlH(DmpN3p-tol)2] proceeds through a different mechanism to those of the remaining complexes where

GAl(2L) > 80%.

Colourless blocks of 53 suitable for X-ray structure determination study were grown from a saturated diethyl ether and hexane solution at -25 °C. Complex 53 crystallises in the monoclinic space group P21/n with a full monomer, a full molecule of diethyl ether, 219 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

and a half molecule of hexane in the asymmetric unit. The molecular structure of 53 and salient bonding parameters are given in Figure 6.4.

Figure 6.4 - Molecular structure of 53 (50% thermal ellipsoids). All hydrogen atoms except hydride H(1) omitted, Cy groups depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and torsion angles (°): Al(1)-H(1) 1.48, Al(1)-N(1) 1.9289(19), Al(1)-N(2) 2.0455(18), Al(1)-N(3) 1.9330(19), Al(1)-N(4) 2.0647(18), C(1)-N(1) 1.341(3), C(1)-N(2) 1.321(3), C(34)-N(3) 1.345(3), C(34)-N(4) 1.321(3), N(1)-Al(1)-N(2) 66.80(7), N(1)-Al(1)-N(3) 124.29(9), N(1)-Al(1)-N(4) 106.60(8), N(2)-Al(1)-N(3) 105.77(8), N(2)-Al(1)-N(4) 165.69(8), N(1)-C(1)-N(2) 110.69(18),

N(3)-C(34)-N(4) 111.19(17), N2C(1):ArC(2) 72.8, N2C(34):ArC(35) 72.7, N2C(1):N2C(34) 41.0, ArC(2):ArC(35) 33.2.

The coordination geometry about the aluminium centre in 53 is best described as a distorted trigonal bipyramid with two apical amidinate nitrogens, one from each amidinate (N(2) and N(4)), and the hydride and remaining nitrogen donors in the equatorial plane. This coordination motif is similar to that displayed by [18a] [AlH(Fiso)2]. For instance, [AlH(Fiso)2] exhibits a similar trans N-Al-N angle (158.23(14)°) to 53 (165.69(8)°). The mean Al-N bonds of the amidinates of 53 display less disparate Al-N binding (apical versus equatorial) relative to those in [AlH(Fiso)2]

(53: mean Al-Naxial 2.046 Å, mean Al-Nequat. 1.929 Å; [AlH(Fiso)2]: mean Al-Naxial

2.078 Å, mean Al-Nequat. 1.912 Å). The hydride ligand of 53 was located from a difference map and refined isotropically (Al-H 1.48 Å). Whilst somewhat unreliable by X-ray methods, the Al-H bond length compares favourably with those of [23] [AlH(DmpN3p-tol)2] and [AlH(DitopN3Mes)2] are 1.45 and 1.60 Å respectively.

220 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.3.2 The Stabilisation of M-H Bonds by N-Aryl Triazenide Ligands

The bis(triazenide)aluminium hydride, [AlH(N3Dipp2)2] (54), was prepared in the same manner as 53. The analogous gallium hydride, [GaH(N3Dipp2)2] (55), and indium hydride [InH(N3Dipp2)2] (56) complexes were successfully prepared by treating the respective [LiMH4] (M = Ga, In) with two equivalents of Dipp2N3H (Scheme 6.11). Selected physical and spectroscopic data for these complexes is listed in Table 6.3 (pg. 222). The successful preparation of gallium and indium hydride complexes 55 and 56 demonstrates (i) the greater acidity of Dipp2N3H relative to 2 cf. failed isolation of Ditop product from reaction of ACyH with [LiMH4] (M = Ga, In), and/or (ii) the increased stability of the hydrides supported by the triazenide ligands.

Scheme 6.11 - Preparation of bis(triazenide) complexes of aluminium, gallium and indium hydride

221 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

IR ν M-H NMR δ M-H Complex Dec. (°C) Reference (cm-1) (ppm)

53 1823 not observed 264 This work

54 1836 5.15 236 This work

[AlH(Fiso)2] 1823 not observed 233 [18a]

[AlH(DitopN3Mes)2] 1889 not observed 258 [23]

[AlH(DmpN3p-tol)2] 1893 not observed 170 [23]

55 1912 6.59 210 This work

[GaH(Fiso)2] 1911 not observed 213 [18a]

56 1747 8.47 172 This work

[InH(Fiso)2] 1748 not observed 170 [19a]

Table 6.3 - Selected spectroscopic and physical data for bis(monoanionic bidentate N,N'-ligand) group 13 metal hydride complexes

The IR spectra of 54-56 exhibit sharp M-H absorption bands (Table 6.3). The frequencies of these are consistent with terminal M-H bonds (like those for the Fiso analogues vide supra). The frequency of the Al-H stretch in the IR spectrum of 54 indicates N3Dipp2 is a stronger donor than DitopN3Mes and DmpN3p-tol, but weaker than the amidinates DitopACy (53) and Fiso (Table 6.3). However, the frequencies of the

M-H IR stretches in the IR spectra of 55 and 56 are consistent with N3Dipp2 possessing comparable donor character to Fiso at these metals.

1 13 The H and C NMR spectra of 54-56 (C6D6) exhibit singular sets of triazenide resonances with minimal broadening. Each spectrum exhibits two distinct methyl environments and a single methine resonance. This is consistent with the 1H NMR spectra of the related halide complexes 37, 39-41, which indicate that rotation about the arene to isopropyl methine C-C bond in the N3Dipp2 ligands of 54-56 is hindered. Very broad hydride resonances are also observed in the 1H NMR spectra of 54-56 (Table 6.3). The broadness of these results from the quadrupolar moments of the metal centres 69 3 71 3 113 9 115 involved ( Ga, 60.4%, I = /2; Ga, 39.6%, I = /2; In, 4.3%, I = /2; In, 95.7%, I = 9 [27] 1 /2). The hydride resonances in the H NMR spectra of 54-56 lie downfield of those

222 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

[28] [29] of the [MH3(IMes)] complexes (M = Al, 2.7 ppm (THF-d8), not observed in C6D6; [6a] [6a] M = Ga, 3.96 ppm; M = In, 5.20 ppm , both C6D6) due to the negative inductive effect of the two triazenide ligands which increase the polarity of the M-H bond.

All three complexes display excellent thermal stability (Table 6.3), decomposing in the solid-state at temperatures that follow the convention for group 13 hydride complexes (Al > Ga > In).[18a] All three species may be handled in air for extended periods without decomposition. This may be ascribed to the steric protection afforded by the triazenide groups to their M-H fragments (vide infra Table 4.2, pg. 225).

Colourless single crystals of 54-56 suitable for X-ray crystallographic study were grown by slow cooling of room temperature saturated hexane solutions to -25 °C over 24 h. As per the related group 13 halides 37 and 39-41, each species is monomeric, indeed 54-56 are isomorphous to the related [MH(Fiso)2] complexes. In all cases the hydride ligand was located from a difference map and refined isotropically. The molecular structure of 56 is depicted in Figure 4.13. The molecular structures of 54 and 55 can be found in the appendix. Relevant metrical parameters for 54-56 are given in Table 4.2 (pg. 225).

Figure 6.5 - Molecular structure of 56 (50% thermal ellipsoids). All hydrogen atoms except hydride H(1) omitted, Dipp groups depicted as wireframes for clarity. Salient bond parameters are listed in Table 4.2.

223 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

The geometries of 54-56 are very similar to those of the related halo triazenide complexes 37, 39-41 (Chapter Four) and Fiso complexes in the literature.[30] Each metal is five coordinate with two chelating triazenide units and one hydride ligand, affording a heavily distorted trigonal bipyramidal metal geometry with one nitrogen from each triazenide; N(1) and N(4) in apical positions and two nitrogens (N(3) and N(6)) that share an equatorial plane with the hydride ligand. Like 37, 39-41 and 53, the apical N-atoms are more distant from the metal centres than the equatorial nitrogens. The steric congestion in these complexes is evidenced in the N3:Ar interplanar angles, which significantly deviate from 90° at the equatorial N-Dipp positions (Table 4.2). Whilst somewhat unreliable by X-ray methods, the M-H bond lengths in 54-56 (Al, 1.60 Å;

Ga, 1.53 Å; In, 1.69 Å) compare favourably with those of [AlH(DitopN3Mes)2] (1.60 [23] Ph [21] Å), [AlH( ASiMe3)2] (1.58 Å) and [MH(Fiso)2] (M = Ga, 1.65 Å; M = In, 1.71 Å).[18a,19a]

224 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Bond Parameter 54 55 56

M-H 1.60 1.53 1.69

M-N(1) 2.0324(19) 2.148(2) 2.275(2)

M-N(3) 1.918(2) 1.972(2) 2.207(2)

M-N(4) 2.0327(18) 2.134(2) 2.2745(19)

M-N(6) 1.919(2) 1.972(2) 2.190(2)

N(1)-N(2) 1.297(2) 1.291(3) 1.285(3)

N(2)-N(3) 1.326(2) 1.311(3) 1.302(2)

N(4)-N(5) 1.301(3) 1.291(4) 1.290(3)

N(5)-N(6) 1.326(2) 1.318(3) 1.296(3)

N(1)-M-N(3) 63.77(8) 61.19(9) 55.98(7)

N(4)-M-N(6) 64.21(8) 61.18(9) 56.25(7)

N(1)-N(2)-N(3) 105.55(17) 107.8(2) 108.83(18)

N(4)-N(5)-N(6) 106.36(17) 107.0(2) 109.03(18)

N3:ArC(1) 81.4 84.2 84.5

N3:ArC(13) 73.4 69.7 64.0

N3:ArC(25) 86.8 83.2 84.4

N3:ArC(37) 71.9 68.6 65.7

N3:N3 43.3 47.0 50.6

G(2L)a 82.72 {82.75} 81.74 {80.75} 75.59 {76.22}

Table 6.4 - Selected bond lengths (Å), angles (°) and torsion angles (°) for 54-56 a Parameters were calculated using Solid-G, parameters for the analogous Fiso complexes are given in braces.

The orientation of the Dipp groups in 54-56 leads to substantial steric shielding of the hydride ligands (Figure 6.6, pg. 226). A similar protective pocket was observed in the [19a] molecular structure of [InH(Fiso)2], which prevents the formation of In-H-In bridges and hinders chemical approach. Evaluation of the sterics eschewed by the monoanionic

225 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

bidentate N,Nʹ-ligands in these complexes (see G(2L) parameters, Table 4.2) indicates there to be little difference between N3Dipp2 and Fiso in this context. This is consistent with the similar solid-state thermal stabilities exhibited by the respective sets of complexes, and indicates that, in this instance, the impact of the ligand’s electronic character on hydride thermal stability is of secondary importance to the ligand’s steric profile.

Figure 6.6 - Space filling model of 56 down the In-H(1) vector (left) and normal to it (right). The hydride ligands are depicted in black.

The considerable thermal stability of 56 warranted an investigation into the isolability of an analogous thallium hydride complex; [TlH(N3Dipp2)2]. The synthetic route used to prepare 54-56 could not be used to prepare a thallium equivalent as there is no available lithium tetrahydriothallate counterpart (cf. Scheme 6.11).[31] As the Ph Ph bis(amidinate) complex, [AlH( ASiMe3)2], was prepared from [AlCl( ASiMe3)2] and [20] [KBEt3H] (viz. Scheme 6.7), wherein the poor Lewis acidity of BEt3 prevents ligand transmetallation, a similar pathway to [TlH(N3Dipp2)2] was conceived. Ligand transmetallation has been observed previously when using group 13 metal hydride sources.[12,32] As a model for the thallium reaction, the preparation of 56 was attempted by chloro-hydride exchange at 40; [InCl(N3Dipp2)2]. To this end, 40 was treated 1 [NaBEt3H] in toluene at -60 °C. A H NMR spectrum (C6D6) collected of the filtered and dried reaction mixture exhibits 1H NMR resonances and an In-H IR stretch consistent with those of 56, demonstrating proof of concept. The successful preparation

226 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

of 56 by chloro-hydride exchange lead to the preparation of a thallium analogue of 40. A survey of the available literature indicates that no bis(monoanionic bidentate N,N'-ligand) complexes of thallium halides have been reported, however, the halo Ph [20] Me [33] amidinate complexes [AlCl( ASiMe3)2] and [InCl( ACy)2] have been prepared through the 2:1 salt metathesis reaction of the respective lithium amidinate and MCl3

(M = Al, In). Herein, the thallium chloride complex [TlCl(N3Dipp2)2] (57) was prepared by treating anhydrous TlCl3 with two equivalents of in situ prepared 24 (Scheme 6.12).

The bromide analogue of 57, [TlBr(N3Dipp2)2] (58) was similarly prepared by treating an in situ prepared solution of TlBr3 (TlBr + Br2) with two equivalents of in situ prepared 24 (Scheme 6.12), however, difficulty in removing excess Br2 (cf. preparation of TlBr3) resulted in depleted yields of pure 58.

Scheme 6.12 - The synthesis of bis(triazenide)thallium halide complexes

1 The H NMR spectra of 57 and 58 (C6D6) exhibit single sets of high symmetry triazenide resonances like those of the thallium(I) complex 42 wherein, in contrast to 37 and 39-41, and indeed 54-56 a single methyl doublet resonance is observed. It may be reasoned that the longer M-N bonds in 57 and 58 (and 42) allow for free rotation about the arene to isopropyl methine C-C bond.

227 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Orange single crystals of 57 and 58 suitable for X-ray crystallographic study were grown by cooling of saturated hexane solutions to -25 °C for 24 h. Complexes 57 and

58 are isomorphous, crystallising in the space group P21/c. The structure of 57 is depicted in Figure 6.7. The molecular structure of 58 can be found in the appendix. Salient metrical parameters for complexes 57 and 58 are listed in Table 6.5 (pg. 229).

Figure 6.7 - Molecular structure of 57 (50% thermal ellipsoids). All hydrogen atoms omitted, Dipp groups depicted as wireframes for clarity. Salient bond parameters are listed in Table 6.5.

228 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Bond Parameter 57 58

Tl-X 2.4362(8) 2.5582(11)

Tl-N(1) 2.279(2) 2.310(6)

Tl-N(3) 2.367(2) 2.319(7)

Tl-N(4) 2.301(2) 2.321(6)

Tl-N(6) 2.354(2) 2.266(6)

N(1)-N(2) 1.288(3) 1.275(8)

N(2)-N(3) 1.288(3) 1.272(8)

N(4)-N(5) 1.287(3) 1.262(8)

N(5)-N(6) 1.288(3) 1.240(8)

N(1)-Tl-N(3) 54.48(8) 54.2(2)

N(4)-Tl-N(6) 54.36(8) 53.9(2)

N(1)-N(2)-N(3) 111.4(2) 111.6(6)

N(4)-N(5)-N(6) 111.4(2) 112.5(6)

N3:ArC(1) 62.2 78.5

N3:ArC(13) 85.3 47.8

N3:ArC(25) 63.9 89.1

N3:ArC(37) 82.2 66.1

N3:N3 43.7 41.3

Table 6.5 - Selected bond lengths (Å), angles (°) and torsion angles (°) for 57 and 58

The Tl-X distances in 57 and 58 are in keeping with those reported for thallium porphyrin complexes; [TlCl(OEP)] (2.452(3) Å),[34] [TlCl(tmpp)] (2.451(2) Å)[35] and [TlBr(tpp)] (2.542(2) Å).[35] As per 37, 39-41 and 54-56, each is five coordinate giving a heavily distorted trigonal bipyramidal complex geometry. Like 37, 39-41 and 54-56, N(3) and N(6) occupy the apical positions in 57 and 58 (Table 6.5), however, unlike the aforementioned [MX(N3Dipp2)2] species, there is no dramatic extension of the apical

229 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

M-N contacts relative to the equatorial M-N contacts, especially in 58, and the interplanar angles N3:Ar appear decoupled from the location of the N-Dipp group.

In an attempt to prepare the hydride analogue of 57, a toluene solution of 57 was treated with one equivalent of [NaBEt3H] (1.0 M in toluene) at -78 °C. This resulted in the deposition of elemental thallium (Scheme 6.13). Repeating the reaction using [KBEt3H] as the hydride source, likewise affords elemental thallium.

Scheme 6.13 - The attempted preparation of [TlH(N3Dipp2)2]

This demonstrates either (i) the solution-state instability of [TlH(N3Dipp2)2] at -78 °C or (ii) the availability of an alternative pathway for decomposition that is unavailable to the aluminium, gallium and indium congeners. For instance, the thermal stability of

[TlH(N3Dipp2)2] may be dramatically reduced relative to 56 and 57 because of increased triazenide lability at thallium or a spontaneous redox process that reductively eliminates Dipp2N3H and 42, followed by decomposition of the latter. In other words, the protective hydride pocket that is responsible for the enhanced thermal stability of 56 is incapable of supporting the hydride of [TlH(N3Dipp2)2].

230 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.3.3 The Stabilisation of M-H Bonds with an N-2,6-Terphenyl Triazenide Ligand

The triazenide complexes of aluminium and gallium dihydride; [AlH2(N3Dmp2)] (59) and [GaH2(N3Dmp2)] (60), were prepared using the same protocol as 54 and 55 with a single equivalent of 1 rather than two equivalents of Dipp2N3H (Scheme 6.14). Selected physical and spectroscopic data for these complexes are listed in Table 6.6.

Scheme 6.14 - Preparation of triazenide complexes of aluminium and gallium dihydride

IR ν M-H NMR δ M-H Complex [MH (L)] Dec. (°C) G(L)a Ref. 2 (cm-1) (ppm)

59 1873 2.99 > 360 69.73 This work

iPr [AlH2( ATI)] 1770, 1800 1.08 53 (m.p.) - [36]

Ph [AlH2( nacnac)] 1754 4.86 127 (m.p.) 46.09 [37]

Xy [AlH2( nacnac)] 1819 4.58 206 (m.p.) 53.52 [9]

Mes [AlH2( nacnac)] 1775, 1815 - 200 53.85 [10]

Dipp [AlH2( nacnac)] 1795, 1832 - 194 (m.p.) 59.22 [11]

60 1940 4.46 270 67.71 This work

Mes [GaH2( nacnac)] 1836, 1876 5.26 149 - [14]

Dipp [GaH2( nacnac)] 1861, 1893 4.58 135 (m.p.) 58.04 [15]

Table 6.6 - Selected spectroscopic and physical data of monomeric group 13 metal dihydride complexes a Parameters were calculated using Solid-G and the crystal structures of the respective complexes.

231 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

The IR spectra of 59 and 60 exhibit strong sharp M-H absorptions at 1873 and 1940 cm-1 respectively. The frequencies of these absorptions are significantly higher than those of analogous β-diketiminate complexes (Table 6.6), which is consistent with the poorer donicity of triazenides (Chapter Two). The lack of any further absorptions in the M-H region of their IR spectra, e.g. lower wavenumber bridging M-H stretches, indicates 59 and 60 are most likely monomeric in the solid-state and free of LiH. The IR -1 -1 spectra additionally display sharp N3 absorptions (59 1262 cm , 60 1268 cm ) which is indicative of triazenide N,N'-chelation in 59 and 60. The Monomeric monoanionic bidentate N,N'-ligand aluminium dihydride complexes are rare and there are no examples of such a complex with amidinate or guanidinate co-ligands. [23] [AlH2(DmpN3Mes)(thf)] is the only example of a triazenide containing complex, though this may be due to the coordination of a THF molecule thereby occupying a coordination site that would otherwise be used in Al-H-Al bridging interactions.

1 13 The H and C NMR spectra of 59 and 60 (C6D6) exhibit sharp triazenide Dmp resonances that are consistent with a high degree of symmetry in solution. Very broad hydride resonances are also observed in their respective 1H NMR spectra (2.99 and 4.46 ppm respectively). These resonances lie at higher field relative to monomeric nacnac coordinated dihydride complexes (Table 6.6), which is as one would predict were inductive effects to lead to a greater polarisation of the M-H bonds. It is also possible the high field shifts arise from π-interactions with the flanking Dmp mesityl groups (viz. 25, Chapters Three and Four).

Both 59 and 60 display exceptional thermal stabilities (dec. 59 > 360 °C; 60 270 °C) that exceed the thermal stabilities of the analogous N-aryl nacnac complexes (Table 6.6).[10,14] This is consistent with the greater steric protection afforded to the hydrides of 59 and 60 by the bulky N-2,6-terphenyl triazenide (Table 6.6).

232 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Bright yellow prisms of 59 and 60 suitable for X-ray crystallographic study were grown by slow cooling saturated hexane (59) or toluene (60) solutions to -25 °C for 24 h. Complexes 59 and 60 are monomeric in the solid-state and crystallise in the space group P1̅ with one full molecule in the asymmetric unit. Complex 60 also crystallises with a half molecule of toluene in its asymmetric unit. The molecular structure of 60 is depicted in Figure 6.8. The molecular structure of 59 can be found in the appendix. Relevant metrical parameters for these complexes are listed in Table 2.5 (pg. 234).

Figure 6.8 - Molecular structure of 60 (50% thermal ellipsoids). All hydrogen atoms excepting hydrides H(1) and H(2) omitted for clarity. Salient bond parameters are listed in Table 2.5.

233 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Bond Parameter 59 60

M-H(1) 1.52(2) 1.49(2)

M-H(2) 1.53(2) 1.45(3)

M-N(1) 1.9470(17) 2.0299(19)

M-N(3) 1.9614(17) 2.0384(19)

N(1)-N(2) 1.321(2) 1.311(3)

N(2)-N(3) 1.324(2) 1.309(3)

H(1)-M-H(2) 125(1) 123.9(15)

N(1)-M-N(3) 64.31(7) 61.37(8)

N(1)-N(2)-N(3) 103.70(14) 104.79(18)

MH2:N3 80.4 82.6

N3:ArC(1) 36.3 36.8

N3:ArC(25) 35.6 33.5

ArC(1):ArC(25) 71.9 70.3

Table 6.7 - Selected bond lengths (Å), angles (°) and torsion angles (°) for complexes 59 and 60

The geometries of complexes 59 and 60 are similar to those of the analogous dimethyl complexes; 4 and 50 (Chapter Five). Each metal centre is four coordinate with a [38] distorted tetrahedral geometry at the metal (τ4 = 0.83, 59 and 60, viz. Chapter Two).

The N-N distances in each N3 donor unit indicate that the electron density is fully delocalised. The hydride ligands in 59 and 60 were located from difference maps and refined isotropically. Whilst somewhat unreliable by X-ray methods, the M-H bond lengths in 59 and 60 (Al, 1.52(2) and 1.53(2) Å; Ga, 1.49(2) and 1.45(3) Å) compare [23] favourably with those of [AlH2(thf)(DmpN3Mes)] (1.52 and 1.53 Å), Dipp [12] Dipp [AlH2( nacnac)] (1.51(2) and 1.518(19) Å) and [GaH2( nacnac)] (1.54(2) and 1.52(2) Å).[15]

The close proximity of the hydride ligands to N-Dmp mesityl groups in 59 and 60 is clearly observed in the space-fill model of 60 in Figure 6.9. This is also consistent with

234 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

magnetic shielding of the hydride resonances (1H NMR spectra, Table 6.6). The orientation of the proximate mesityl groups in 59 and 60 sterically sandwiches the hydrides between the two mesityl rings (Figure 6.9). This contrasts the bowl shaped M-H pocket generated by the triazenides of 54-56 (Figure 6.6).

Figure 6.9 - Space filling model of 60 down the Ga-N(2) vector (left) and normal to it (right). The hydride ligands are depicted in black.

The excellent thermal stabilities of 59 and 60 were encouraging for the preparation of an indium analogue. The synthesis of [InH2(N3Dmp2)] was attempted using the same route as the preparations of 59 and 60. At -30 °C, this led to a bright yellow solution that is indicative of deprotonation of the triazene. However, upon warming to ambient temperature, this solution deposited a grey precipitate, presumably indium, at 0 °C. The solution instability of this product is consistent with the formation of a LiH inclusion 1 product, e.g. [Li(OEt2)(μ-H)(μ-κ -N3Dmp2)InH2]. A similarly unstable LiH inclusion product, [{Li(Et2O)(μ-H)(μ-Fiso)InH2}2], was isolated from the 1:1 reaction of [LiInH4] with FisoH.[19a] There is also precedent for LiH inclusion in terphenyl substituted triazenide complexes, as evidenced by the report of [Li(THF)(μ-H)(μ-κ1- [23] DmpN3Mes)GaH2].

In order to prevent the formation of the LiH inclusion product a neutral non-LiH adducted indane precursor was used. [InH3(PCy3)] was chosen due to its good solution stability and its poor solubility in diethyl ether. The latter enables residual [LiInH4] and the other undesirables in Scheme 6.15 (pg. 236) to be removed.[39] This procedure also

235 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

afforded a bright yellow reaction mixture that decomposed on warming above 0 °C, viz.

[LiInH4] route. The failure of this protocol to yield a dihydridoindium triazenide may highlight the poor solution state thermal stability of [InH2(N3Dmp2)] or an arene mediated decomposition path that is encouraged by the short Mes···H-In distances (viz. Chapter Seven).

Scheme 6.15 - Attempted preparation [InH2(N3Dmp2)] by protolysis

To this end, two other routes to [InH2(N3Dmp2)] were investigated (Scheme 6.16); treatment of the dibromoindium triazenide complex 48 with two equivalents of

[NaBEt3H] in toluene at -78 °C, viz. the preparation of 56 by halide-hydride exchange, and the oxidative addition of dihydrogen to the indium(I) triazenide complex 44 (cf. the Dipp [16] preparation of [GaH2( nacnac)]). The first resulted in the deposition of a grey precipitate upon warming to ambient temperature. Bubbling dihydrogen through a toluene solution of 44 at 0 °C resulted in a colour change from orange to yellow with the concurrent deposition of a grey precipitate. Repeating this protocol at sub zero 1 temperatures results in no visible colour change, indeed a H NMR spectrum (C6D6) of a vacuum dried aliquot displayed resonances consistent with those of 44.

Scheme 6.16 - Other attempts to prepare [InH2(N3Dmp2)]

236 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

This demonstrates either the significant solution-state instability of [InH2(N3Dmp2)] or indicates that an alternative pathway to decomposition, i.e. one that is absent for its aluminium and gallium congeners, is available to [InH2(N3Dmp2)].

The direct reaction of dihydrogen with the indium(I) triazenide 44 at 0 °C likely affords

[InH2(N3Dmp2)] (cf. colour change) as a short-lived species. Extending this method to thallium, a toluene solution of the thallium(I) triazenide complex 45 was sparged with dihydrogen at ambient temperature, without any colour change or metal deposition. A 1 H NMR spectrum (C6D6) of the vacuum dried crude reaction mixture displays resonances consistent with those of 45.

237 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.4 Conclusions

This Chapter describes the preparation of a number of the amidinate and triazenide complexes of group 13 metallohydrides and related precursors.

Ditop The 1:1 reaction of ACyH with [LiAlH4] affords the bis(amidinate)aluminium Ditop hydride [AlH( ACy)2] (53). Complex 53 exhibits considerable thermal stability in the solid-state, which may be attributed to the high degree of kinetic stabilisation afforded by the amidinate ligands to the Al-H bond. Attempts to isolate analogous gallium and indium complexes were unsuccessful.

The 2:1 reaction of Dipp2N3H with [LiMH4] (M = Al, Ga, In) affords the bis(triazenide)metallohydride complexes 54 (M = Al), 55 (M = Ga) and 56 (M = In). Complex 55 is the first bis(triazenide)gallium hydride and 56 the second example of a bis(monoanionic bidentate N,Nʹ-ligand)indium hydride complex. Complexes 54-56 display excellent thermal stabilities in the solid-state that are akin to those of their bis(Fiso) analogues. Complexes 54-56 were crystallographically characterised and studies of their solid-state structures reveal that the triazenide ligands afford the same encapsulation of the M-H bond as that observed for Fiso in the solid-state structures of the [MH(Fiso)2] complexes. This indicates that the impact of the ligand’s electronic character on hydride thermal stability is of secondary importance to the impact of the ligand’s steric profile in this instance. The successful preparations of three thermally robust group 13 metallohydride complexes led to attempts to prepare a related thallium hydride complex to 54-56. The reaction of [TlCl(N3Dipp2)2] (57) with [NaBEt3H] results in the immediate deposition of thallium metal.

The 1:1 reaction of Dmp2N3H with [LiMH4] (M = Al, Ga) affords the mono(triazenide)metallohydride complexes 59 (M = Al) and 60 (M = Ga). Complexes 59 and 60 display considerable thermal stabilities in the solid-state such that they are the most thermally robust alumino- and gallohydrides to date. The crystal structures of 59 and 60 highlight that the MH2 moiety is encapsulated by two pendant mesityl rings of the triazenide. This has been postulated as the origin of the enhanced thermal stabilities of 59 and 60. Several attempts were made to prepare the analogous indium complex.

Thus, it is thought that the aforementioned mesityl ring steric protection of the MH2 groups in 59 and 60 leads to conversely poor thermal stability for [InH2(N3Dmp2)].

238 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

Attempts to prepare a [TlH2(N3Dmp2)] complex by oxidative addition of H2 to

[Tl(N3Dmp2)] were also unsuccessful, no reactivity was observed.

239 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.5 Future Directions

Methyl abstraction from amidinate and β-diketiminate complexes of dimethylaluminium has previously been reported.[40] Jones reported that attempts to tBu + tBu prepare [AlH( Aiso)] through the reaction of [{AlH2( Aiso)}2] with F F [H(OEt2)2][BAr ] or [CPh3][BAr ] afforded intractable mixtures which lack Al-H IR stretching absorptions.[18a] No attempts to prepare cationic gallium hydride complexes have been reported. Given the greater steric bulk of the N3Dmp2 ligand vis-à-vis F amidinate and β-diketiminate ligands (Chapter Two), the addition of [CPh3][BAr ] to 59 and 60 may afford the first examples of cationic aluminium and gallium hydrides. Cationic aluminium complexes containing monoanionic bidentate N,Nʹ-ligand are of interest in catalytic applications such as olefin polymerisation due to the their vacant coordination site and the increased electrophilicity at aluminium.

Dipp Roesky has reported that the reaction of [AlH2( nacnac)] with elemental chalcogens in the presence of a catalytic quantity of phosphine affords chalcogen bridged Dipp [41] complexes e.g. [{Al( nacnac)(μ-S)}2]. As discussed in Chapter Four, the excellent Dipp steric encumbrance afforded by N3Dmp2 vis-à-vis nacnac may afford terminal metal chalcogen bonds about a three coordinate group 13 metal.

A number of attempts were made to isolate [InH2(N3Dmp2)] all of which proving unsuccessful. This may reflect the poor solution state stability of [InH2(N3Dmp2)]. Proof of the successful preparation of [InH2(N3Dmp2)] or otherwise could be determined by the addition of diphenyldichalogenides, E2Ph2 E = S, Se, Te, to preparative media for

[InH2(N3Dmp2)]. It is noteworthy that [InH3(PCy3)] reacts with one and a half [42] equivalents of diphenyldichalogenides to afford [In(EPh)3(PCy3)] and that successful preparation of [InH2(N3Dmp2)] would be identified by the isolation of

[In(SPh)2(N3Dmp2)].

240 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6 Experimental

6.6.1 General Synthetic Procedures

[43] [44] [45] [46] [47] [48] [LiGaH4], Dipp2N3H, TlCl3, TlBr3, [KBEt3H], [InH3(NMe3)] and [42] [InH3(PCy3)] were synthesised by literature procedures. TlCl3·4H2O was stored in a desiccator over silica gel. [NaBEt3H] (1.0 M in toluene) was purchased from Sigma-Aldrich and stored in a J Youngs tapped vessel.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

[49] 6.6.2 General Preparation of [LiInH4]

Lithium tetrahydridoindate was generated in situ due to its poor thermal stability. A -1 cool (-78 °C) solution of InBr3 (1 equiv.) in diethyl ether (40 mL mmol ) was added to a cooled diethyl ether (20 mL) slurry of LiH (40 equiv.) at -78 °C. Over the next 2 h the solution was permitted to warm to -30 °C and kept at that temperature for a further 4 h. The mixture was then recooled to -78 °C, stirring was stopped and the excess LiH was allowed to settle. The reaction mixture was then filtered into a precooled schlenk flask, which was immediately used in further preparations.

Ditop 6.6.3 Synthesis of [AlH( ACy)2] (53)

Amidine 2 (295 mg, 0.64 mmol) in diethyl ether (25 mL) was added to a solution of

[LiAlH4] (13 mg, 0.33 mmol) in diethyl ether (40 mL) at -30 °C, and the mixture was allowed to warm to ambient temperature. After 3 h, the solvent was removed in vacuo and the colourless residue was recrystallised from diethyl ether and hexane to afford colourless blocks suitable for X-ray diffraction structure determination (99 mg, 26%); 1 m.p. 264 ºC (dec.). H NMR (400 MHz, C6D6) δ 0.89-1.75 (m, 40H, CH2), 2.22 (s, 12H,

CH3), 3.03 (m, 4H, NCH), 4.23 (br s, 1H, Al-H), 7.10-7.29 (m, 10H, p-ArCH and o- or m-Ar’CH), 7.40 (d, 4H, m-ArCH), 7.77 (d, 8H, o- or m-Ar’CH). 13C NMR (100 MHz,

C6D6) δ 20.8 (CH3), 26.1, 26.6, 35.3 (CH2), 56.1 (NCH), 129.0, 129.5, 130.0, 130.1 (ArCH), 137.1, 139.5, 141.3, 151.7 (ArCH), 171.2 (NCN). IR (Nujol, cm-1) 1823 (br s,

Al-H). Anal. Calc. for C69H81AlN4·(OC4H10): C, 81.51; H, 8.89; N, 5.43. Found: C, 78.19; H, 8.68; N, 5.44%.

241 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6.4 Synthesis of [AlH(N3Dipp2)2] (54)

A solution of Dipp2N3H (3.65 g, 10 mmol) in diethyl ether (30 mL) was added dropwise to a suspension of [LiAlH4] (190 mg, 5.0 mmol) in diethyl ether (20 mL) at room temperature. Gas evolution was observed immediately. After 12 h, the reaction mixture was filtered and the solvent was removed in vacuo. The colourless residue was then extracted with warm hexane (3×40 mL), concentrated and cooled to -25 °C to afford colourless cubes suitable for X-ray diffraction structure determination (2.30 g, 61%); 1 3 m.p. 230-236 °C (dec.). H NMR (400 MHz, C6D6) δ 1.04 (d, JHH = 6.8 Hz, 24H, 3 3 CH(CH3)2), 1.10 (d, JHH = 6.8 Hz, 24H, CH(CH3)2), 3.44 (sept, JHH = 6.8 Hz, 8H, 13 CH(CH3)2), 5.15 (br s, 1H, Al-H), 7.04-7.14 (m, 12H, m- and p-ArH). C NMR (100

MHz, C6D6) δ 23.8, 24.1 (CH(CH3)2), 28.8 (CH(CH3)2), 124.0, 127.9 (ArCH), 140.1, -1 144.6 (ArC). IR (Nujol, cm ) 1836 (sh s, Al-H). Anal. Calc. for C48H69AlN6: C, 76.15; H, 9.19; N, 11.10. Found: C, 75.85; H, 9.32; N, 11.16%.

6.6.5 Synthesis of [GaH(N3Dipp2)2] (55)

A solution of Dipp2N3H (645 mg, 1.76 mmol) in diethyl ether (10 mL) was added dropwise to a cool (-10 °C) solution of [LiGaH4] (ca. 0.88 mmol) in diethyl ether (30 mL). Gas evolution was observed immediately. After 2 h, the reaction was allowed to warm to ambient temperature. The solvent was removed in vacuo and the colourless residue was extracted with warm hexane (100 mL). Concentration in vacuo followed by cooling to -25 °C afforded colourless cubes suitable for X-ray diffraction structure 1 determination (130 mg, 19%); m.p. 190-210 °C (dec.). H NMR (400 MHz, C6D6) δ 3 3 1.06 (d, JHH = 6.8 Hz, 24H, CH(CH3)2), 1.12 (d, JHH = 6.8 Hz, 24H, CH(CH3)2), 3.40 3 (sept, JHH = 6.8 Hz, 8H, CH(CH3)2), 6.59 (br s, 1H, Ga-H), 7.04-7.15 (m, 12H, ArH). 13 C NMR (100 MHz, C6D6) δ 23.7, 24.3 (CH(CH3)2), 28.8 (CH(CH3)2), 123.9, 127.7 (ArCH), 140.6, 144.6 (ArC). IR (Nujol, cm-1) 1912 (sh s, Ga-H). Anal. Calc. for

C48H69GaN6: C, 72.08; H, 8.70; N, 10.51. Found: C, 72.52; H, 8.77; N, 10.51%.

242 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6.6 Synthesis of [InH(N3Dipp2)2] (56)

Method A: A solution of Dipp2N3H (760 mg, 2.0 mmol) in diethyl ether (30 mL) was added dropwise to a solution of [LiInH4] (ca. 1.0 mmol) in diethyl ether (40 mL) at -78 °C. The reaction mixture was allowed to slowly warm to ambient temperature over 6 h. The mixture was filtered and the solvent removed in vacuo. The resultant colourless residue was extracted into hexane (40 mL). Concentration in vacuo followed by cooling to -25 °C afforded colourless cubes suitable for X-ray diffraction structure 1 determination (380 mg, 45%); m.p. 164-172 °C (dec.). H NMR (400 MHz, C6D6) δ 3 3 1.06 (d, JHH = 6.8 Hz, 24H, CH(CH3)2), 1.14 (d, JHH = 6.8 Hz, 24H, CH(CH3)2), 3.39 3 (sept, JHH = 6.8 Hz, 8H, CH(CH3)2), 7.04-7.15 (m, 12H, m- and p-ArH), 8.47 (br s, 1H, 13 In-H). C NMR (100 MHz, C6D6) δ 23.5, 24.4 (CH(CH3)2), 28.8 (CH(CH3)2), 123.8, 127.4 (ArCH), 141.3, 144.2 (ArC). IR (Nujol, cm-1) 1747 (sh s, In-H). Anal. Calc. for

C48H69InN6: C, 68.23; H, 8.23; N, 9.95. Found: C, 67.96; H, 8.27; N, 9.91%.

6.6.7 Synthesis of [TlCl(N3Dipp2)2] (57)

A solution of 24 (180 mg, 0.50 mmol) in diethyl ether (20 mL) was added dropwise to a suspension of TlCl3 (90 mg, 0.25 mmol) in diethyl ether (20 mL). Upon complete addition, the solution went from pale yellow to bright orange with the formation of a colourless precipitate. The reaction mixture was filtered after 12 h and the solvent removed in vacuo. The resulting orange residue was then extracted into hexane (2×30 mL), concentrated and cooled to ambient temperature to afford a crop of orange cubes suitable for X-ray diffraction structure determination (110 mg, 45%); 147-148 °C 1 3 (dec.). H NMR (400 MHz, C6D6) δ 1.12 (d, JHH = 6.8 Hz, 48H, CH(CH3)2), 3.52 (sept, 3 13 JHH = 6.8 Hz, 8H, CH(CH3)2), 7.00-7.14 (m, 12H, m- and p-ArH). C NMR (100

MHz, C6D6) δ 23.7, 23.9 (CH(CH3)2) 28.8, 29.0 (CH(CH3)2), 123.7, 124.1, 128.8 (ArCH), 140.1, 140.4, 145.2, 145.6 (ArC). IR (Nujol, cm-1) 3062 (m), 1587 (m), 1324 (br s), 1256 (m, N=N), 1183 (s), 1098 (m), 1058 (m), 832 (w), 799 (s), 770 (s), 754 (s),

727 (s), 665 (w), 623 (w). Anal. Calc. for C48H68TlClN6: C, 59.50; H, 7.07; N, 8.67. Found: C, 59.77; H, 7.13; N, 8.72%.

243 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6.8 Synthesis of [TlBr(N3Dipp2)2] (58)

Bromine (300 μL, 5.8 mmol) was added dropwise to a stirred suspension of TlBr (298 mg, 1.05 mmol) in THF (20 mL). The resultant red solution was stirred for 1 h at which point no residual solid was evident. The solvent and excess bromine were removed in vacuo to afford a viscous pale brown oil that was redissolved in THF (30 mL). A solution of 24 (770 mg, 2.07 mmol) in THF (10 mL), was then added at ambient temperature. The reaction mixture changed colour from brown to red with the formation of a colourless precipitate. After 12 h, the solvent was removed in vacuo and the residue extracted with toluene (2×20 mL). Drying in vacuo followed by extraction of the red solid into hexane (30 mL) concentration in vacuo and cooling to -25 °C, afforded a small number of orange cubes suitable for X-ray diffraction structure determination and 1 13 1 the collection of H and C NMR spectra (40 mg, 4%). H NMR (300 MHz, C6D6) δ 3 3 1.12 (d, JHH = 6.8 Hz, 48H, CH(CH3)2), 3.51 (sept, JHH = 6.8 Hz, 8H, CH(CH3)2), 13 6.97-7.14 (m, 12H, m- and p-ArH). C NMR (76 MHz, C6D6) δ 23.8, 24.1 (CH(CH3)2),

28.8, 28.9 (CH(CH3)2), 123.6, 124.2, 128.8 (ArCH), 140.1, 140.6, 145.2, 145.7 (ArC).

6.6.9 The Attempted Synthesis of [TlH(N3Dipp2)2]

[NaBEt3H] (1.0 M in toluene, 0.10 mL, 0.1 mmol) was added dropwise to a solution of 57 (100 mg, 0.1 mmol) in toluene at -78 °C. The rapid formation of a formation of a grey precipitate was observed. The resultant slurry was warmed to ambient temperature. Filtration followed by solvent removal in vacuo afforded a pale yellow solid that 1 [44] characterises as Dipp2N3H by H NMR spectroscopy.

244 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6.10 Synthesis of [AlH2(N3Dmp2)] (59)

A pale yellow solution of 1 (461 mg, 0.69 mmol) in diethyl ether (40 mL) was added dropwise to a cooled (0 °C) solution of [LiAlH4] (39 mg, 1.03 mmol) in diethyl ether (20 mL). The resultant solution was stirred for a further 2 h at 0 °C, over this period the colour changed from pale yellow to radiant yellow. The solution was stirred at ambient temperature overnight. The volatiles were removed in vacuo and the yellow solid was extracted with hexane (60 mL), concentrated to ca. 20 mL and slow cooled to -25 °C to afford large yellow prisms suitable for X-ray diffraction structure determination (240 1 mg, 50%); m.p. > 360 °C. H NMR (500 MHz, C6D6) δ 1.96 (s, 24H, o-CH3), 2.15 (s,

12H, p-CH3), 2.99 (br s, 2H, Al-H), 6.77-6.79 (m, 4H, m-ArH), 6.84 (s, 8H, m-Ar’H), 13 6.84-6.86 (m, 2H, p-ArH). C NMR (100 MHz, C6D6) δ 21.2 (p-CH3), 21.3 (o-CH3), 126.0, 129.2, 130.3 (ArCH), 133.7, 136.0, 36.5, 136.9, 139.4 (ArC). IR (Nujol, cm-1)

1873 (br m, Al-H). Anal. Calc. for C48H52AlN3: C, 82.60; H, 7.51; N, 6.02. Found: C, 81.50; H, 7.64; N, 5.83%.

6.6.11 Synthesis of [GaH2(N3Dmp2)] (60)

A pale yellow solution of 1 (117 mg, 0.175 mmol) in diethyl ether (20 mL) was added dropwise to a cooled (-78 °C) solution of [LiGaH4] (0.18 mmol) in diethyl ether (40 mL). The resultant pale yellow mixture was allowed to warm to ambient temperature overnight, with a noticeable colour change to bright yellow. The solution was isolated by filtration and removal of volatiles in vacuo afforded a yellow solid that was washed with cold (0 °C) hexane (3×3 mL), then extracted with toluene (30 mL), concentrated to 10 mL and slow cooled to -25 °C to afford large yellow prisms suitable for X-ray diffraction structure determination (100 mg, 70%); m.p. 270-272 °C (dec.). 1H NMR

(500 MHz, C6D6) δ 1.95 (s, 24H, o-CH3), 2.15 (s, 12H, p-CH3), 4.46 (br s, 2H, Ga-H), 6.75-6.79 (m, 4H, m-ArH), 6.83 (s, 8H, m-Ar’H), 6.83-6.85 (m, 2H, p-ArH). 13C (100

MHz, C6D6) δ 21.2 (p-CH3), 21.3 (o-CH3), 125.5, 129.0, 130.2 (ArCH), 133.6, 136.0, 136.6, 136.9, 140.0 (ArC). IR (Nujol, cm-1) 1940 (br m, Ga-H). Anal. Calc. for

C48H52GaN3·0.5(C7H8): C, 78.62; H, 7.17; N, 5.34. Found: C, 78.17; H, 7.71; N, 5.09%.

245 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.6.12 Attempted Synthesis of [InH2(N3Dmp2)]

Method A: A pale yellow solution of 1 (222 mg, 0.33 mmol) in diethyl ether (20 mL) was added dropwise to a cooled (-78 °C) solution of [LiInH4] (ca. 0.32 mmol) in diethyl ether (40 mL). The resultant pale yellow mixture was allowed to warm to -10 °C over 8 h, during which time a noticeable colour change from pale yellow to bright yellow occurred. Further warming to 0 °C resulted in the rapid formation of a grey precipitate. Filtration followed by solvent removal in vacuo afforded a yellow solid that characterises as 1 by 1H NMR spectroscopy.

Method B: A pale yellow solution of 1 (674 mg, 1.0 mmol) in toluene (40 mL) was added dropwise to a cooled (-78 °C) solution of [InH3(PCy)] (ca. 1.0 mmol) in toluene (40 mL). The resultant pale yellow mixture was allowed to warm to -10 °C over 8 h, during which time a noticeable colour change from pale yellow to bright yellow occurred. Further warming to 0 °C resulted in the rapid formation of a grey precipitate. Filtration followed by solvent removal in vacuo afforded a yellow solid that 1 characterises as a mixture of 1 and PCy3 by H NMR spectroscopy.

Method C: [NaBEt3H] (1.0 M in toluene, 0.07 mL, 0.07 mmol) was added to a solution of 48 (33 mg, 0.035 mmol) in toluene (5 mL) at -78 °C. The reaction mixture was stirred at -78 C for 2 h, during which time the solution became cloudy. Warming to 0 °C over 4 h resulted in the rapid formation of a grey precipitate. Filtration followed by the removal of volatiles in vacuo afforded a yellow solid that characterises as 1 by 1H NMR spectroscopy.

Method D: A solution of 44 (100 mg, 0.125 mmol) in toluene (10 mL) was sparged with

H2(g) at -10 °C. Sparging was continued at this temperature for 2 h, the mixture was then allowed to slowly warm to -5 °C at which point the colour of the solution changed from orange to yellow. Further warming to 0 °C resulted in the rapid formation of a grey precipitate. Filtration followed by the removal of volatiles in vacuo afforded a yellow solid that characterises as 1 by 1H NMR spectroscopy.

246 References for this chapter begin on pg. 247. Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

6.7 References

[1] Gardiner, M. G.; Raston, C. L., Coord. Chem. Rev. 1997, 166, 1-34. [2] Jones, A. C.; Holliday, A. K.; Cole-Hamilton, D. J.; Ahmad, M. M.; Gerrard, N. D., J. Cryst. Growth 1984, 68, 1-9. [3] Downs, A. J.; Pulham, C. R., Chem. Soc. Rev. 1994, 23, 175-184. [4] Goode, M. J.; Downs, A. J.; Pulham, C. R.; Rankin, D. W. H.; Robertson, H. E., J. Chem. Soc., Chem. Commun. 1988, 768-769. [5] Andrews, L.; Wang, X., Angew. Chem. Int. Ed. 2004, 43, 1706-1709. [6] (a) Abernethy, C. D.; Cole, M. L.; Jones, C., Organometallics 2000, 19, 4852- 4857; (b) Baker, R. J.; Jones, C.; Kloth, M.; Platts, J. A., Angew. Chem. Int. Ed. 2003, 42, 2660-2663. [7] Kuhn, N.; Fuchs, S.; Steimann, M., Z. Anorg. Allg. Chem. 2000, 626, 1387- 1392. [8] Kuhn, N.; Fuchs, S.; Steimann, M., Eur. J. Inorg. Chem. 2001, 359-361. [9] Yang, Y.; Li, H.; Wang, C.; Roesky, H. W., Inorg. Chem. 2012, 51, 2204-2211. [10] González-Gallardo, S.; Jancik, V.; Cea-Olivares, R.; Toscano, R. A.; Moya- Cabrera, M., Angew. Chem. Int. Ed. 2007, 46, 2895-2898. [11] Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer, M., Angew. Chem. Int. Ed. 2000, 39, 1815-1817. [12] Twamley, B.; Hardman, N. J.; Power, P. P., Acta Crystallogr., Sect. E 2001, 57, m227-m228. [13] Chu, T.; Korobkov, I.; Nikonov, G. I., J. Am. Chem. Soc. 2014, 136, 9195-9202. [14] Bernabé-Pablo, E.; Jancik, V.; Moya-Cabrera, M., Inorg. Chem. 2013, 52, 6944- 6950. [15] Singh, S.; Ahn, H.-J.; Stasch, A.; Jancik, V.; Roesky, H. W.; Pal, A.; Biadene, M.; Herbst-Irmer, R.; Noltemeyer, M.; Schmidt, H.-G., Inorg. Chem. 2006, 45, 1853-1860. [16] Seifert, A.; Scheid, D.; Linti, G.; Zessin, T., Chem. Eur. J. 2009, 15, 12114- 12120. [17] (a) Turner, J.; Abdalla, J. A. B.; Bates, J. I.; Tirfoin, R.; Kelly, M. J.; Phillips, N.; Aldridge, S., Chem. Sci. 2013, 4, 4245-4250; (b) Pulham, C. R.; Downs, A. J.; Goode, M. J.; Rankin, D. W. H.; Robertson, H. E., J. Am. Chem. Soc. 1991,

247 Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

113, 5149-5162; (c) Brower, F. M.; Matzek, N. E.; Reigler, P. F.; Rinn, H. W.; Roberts, C. B.; Schmidt, D. L.; Snover, J. A.; Terada, K., J. Am. Chem. Soc. 1976, 98, 2450-2453. [18] (a) Cole, M. L.; Jones, C.; Junk, P. C.; Kloth, M.; Stasch, A., Chem. Eur. J. 2005, 11, 4482-4491; (b) Bonyhady, S. J.; Collis, D.; Frenking, G.; Holzmann, N.; Jones, C.; Stasch, A., Nat. Chem. 2010, 2, 865-869. [19] (a) Baker, R. J.; Jones, C.; Junk, P. C.; Kloth, M., Angew. Chem. Int. Ed. 2004, 43, 3852-3855; (b) Rudolf, D.; Kaifer, E.; Himmel, H.-J., Eur. J. Inorg. Chem. 2010, 4952-4961; (c) Rudolf, D.; Storch, G.; Kaifer, E.; Himmel, H.-J., Eur. J. Inorg. Chem. 2012, 2368-2372. [20] Duchateau, R.; Meetsma, A.; Teuben, J. H., Chem. Commun. 1996, 223-224. [21] Brazeau, A. L.; Wang, Z.; Rowley, C. N.; Barry, S. T., Inorg. Chem. 2006, 45, 2276-2281. [22] Hauber, S. O.; Lissner, F.; Deacon, G. B.; Niemeyer, M., Angew. Chem. Int. Ed. 2005, 44, 5871-5875. [23] Alexander, S. G.; Cole, M. L.; Forsyth, C. M.; Furfari, S. K.; Konstas, K., Dalton Trans. 2009, 2326-2336. [24] Yow, S.; Gates, S. J.; White, A. J. P.; Crimmin, M. R., Angew. Chem. Int. Ed. 2012, 51, 12559-12563. [25] (a) Riddlestone, I. M.; Edmonds, S.; Kaufman, P. A.; Urbano, J.; Bates, J. I.; Kelly, M. J.; Thompson, A. L.; Taylor, R.; Aldridge, S., J. Am. Chem. Soc. 2012, 134, 2551-2554; (b) Riddlestone, I. M.; Urbano, J.; Phillips, N.; Kelly, M. J.; Vidovic, D.; Bates, J. I.; Taylor, R.; Aldridge, S., Dalton Trans. 2013, 42, 249-258. [26] Abdalla, J. A. B.; Riddlestone, I. M.; Turner, J.; Kaufman, P. A.; Tirfoin, R.; Phillips, N.; Aldridge, S., Chem. Eur. J. 2014, 20, 17624-17634. [27] Chemistry of Aluminium, Gallium, Indium and Thallium, Ed. Downs, A. J., 1993, Blackie Academic and Professional: Glasgow, UK. [28] Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F., J. Am. Chem. Soc. 1992, 114, 9724-9725. [29] Alexander, S. G.; Cole, M. L.; Forsyth, C. M., Chem. Eur. J. 2009, 15, 9201- 9214.

248 Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

[30] Jones, C.; Junk, P. C.; Kloth, M.; Proctor, K. M.; Stasch, A., Polyhedron 2006, 25, 1592-1600. [31] (a) Wiberg, E.; Dittmann, O.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 60- 61; (b) Wiberg, E.; Dittmann, O.; Noth, H.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 61-62. [32] Isom, H. S.; Cowley, A. H.; Decken, A.; Sissingh, F.; Corbelin, S.; Lagow, R. J., Organometallics 1995, 14, 2400-2406. [33] Zhou, Y.; Richeson, D. S., Inorg. Chem. 1996, 35, 2448-2451. [34] Cullen, D. L.; Meyer, E. F.; Smith, K. M., Inorg. Chem. 1977, 16, 1179-1186. [35] Senge, M. O.; Ruhlandt-Senge, K.; Regli, K. J.; Smith, K. M., J. Chem. Soc., Dalton Trans. 1993, 3519-3538. [36] Dias, H. V. R.; Jin, W.; Ratcliff, R. E., Inorg. Chem. 1995, 34, 6100-6105. [37] Uhl, W.; Jana, B., Chem. Eur. J. 2008, 14, 3067-3071. [38] Yang, L.; Powell, D. R.; Houser, R. P., Dalton Trans. 2007, 955-964. [39] Hibbs, D. E.; Jones, C.; Smithies, N. A., Chem. Commun. 1999, 185-186. [40] (a) Radzewich, C. E.; Coles, M. P.; Jordan, R. F., J. Am. Chem. Soc. 1998, 120, 9384-9385; (b) Radzewich, C. E.; Guzei, I. A.; Jordan, R. F., J. Am. Chem. Soc. 1999, 121, 8673-8674; (c) Schmidt, J. A. R.; Arnold, J., Organometallics 2002, 21, 2306-2313. [41] Jancik, V.; Moya Cabrera, M. M.; Roesky, H. W.; Herbst-Irmer, R.; Neculai, D.; Neculai, A. M.; Noltemeyer, M.; Schmidt, H.-G., Eur. J. Inorg. Chem. 2004, 3508-3512. [42] Cole, M. L.; Hibbs, D. E.; Jones, C.; Smithies, N. A., J. Chem. Soc., Dalton Trans. 2000, 545-550. [43] Shirk, A. E.; Shriver, D. F. In Inorganic Syntheses, Vol. 17, pp. 45-47, 1977, John Wiley & Sons, Inc.: New York, USA. [44] (a) Nimitsiriwat, N.; Gibson, V. C.; Marshall, E. L.; Takolpuckdee, P.; Tomov, A. K.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.; Dale, S. H., Inorg. Chem. 2007, 46, 9988-9997; (b) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou, P. A., Inorg. Chem. 2008, 47, 7366-7376. [45] Uson, R.; Laguna, A.; Spencer, J. L.; Turner, D. G. In Inorganic Syntheses, Vol. 21, pp. 71-74, 1982, John Wiley & Sons, Inc.: New York, USA.

249 Chapter Six: The Stabilisation of Group 13 Hydrides with Triazenide Ligands

[46] Cole, M. L.; Davies, A. J.; Jones, C., J. Chem. Soc., Dalton Trans. 2001, 2451- 2452. [47] Fryzuk, M. D.; Lloyd, B. R.; Clentsmith, G. K. B.; Rettig, S. J., J. Am. Chem. Soc. 1994, 116, 3804-3812. [48] Hibbs, D. E.; Hursthouse, M. B.; Jones, C.; Smithies, N. A., Chem. Commun. 1998, 869-870. [49] (a) Wiberg, E.; Schmidt, M., Z. Naturforsch., Teil B 1957, 12, 54-55; (b) Kummel, C.; Meller, A.; Noltemeyer, M., Z. Naturforsch., Teil B 1996, 51, 209- 219.

250

Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with N-Heterocyclic Carbenes

7.1 Introduction

From an inorganic synthetic chemist’s viewpoint, among the most challenging air and moisture sensitive targets are complexes of the heavier group 13 metallanes, namely indane and thallane. This is simply because the metal centre features three hydride ligands, which significantly reduces the scope for steric and electronic saturation of the metal centre. In terms of the proposed decomposition pathways for heavy group 13 hydrides, such systems are inherently more prone to associative decomposition pathways that involve formation of M-H-M bridges. Moreover, the fact that potential Lewis base donors, such as tertiary amines, have been calculated to form weaker bonds to the heavier metals than even the hydride ligand itself,[1] implies that Lewis base dissociation may offer a second viable decomposition pathway. Moreover, the redox chemistry of thallium and its proclivity for reduction indicate thallane (TlH3) chemistry will be even more challenging and potentially prone to photochemical decomposition. With these considerations in mind, it is perhaps unsurprising that it took until 1998 for the first complexes of indane to be synthesised,[2] and that the chosen Lewis base, an N-heterocyclic carbene (NHC), was a strong σ-donor. Since this time the development of indane chemistry has focused on sterically demanding ligands.[3]

7.1.1 Amine and Phosphine Complexes of Group 13 Metallanes

Tertiary amine adducts of alane and gallane have been known for many years.[4] Bridging hydride moieties are often observed in the solid-state structures of amine adducts of alane due to the poor donicity of the amine and the electron deficiency of the aluminium.[5] Bridging interactions may be cleaved by the addition of a secondary donor, which affords a more stable metallane complex, e.g. [AlH3(Quin)2], (Table 7.1, pg. 252).[6] Bridging hydride moieties have not been observed in the solid-state structures of amine adducts of gallane.[7] This is likely due to gallane being a weaker Lewis acid than alane.[8] This reduced Lewis acidity also contributes to the instability of [9] bis(ligand) gallane adducts, e.g. [GaH3(NMe3)2] (Table 7.1). Amine adducts of indane

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have very poor thermal stability and aside from trimethylamine, quinuclidine and DABCO,[10] have not been examined to a great extent.

M-H IR Stretch Complex Dec. (°C) Reference (cm-1)

[AlH3(NMe3)] 1792 > 75 [11]

a [AlH3(NMe3)2] 1709 > 25 [11-12]

[GaH3(NMe3)] 1852 70 [9,13]

a [GaH3(NMe3)2] not reported > -22 [9]

b [InH3(NMe3)] not reported -30 [14]

[AlH3(Quin)] 1795 108 [15]

[AlH3(Quin)2] 1685 175 [15]

[GaH3(Quin)] 1810 100 [7]

[InH3(Quin)] 1640 -5 [10b]

t [AlH3(P Bu3)] 1786 > 180 [16]

t [GaH3(P Bu3)] 1835 115 [16]

[AlH3(PCy3)] 1750 161 [17]

[GaH3(PCy3)] 1800 130 [18]

[InH3(PCy3)] 1661 50 [19]

[InH3(PCy3)2] 1666 37 [20]

Table 7.1 - Thermal stabilities of amine and phosphine adducts of alane, gallane and indane a Complex decomposes to its 1:1 analogue. b Solution state, less than 0.1 M.[14]

Despite calculations suggesting tertiary phosphines would be poorer donors relative tertiary amines towards alane and gallane,[1] 1:1 phosphine complexes of alane and gallane have been found to be considerably more thermally stable than amine complexes (Table 7.1).[17-18] This is likely due to the larger steric profile of tertiary phosphines, which imparts increased kinetic stabilisation by preventing hydride bridge formation. These data may also suggest metallane-phosphine dissociation energies are

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[1] greater than those reported in theoretical studies. It should be noted that the PCy3 complex of gallane is reported to be air stable.[18] Remarkably, 1:1 and 2:1 tertiary phosphine complexes of indane have been found to possess exceptional thermal stabilities such that they may be handled for short periods at room temperature.[19-20] The larger atomic radii of gallium and indium leads to a decrease in the stability of five coordinate gallanes and indanes relative to four coordinate analogues cf. [InH3(PCy3)2] [19-20] and [InH3(PCy3)], Table 7.1. It is noteworthy that 2:1 ligand complexes of gallane [9] decompose to their respective 1:1 complexes cf. [GaH3(NMe3)2], Table 7.1. By contrast the known 2:1 ligand complex of indane, [InH3(PCy3)2], decomposes to [20] elemental indium, H2 and free ligand (Table 7.1). This is contrary to five versus four coordinate alanes which exhibit greater stability with increased valency cf. [15] [AlH3(Quin)] and [AlH3(Quin)2], Table 7.1, and alludes to a different decomposition path other than simple ligand dissociation for indanes.[20]

Amine complexes of aluminium, gallium and indium trihydrides can be prepared by the addition of one equivalent of amine hydrochloride to the respective lithium tetrahydridometallate (Scheme 7.1).[7]

Scheme 7.1 - Preparation of amine adducts of group 13 metallanes

Phosphine complexes of alane and gallane can be accessed by the addition of one equivalent of phosphine hydrochloride to the respective lithium tetrahydridometallate (Scheme 7.2, pg. 254).[16-17] Phosphine complexes of gallane are also accessible by the addition of one equivalent of phosphine to the respective lithium tetrahydridogallate with elimination of LiH.[18] Neither of the aforementioned procedures yield phosphine adducts of indane.[19] These complexes may only be prepared through ligand displacement of amine adducts (Scheme 7.2).[19] Bis(ligand) complexes of all three metallanes have typically been prepared through the addition of one equivalent of amine or phosphine to a monoamine or phosphine coordinated metallane.[15]

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Scheme 7.2 - Preparation of phosphine adducts of group 13 metallanes

7.1.2 NHC Complexes of Group 13 Metallanes

N-heterocyclic carbenes (NHCs) have featured prominently as superior support ligands to phosphines in transition metal catalysis.[21] The steric profiles of many NHCs afford wing span like steric protection of the metal centre which, coupled with the high nucleophilicity of the carbenic donor, make NHCs attractive ligands for the stabilisation of group 13 metallanes. Shortly after the first NHCs were first isolated in 1991, [22] Arduengo reported the first main group complex of an NHC; the alane [AlH3(IMes)].

At that time, the thermal stability of [AlH3(IMes)] exceeded that of all known amine and phosphine alane complexes (Figure 7.1, pg. 255). This was duly followed by reports [3] of [GaH3(IMes)] and [InH3(IMes)] in 2000. These complexes, likewise, are the most thermally stable reported adducts of gallane and indane (Figure 7.1).

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Figure 7.1 - Thermal stabilities of NHC metallane complexes

A number of other NHC metallane adducts have been reported.[2,14,23] Despite their similarities, the thermal stabilities of IMes, IPr and IiPrMe metallane adducts vary significantly (Figure 7.1).[2-3,14,23-24] For example, although IiPrMe yields a highly stable alane and gallane the indane is of far lower stability than expected on periodic trend alone. The IMes and IPr adducts provide the expected moderate decline in stability from alane to gallane with the IMes adduct of indane ca. 100 °C less stable, and that of IPr dramatically less stable. This may be rationalised on the basis of the greater proximity of pendant alkane substituents to the M-H moiety in the IPr and IiPrMe complexes, which “could” provide a low energy pathway to H2 elimination through C-H activation.[25] It is also noteworthy that indium metal has been observed to catalyse the decomposition of a number of indane complexes and that the decomposition of indane complexes may therefore be considered autocatalytic.[3]

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The NHC complexes in Figure 7.1 were prepared by the addition of one equivalent of NHC to the respective lithium tetrahydridometallate or metallane trimethylamine adduct (Scheme 7.3).[3,22]

Scheme 7.3 - Preparation of NHC adducts of group 13 metallanes

NHC ligands have also been used to stabilise a number of monomeric 3+ oxidation state group 13 metal alkyls, aryls and halides.[23b,26]

7.1.3 The Stabilisation of 6th Period Metal Hydride Moieties with NHCs

In recent years, gold hydride complexes have been postulated as intermediates in a number of homogeneous gold catalysis reactions. However, there have been very few reported examples of gold hydrides. One recent example is the NHC supported gold(I) hydride of Tsui.[27] This hydride complex was prepared through halide-hydride exchange and tbutylalkoxide abstraction by silane metathesis (Scheme 7.4).

Scheme 7.4 - Preparation of an NHC stabilised gold(I) hydride complex

The presence of the hydride was evidenced by a strong Au-H stretch at 1976 cm-1 in the IR spectrum of the spectroscopically identical products of each reaction. This product was found to be indefinitely stable at room temperature, and represents the first example of a hydride complex of a 6th period metal stabilised by an NHC. The isolation of a stable gold(I) hydride is of note to this study as “TlH” is the major product of the [28] reaction of thallium and H2 in an argon matrix upon irradiation.

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257 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

7.1.4 Super Bulky NHCs

The use of super bulky ligands to kinetically stabilise unusual or unprecedented chemical functionalities is a common feature of contemporary organometallic chemistry.[29] Landmark examples include the isolation of low oxidation state metal complexes, one coordinate metal complexes and complexes which feature multiple metal-metal bonding motifs (viz. Chapter Four). Success in these areas has encouraged many research groups to introduce super bulk to a variety of ligand classes, such as cyclopentadienyls,[30] amidinates[31] and β-diketiminates,[32] to evaluate the impact of such ‘steric engineering’ on their coordination chemistry.[33] Beyond these fundamental studies, the selective introduction of bulk has been a major area of interest in catalyst design and small molecule activation.[34]

Our group recently reported the preparation of the first N,N'-bis(2,6-terphenyl) substituted NHC; IDitop (Figure 7.2).[35] This report was closely followed by those of the even bulkier NHCs IPr*,[36] which features N-2,6-bis(diphenylmethyl)-4- methylphenyl substituents and IPr*(2-Np),[37] which features N-2,6-bis(di(2- naphthyl)methyl)-4-methylphenyl substituents (Figure 7.2). Preliminary studies indicate IPr* to be a stronger donor than IPr.[38] These super bulky NHCs have been used to stabilise low coordinate transition metal complexes[38a] and to develop highly active catalysts.[39]

Figure 7.2 - Examples of super bulky NHCs

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7.2 Project Outline

Since the first example in 1992,[22] numerous main group metal NHC complexes have been reported. The application of NHCs to the stabilisation of group 13 metallanes has proved particularly fruitful, as evidenced by the development of rare thermally robust indane complexes.[3] These metallane complexes possess exclusively 1:1 metal:NHC ratios. There has been no attempt to use NHCs to stabilise and isolate thallane (TlH3) or thallium(I) hydride complexes.

The aim of this study is to investigate the impact of NHC steric and electronic character on metallane stability. In view of the reported stabilising influence of IMes in

[InH3(IMes)], the use of more sterically demanding NHCs will be studied with the objective of preparing more thermally robust indane complexes. In the event of successful outcomes, the stabilities and reactivities of these species will be investigated. This study will also focus on the best stabilising techniques to thallium and the preparation of an isolable thallane complex.

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7.3 Results and Discussion

7.3.1 The Role of Sterics in the Stability of NHC Complexes of Alane

The increased stability of group 13 metal hydride moieties coordinated by NHC ligands has been well documented.[3] All reported NHC metallane complexes feature large N- aryl or sterically imposing alkyl groups. Thus, it is difficult to differentiate the impact of electronic and steric effects on the thermal stability of the resultant complex. To deconvolute these influences, the synthesis of a non-sterically demanding NHC complex of alane was targeted. 1,3-Dimethylimidazol-2-ylidene (IMe) is one of the least sterically demanding NHCs reported and therefore highly suitable to evaluate the role of NHC electronic stabilisation on the overall thermal stability of NHC metallanes.

The IMe complex [AlH3(IMe)] (61) was prepared by a similar method to that used to i [14] prepare [AlH3(I PrMe)]. Lithium tetrahydridoaluminate was treated with one equivalent of IMe in diethyl ether, volatiles were removed in vacuo and the resultant colourless solid was recrystallised from diethyl ether (Scheme 7.5).

Scheme 7.5 - The preparation of 61

The IR spectrum of 61 features a broad intense Al-H absorption at 1728 cm-1 that is consistent with the Al-H absorptions reported for the similar alane NHC adducts i -1 [AlH3(IMes)], [AlH3(I PrMe)] and [AlH3(IPr)] (1743, 1730 and 1729 cm respectively).[14,22,23b] Unfortunately, like those adducts, an Al-H 1H NMR resonance could not be located for 61 (cf. quadrupolar nature of 27Al). However, successful formation of 61 is evidenced by the significant upfield shift of the 4,5-imidazol protons 1 in the H NMR spectrum of 61 (5.78 ppm, C6D6) relative to those of the free carbene

(6.34 ppm, C6D6).

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Complex 61 displays poor thermal stability (dec. 124 °C) relative to its bulkier counterparts (Table 7.2). The data in Table 7.2 indicate there is very little correlation between the frequency of the Al-H IR stretching absorbance and the alane complex solid-state thermal stability. There is, however, a strong correlation between the steric character of the support ligand and the solid-state thermal stability of the adduct formed. Thus, while alane thermal stability can be said to have both electronic and kinetic contributions, the impact of the ligand’s electronic character is very much of secondary importance to the ligand’s steric profile.

Ligand -1 Dec. (°C) IR ν M-H (cm ) GAl(L) (%) Reference [AlH3(L)]

Quin 108 1795 21.41a [15]

IMe (61) 124 1728 23.87 This work

IiPrMe > 160 1730 27.99b [14]

PCy3 161 1750 29.75 [17]

t P( Bu)3 > 180 1786 33.82 [16]

IPr 229 1729 43.47 [23b]

IMes 257 1743 37.87 [22,24]

Table 7.2 - Correlation between thermal stability of alane adduct and ligand stereoelectronic character a The reported structure does not contain hydrogen atoms on the ligand. b Average G parameter calculated for the two unique molecules

Colourless needles of 61 suitable for X-ray diffraction structure determination were grown from a concentrated diethyl ether solution at -25 °C. The molecular structure of 61 and salient bonding parameters are listed in Figure 7.3 (pg. 262). Complex 61 crystallises in the monoclinic space group P21/m with a half molecule in the asymmetric unit. The molecule lies on a mirror plane which lies in the plane of the carbene heterocycle.

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Figure 7.3 - Molecular structure of 61 (50% thermal ellipsoids). All hydrogen atoms excepting the hydride ligands removed for clarity. Symmetry operation used to generate # atoms: x, ½-y, z. Selected bond lengths (Å), angles (°) and steric parameters: Al(1)-C(1) 2.0334(18), Al(1)-H(1A) 1.45(3), Al(1)-H(1B) 1.59(3), C(1)-N(1) 1.343(2), C(1)-N(2) 1.351(2), C(1)-Al(1)-H(1A) 109.9, C(1)-Al(1)-H(1A) 106.4, N(1)-C(1)-N(2)

104.63(15), GAl(IMe) (%) 23.87, GAl(all ligands) (%) 59.70, Gγ(ligand overlap) (%) 0.41.

The hydride ligands of 61 were located from difference maps and refined isotropically. The geometry about the aluminium in 61 is best described as a flattened tetrahedron that is similar to those of other NHC alane complexes. The Al-H bond lengths (1.45(3) and [22] 1.59(3) Å) lie within the range reported for [AlH3(IMes)] (1.48-1.63 Å). The Al- [22] CNCN distance in 61 (2.0334(18) Å) is similar to that of [AlH3(IMes)] (2.034(3) Å) i and slightly shorter than those reported for [AlH3(I PrMe)] and [AlH3(IPr)] (2.046(5) and 2.0556(13) Å respectively).[14,23b]

7.3.2 The Stability of NHC Complexes of Indane

A considerable number of NHC complexes of alane and gallane have been reported. In contrast, only four structurally authenticated indane complexes have been reported.[2- 3,19,23a] Of these, just two exhibit room temperature stability in the solid-state; [3] [19] [InH3(IMes)] (dec. 115 °C) and [InH3(PCy3)] (dec. 50 °C). Both complexes exhibit diminished stability in solution and only [InH3(IMes)] exhibits solution stability at room temperature.[3,19] It has been proposed that the instability of indane complexes arises from a low In-H bond enthalpy and a predisposition towards reductive dehydrogenation mediated by In-H-In bridging interactions vide infra.[10a] 262 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

To build on the successful application of IMes to the stability of indane, it was thought that bulkier NHCs with superior donicity relative to IMes would generate indane complexes of even greater stability. As noted in Figure 7.2, a number of bulky NHCs have been reported since the preparation of [InH3(IMes)]. The G steric parameters of a number of silver(I) halide NHC complexes were used to assess the relative merits of these (Table 7.3. pg. 264). Silver NHC complexes were used because the mean Ag-

CNHC distance in NHC complexes of form [AgX(NHC)] (X = halide) provides a reasonable model for the mean In-CNCN distance in the known indane NHC complexes. This survey identified the substantial steric bulk of the ring expanded NHC (RENHC) 7Dipp (Figure 7.4 and Table 7.3, pg. 264),[40] which eclipses those of IMes[41] and its bulkier relatives IPr[41] and 6Mes.[42] Further to greater steric encumbrance, 6- and 7-membered RENHCs like 7Dipp are also attractive as, based on Tolman electronic parameter studies conducted by Cavell, they exhibit markedly superior donor characteristics relative to imidazol-2-ylidenes like IMes.[43] In light of Table 7.3, 7Dipp was applied to the preparation of an indane.

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NHC Halide (X) GAg(NHC) (%) Reference

IPr*(2-Np) Cl 67.98 [37]

IPr* Cl 59.53 [36]

7Dipp Br 53.50 [40]

IDitop Cl 52.47 [35]

6Dipp Br 51.20 [40]

8Mes Br 46.61 [44]

IPr Cl 46.53 [41]

6Mes Cl 43.46 [42]

IMes Cl 39.28 [41]

IAd Cl 39.08 [45]

IiPrMe Cl 34.94 [45]

Table 7.3 - Quantification of NHC sterics using [AgX(NHC)] complexes

Figure 7.4 - Examples of N-aryl RENHCs and partial key for Table 7.3

Treatment of [LiInH4] with one equivalent of 7Dipp in diethyl ether affords

[InH3(7Dipp)] (62) as a light-brown precipitate. The poor solubility of 62 in common apolar solvents made its separation from its LiH co-product troublesome, as did its spontaneous decomposition in the presence of very small quantities of indium deposited. To address this the tricyclohexylphosphine adduct of indane; [19] [InH3(PCy3)], was used as an isolable indane precursor from which the support ligand could be removed by washing. The reaction of [InH3(PCy3)] with a small excess of 7Dipp at -50 °C, followed by filtration and washing of the filtrant with cold diethyl

264 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

ether afforded analytically pure 62 in good yield (71%, Scheme 7.6). 6 Indane 62 represents the first main group complexes of the 7-membered RENHC subclass.[46]

Scheme 7.6 - The preparation of RENHC indane complex 62

The aforementioned steric bulk of 7Dipp confers considerable stability to 62 in the solid-state (dec. 92 °C). While this is impressive relative to those of amine and [10b] phosphine adducts of indane, e.g. [InH3(Quin)] (dec. -5 °C) and [InH3(PCy3)] (dec. [19] [3] 50 °C), it is inferior to that of [InH3(IMes)] (dec. 115 °C) and surprising given the steric argument presented in Table 7.3. The solution phase stability of 62 is also substantially diminished relative to expectation and necessitates manipulation at temperatures below -30 °C to ensure indium metal remains absent.

1 The H NMR spectrum of 62 (toluene-d8, 248 K) exhibits the expected resonances for 113 115 9 the coordinated 7Dipp ligand and a metal quadrupole broadened ( In/ In; I = /2) hydride resonance at 4.78 ppm (½  40 Hz). The hydride resonance lies at substantially higher field relative to the hydride resonances of the indanes [InH3(IMes)] [3] [19] (5.20 ppm) and [InH3(PCy3)] (5.61 ppm). This is consistent with the superior donicity of the RENHC in 62,[43] which increases the electronic shielding of the hydride ligands. The In-H infrared stretching absorbance of 62 lies at 1650 cm-1 and is inconclusive in terms of greater electronic stabilisation for 62. For instance, the In-H -1 [3] absorbance of 62 is identical to that of [InH3(IMes)] (1650 cm ) and red shifted -1 [19] relative to that of [InH3(PCy3)] (1661 cm ). As mentioned earlier in this thesis, it is conceivable that these data are affected by the contrasting geometries at the metal centres, i.e. the extent of pyramidalisation at the MH3 unit, the contrasting π-acidities of phosphines and NHCs, and the breadth of a typical IR M-H stretching absorbance.

6 The preparations of compounds 62-65 were undertaken in collaboration with Mr Anthony R. Leverett as part of an Honours degree project. 265 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

1 A H NMR spectroscopic study of the decomposition of 62 in toluene-d8 at 253 K identifies the gradual formation of the aminal 7Dipp·HH (63) and dissolved H2 (4.47 ppm)[47] with the deposition of an indium mirror (Scheme 7.7). Compound 63 was intentionally prepared by the reaction of 7Dipp·HBr with [LiAlH4] in diethyl ether and the 1H NMR resonances of this compound are consistent with those observed in the solution phase decomposition of 62.

Scheme 7.7 - Studies of the solution phase decomposition of 62

It is noteworthy that during the toluene-d8 decomposition study of 62, the loss of the resonance integrals for the signals 62 correlate well with the growth of resonance signals for 63. This indicates that hydrolysis is not responsible for the decomposition of 62 and that its decomposition is not accompanied by amidinium formation. Resonances corresponding to uncoordinated 7Dipp were also not observed. From these data it was concluded that H2 addition at the NCN carbon, i.e. formation of 63, is dependent on the rate of decomposition. It is noteworthy that deuteration of the products, e.g. HD,

7Dipp·HD or 7Dipp·DD (cf. toluene-d8 solvent), were not observed and therefore the evolved H2 must derive from 62. Moreover, a brief investigation of the kinetics of the st decomposition of 62 at different concentrations (253 K) in toluene-d8 indicate a 1 order dependence on 62.

The decreased solution phase stability of 62 relative to [InH3(IMes)] indicates that the presumed and modelled (Table 7.3) greater projection of 7Dipp’s N-aryl groups into the indium coordination sphere, which is typically viewed as a positive feature of this ligand class regarding steric encumbrance, may actually invite decomposition. In addition to the suggestion by Downs and co-workers that indium hydride decomposition is aided by In-H-In bridging and subsequent reductive dehydrogenation,[48] Jones has suggested that geometrically accessible ligand C-H functions proximate to In-H bonds may expedite indane decomposition.[2] Attempts were made to crystallise 62 for X-ray structure determination in order to evaluate the relative proximity of its alkyl functions

266 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

to the InH3 moiety. Unfortunately all attempts to crystallise 62 were frustrated by its low solubility and its rapid decomposition in solution, even at sub -30 °C temperatures cf. 253 K study above.

To provide a model compound to represent 62, the gallane and indium tribromide congeners; [GaH3(7Dipp)] (64) and [InBr3(7Dipp)] (65), were prepared. Analytically pure 64 was prepared by treating [LiGaH4] with 7Dipp, followed by extraction of the crude vacuum dried reaction mixture into toluene. Complex 65 was prepared by treating

InBr3 with 7Dipp.

1 The H NMR spectrum of 64 (C6D6, 298 K) exhibits the expected resonances including a 69 71 3 broad hydride resonance ( Ga/ Ga; I = /2) that overlaps with the methine resonance of the 7Dipp ligand at 3.27 ppm. The chemical shift of the hydride resonance is in accord [3] with that of [GaH3(IMes)] (3.96 ppm). The IR spectrum of 64 displays a broad Ga-H stretching absorbance at 1798 cm-1. These data highlight the superior donicity of 7Dipp relative to other Lewis bases vide infra (see Table 7.1 for IR comparisons). Complex 64 displays excellent thermal stability in the solid-state (dec. 152 °C), but surprisingly also exhibits similar, albeit significantly slower, solution phase decomposition behaviour to

62 at room temperature in C6D6 to also afford gallium, 63 and H2.

Colourless octahedrons of 64 suitable for X-ray structure determination were grown by cooling a room temperature saturated toluene solution to -25 °C. Colourless rods of 65 were grown by slow cooling a room temperature saturated THF solution to 4 °C. Complex 64 crystallises in the monoclinic space group C2/c. The molecular structure and Ω representation of 64 are depicted in Figures 7.5 and 7.6 respectively (pg. 268). Complex 65 crystallises in the orthorhombic space group Pbca with a molecule of THF in its asymmetric unit, the molecular structure and Ω representation of 65 are depicted in Figures 7.7 and 7.8 respectively (pg. 269).

267 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

Figure 7.5 - Molecular structure of 64 (50% thermal ellipsoid plot and space fill representation with hydrides in green, NHC in grey and gallium in pink. Unfavourable contacts are boxed in yellow, see Solid-G analysis in Figure 7.6). Symmetry operation used to generate # atoms: 1-x, y, ½-z. All hydrogen atoms excepting hydride ligands H(1A)-H(1C), and lower occupancy disordered atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Ga(1)-H(1A) 1.52(5), Ga(1)-H(1B) 1.55(5), Ga(1)-H(1C) 1.62(7), Ga(1)-C(1) 2.111(3), C(1)-N(1) 1.342(2), C(1)-N(1)# 1.342(2), H(1A)-Ga(1)-H(1B) 112(3), H(1A)-Ga(1)-H(1C) 111(3), H(1B)-Ga(1)-H(1C) 105(3), H(1A)-Ga(1)-C(1) 111(2), H(1B)-Ga(1)-C(1) 104(2), H(1C)-Ga(1)-C(1) 113(3), N(1)-C(1)-N(1)# 118.7(3). Unfavourable close contacts (yellow box above): C(11A)#···H(1B) 2.43(5) Å (sum of C,H radii 2.539 Å), H(11E)#···H(1B) 1.54(5) Å (sum of H,H radii 2.000 Å).

Figure 7.6 - Solid angle representation of 64. Normal to the 7Dipp NCN plane (left) and along the Ga(1)-C(1) vector (right). Image generated using a 8 Å red sphere,

7Dipp in blue. GGa(7Dipp) (%) 50.60, GGa(all ligands) (%) 75.79, Gγ(ligand overlap) (%) 9.51.

268 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

Figure 7.7 - Molecular structure of 65 (50% thermal ellipsoid plot). All hydrogen atoms and lattice THF omitted for clarity. Selected bond lengths (Å) and angles (°): In(1)-Br(1) 2.5054(3), In(1)-Br(2) 2.5163(3), In(1)-Br(3) 2.5209(3), In(1)-C(1) 2.2603(19), C(1)-N(1) 1.333(2), C(1)-N(2) 1.336(3), Br(1)-In(1)-Br(2) 100.205(9), Br(1)-In(1)-Br(3) 106.728(10), Br(2)-In(1)-Br(3) 103.190(10), Br(1)-In(1)-C(1) 123.71(5), Br(2)-In(1)-C(1) 119.08(5), Br(3)-In(1)-C(1) 101.81(5), N(1)-C(1)-N(2) 121.44(17). Unfavourable close contacts: Br(3)···H(13C) 2.826 Å (H(13C) = C(13) methyl hydrogen, sum of Br,H radii 2.845 Å).

Figure 7.8 - Solid angle representation of 65 normal to the 7Dipp NCN plane. Image generated using a 8 Å red sphere, 7Dipp in blue, bromides in green. GIn(7Dipp) (%) 45.46, GIn(all ligands) (%) 86.88, Gγ(all ligands) (%) 6.67.

269 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

The M-CNCN distances of 64 and 65 (2.111(3) and 2.2603(19) Å) are extended and [23c] similar respectively relative to those of [GaClH2(IMes)] (2.005(6) Å) and [3] [InH3(IMes)] (2.253(5) Å). With respect to the proximity of the alkyl groups to the

GaH3 or InBr3 units of 64 and 65, it is noteworthy that both structures contain short 7Dipp methyl C-H···X-M distances (64: X = H, M = Ga, Figure 7.6; 65: X = Br, M = In, Figure 7.8) that are within the combined zero point radii of the elements.[49] Although the greater size of the bromides in 65 relative to hydrides in 62 limit the extent to which the 7Dipp in 65 accurately describes the bonding in 62, the short 7Dipp alkyl to metal distances in 64 and 65 are suitable for hydride-alkyl activation as a pathway for the solution state decomposition of 62 (and 64).

To further explore this theme, the IPr analogue of 62 was targeted. IPr provides a compromise between IMes and 7Dipp in terms of overall steric character and the likely

M-H···H-Calkyl distance and will, therefore, present with an intermediate stability to 62 and [InH3(IMes)]. It should be noted that Jones and co-workers have previously indicated that an IPr adduct of indane is of dramatically lower stability relative to its IMes cousin and could not be isolated in their hands.[23b]

Scheme 7.8 - Preparation of indane 66

The treatment of [LiInH4] with IPr in diethyl ether at -78 °C followed by slow warming to ambient temperature and recrystallisation from toluene affords [InH3(IPr)] (66) in high yield (77%, Scheme 7.8).

1 The H NMR spectrum of 66 (C6D6, 298 K) exhibits the expected IPr ligand resonances [23b] (cf. [AlH3(IPr)] ) and an additional broad hydride resonance at 5.05 ppm (½  60 Hz). The IR spectrum of 66 exhibits a broad In-H stretching absorbance at 1651 cm-1. -1 [3] These data are consistent with those of [InH3(IMes)] (5.20 ppm and 1640 cm ) and 62 vide supra. Indane 66 exhibits excellent thermal stability in the solid state (dec. 94 °C;

[InH3(IMes)] dec. 115 °C). It may be handled in solution at 0 °C without appreciable

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decomposition, however slow decomposition to the aminal IPr·HH[50] and 1 uncoordinated IPr in C6D6 at ambient temperature was observed by H NMR spectroscopy.

Colourless prisms of 66 suitable for X-ray structure determination were grown by cooling a 0 °C saturated toluene solution to -25 °C. Complex 66 crystallises in the triclinic space group P 1̅ with two unique molecules in its asymmetric unit. The molecular structure and Ω representation of one unique molecule of 66 are depicted in Figures 7.9 and 7.10 (pg. 272) respectively.

Figure 7.9 - Molecular structure of 66 (50% thermal ellipsoid plot and space fill representation with hydrides in green, NHC in grey and indium in pink). All hydrogen atoms excepting hydride ligands H(1)-H(3) have been omitted for clarity. Selected bond lengths (Å), angles (°) and steric parameters (values in braces refer to 2nd (B) unique molecule in the ASU): In(1A)-H(1) 1.49(6) {1.47(5)}, In(1A)-H(2) 1.75(6) {1.67(4)}, In(1A)-H(3) 1.72(5) {1.89(5)}, In(1A)-C(1A) 2.280(3) {2.260(3)}, C(1A)-N(1A) 1.338(4) {1.350(4)}, C(1A)-N(2A) 1.344(4) {1.353(4)}, H(1)-In(1A)-H(2) 116(3) {109(2)}, H(1)-In(1A)-H(3) 114(3) {119(2)}, H(2)-In(1A)-H(3) 117(3) {102(2)}, H(1)-In(1A)-C(1A) 98(2) {105.5(14)}, H(2)-In(1A)-C(1A) 105(2) {107(2)}, H(3)-In(1A)-C(1A) 103.2(18) {113.5(16)}, N(1A)-C(1A)-N(2A) 104.0(3) {104.3(2)},

In···Calkyl 4.030-4.888 Å.

271 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

Figure 7.10 - Solid angle representation of 66. Molecule A (left) and Molecule B

(right). Image generated using a 8 Å red sphere, IPr in blue, hydrides in green. GIn(IPr) (%) 40.88 {41.04}, GIn(all ligands) (%) 65.18 {66.97}, Gγ(ligand overlap) (%) 6.25 {4.66}.

The hydride ligands of 66 were located from difference maps and refined isotropically, it geometry is similar to that of other indane NHC complexes. The metal centres in 66 exhibit flattened tetrahedral environments, the In-H bond lengths (1.47(5)-1.89(5) Å) which although somewhat unreliable by X-ray methods, lie close to the range reported for

[InH3(PCy)3] (1.61-1.81 Å). The In-CNCN distances in 66 (2.280(3) and 2.260(3) Å) are [3] similar to that of [InH3(IMes)] (2.253(5) Å). With respect to the proximity of the IPr alkyl groups to the InH3 units of 66, it is noteworthy that in both molecules all of the C-H···H-In distances lie outside of the combined zero point radii of the elements.

A plot of the solid-state decomposition temperatures of the five structurally characterised indane complexes against their shortest In···Calkyl distance affords a near linear correlation (Table 7.4 and Figure 7.11, pg. 273). This is in keeping with Jones’ hypothesis that close C-H functions can facilitate indane decomposition.

272 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

Shortest Indane Complex Dec. (K) GIn(L) (%) Ref. In···Calkyl (Å)

i [InH3(I PrMe)] 268 3.511 24.52 [2]

t [(InH3)2(µ-I BuEt)] 283 3.545(2) 29.01 [23a]

[InH3(PCy3)] 323 3.645(2) 27.83 [19]

62 365 4.168(3)a 45.46a This work

66 367 4.030(3) 41.71 This work

[InH3(IMes)] 392 4.137(7) 34.92 [3]

Table 7.4 - Selected solid-state data for the known crystallographic characterised indane complexes and 62 and 66 a The structural data used is that of tribromide 65 as a model for 62. It is likely that 62 has shorter

In-H···H-Calkyl contacts than 66 due to the increased steric profile of 7Dipp vs IPr (Table 7.3).

400

350

dec. T = 155.99(In···C) - 265.9

R² = 0.91 Dec. (K) Dec. 300

250 3.45 3.55 3.65 3.75 3.85 3.95 4.05 4.15 4.25

Shortest In···C (Å) Figure 7.11 - Correlation between solid-state thermal stability of indane complexes and

their shortest In···Calkyl distance

Given the poor solution state stabilities of 62, 64 and 66, the preparation of the gallane congener of 66 was targeted. The gallane complex [GaH3(IPr)] (67) was previously reported,[23c] however no mention of the solution phase stability of 67 was made. In [23c] addition the reported crystal structure of 67 contains a DippNH2 contaminate, which renders the examination of Ga-H···H-Calkyl contacts moot.

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To this end, complex 67 was prepared using the same procedure as that used to prepare 1 64. Its H NMR spectrum (C6D6) exhibits the expected IPr resonances and a broad hydride resonance at 3.73 ppm which is comparable to that of [GaH3(IMes)] (3.96 ppm).[3] The IR spectrum of 67 displays a broad Ga-H stretching absorbance at 1800 cm-1 which is comparable to that of 64 (1798 cm-1). In contrast to the aforementioned metallanes, saturated solutions of 67 (C6D6) exhibit no evidence of decomposition over a two week period as determined by 1H NMR spectroscopy. Colourless blocks of 67 suitable for X-ray structure determination were grown by slow cooling a room temperature saturated toluene solution to -25 °C. Complex 66 crystallises in the monoclinic space group P21/c with a single monomer in its asymmetric unit. The molecular structure of 67 can be found in the appendix.

As gallane complex 67 demonstrates enhanced solution state stability relative to 66 in marked contrast to gallane 64 and indane 62, the solution state decomposition of 66 was further probed. An investigation of the solution stability of 66 at room temperature (1H

NMR spectroscopy, C6D6) reveals that its decomposition occurs in two distinct stages (Figures 7.12 and 7.13, pg. 275). The first stage comprises the initial slow formation of the aminal IPr·HH.[50] This stage is followed by a second stage that is characterised by the rapid liberation of uncoordinated IPr concurrent to the deposition of an indium mirror. The first stage is consistent with observations made during studies of the solution phase decomposition profile of 62, whilst the latter stage is consistent with some of the indium metal catalysed indane decompositions reported by Jones.[3] The [47] generation of H2 (4.47 ppm) accompanies both stages of the decomposition.

Figure 7.12 - Solution state IPr containing decomposition products of 66 in C6D6

274 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

100

[Indium Metal 80 Present]

InH3(IPr) 66 60 [No Indium] IPr 40 IPr·HH

20 % % Compound Present

0 0 1 2 3 4 Time/Days

Figure 7.13 - Decomposition profile of 66 in solution

Quantitative monitoring of the decomposition process of 66 at high and low concentrations7 during the early phase of stage one (Figure 7.14) affords data that is consistent with a (first order) unimolecular process and poorly correlates with a second order evaluation (R2 = 0.98 and 0.97).

-4 0 200 400 600 800 1000 -4.2 higher concentration of 66 -4.4 ln[66]t = -0.0001k + ln[66]o R² = 0.98

-4.6

t

-4.8 In[66] -5 ln[66]t = -0.0001k + ln[66]o R² = 0.97 -5.2 lower concentration of 66 -5.4

-5.6

Time Elapsed/minutes

Figure 7.14 - Kinetic study of the first stage of the decomposition of 66 in C6D6

7 Decomposition monitored by 1H NMR spectroscopy. The relative quantities of 66, IPr·HH and IPr were calculated employing the integrals of the “IPr” 4,5-NCH singlets at δ = 6.52, 5.62[50] and 6.57[51] ppm respectively. 275 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

This is consistent with an intramolecular decomposition pathway such as alkyl C-H activation by the InH3 moiety leading to H2 elimination and the formation of a metallacycle (Scheme 7.9). It is conceivable that such an event would be followed by reductive alkane elimination to afford a low oxidation state indium hydride (Scheme 7.9). Precedent for these mechanistic steps can be found in the cyclometallation of IPr on platinum(II),[52] the formation of low oxidation state indium hydrides in matrix isolation studies,[53] and the isolation of NHC supported indium(II) complexes from indium(I) halide reactions.[54]

Scheme 7.9 - A predicted route for the first stage of the decomposition of 66

The trideuteride [InD3(IPr)] (68) (Scheme 7.8, LiInD4 as precursor) was prepared to facilitate the further investigation of stage one of the decomposition of 66. Indane 68 provides a valuable means to investigate the degenerative role of the ligand in the decomposition of indanes 62 and 66, either by the indirect observation of indium deuteride C-H activation (viz. HD(g) elimination, Scheme 7.9) or the indirect observation of isopropyl group deuteration through loss of the 1H NMR resonance integral or direct observation through 2H NMR spectroscopy (reductive elimination of a deuterated alkane, Scheme 7.9). The latter can also be readily identified using 13C NMR spectroscopy.

Indane 68 characterises as per 66 with replacement of the broad 1H NMR trihydride resonance and In-H IR stretch of 66 with a broad 2H NMR trideuteride resonance 1 centred at 5.09 ppm (cf. InH3 66 H NMR 5.05 ppm) and an In-D IR stretch at 1181 cm-1. The latter is consistent with the reduced mass of InD relative to InH (calc. absorbance at 1177 cm-1).

276 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

The decomposition of 68 in C6D6 was studied over a period of three days at 298 K using the aforementioned spectroscopies. During this period the following observations were 1 1 made (Scheme 7.10): (i) HD gas is evolved ( H NMR 1:1:1 triplet at 4.43 ppm, JHD = 42.5 Hz), (ii) IPr·HD is the single aminal decomposition product (13C NMR 1:1:1 triplet 1 2 at 78.32 ppm, JCD = 23.1 Hz, H NMR 5.28 ppm br s), (iii) the IPr·HD formed is partially deuterated at the isopropyl methyl (2H NMR 1.28 ppm br s, cf. 1H NMR resonances of 66 1.05 and 1.42 ppm; IPr·HD 1.26 ppm), and (iv) an unidentified “IPr” containing intermediate exhibiting distinct resonances to those of IPr, IPr·HD and 68 is initially observed in 1H NMR spectra but depletes in resonance intensity within 24 h to be absent after 72 h. It should be noted that the low signal resolution of 2H NMR spectroscopy relative to 1H NMR spectroscopy would frustrate the direct observation of

D2 as a co-product (Scheme 7.10).

Scheme 7.10 - Actual decomposition outcome for 68

The exclusive generation of IPr·HD during the decomposition of 68 in C6D6 is consistent with a concerted pathway that combines IPr methyl proton abstraction (Scheme 7.9) and HD reduction of the IPr NCN carbon. Control experiments confirm that neither 66 nor IPr react directly with H2 to generate IPr·HH. Corollaries can be drawn between the generation of IPr·HD herein and the activation of H2 by NHC containing frustrated Lewis pairs (FLP)[55] as well as the group 13 hydride reduction of imidazolium salts to afford aminals (cf. preparation of 63).[56]

On the basis of these studies (of 66 and 68) it can be concluded that 66, and by extension 62, decomposes through two distinct pathways; (I) ligand mediated H2 elimination and (II) indium catalysed ligand dissociation accompanied by H2 elimination. Thus, in addition to the steric frustration of In-H-In bridging and electronic stabilisation of indane complexes using a strong donor, a further strategy for the stabilisation of indane complexes is to minimise alkyl functions proximate to the coordinated InH3 unit. To apply these strategies, a bulky NHC devoid of readily

277 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

available alkyl functions was sought. One prime example is IPr* (Figure 7.2) which exhibits substantially greater steric bulk than the indane supports used thus far [36] (GAg(IPr*) = 59.53%, Table 7.3). The longest M-C bond length exhibited by the 19 [46] reported metal complexes of IPr* is 2.13(1) Å in [RuCl2(PPh3)(IPr*)=Ind] (Ind = 3-phenylinden-1-ylidene),[39f] which is substantially shorter than the In-C bond of 66 (2.280(3) Å). Thus it is conservatively estimated that the indium to methine distances of

[InH3(IPr*)] will be greater than the ruthenium to methine distances in

[RuCl2(PPh3)(IPr*)=Ind] (4.311(9) to 5.11(1) Å), which in turn are substantially longer [4c] than the shortest In···Calkyl distance in [InH3(IMes)] (4.137(7) Å).

Under conditions akin to those used to prepare 66, [InH3(IPr*)] (69) was prepared in moderate yield (58%) from the direct reaction of IPr* with [LiInH4]. Indane 69 exhibits a broad hydride resonance in its 1H NMR spectrum that is substantially downfield [3] relative to those of [InH3(IMes)] and 66 (5.68 ppm, [InH3(IMes)] 5.20 ppm, 66 5.05 ppm). This is accompanied by a noticeable red shift in its IR In-H stretching frequency -1 -1 [3] -1 (1633 cm , [InH3(IMes)] 1640 cm , 66 1651 cm ) and an unusually downfield NCN 13C NMR resonance (182.6 ppm, 66 150.0 ppm). Crystalline 69 is stable to air for an indefinite period and decomposes at 182 °C under argon. Microcrystalline 69 exhibits reduced but impressive stability. For example, open storage with a silica drying tube leads to < 3% decomposition over two weeks, while exposure to air without a desiccant leads to < 10% decomposition over five days (monitoring by 1H NMR spectroscopy). The IPr* containing product of both processes is the IPr*·HH aminal (70).

The solution behaviour of 69 is also remarkable. It may be handled at ambient temperature in dry degassed toluene or diethyl ether without decomposition and undergoes slow decomposition over a six day period as a saturated solution in C6D6 (298 K, sealed NMR tube cf. first order decomposition of 66 and 68) affording small quantities of 70 and IPr* (Figure 7.15, pg. 279).8 The latter is in agreement with the decomposition profile of 66. Notably, the rate of decomposition increases upon deposition of indium metal leading to a marked shift from 70 to IPr* as the primary product of decomposition (cf. stage two for 66, Figure 7.15).

8 Decomposition monitored by 1H NMR spectroscopy. The relative quantities of 69, IPr*·HH and IPr* were calculated employing the integrals of the “IPr*” 4,5-NCH singlets at δ = 5.30, 5.71 and 5.78[39a] ppm respectively. 278 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

100

[Indium Metal Present] 80

[InH3(IPr*)] (69) 60 [No Indium] 40 IPr*·HH (70) IPr*

20 % % Compound Present

0 0 1 2 3 4 5 6 Time/Days

Figure 7.15 - Decomposition profile of 69 as a saturated solution

Variable temperature NMR studies indicate that dilute solutions of 69 are stable up to temperatures approaching the boiling point of C6D6 (b.p. 79 °C), however saturated solutions decompose rapidly upon standing at 75 °C, with total decomposition over several hours to yield free IPr* and 70 in a 4:1 ratio. This is consistent with the acceleration of stage two type NHC dissociation. Thus, the solution phase decomposition profile of 69 is similar to that of 66. The decreased rate of decomposition of 69 at ambient temperature in solution relative to 66 is representative of a more substantial barrier to access suitable C-H moiety for activation (cf. Scheme 7.9).

Colourless prisms of 69 suitable for X-ray structure determination were grown over five days from a room temperature toluene solution layered with pentane. Complex 69 crystallises in the monoclinic space group P21/n. The molecular structure and Ω representation of 69 are depicted in Figures 7.16 and 7.17 (pg. 280) respectively.

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Figure 7.16 - Molecular structure of 69 (50% thermal ellipsoid plot and space fill representation with hydrides in green, NHC in grey and indium in pink). All hydrogen atoms excepting hydride ligands H(1)-H(3) omitted and phenyl groups depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and steric parameters for 69: In(1)-H(1) 1.80(4), In(1)-H(2) 1.68(4), In(1)-H(3) 1.67(4), In(1)-C(1) 2.276(2), C(1)-N(1) 1.355(3), C(1)-N(2) 1.392(3), H(1)-In(1)-H(2) 114.3(19), H(1)-In(1)-H(3) 111(2), H(2)-In(1)-H(3) 122(2), H(1)-In(1)-C(1) 101.6(13), H(2)-In(1)-C(1) 105.2(15),

H(3)-In(1)-C(1) 98.5(15), N(1)-C(1)-N(2) 104.31(18), In···Calkyl 4.216(3)-4.682(2) Å.

Figure 7.17 - Solid angle representation of 69. Image generated using a 8 Å red sphere,

IPr* in blue, hydrides in green. GIn(IPr*) (%) 52.69, GIn(all ligands) (%) 72.60, Gγ(all ligands) (%) 8.39.

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The geometry of 69 is similar to that of 66. The hydride ligands were located from difference maps and refined isotropically. The metal centre in 69 has a flattened tetrahedral environment with the In-H bond lengths (1.67-1.80 Å) lying in the normal range (viz. 66 1.47-1.89 Å). The In-CNCN distance in 69 (2.276(2) Å) is in accord with those of 66 (2.280(3) and 2.260(3) Å) and [InH3(IMes)] (2.253(5) Å). The

In-H···H-Calkyl distances range from 2.865 to 4.570 Å, with the closest In···Calkyl distance being 4.216 Å, which is greater than those observed in [InH3(IMes)] (shortest distance 4.137(7) Å, Table 7.4)[3] and consistent with the enhanced thermal stability of 69 (Figure 7.11).

The gallane analogue of 69; [GaH3(IPr*)] (71) was also prepared using the same procedure as that used to prepare 69 replacing [LiInH4] with [LiGaH4] (Scheme 7.8). Its 1 H NMR spectrum (C6D6) exhibits the expected resonances and a broad hydride 69 71 3 resonance (Δν½ ≈ 10 Hz, Ga/ Ga; I = /2) at 4.44 ppm which lies downfield relative to that of 64 (3.27 ppm). The IR spectrum of 71 displays a broad Ga-H stretching absorbance at 1790 cm-1. The frequency of this absorbance is consistent with those of 64 (1798 cm-1) and 68 (1800 cm-1). Crystalline 71 displays exceptional thermal stability in the solid-state (dec. 226 °C) and can be handled in air for fourteen days with no evidence of decomposition, as determined by 1H NMR spectroscopy. Saturated solutions of 71 (C6D6) also exhibit no evidence of decomposition over a period of one month as determined by 1H NMR spectroscopy.

Colourless plates of 71 suitable for X-ray diffraction structure determination were grown by cooling a saturated room temperature toluene solution to -25 °C. Complex 71 crystallises in the triclinic space group P1̅ with a molecule of toluene in the asymmetric unit. The molecular structure of 71 can be found in the appendix.

The excellent solid-state and solution stabilities of 69 and 71, lead to the investigation of IPr* as a stabilising ligand for thallane (TlH3). As [LiTlH4] is unknown a halide- hydride exchange route (viz. Chapter Six) was devised. The thallium trichloride precursor [TlCl3(IPr*)] (72) was prepared in moderate yield (49%) from the reaction of anhydrous TlCl3 with IPr* in THF (Scheme 7.11, pg. 282). Complex 75 is poorly soluble in toluene but exhibits good solubility in THF and dichloromethane.

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Scheme 7.11 - Preparation of 72

The 1H and 13C NMR spectra of 72 display the expected resonances with exception of the 13C NMR resonance of the carbenic carbon. It is conceivable that the poor solubility 13 of 72 in C6D6 and coupling of the carbenic carbon C resonance to the spin active thallium (203Tl/205Tl, I = ½) frustrate the observation of this signal. It is noteworthy that 3 the 4,5-carbons of the IPr* heterocycle couple to thallium ( JTlC = 195 Hz) and that this [57] coupling constant is comparable to that reported for [TlCl3(IMes)] (221 Hz). The 1 4 4,5-proton H NMR resonance is also coupled to the thallium ( JTlH = 80 Hz, [57] [TlCl3(IMes)] 89 Hz).

Colourless prisms of 72 suitable for X-ray diffraction structure determination were grown at room temperature from a saturated THF solution layered with hexane over three days. Complex 75 crystallises in the monoclinic space group P21/n with a single molecule in the asymmetric unit. Its molecular structure and salient bonding parameters are listed in Figure 7.18 (pg. 283).

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Figure 7.18 - Molecular structure of 72 (50% thermal ellipsoid plot). All hydrogen atoms omitted and phenyl groups depicted as wireframes for clarity. Selected bond lengths (Å), angles (°) and steric parameters: Tl(1)-Cl(1) 2.4036(17), Tl(1)-Cl(2) 2.4105(14), Tl(1)-Cl(3) 2.4200(18), Tl(1)-C(1) 2.224(5), C(1)-N(1) 1.348(6), C(1)-N(2) 1.343(6), Cl(1)-Tl(1)-Cl(2) 103.31(7), Cl(1)-Tl(1)-Cl(3) 105.61(8), Cl(2)-Tl(1)-Cl(3) 105.39(6), Cl(1)-Tl(1)-C(1) 115.09(15), Cl(2)-Tl(1)-C(1) 117.76(13), Cl(3)-Tl(1)-C(1)

108.74(14), N(1)-C(1)-N(2) 106.7(4), Tl···Calkyl 4.267-4.690 Å, GTl(IPr*) (%) 48.77, GTl(all ligands) (%) 81.28, Gγ(all ligands) (%) 5.26.

Complex 72 is monomeric in the solid-state. The thallium centre sits in a flattened tetrahedral environment (mean C(1)-Tl-Cl 113.9°, mean Cl-Tl-Cl 104.8°) with three similar Tl-Cl bond lengths. The Tl-CNCN distance (2.224(5) Å) is longer than that [58] observed for [TlCl3(IMes)] (2.179(9) Å), presumably due to increased steric congestion in the former. The steric congestion afforded by the chlorides leads to the

IPr* in 72 being significantly less sterically demanding than in 69 (GM(IPr*) = 48.77 and 52.69% respectively).

The preparation of [TlH3(IPr*)] was attempted through the treatment of a toluene slurry of 72 with three equivalents of [NaBEt3H] in toluene at -78 °C. This led to the immediate formation of thallium metal, IPr* and aminal 70. This outcome is indicates that a reaction occurs and that the resultant product exhibits considerable instability in solution. The instability of the product may arise because (i) the increased ionic radius of thallium relative to indium (In3+ 0.800 Å, Tl3+ 0.880 Å)[59] accelerates the decomposition of “[TlH3(IPr*)]” by the same pathways observed for 66, (ii) thallane

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demonstrates such poor stability in solution such that even IPr* cannot stabilise it, (iii)

[TlH3(IPr*)] spontaneously eliminates “TlH(IPr*)” which subsequently decomposes, or (iv) the borohydride reagent initially reduces the IPr* of 72 to the aminal 70 after its dissociation from thallium then the remaining borohydride reacts with the uncoordinated TlCl3 leading to immediate decomposition of free TlH3 or a chlorohydride derivative thereof.

7.3.3 Preliminary Studies of the Reactivity of the Indane and Gallane Complexes Developed Herein with Group 6 Carbonyls

Transition metal σ-complexes containing M-H-E (M = transition metal, E = B, Al, Ga) σ-interactions (Figure 7.19) have received considerable recent interest as they represent key intermediates in the transition metal catalysed reductive dehydrogenation of boranes and the lighter group 13 metallanes.[60] The mechanism of reductive dehydrogenation for the heavier metals of group 13 has received far less attention.

Figure 7.19 - Bonding model for E-H σ-complexes[61]

1 [62] The first σ-gallane complex, [W(CO)5(κ -H3Ga·Quin)], was reported in 2002. This complex was prepared through the photochemical reaction of [W(CO)6] and

[GaH3(Quin)] in <40% yield (Scheme 7.12, left, pg. 285), and found to decompose readily to hydrogen, quinuclidine and a black deposit at ambient temperature.[62] More 2 2 recently κ -σ-gallane complexes of the form [M(CO)4(κ -H3Ga·RENHC)] (M = Mo and Cr, RENHC = 6Mes and 6Dipp) have been prepared through the reaction of [63] [M(CO)4(cod)] with [GaH3(RENHC)] (Scheme 7.12, right). There are no reported σ-indane complexes.

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Scheme 7.12 - Preparation of σ-gallane complexes

Given the robust stability of 69 (vide supra) an investigation of its coordination chemistry was undertaken. Equimolar quantities of 69 and [W(CO)6] (C6D6 solution) were irradiated (300 W Hg lamp) for five minutes at ambient temperature. During this period the colour of solution changed from colourless to pale yellow. The 1H NMR spectrum of the resultant mixture exhibits a new set of IPr* resonances and an additional upfield broad triplet (J = 13.4 Hz) resonance at -5.82 ppm (cf. 69 InH3 5.68 ppm). The chemical shift and coupling constant of this resonance are consistent with 1 1 those of the Ga-H-W H NMR resonance of [W(CO)5(κ -H3Ga·Quin)] (-7.32 ppm, 2 [62] 1 triplet, JHH = 12 Hz). The non-bridging In-H H NMR resonance is located under the aryl resonances (ca. 7.05 ppm), as determined using a 1H-1H COSY NMR experiment. The downfield shift of the terminal M-H resonance is consistent with that of 1 [7] [W(CO)5(κ -H3Ga·Quin)] (5.51 ppm, GaH3(Quin) 4.80 ppm ) and almost certainly arises due to the greater electropositivity of the metal once σ-coordinated. The IR spectrum of the vacuum dried reaction mixture exhibits two intense carbonyl stretching absorptions at 1980 and 1934 cm-1 which are also consistent with those of 1 -1 [62] [W(CO)5(κ -H3Ga·Quin)] (1998 and 1948 cm ). A blue shifted In-H stretching absorption is also displayed in the IR spectrum (1667 cm-1, 69 1633 cm-1), which is similarly consistent with greater electropositivity at the indium. These data lead to the 1 tentative assignment of this complex as [W(CO)5(κ -H3In·IPr*)] (73) (Scheme 7.13, pg. 286).

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Scheme 7.13 - Preparation of a σ-indane complex

Attempts to prepare the κ2 analogue of 73 by further irradiation (1 h, ambient temperature) resulted in indane decomposition as evidenced by the formation of an indium mirror on the walls of the reaction vessel (cf. thermal stability of 1 [62] [W(CO)5(κ -H3Ga·Quin)]). The major IPr* containing decomposition product is the aminal 70 with trace amounts of uncoordinated IPr* (1H NMR spectroscopy). This decomposition may arise through a tungsten mediated reductive dehydrogenation from 2 the “short-lived” [W(CO)4(κ -H3In·IPr*)], which is consistent with the theorised decomposition pathway of the uncoordinated heavy group 13 metallanes. To further evaluate this theory the synthesis of an analogous κ2-σ-gallane was targeted. Irradiation

(five minutes, 298 K) of equimolar quantities of the gallane 71 and [W(CO)6] (C6D6 solution) results in a colour change from colourless to pale yellow. The 1H and 1H-1H COSY NMR spectra of this mixture locate a bridging hydride resonance at -6.68 ppm 2 2 (triplet, JHH = 10.9 Hz) and a terminal hydride resonance at 5.54 ppm (doublet, JHH =

10.9 Hz; 71: GaH3 4.44 ppm, 73: ~7.05 ppm, 69: 5.68 ppm), with relative intensities of 1 1:2. These spectroscopic studies lead to the tentative assignment [W(CO)5(κ -

H3Ga·IPr*)] (74) (Scheme 7.14, pg. 287). Further irradiation (40 minutes, C6D6 solution, 298 K) affords a deep yellow solution. The 1H and 1H-1H COSY NMR spectra 2 of this mixture indicate a bridging hydride resonance at -4.86 ppm (doublet, JHH = 11.5 2 Hz) and a terminal hydride resonance at 8.26 ppm (broad triplet, JHH = 11.5 Hz) in a 2:1 integral ratio. The multiplicities of these resonances lead to the tentative assignment 2 [W(CO)4(κ -H3Ga·IPr*)] (75) (Scheme 7.14).

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Scheme 7.14 - Preparation of σ-gallane complexes

1 Monitoring 75 by H NMR spectroscopy over 24 h reveals no H2 formation or metal deposition which contrasts the solution instability observed for its indane congener. It may therefore be concluded that the In-H bonds are sufficiently weak that tungsten mediated reductive dehydrogenation occurs readily, proceeding through a κ2-σ-indane transition state, and that decomposition of the resultant “InH(IPr*)” species is rapid, affording 70, indium metal and H2 (Scheme 7.15, cf. thermal stability of 1 [62] [W(CO)5(κ -H3Ga·Quin)]). It is noteworthy that the latter step is consistent with the proposed stage one solution state decomposition of indane 66 (Scheme 7.9).

Scheme 7.15 - A predicted route for the photochemical decomposition of 73 through a κ2-σ-indane transition state

To further investigate this theme the reaction of [InH3(IPr)] 66 and [Mo(CO)4(cod)] was undertaken. [Mo(CO)4(cod)] was chosen as it functions as a facile source of “Mo(CO)4” thus eliminating any photochemical indane decomposition pathways.

The equimolar treatment of [InH3(IPr)] 66 with [Mo(CO)4(cod)] in toluene at ambient temperature results in immediate gas evolution accompanied by a change in colour from colourless to yellow with the concurrent deposition of indium metal. The 1H NMR spectrum of the vacuum dried filtrate exhibits resonances consistent with those of [50] IPr·HH (vide supra). This outcome is comparable to the W(CO)n mediated

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1 decomposition of 69 upon progression from [W(CO)5(κ -H3In·IPr*)] 73 to 2 [W(CO)4(κ -H3In·IPr*)].

The treatment of gallane 67 with [Mo(CO)4(cod)] in C6D6 at ambient temperature affords a pale yellow solution (Scheme 7.16). A 1H NMR spectrum of a reaction aliquot collected ten minutes after mixing displays an upfield doublet resonance at -5.04 ppm (J = 10.6 Hz). The chemical shift, multiplicity and coupling constant are consistent with 2 those of the Ga-H-Mo resonance of [Mo(CO)4(κ -H3Ga·6Dipp)] (-5.62 ppm, doublet, 2 [63] JHH = 10.5 Hz, spectrum recorded in o-F2C6H4). This leads to the tentative 2 assignment of the product herein as [Mo(CO)4(κ -H3Ga·IPr)] (76). The terminal Ga-H resonance could not be located and is assumed to be obscured by the aromatic region.

Scheme 7.16 - Preparation of a κ2-σ-gallane complex

Upon standing the reaction mixture above afforded pale yellow plates of 76 suitable for X-ray diffraction structure determination. Complex 76 crystallises in the triclinic space group P1̅ with a molecule of C6D6 in the asymmetric unit. The molecular structure of 76 and salient bonding parameters are listed in Figure 7.20 (pg. 289).

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Figure 7.20 - Molecular structure of 76 (50% thermal ellipsoid plot). All hydrogen atoms excepting hydrides H(1)-H(3) omitted and Dipp groups depicted as wireframes for clarity. Selected bond lengths (Å) and angles (°): Ga(1)-C(5) 2.003(10), Ga(1)-H(1) 1.836, Ga(1)-H(2) 1.722, Ga(1)-H(3) 1.363, Ga(1)···Mo(1) 2.5939(15), Mo(1)-C(1) 2.033(11), Mo(1)-C(2) 1.963(13), Mo(1)-C(3) 1.979(10), Mo(1)-C(4) 2.029(11), C(1)-O(1) 1.146(11), C(2)-O(2) 1.152(12), C(3)-O(3) 1.138(11), C(4)-O(4) 1.138(11), C(5)-Ga(1)-Mo(1) 122.5(2).

2 [63] Complex 76 is isomorphous to its alane congener [Mo(CO)4(κ -H3Al·IPr)]. The hydride ligands were located from difference maps and refined isotropically. The 2 Ga···Mo distance (2.5939(15) Å) is comparable to those of [Mo(CO)4(κ -H3Al·IPr)] 2 [63] and [Mo(CO)4(κ -H3Ga·6Dipp)] (2.581(1) and 2.594(1) Å respectively). The

Ga-CNHC bond length in 76 (2.003(10) Å) is contracted relative to that of 67 (2.0652(19) Å). This likely reflects the increased electrophilicity of the gallium in 76. The Mo-C bond length for the carbonyl ligands trans to the Ga-H σ-donor (1.963(13) and 1.979(10) Å) are shorter than those for the cis carbonyls (2.033(11) and 2.029(11) Å). A 2 similar shortening has been observed in [Mo(CO)4(κ -H3Al·IPr)] and 2 [Mo(CO)4(κ -H3Ga·6Dipp)], reflecting the weaker π-acceptor character of the M-H σ-bonds relative to carbon monoxide.[63]

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[3] As [InH3(IMes)] is known to exhibit superior solution state stability relative to 66, an 1 in situ H NMR study of the reaction of [InH3(IMes)] with [Mo(CO)4(cod)] was proposed. The addition of C6D6 to a mixture of [InH3(IMes)] and [Mo(CO)4(cod)] results in a rapid colour change to a pale yellow solution from colourless accompanied by gas evolution. Initial 1H NMR spectra exhibit two high field singlet resonances [47] at -4.49 ppm and -3.76 ppm, and a resonance at 4.47 ppm corresponding to H2. The former high field resonance is very broad (½  35 Hz) whilst the latter is relatively sharp (½  5 Hz). The chemical shifts of these resonances suggest that the n elimination of H2 may proceed through a κ -σ-indane transition state. To further explore this theme, treatment of [InH3(IMes)] with an equimolar amount [Mo(CO)4(cod)] in toluene at -20 °C affords a pale yellow solution with steady gas evolution. Thin yellow plates were obtained upon standing the solution at -25 °C for 24 h. Although of poor quality, X-ray diffraction data collections on several of the crystals allowed the underlying connectivity of the product (77) to be established. The molecular structure of 77 and salient metrical data are given in Figure 7.21 (pg. 291). Complex 77 crystallises in the triclinic space group P1̅ with a highly disordered full molecule of toluene in the asymmetric unit.

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Figure 7.21 - Molecular structure of 77 (10% RvdW), view normal to the In(1)-Mo(1)-In(2) plane (left) and view normal to the In(1)-In(2) vector (right) showing anti arrangement of the IMes ligands. All hydrogen atoms omitted and mesityl groups depicted as wireframes for clarity. Selected bond lengths (Å) and angles (°): In(1)-In(2) 2.895(2), In(1)-Mo(1) 2.909(3), In(2)-Mo(1) 2.850(3), In(1)-C(5) 2.26(2), In(2)-C(26) 2.24(3), Mo(1)-C(1) 2.05(3), Mo(1)-C(2) 1.92(4), Mo(1)-C(3) 1.98(2), Mo(1)-C(4) 2.02(3), C(1)-O(1) 1.11(3), C(2)-O(2) 1.19(4), C(3)-O(3) 1.12(2), C(4)-O(4) 1.15(3), In(1)-Mo(1)-In(2) 60.34(7), C(5)-In(1)-In(2) 113.8(5), C(5)-In(1)-Mo(1) 115.3(6), C(26)-In(2)-In(1) 113.0(5), C(26)-In(2)-Mo(1) 121.4(6), C(2)-Mo(1)-In(2) 173.7(13), C(3)-Mo(1)-In(1) 147.1(7), C(1)-Mo(1)-C(4) 177.9(11).

The molecular structure of 77 contains an In2IMes2 unit bridged by a Mo(CO)4 moiety. The length of the In-In interaction (2.895(2) Å) is significantly longer than that of the [54] indium(II) NHC complex [{InBr2(IMes)}2] (2.7436(7) Å). The IMes ligands lie in an anti configuration which is evidenced by a CIMes-In(1)-In(2)-CIMes torsion angle of 140° [54] (Figure 7.21, right). This is similarly observed in [{InBr2(IMes)}2] (166°). The

In-CIMes bond lengths (2.26(2) and 2.24(3) Å) are consistent with those of [54] [3] [{InBr2(IMes)}2] (2.267(5) and 2.252(6) Å) and [InH3(IMes)] (2.253(5) Å). The lengths of the In-Mo interactions (2.909(3) and 2.850(3) Å) are significantly longer than t those of [{In(μ-O Bu)3Sn(Cr{CO}5)}2(μ-Mo{CO}4)] (2.705 and 2.714 Å) which [64] displays a similar cis-[Mo(CO)4(InRn)2] subunit. The Mo-CCO bonds range 1.92(4) to 2.05(3) without any clear difference between those CO groups cis or trans to the

In2IMes2 subunit. Unfortunately, no hydride ligands could be located from the difference maps, however, the IR spectrum of 77 exhibits an absorbance at 1678 cm-1

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-1 -1 [3] which is consistent with an In-H stretch (cf. [InH3(IMes)] 1640 cm , 73 1667 cm ). The IR spectrum also exhibits sharp carbonyl stretches at 2002 and 1982 cm-1.

Subhydrides of indium have been characterised in argon matrices.[53a-c] Both the hydride bridged isomer of In2H2; In(μ-H)2In, and the anti-bent isomer; H-In-In-H are known (Figure 7.22).[53b,c] Both structures have been established theoretically at the B3PW91 level of theory. The calculated In···In contacts for the isomers are 3.4082 Å, for the hydride bridged, and 3.0596 Å for the anti-bent geometry and the observed IR In-H stretch for the latter is 1518 cm-1.[53c] In light of the ready elimination of indium metal from the equimolar reaction of [Mo(CO)4(cod)] with 66, and the postulated decomposition of 73 upon formulation of its κ2 tetracarbonyl cousin, it is reasonable to suppose that 77 (In-In 2.895(2) Å, In-H 1678 cm-1) represents a trapped form of the indium(I) hydride eliminated upon reductive dehydrogenation of [InH3(IMes)].

Figure 7.22 - Known isomers of In2H2, hydride bridged (left) and anti-bent (right)

The potential formation of indium(I) hydride and subsequent isolation of 77 are consistent with the dimerisation of the by-product of reductive dehydrogenation at the indium centres of 66 and 69 (viz. Scheme 7.9). It is apparent, therefore, that κ2-σ-indane complexes of the tetracarbonyls of molybdenum and tungsten are heavily disfavoured relative to reductive dehydrogenation, and that future studies in this area should focus on the use of substoichiometric quantities (cf. 2:1 ratio of In:Mo in 77) of the lighter group 6 metal carbonyls.

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7.4 Conclusions

The low steric bulk of IMe leads to an alane complex (61) with poor solid-state thermal stability relative to other more bulky NHC alane complexes. This result demonstrates the impact of the stabilising ligand’s electronic character is very much of secondary importance to the ligand’s steric profile.

The greater steric bulk and increased ligand donicity of 7Dipp do not lead to a gain in thermal stability for gallane and indane complexes. Solution phase studies of the decomposition of 62 by 1H NMR spectroscopy, and observations made regarding the diminished stability of 64 in solution, have identified aminal 63 as the principal ligand derived decomposition product in addition to H2 and indium metal. The short distances between the hydride (or bromide) ligands and 7Dipp alkyl functions in 64 (and 65) support the viability of a hydride alkyl-activation decomposition pathway.

The indane 66 was prepared due to the intermediate steric steric bulk of IPr to IMes and 7Dipp. Indane 66 displays excellent solid-state stability; however it decomposes in solution at ambient temperature over a number of days. A spectroscopic study of the decomposition of 66 revealed a two stage decomposition profile. Deuteration studies confirm that stage one of the decomposition is unimolecular and ligand mediated. This initiates a second decomposition stage that is catalysed by indium metal. The outcomes of this study prompted the synthesis of the indane complex, 69, which exhibits unparalleled solution and solid state stability such that it is the first air stable indane reported. The gallane analogue, 71, was also prepared and likewise exhibits exceptional solid-state and solution stability. Success in this area invited the attempted synthesis of a thallane complex through halide-hydride exchange reaction at complex 72. Unfortunately, the product of this reaction is unstable and rapidly decomposes to afford thallium metal, IPr* and IPr*·HH (70).

The exceptional solution state stability of 69 invited an investigation of its reactivity with coordinatively unsaturated group 6 carbonyls. UV irradiation of a mixture of 69 1 and [W(CO)6] affords the σ-complex, [W(CO)5(κ -H3In·IPr*)] (73). An attempt to prepare a κ2-σ-complex by further irradiation results in indium metal deposition and the 1 isolation of 70. By contrast, further irradiation of [W(CO)5(κ -H3Ga·IPr*)] (74) affords 2 [W(CO)4(κ -H3Ga·IPr*)] (75). [Mo(CO)4(cod)] was investigated as a facile, non-photoactivated, source of “Mo(CO)4”. However, the reaction of [Mo(CO)4(cod)]

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with indane 66 affords indium metal, H2 and IPr·HH. The reaction of gallane (67) with 2 1 [Mo(CO)4(cod)] affords [Mo(CO)4(κ -H3Ga·IPr)] (76) as a stable crystalline solid. A H

NMR spectroscopic study of the reaction of [InH3(IMes)] and [Mo(CO)4(cod)] reveals that group six mediated reductive dehydrogenation of indanes likely proceeds through a κ2-σ-transition state. Repeating this reaction on a preparative scale affords complex 77 which contains an In2IMes2 unit bridged by a Mo(CO)4 moiety. IR spectroscopy confirms the presence of a hydride ligand, which indicates complex 77 could be a

Mo(CO)4 trapped In2H2 coordinated by IMes. This complex supports the assumption that the reductive dehydrogenation of NHC indane complexes affords NHC complexes of indium(I) hydride as transient products in the decomposition pathway.

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7.5 Future Directions

The aforementioned preliminary studies invite considerable further development. To this end, protocols which enable an indane complex to be continuously irradiated with UV light while in the NMR spectrometer and at low temperature have been developed at the University of New South Wales.[65] These protocols have been used to study transition metal-alkane σ-complexes by 1H NMR spectroscopy,[66] and therefore may enable further insight into the mechanism of the group 6 carbonyl mediated reductive dehydrogenation of indanes reported herein.

Dipp The group 6 carbonyl mediated reductive dehydrogenation of [GaH2( nacnac)] has [63,67] Dipp been reported previously (cf. Section 6.1.4). The reaction of [GaH2( nacnac)] with [M(CO)4(cod)] (M = Mo, W) affords the sub-valent carbenoid complexes Dipp [67] [M(CO)5(Ga{ nacnac})], by contrast the analogous reaction with [Cr(CO)4(cod)] Dipp affords a mixture of [Cr(CO)5(Ga{ nacnac})] and the σ-complex 2 Dipp [63] 2 [Cr(CO)4(κ -H2Ga{ nacnac})]. To this end, chromium κ -σ-indane complexes may exhibit greater stabilities than the molybdenum and tungsten systems studied herein.

The isolation of a low oxidation state indium hydride from the reaction [InH3(IMes)] and [Mo(CO)4(cod)] at low temperature, invites the analogous reactivities of 66 and 69 with [Mo(CO)4(cod)] at low temperature to be explored. These may also afford analogous NHC coordinated In2H2 units.

The addition of NHCs to commercially available indium(I) halides results in disproportionation and the isolation of dimeric indium(II) NHC complexes.[54] Coordinatively unsaturated group 6 carbonyls could also be used to trap NHC complexes of indium(I) halides.

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7.6 Experimental

7.6.1 General Synthetic Procedures

[40] [68] [69] [39a] [70] [71] 7Dipp·HBr, [LiGaH4], IPr·HCl, IPr*, TlCl3 and [Mo(CO)4(cod)] were synthesised by literature procedures. 7Dipp and IPr were prepared by the addition of nBuLi (1.0 equiv.) to 7Dipp·HBr and IPr·HCl (1.0 equiv., respectively) in THF, followed by recrystallised from toluene. [LiInH4] was prepared by the method previously detailed (Chapter Six). [LiInD4] was prepared as per [LiInH4] using LiD instead of LiH. [NaBEt3H] (1.0 M in toluene) was purchased from Sigma-Aldrich and decanted into a J. Youngs tapped flask under argon. [W(CO)6] was sublimed prior to use.

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

7.6.2 Synthesis of [AlH3(IMe)] (61)

A solution of IMe (420 mg, 4.30 mmol) in diethyl ether (40 mL) was added at ambient temperature to a solution of [LiAlH4] (163 mg, 4.30 mmol) in diethyl ether (20 mL). After 6 h, the resultant pale yellow solution was isolated by filtration. Concentration of the solution to ca. 20 mL and subsequent cooling to -25 °C overnight afforded large 1 colourless needles of 61 (145 mg, 30%), m.p. 124 °C (dec.). H NMR (400 MHz, C6D6) 13 δ 3.14 (s, 6H, CH3), 5.78 (s, 2H, NCH). C NMR (100 MHz, C6D6) 36.4 (CH3), 121.6 (NCH). IR (Nujol, cm-1) 1728 (br w, Al-H).

7.6.3 Synthesis of [InH3(7Dipp)] (62)

A cold (-30 °C) slurry of 7Dipp (200 mg, 0.48 mmol) in diethyl ether (40 mL) was added to a cold (-30 °C) suspension of [InH3(PCy3)] (180 mg, 0.45 mmol) in diethyl ether (15 mL) with continuous stirring. After 2 hours at -30 °C the colourless solid was isolated by filtration and washed with cold (-20 °C) diethyl ether (2×5 mL), which 1 afforded analytically pure [InH3(7Dipp)] (170 mg, 71%), dec. 92 °C. H NMR (500 3 MHz, C6D5CD3, 248 K) δ 1.18 (d, JHH = 6.7 Hz, 12H, CH3), 1.57-1.70 (br m, 16H, CH3 3 and NCH2CH2), 3.22 (sept, JHH = 6.7 Hz, 4H, CH(CH3)2), 3.41 (br m, 4H, NCH2CH2), 13 4.77 (br s, Δν½ ≈ 40 Hz, 3H, InH3), 7.03-7.18 (m, 6H, m- and p-ArH). C NMR (125

MHz, C6D5CD3, 248 K) δ 24.2 (CH(CH3)2), 25.0 (NCH2CH2), 26.1 (CH(CH3)2), 28.9 296 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

(CH(CH3)2), 55.1 (NCH2CH2), 124.5, 127.4 (ArCH), 144.8, 145.3 (ArC), 148.69 -1 (NCN). IR (Nujol, cm ) 1650 (br s, In-H). Anal. Cal. for C29H45InN2: C, 64.92; H, 8.45; N, 5.22. Found: C, 64.58; H, 8.48; N, 5.19%.

7.6.4 Intentional Synthesis of 7Dipp·HH (63)

Diethyl ether (30 mL) was added to a mixture of 7Dipp·HBr (200 mg, 0.40 mmol) and

[LiAlH4] (20 mg, 0.53 mmol) and stirred for 12 hours. The solution was dried in vacuo to afford a white solid. Purification by extraction into toluene and cooling to -25 °C overnight yielded 7Dipp·HH as colourless truncated blocks (160 mg, 95%). 1H NMR 3 3 (400 MHz, C6D6) δ 1.22 (d, 12H, JHH = 6.7 Hz, CH3), 1.29 (d, 12H, JHH = 6.7 Hz, 3 CH3), 1.68 (br m, 4H, NCH2CH2), 3.55 (br m, 4H, NCH2CH2), 3.78 (sept, 4H, JHH = 13 6.7 Hz, CH(CH3)2), 4.30 (s, 2H, NCH2N), 7.14-7.22 (m, 6H, m- and p-ArH). C NMR

(100 MHz, C6D6) δ 24.7, 25.1 (CH(CH3)2), 28.4 (NCH2CH2), 31.7 (CH(CH3)2), 54.3 (s, -1 NCH2CH2), 124.7, 127.2 (ArCH), 136.1 (NCH2N), 145.7, 149.1 (ArC). IR (Nujol, cm ) 1465 (br s), 1407 (m), 1379 (m), 1326 (m), 1264 (m), 1152 (m), 1105 (br m), 1053 (br m), 980 (w), 933 (w), 805 (m), 763 (m), 665 (w).

7.6.5 Synthesis of [GaH3(7Dipp)] (64)

A solution of 7Dipp (410 mg, 0.98 mmol) in diethyl ether (40 mL) at -20 °C was added to a stirred solution of [LiGaH4] (ca. 0.95 mmol) in diethyl ether (30 mL) at -20 °C and gradually warmed to ambient temperature overnight. Filtration and removal of volatiles in vacuo afforded a white powder that was extracted into toluene (30 mL), concentrated to incipient crystallisation and cooled to -25 °C, to afford [GaH3(7Dipp)] as colourless 1 3 octahedra (350 mg, 75%), dec. 152 °C. H NMR (400 MHz, C6D6) δ 1.21 (d, JHH = 6.7 3 Hz, 12H, CH(CH3)2), 1.64 (d, JHH = 6.7 Hz, 12H, CH(CH3)2), 1.68 (br m, 4H,

NCH2CH2), 3.27 (br m, 7H, GaH3 and CH(CH3)2), 3.51 (br m, 4H NCH2CH2), 7.10- 13 7.21 (m, 6H, m- and p-ArH). C NMR (100 MHz, C6D6) δ 24.3 (CH3), 24.8

(NCH2CH2), 25.9 (CH(CH3)2), 29.1 (CH(CH3)2), 56.2 (NCH2CH2), 124.8, 127.9 (ArCH), 128.2, 129.1 (ArC), 145.0 (NCN). IR (Nujol, cm-1) 1798 (br s, Ga-H). Anal.

Cal. for C29H45GaN2: C, 70.88; H, 9.23; N, 5.70. Found: C, 70.48; H, 8.87; N, 5.67%.

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7.6.6 Synthesis of [InBr3(7Dipp)] (65)

A solution of 7Dipp (200 mg, 0.48 mmol) in THF (30 mL) was added to a stirred solution of InBr3 (180 mg, 0.51 mmol), also in THF (20 mL), at room temperature. The solution was stirred for 15 minutes, concentrated to the point of incipient crystallisation and stored at 4 °C overnight. This afforded colourless rods of [InBr3(7Dipp)] as its THF solvate (270 mg, 67%), m.p. 230 °C (dec. point beyond range of instrument, > 300 °C). 1 3 H NMR (300 MHz, C6D6) δ 1.07 (d, 12H, JHH = 6.7 Hz, CH(CH3)2), 1.54 (br m, 4H, 3 3 NCH2CH2), 1.64 (d, 12H, JHH = 6.7 Hz, CH(CH3)2), 3.32 (sept, 4H, JHH 6.7 Hz, 13 CH(CH3)2), 3.49 (br m, 4H, NCH2CH2), 7.13-7.23 (m, 6H, m- and p-ArH). C NMR

(75 MHz, C6D6) δ 24.8 (CH(CH3)2), 25.4 (NCH2CH2), 26.5 (CH(CH3)2), 28.7

(CH(CH3)2), 56.2 (NCH2CH2), 124.2, 128.6 (ArCH), 129.0, 141.8 (ArC), 145.5 (NCN). IR (Nujol, cm-1) 1649 (w), 1589 (w), 1465 (br s), 1388 (m), 1365 (m), 1304 (m), 1260 (m), 1172 (w), 1064 (m), 944 (br w), 803 (m), 760 (m), 698 (w), 665 (w).

7.6.7 Synthesis of [InH3(IPr)] (66)

A cooled (-40 °C) diethyl ether (50 mL) solution of IPr (780 mg, 2.01 mmol) was added to a cooled (-78 °C) diethyl ether (40 mL) solution of [LiInH4] (ca. 2.00 mmol) and allowed to slowly warm to 0 °C over a period of 4 hours. The resulting colourless solution was dried in vacuo, extracted into cold (0 °C) toluene (60 mL) and concentrated under reduced pressure at 0 °C (ca. 30 mL). Gradual cooling to -25 °C afforded colourless prisms of [InH3(IPr)]. A second crop was obtained by further concentration of the supernatant at 0 °C followed by cooling to -25 °C (combined yield 1 3 776 mg, 77%), dec. 94 °C. H NMR (400 MHz, C6D6) δ 1.05 (d, JHH = 6.9 Hz, 12H, 3 3 CH3), 1.42 (d, JHH = 6.9 Hz, 12H, CH3), 2.68 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), AAB 5.05 (br s, Δν½ ≈ 60 Hz, 3H, InH3), 6.52 (s, 2H, NCH), 7.12 (d, JHH = 7.8 Hz, 4H, AAB 13 m-ArH), 7.26 (t, JHH = 7.8 Hz, 2H, p-ArH). C NMR (100 MHz, C6D6) δ 23.6, 25.0

(CH(CH3)2), 29.0 (CH(CH3)2), 123.8 (NCH), 124.2 (m-ArC), 130.6 (p-ArC), 135.7 (ipso-ArC), 145.7 (o-ArC), 150.0 (NCN). IR (Nujol, cm-1) 1651 (br s, In-H). Anal. Cal. for C27H39InN2: C, 64.03; H, 7.76; N, 5.53. Found: C, 64.55; H, 7.80; N, 5.69%. C, H, N elemental analysis sample stored under argon at 22 °C for 12 months without decomposition.

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7.6.8 Synthesis of [GaH3(IPr)] (67)

A cooled (-40 °C) diethyl ether (40 mL) solution of IPr (660 mg, 1.7 mmol) was added to a cooled (-78 °C) diethyl ether (40 mL) solution of [LiGaH4] (1.7 mmol) and allowed to slowly warm to ambient temperature over a period of 12 hours. The resulting colourless solution was dried in vacuo, extracted into cold (0 °C) toluene (60 mL) and concentrated under reduced pressure at 0 °C (ca. 20 mL). Gradual cooling to -25 °C afforded colorless prisms of [GaH3(IPr)]. A second crop was obtained by further concentration of the supernatant at 0 °C followed by cooling to -25 °C (combined yield 1 3 610 mg, 71%). H NMR (400 MHz, C6D6) δ 1.05 (d, JHH = 6.9 Hz, 12H, CH3), 1.43 (d, 3 3 JHH = 6.9 Hz, 12H, CH3), 2.67 (sept, JHH = 6.9 Hz, 4H, CH(CH3)2), 3.73 (br s, 3H, AAB AAB GaH3), 6.46 (s, 2H, NCH), 7.12 (d, JHH = 7.8 Hz, 4H, m-ArH), 7.25 (t, JHH = 7.8 13 Hz, 2H, p-ArH). C NMR (100 MHz, C6D6) δ 23.4, 25.0 (CH(CH3)2), 29.1

(CH(CH3)2), 123.7 (NCH), 124.2 (m-ArC), 130.6 (p-ArC), 135.2 (ipso-ArC), 145.7 (o- ArC), 181.5 (NCN). IR (Nujol, cm-1) 1800 (br s, Ga-H).

7.6.9 Synthesis of [InD3(IPr)] (68)

Following the procedure outlined for 66 (50% scale) and substituting LiInD4 for LiInH4,

[InD3(IPr)] was isolated as a colourless powder upon extraction into cold (0 °C) toluene and removal of volatiles in vacuo. [InD3(IPr)] characterised as per [InH3(IPr)] excepting 2 the following data: H NMR (92 MHz, C6H6) δ 5.09 (br s, Δν½  4 Hz, InD3). IR (Nujol, cm-1) 1181 (br s, In-D).

7.6.10 Synthesis of [InH3(IPr*)] (69)

IPr* (630 mg, 0.69 mmol) was added as a solid to a cooled (-78 °C) solution of [LiInH4] (ca. 0.69 mmol) in diethyl ether (60 mL). Gradual warming to room temperature overnight, filtration, extraction into toluene (20 mL) and layering with pentane afforded colourless prisms of [InH3(IPr*)] after standing for 7 days at room temperature (410 1 mg, 58%), dec. 182 °C. H NMR (400 MHz, C6D6) δ 1.71 (s, 6H, CH3), 5.30 (s, 2H,

NCH), 5.64 (s, 4H, CHPh2), 5.68 (br s, Δν½ ≈ 25 Hz, 3H, InH3), 6.86-7.04 (m, 24H, Ar’H), 7.05 (s, 4H, m-ArH), 7.20 (br t, 8H, Ar’H), 7.66 (br d, 8H, Ar’H). 13C NMR

(100 MHz, C6D6) δ 21.3 (CH3), 52.1 (CHPh2), 124.1 (NCH), 126.7, 127.2, 128.5, 128.8, 129.9, 130.5, 131.0, 135.1, 140.4, 141.9, 143.4, 144.4 (ArC), 182.5 (NCN). IR (Nujol,

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-1 cm ) 1633 (br s, In-H). Anal. Cal. for C69H59InN2: C, 80.38; H, 5.77; N, 2.72. Found: C, 80.65; H, 5.87; N, 2.90%. C, H, N elemental analysis sample stored under argon at 22 °C for 3 months without decomposition.

7.6.11 Spectroscopic Data for IPr*·HH (70)

1 H NMR (400 MHz, C6D6) δ 1.82 (s, 6H, CH3), 5.02 (s, 2H, NCH2N), 5.71 (s, 2H,

NCH), 6.52 (s, 4H, CHPh2), 6.90-7.18 (m, 36H, ArH), 7.36 (br d, 8H, ArH).

7.6.12 Synthesis of [GaH3(IPr*)] (71)

IPr* (460 mg, 0.50 mmol) was added as a solid to a cooled (-78 °C) solution of

[LiGaH4] (0.50 mmol) in diethyl ether (50 mL). After gradual warming to room temperature overnight the solvent was removed in vacuo and the residue extracted into room temperature toluene (40 mL). Concentration to insipient crystallisation (ca. 20 mL) and placement at -25 °C afforded the mono toluene solvate of [GaH3(IPr*)] as colourless plates suitable for X-ray diffraction structure determination (210 mg, 38%), 1 dec. 226 °C. H NMR (400 MHz, C6D6, vacuum dried sample) δ 1.70 (s, 6H, CH3), 4.44

(br s, Δν½ ≈ 10 Hz, 3H, GaH3), 5.34 (s, 2H, NCH), 5.68 (s, 4H, CHPh2), 6.84-6.91 (m, 8H, ArH), 6.92-7.03 (m, 16H, ArH), 7.04 (s, 4H, m-ArH), 7.16-7.19 (m, 8H, ArH), 13 7.65-7.68 (m, 8H, ArH). C NMR (100 MHz, C6D6, vacuum dried sample) δ 21.3

(CH3), 52.0 (CHPh2), 123.9 (NCH), 126.7, 127.1, 128.5, 128.8, 129.9, 130.5, 130.8, 134.8, 140.4, 141.9, 143.7, 144.2 (ArC), 180.0 (NCN). IR (Nujol, cm-1) 1790 (br s,

Ga-H). Anal. Cal. for C69H59GaN2: C, 84.06; H, 6.03; N, 2.84. Found: C, 83.04; H, 6.22; N, 3.46% (vacuum dried sample).

7.6.13 Synthesis of [TlCl3(IPr*)] (72)

THF (40 mL) was added to a mixture of anhydrous TlCl3 (170 mg, 0.50 mmol) and IPr* (460 mg, 0.50 mmol) at ambient temperature. The resultant slurry was stirred for a further 16 h at room temperature. The mixture was filtered and the solvent removal in vacuo. The resultant colourless residue was extracted into dichloromethane (20 mL) and layer with hexane (40 mL) to afford colourless prisms suitable for X-ray diffraction structure determination after standing at ambient temperature for 24 h (295 mg, 49%). 1 4 H NMR (400 MHz, C6D6) δ 1.70 (s, 6H, CH3), 5.14 (d, JTlH = 80.4 Hz, 2H, NCH),

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5.59 (s, 4H, CHPh2), 6.73-6.76 (m, 8H, ArCH), 6.83-7.07 (m, 16H, ArCH), 7.11 (br s, 4H, ArCH), 7.17-7.22 (m, 8H, ArCH), 7.60 (m, 8H, ArCH). 1H NMR (400 MHz, 4 CDCl3) δ 2.25 (s, 6H, CH3), 5.13 (d, JTlH = 85.5 Hz, 2H, NCH), 5.22 (s, 4H, CHPh2), 6.75-6.94 (m, 14H, ArCH), 7.10-7.16 (m, 10H, ArCH), 7.23-7.30 (m, 20H, ArCH). 13C 3 NMR (100 MHz, C6D6) δ 21.3 (CH3), 52.3 (CHPh2), 125.9 (d, JTlC = 195.2 Hz, NCH), 127.0, 127.5, 128.6, 129.0, 129.8, 131.1, 131.4 (ArCH), 141.9, 142.4, 142.5, 142.6,

144.5 (ArC). Anal. Cal. for C69H56TlCl3N2·0.5(CH2Cl2): C, 65.91; H, 4.53; N, 2.21. Found: C, 65.42; H, 4.52; N, 2.38%.

7.6.14 The Attempted Synthesis of [TlH3(IPr*)]

[NaBEt3H] (1.0 M in toluene, 0.25 mL, 0.25 mmol) was added dropwise to a slurry of 72 (100 mg, 0.08 mmol) in toluene at -78 °C. The rapid formation of a formation of a grey precipitate was observed. The resultant slurry was warmed to ambient temperature. Filtration followed by solvent removal in vacuo afforded a colourless solid that characterises as a (1:4) mixture of 70 and IPr*.[39a]

7.6.15 The Photochemical Reaction of 69 with Tungsten Hexacarbonyl

A mixture of 69 (20 mg, 0.02 mmol) and [W(CO)6] (7 mg, 0.02 mmol) in C6D6 (0.6 mL) was subjected to UV photolysis (300 W Hg lamp) for 5 minutes at ambient temperature. During this period a colour change from colourless to pale yellow was observed. The sample was evaluated as soon as practicable by 1H NMR spectroscopy. 1 2 H NMR (600 MHz, C6D6) δ -5.82 (t, JHH = 13.4 Hz, 1H, In-H-W), 7.05 (br m, 2 H, InH). The solvent was then removed in vacuo to afford a yellow powder. IR (Nujol, -1 cm ) 1980 (s, CO), 1934 (s, CO), 1667 (br s, In-H). Extraction into C6D6 and further subjection to UV photolysis for 60 minutes at ambient temperature, affords an indium mirror on the walls of the vessel. Filtration followed by solvent removal in vacuo affords an off-white powder which characterises as 70 by 1H NMR spectroscopy.

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7.6.16 The Photochemical Reaction of 71 with Tungsten Hexacarbonyl

A mixture of 71 (20 mg, 0.02 mmol) and [W(CO)6] (7 mg, 0.02 mmol) in C6D6 (0.6 mL) was subjected to UV photolysis (300 W Hg lamp) for 5 minutes at ambient temperature. During this period a colour change from colourless to pale yellow was observed. The sample was evaluated as soon as practicable by 1H NMR spectroscopy. 1 2 H NMR (500 MHz, C6D6) δ -6.68 (br t, JHH = 10.9 Hz, 1H, Ga-H-W), 5.54 (br s, 2H, GaH). Further subjection to UV photolysis for 40 minutes at ambient temperature, affords a yellow solution. The sample was evaluated as soon as practicable by 1H NMR 1 2 spectroscopy. H NMR (500 MHz, C6D6) δ -4.86 (br d, JHH = 11.5 Hz, 2H, Ga-H-W), 2 8.26 (br t, JHH = 11.5 Hz, 1H, GaH).

7.6.17 The Reaction of 66 with [Mo(CO)4(cod)]

A solution of 66 (20 mg, 0.04 mmol) in toluene (5 mL) was added to [Mo(CO)4(cod)] (14 mg, 0.04 mmol) at ambient temperature. Immediate gas evolution with concurrent change of colour of solution from colourless to yellow was observed. After 5 minutes the deposition of a grey solid was observed. Filtration after 24 h followed by solvent removal in vacuo affords an off-white powder which characterises as IPr·HH by 1H NMR spectroscopy.[50]

2 7.6.18 Synthesis of [Mo(CO)4(κ -H3Ga·IPr)] (76)

A solution of 67 (21 mg, 0.046 mmol) in C6D6 was added to [Mo(CO)4(cod)] (14 mg, 0.044 mmol) at ambient temperature. The resultant pale yellow solution was evaluated 1 1 as soon as practicable by H NMR spectroscopy. H NMR (400 MHz, C6D6) δ -5.04 (br 2 3 3 d, JHH = 10.6 Hz, 2H, GaH), 0.91 (d, JHH = 6.8 Hz, 12H, CH3), 1.39 (d, JHH = 6.8 Hz, 3 12H, CH3), 2.58 (sept, JHH = 6.8 Hz, 4H, CH(CH3)2), 6.42 (s, 2H, NCH), 7.00 (d, AAB AAB JHH = 7.8 Hz, 4H, m-ArH), 7.13 (t, JHH = 7.8 Hz, 2H, p-ArH). Yellow plates suitable for X-ray diffraction structure determination deposited upon standing at ambient temperature for 24 h (19 mg, 64%).

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7.6.19 The Reaction of [InH3(IMes)] with [Mo(CO)4(cod)]

Toluene (10 mL) was added to a mixture of [InH3(IMes)] (99 mg, 0.23 mmol) and

[Mo(CO)4(cod)] (73 mg, 0.23 mmol) at ambient temperature. The resultant pale yellow solution was stirred at ambient temperature for 5 minutes, follow by cooling to -20 °C. Yellow plates suitable for X-ray diffraction structure determination deposited upon standing at -25 °C for 24 h. IR (Nujol, cm-1) 2002 (s, CO), 1982 (s, CO), 1678 (br s, In-H)

303 References for this chapter begin on pg. 304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

7.7 References

[1] Chaillet, M.; Dargelos, A.; Marsden, C. J., New J. Chem. 1994, 18, 693-700. [2] Hibbs, D. E.; Hursthouse, M. B.; Jones, C.; Smithies, N. A., Chem. Commun. 1998, 869-870. [3] Abernethy, C. D.; Cole, M. L.; Jones, C., Organometallics 2000, 19, 4852-4857. [4] Greenwood, N. N.; Storr, A.; Wallbridge, M. G. H., Inorg. Chem. 1963, 2, 1036- 1039. [5] Atwood, J. L.; Bennett, F. R.; Elms, F. M.; Jones, C.; Raston, C. L.; Robinson, K. D., J. Am. Chem. Soc. 1991, 113, 8183-8185. [6] Heitsch, C. W.; Nordman, C. E.; Parry, R. W., Inorg. Chem. 1963, 2, 508-512. [7] Atwood, J. L.; Bott, S. G.; Elms, F. M.; Jones, C.; Raston, C. L., Inorg. Chem. 1991, 30, 3792-3793. [8] El Guerraze, A.; Anane, H.; Serrar, C.; Es-sofi, A.; Lamsabhi, A. M.; Jarid, A., J. Mol. Struc.-Theochem 2004, 709, 117-122. [9] Shriver, D. F.; Parry, R. W., Inorg. Chem. 1963, 2, 1039-1042. [10] (a) Jones, C., Chem. Commun. 2001, 2293-2298; (b) Cole, M. L.; Jones, C.; Kloth, M., Inorg. Chem. 2005, 44, 4909-4911. [11] Fraser, G. W.; Greenwood, N. N.; Straughan, B. P., J. Chem. Soc. 1963, 3742- 3749. [12] Jones, C.; Koutsantonis, G. A.; Raston, C. L., Polyhedron 1993, 12, 1829-1848. [13] Shriver, D. F.; Amster, R. L.; Taylor, R. C., J. Am. Chem. Soc. 1962, 84, 1321- 1322. [14] Francis, M. D.; Hibbs, D. E.; Hursthouse, M. B.; Jones, C.; Smithies, N. A., J. Chem. Soc., Dalton Trans. 1998, 3249-3254. [15] Greenwood, N. N.; Thomas, B. S., J. Chem. Soc. A 1971, 814-817. [16] Elms, F. M.; Gardiner, M. G.; Koutsantonis, G. A.; Raston, C. L.; Atwood, J. L.; Robinson, K. D., J. Organomet. Chem. 1993, 449, 45-52. [17] Bennett, F. R.; Elms, F. M.; Gardiner, M. G.; Koutsantonis, G. A.; Raston, C. L.; Roberts, N. K., Organometallics 1992, 11, 1457-1459. [18] Atwood, J. L.; Robinson, K. D.; Bennett, F. R.; Elms, F. M.; Koutsantonis, G. A.; Raston, C. L.; Young, D. J., Inorg. Chem. 1992, 31, 2673-2674. [19] Hibbs, D. E.; Jones, C.; Smithies, N. A., Chem. Commun. 1999, 185-186.

304 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

[20] Cole, M. L.; Hibbs, D. E.; Jones, C.; Smithies, N. A., J. Chem. Soc., Dalton Trans. 2000, 545-550. [21] (a) N-Heterocyclic Carbenes in Synthesis, Ed. Nolan, S. P., 2006, Wiley-VCH: Weinheim, Germany; (b) de Fremont, P.; Marion, N.; Nolan, S. P., Coord. Chem. Rev. 2009, 253, 862-892; (c) Kirmse, W., Angew. Chem. Int. Ed. 2010, 49, 2-6; (d) N-Heterocyclic Carbenes in Transition Metal Catalysis, Glorius, F., 2007, Springer: New York, USA. [22] Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F., J. Am. Chem. Soc. 1992, 114, 9724-9725. [23] (a) Baker, R. J.; Cole, M. L.; Jones, C.; Mahon, M. F., J. Chem. Soc., Dalton Trans. 2002, 1992-1996; (b) Baker, R. J.; Davies, A. J.; Jones, C.; Kloth, M., J. Organomet. Chem. 2002, 656, 203-210; (c) Cole, M. L.; Furfari, S. K.; Kloth, M., J. Organomet. Chem. 2009, 694, 2934-2940. [24] Alexander, S. G.; Cole, M. L.; Forsyth, C. M., Chem. Eur. J. 2009, 15, 9201- 9214. [25] Alexander, S. G.; Cole, M. L.; Forsyth, C. M.; Furfari, S. K.; Konstas, K., Dalton Trans. 2009, 2326-2336. [26] (a) Cotgreave, J. H.; Colclough, D.; Kociok-Kohn, G.; Ruggiero, G.; Frost, C. G.; Weller, A. S., Dalton Trans. 2004, 1519-1520; (b) Ghadwal, R. S.; Roesky, H. W.; Herbst-Irmer, R.; Jones, P. G., Z. Anorg. Allg. Chem. 2009, 635, 431- 433; (c) Marion, N.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Stevens, E. D.; Fensterbank, L.; Malacria, M.; Nolan, S. P., Organometallics 2007, 26, 3256- 3259; (d) Quillian, B.; Wei, P.; Wannere, C. S.; Schleyer, P. v. R.; Robinson, G. H., J. Am. Chem. Soc. 2009, 131, 3168-3169; (e) Li, X.-W.; Su, J.; Robinson, G. H., Chem. Commun. 1996, 2683-2684; (f) Stasch, A.; Singh, S.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G., Eur. J. Inorg. Chem. 2004, 4052-4055; (g) Schmitt, A.-L.; Schnee, G.; Welter, R.; Dagorne, S., Chem. Commun. 2010, 46, 2480-2482; (h) Zhang, Y.; Miyake, G. M.; Chen, E. Y. X., Angew. Chem. Int. Ed. 2010, 49, 10158-10162; (i) Bantu, B.; Manohar Pawar, G.; Wurst, K.; Decker, U.; Schmidt, A. M.; Buchmeiser, M. R., Eur. J. Inorg. Chem. 2009, 1970-1976; (j) Horeglad, P.; Szczepaniak, G.; Dranka, M.; Zachara, J., Chem. Commun. 2012, 48, 1171-1173; (k) Kennedy, A. R.; Mulvey, R. E.; Robertson, S. D., Dalton Trans. 2010, 39, 9091-9099.

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[27] Tsui, E. Y.; Müller, P.; Sadighi, J. P., Angew. Chem. Int. Ed. 2008, 47, 8937- 8940. [28] Wang, X.; Andrews, L., J. Phys. Chem. A 2004, 108, 3396-3402. [29] Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P., J. Am. Chem. Soc. 2005, 127, 3516-3526. [30] (a) Zhang, R.; Tsutsui, M.; E. Bergbreiter, D., J. Organomet. Chem. 1982, 229, 109-112; (b) Dohmeier, C.; Baum, E.; Ecker, A.; Koppe, R.; Schnöckel, H., Organometallics 1996, 15, 4702-4706; (c) Harder, S.; Naglav, D.; Schwerdtfeger, P.; Nowik, I.; Herber, R. H., Inorg. Chem. 2014, 53, 2188-2194. [31] Wong, E. W. Y.; Dange, D.; Fohlmeister, L.; Hadlington, T. J.; Jones, C., Aust. J. Chem. 2013, 66, 1144-1154. [32] (a) Eberhardt, R.; Allmendinger, M.; Luinstra, G. A.; Rieger, B., Organometallics 2003, 22, 211-214; (b) Cowley, R. E.; Holland, P. L., Inorg. Chem. 2012, 51, 8352-8361. [33] Dible, B. R.; Cowley, R. E.; Holland, P. L., Organometallics 2011, 30, 5123- 5132. [34] (a) Smith, J. M.; Sadique, A. R.; Cundari, T. R.; Rodgers, K. R.; Lukat-Rodgers, G.; Lachicotte, R. J.; Flaschenriem, C. J.; Vela, J.; Holland, P. L., J. Am. Chem. Soc. 2006, 128, 756-769; (b) Rodriguez, M. M.; Bill, E.; Brennessel, W. W.; Holland, P. L., Science 2011, 334, 780-783. [35] Alexander, S. G.; Cole, M. L.; Morris, J. C., New J. Chem. 2009, 33, 720-724. [36] Berthon-Gelloz, G.; Siegler, M. A.; Spek, A. L.; Tinant, B.; Reek, J. N. H.; Marko, I. E., Dalton Trans. 2010, 39, 1444-1446. [37] Dierick, S.; Dewez, D. F.; Markó, I. E., Organometallics 2014, 33, 677-683. [38] (a) Laskowski, C. A.; Miller, A. J. M.; Hillhouse, G. L.; Cundari, T. R., J. Am. Chem. Soc. 2010, 133, 771-773; (b) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.; Cavallo, L.; Hoff, C. D.; Nolan, S. P., J. Am. Chem. Soc. 2005, 127, 2485-2495. [39] (a) Gómez-Suárez, A.; Ramón, R. S.; Songis, O.; Slawin, A. M. Z.; Cazin, C. S. J.; Nolan, S. P., Organometallics 2011, 30, 5463-5470; (b) Chartoire, A.; Lesieur, M.; Falivene, L.; Slawin, A. M. Z.; Cavallo, L.; Cazin, C. S. J.; Nolan, S. P., Chem. Eur. J. 2012, 18, 4517-4521; (c) Meiries, S.; Speck, K.; Cordes, D. B.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2012, 32, 330-339; (d)

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Martin, A. R.; Chartoire, A.; Slawin, A. M. Z.; Nolan, S. P., Beilstein J. Org. Chem. 2012, 8, 1637-1643; (e) Chartoire, A.; Frogneux, X.; Boreux, A.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2012, 31, 6947-6951; (f) Manzini, S.; Urbina Blanco, C. A.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2012, 31, 6514-6517; (g) Chartoire, A.; Frogneux, X.; Nolan, S. P., Adv. Synth. Catal. 2012, 354, 1897-1901; (h) Meiries, S.; Chartoire, A.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2012, 31, 3402-3409; (i) Balogh, J.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2012, 31, 3259-3263; (j) Martin, A. R.; Makida, Y.; Meiries, S.; Slawin, A. M. Z.; Nolan, S. P., Organometallics 2013, 32, 6265- 6270; (k) Izquierdo, F.; Chartoire, A.; Nolan, S. P., ACS Catal. 2013, 3, 2190- 2193; (l) Bastug, G.; Nolan, S. P., J. Org. Chem. 2013, 78, 9303-9308; (m) Poater, A.; Falivene, L.; Urbina-Blanco, C. A.; Manzini, S.; Nolan, S. P.; Cavallo, L., Dalton Trans. 2013, 42, 7433-7439; (n) Brule, E.; Guerineau, V.; Vermaut, P.; Prima, F.; Balogh, J.; Maron, L.; Slawin, A. M. Z.; Nolan, S. P.; Thomas, C. M., Polym. Chem. 2013, 4, 2414-2423; (o) Chartoire, A.; Boreux, A.; Martin, A. R.; Nolan, S. P., RSC Adv. 2013, 3, 3840-3843; (p) Gomez- Suarez, A.; Oonishi, Y.; Meiries, S.; Nolan, S. P., Organometallics 2013, 32, 1106-1111. [40] Kolychev, E. L.; Portnyagin, I. A.; Shuntikov, V. V.; Khrustalev, V. N.; Nechaev, M. S., J. Organomet. Chem. 2009, 694, 2454-2462. [41] Ramnial, T.; Abernethy, C. D.; Spicer, M. D.; McKenzie, I. D.; Gay, I. D.; Clyburne, J. A. C., Inorg. Chem. 2003, 42, 1391-1393. [42] Herrmann, W. A.; Schneider, S. K.; Öfele, K.; Sakamoto, M.; Herdtweck, E., J. Organomet. Chem. 2004, 689, 2441-2449. [43] Iglesias, M.; Beetstra, D. J.; Kariuki, B.; Cavell, K. J.; Dervisi, A.; Fallis, I. A., Eur. J. Inorg. Chem. 2009, 1913-1919. [44] Lu, W. Y.; Cavell, K. J.; Wixey, J. S.; Kariuki, B., Organometallics 2011, 30, 5649-5655. [45] de Frémont, P.; Scott, N. M.; Stevens, E. D.; Ramnial, T.; Lightbody, O. C.; Macdonald, C. L. B.; Clyburne, J. A. C.; Abernethy, C. D.; Nolan, S. P., Organometallics 2005, 24, 6301-6309. [46] As determined by a survey of the Cambridge Structural Database v. 5.36 with updates for November 2014.

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[47] Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I., Organometallics 2010, 29, 2176- 2179. [48] Downs, A. J.; Pulham, C. R., Chem. Soc. Rev. 1994, 23, 175-184. [49] Guzei, I. A.; Wendt, M., Dalton Trans. 2006, 3991-3999. [50] Al-Rafia, S. M. I.; Malcolm, A. C.; Liew, S. K.; Ferguson, M. J.; Rivard, E., J. Am. Chem. Soc. 2011, 133, 777-779. [51] Jafarpour, L.; Stevens, E. D.; Nolan, S. P., J. Organomet. Chem. 2000, 606, 49- 54. [52] (a) Rivada-Wheelaghan, O.; Donnadieu, B.; Maya, C.; Conejero, S., Chem. Eur. J. 2010, 16, 10323-10326; (b) Rivada-Wheelaghan, O.; Ortuño, M. A.; Díez, J.; García-Garrido, S. E.; Maya, C.; Lledós, A.; Conejero, S., J. Am. Chem. Soc. 2012, 134, 15261-15264. [53] (a) Pullumbi, P.; Bouteiller, Y.; Manceron, L.; Mijoule, C., Chem. Phys. 1994, 185, 25-37; (b) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P., J. Am. Chem. Soc. 2002, 124, 4448-4457; (c) Himmel, H.-J.; Manceron, L.; Downs, A. J.; Pullumbi, P., Angew. Chem. Int. Ed. 2002, 41, 796-799; (d) Andrews, L.; Wang, X., Angew. Chem. Int. Ed. 2004, 43, 1706-1709. [54] Baker, R. J.; Farley, R. D.; Jones, C.; Kloth, M.; Murphy, D. M., Chem. Commun. 2002, 1196-1197. [55] Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.; Tamm, M., Angew. Chem. Int. Ed. 2008, 47, 7428-7432. [56] Sabourin, K. J.; Malcolm, A. C.; McDonald, R.; Ferguson, M. J.; Rivard, E., Dalton Trans. 2013, 42, 4625-4632. [57] Cole, M. L.; Davies, A. J.; Jones, C., J. Chem. Soc., Dalton Trans. 2001, 2451- 2452. [58] Davies, R. P.; Linton, D. J.; Schooler, P.; Snaith, R.; Wheatley, A. E. H., Eur. J. Inorg. Chem. 2001, 619-622. [59] The Group 13 Metals Aluminium, Gallium, Indium and Thallium: Chemical Patterns and Peculiarities, Eds. Downs, A. J.; Aldridge, S., 2011, John Wiley & Sons, Ltd: Chichester, UK. [60] (a) Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I., J. Am. Chem. Soc. 2003, 125, 9424-9434; (b) Jaska, C. A.; Manners, I., J. Am. Chem. Soc. 2004, 126,

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9776-9785; (c) Denney, M. C.; Pons, V.; Hebden, T. J.; Heinekey, D. M.; Goldberg, K. I., J. Am. Chem. Soc. 2006, 128, 12048-12049; (d) Ciobanu, O.; Allouti, F.; Roquette, P.; Leingang, S.; Enders, M.; Wadepohl, H.; Himmel, H.- J., Eur. J. Inorg. Chem. 2008, 5482-5493; (e) Wagner, A.; Kaifer, E.; Himmel, H.-J., Chem. Commun. 2012, 48, 5277-5279; (f) Kawano, Y.; Uruichi, M.; Shimoi, M.; Taki, S.; Kawaguchi, T.; Kakizawa, T.; Ogino, H., J. Am. Chem. Soc. 2009, 131, 14946-14957. [61] Muraoka, T.; Ueno, K., Coord. Chem. Rev. 2010, 254, 1348-1355. [62] Ueno, K.; Yamaguchi, T.; Uchiyama, K.; Ogino, H., Organometallics 2002, 21, 2347-2349. [63] Abdalla, J. A. B.; Riddlestone, I. M.; Turner, J.; Kaufman, P. A.; Tirfoin, R.; Phillips, N.; Aldridge, S., Chem. Eur. J. 2014, 20, 17624-17634. [64] Veith, M.; Weidner, S.; Kunze, K.; Käfer, D.; Hans, J.; Huch, V., Coord. Chem. Rev. 1994, 137, 297-322. [65] Ball, G. E. In Spectroscopic Properties of Inorganic and Organometallic Compounds, Vol. 41, pp. 262-287, 2010, The Royal Society of Chemistry: [66] (a) Geftakis, S.; Ball, G. E., J. Am. Chem. Soc. 1999, 121, 6336-6336; (b) Lawes, D. J.; Geftakis, S.; Ball, G. E., J. Am. Chem. Soc. 2005, 127, 4134-4135; (c) Lawes, D. J.; Darwish, T. A.; Clark, T.; Harper, J. B.; Ball, G. E., Angew. Chem. Int. Ed. 2006, 45, 4486-4490; (d) Ball, G. E.; Brookes, C. M.; Cowan, A. J.; Darwish, T. A.; George, M. W.; Kawanami, H. K.; Portius, P.; Rourke, J. P., Proceedings of the National Academy of Sciences of the United States of America 2007, 104, 6927-6932; (e) Calladine, J. A.; Torres, O.; Anstey, M.; Ball, G. E.; Bergman, R. G.; Curley, J.; Duckett, S. B.; George, M. W.; Gilson, A. I.; Lawes, D. J.; Perutz, R. N.; Sun, X.-Z.; Vollhardt, K. P. C., Chem. Sci. 2010, 1, 622-630; (f) Young, R. D.; Hill, A. F.; Hillier, W.; Ball, G. E., J. Am. Chem. Soc. 2011, 133, 13806-13809; (g) Young, R. D.; Lawes, D. J.; Hill, A. F.; Ball, G. E., J. Am. Chem. Soc. 2012, 134, 8294-8297. [67] Turner, J.; Abdalla, J. A. B.; Bates, J. I.; Tirfoin, R.; Kelly, M. J.; Phillips, N.; Aldridge, S., Chem. Sci. 2013, 4, 4245-4250. [68] Shirk, A. E.; Shriver, D. F. In Inorganic Syntheses, Vol. 17, pp. 45-47, 1977, John Wiley & Sons, Inc.: New York, USA. [69] Hintermann, L., Beilstein J. Org. Chem. 2007, 3, 1-5.

309 Chapter Seven: Stabilisation of Heavy Group 13 Trihydrides with NHCs

[70] Uson, R.; Laguna, A.; Spencer, J. L.; Turner, D. G. In Inorganic Syntheses, Vol. 21, pp. 71-74, 1982, John Wiley & Sons, Inc.: New York, USA. [71] Tekkaya, A.; Kayran, C.; Ozkar, S.; Kreiter, C. G., Inorg. Chem. 1994, 33, 2439-2443.

310

Chapter Eight: N-Heterocyclic Carbene Complexes of Low Oxidation State Group 13 Metals

8.1 Introduction

The ability of highly nucleophilic N-heterocyclic carbenes (NHCs) to stabilise transition metals in the zero oxidation state has been extensively documented (Figure 8.1).[1] NHCs have also enabled the isolation of the first examples of stable 14-electron complexes of group 9 and 10 metals.[2] These show remarkable reactivity, including the [3] activation of dioxygen, CO2 and C-H bonds (Scheme 8.1).

Figure 8.1 - Zero oxidation state metal NHC complexes

Scheme 8.1 - Reactivity of a 14-electron bis(NHC)palladium complexes

8.1.1 The Stabilisation of Reactive Main Group Molecules using NHCs

It was not until recently that NHC complexes of p-block metallic elements in low oxidation states were reported.[4] This was followed by reports of NHC complexes of p-block elements in the zero formal oxidation state (Figure 8.2, left, pg. 311).[5] The

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NHC complexes of neutral zero oxidation state group 14 metals and metalloids feature very short E-E bonds and computational studies have suggested that these are best described as double bonds.[5a-c] Related “complexes” of the heavier group 15 elements have been identified as singly bonded, with each group 15 element exhibiting two lone pairs.[5d-f] Generally, these complexes were isolated by alkali metal reduction of a higher oxidation state halide species,[5a-e] although Bertrand isolated NHC complexes of diphosphorus and tetraphosphorus from the direct reaction of acyclic singlet carbenes or CAAC NHCs with white phosphorus.[5f] Possibly the most exciting discovery is that of the first stable carbodicarbene or “carbone”, which is a carbon(0) system ligated by two NHCs (Figure 8.2, right).[6] Preliminary studies have shown carbones to be exceptionally strong σ-donors.[7]

Figure 8.2 - NHC stabilisation of low oxidation state p-block systems

8.1.2 The Stabilisation of Low Oxidation State Group 13 Elements using NHCs

Attempts have been made to prepare analogous NHC stabilised low oxidation state group 13 molecules. For instance, the reduction of [BBr3(IPr)] with three equivalents of potassium graphite fails to afford a boron(0) NHC complex like [{B(IPr)}2], instead yielding [{BH(IPr)}2] and [{BH2(IPr)}2] (Scheme 8.2, top, pg. 312). The hydrogen in the dimeric borohydride products is thought to derive from proton abstraction from the [8] ether solvent. Braunschweig recently succeeded in isolating [{B(IPr)}2] through a stepwise reduction of a formal B(II) dibromide NHC dimer with sodium naphthalide (Scheme 8.2, bottom).[9] This complex contains the first example of a stable formal boron-boron triple bond.

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Scheme 8.2 - The preparation of low oxidation state boron NHC complexes

There have been no reports of attempts to prepare zero oxidation state group 13 metal complexes, however a number of interesting low oxidation state NHC complexes of [10] group 13 metals have been reported. Reduction of [AlH3(IPr)] with Mes [{Mg( nacnac)}2] affords the highly stable dihydrido aluminium(II) dimer; [11] [{AlH2(IPr)}2] (Figure 8.3, top, pg. 313). Similarly, reduction of i [GaCl2(Mes)(I PrMe)] with potassium graphite affords the gallium(II) dimer i [12] [{GaCl(Mes)(I PrMe)}2], whilst repeating the reaction with elemental potassium i i [12] affords a bis(NHC) Ga6 octahedral cluster; [Ga(I PrMe){Ga4(Mes)4}Ga(I PrMe)]. Treatment of indium monobromide with an NHC results in partial disproportionation to [13] form the indium(II) NHC complex [{InBr2(IMes)}2] (Figure 8.3, top). Very recently, Krossing has reported that bis(NHC) complexes of gallium(I) and indium(I) (Figure 8.3, bottom) are isolable if a weakly coordinating anion, such as tetrakis(perfluoro-tert- butoxy)aluminate, is employed.[14]

312 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

Figure 8.3 - Low oxidation state NHC complexes of aluminium, gallium and indium

Only two thallium(I) NHC complexes have been reported to date; the first being the highly temperature sensitive (dec. -35 °C) thallium complex of a chelating tris(NHC) (Figure 8.4, left),[15] the second being that of a chelating alkoxy-bis(NHC) (Figure 8.4, right).[16]

Figure 8.4 - Thallium(I) NHC complexes

313 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

8.2 Project Outline

Numerous main group metal NHC complexes have been reported.[17] The application of NHCs to the stabilisation of group 13 metallanes has proved particularly fruitful (cf. Chapter Seven). By contrast NHC complexes of low oxidation state group 13 metals are relatively scarce.

The aim of this study is to investigate the impact of NHC steric and electronic character on the stability of low oxidation state group 13 metals. It is believed that the strong donicity and steric encumbrance of NHCs may lead to the stability of low oxidation state metals by preventing disproportionation reactivity. In the event of successful outcomes, the stabilities and geometries of these species will be investigated.

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8.3 Results and Discussion

8.3.1 NHC Complexes of Low Oxidation State Gallium and Indium

Schmidbaur has previously reported that the treatment of Ga[GaCl4] with PEt3 affords the symmetrical Ga-Ga bonded complex [{GaCl2(PEt3)}2], which has an ethane-like structure in the solid-state with the phosphine ligands in a single-trans conformation.[18] Similarly, treatment of “GaI” with primary and secondary amines or phosphines affords the symmetrical Ga-Ga bonded complexes [{GaI2(L)}2] (L = RNH2, R2NH and [19] R2PH). Herein, it was proposed that repeating these reactions with an NHC would afford dimeric gallium(II) complexes, e.g. [{GaX2(NHC)}2], and that similar outcomes may arise from the use of indium(II) halides.

The reaction of IMes with Ga[GaCl4] or “GaI” at -78 °C followed by gradual warming to room temperature, or In[InCl4] at ambient temperature, afforded the colourless complexes [{GaCl2(IMes)}2] (78), [{GaI2(IMes)}2] (79) and [{InCl2(IMes)}2] (80) in moderate to good yield (Scheme 8.3). For the preparations of 78 and 79, the addition of IMes initially affords bright orange reaction mixtures that fade to pale yellow, with the deposition of gallium for 79, upon gradual warming to room temperature. All three compounds are air and moisture sensitive, particularly 78 and 79 for which satisfactory elemental analyses could not be acquired.

Scheme 8.3 - Preparation of low oxidation state complexes 78-80. Reagents and conditions (i) M = Ga, X = Cl, 1.0 equiv. Ga[GaCl4], -78 °C to RT, toluene; (ii) M = Ga, X = I, 1.0 equiv. “GaI”, -Ga(s), -78 °C to RT, toluene; (iii) M = In, X = Cl, 1.0 equiv. In[InCl4], RT, 16 h, toluene.

1 The H NMR spectra of compounds 78 and 79 (C6D6) exhibit sharp signals, are near identical, and possess a unique spectroscopic feature relative to IMes adducts of [20] [21] trivalent hydrido and halo gallium species such as [GaH3(IMes)], [GaCl3(IMes)] [22] and [GaCl2H(IMes)], wherein the mesityl methyl resonances are markedly shifted

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downfield (Table 8.1, pg. 317). This is particularly pronounced for the mesityl ortho-methyl 1H resonances of 78 and 79. For example, the 1H ortho-methyl resonance of 79 is 0.19 ppm downfield of the analogous resonance for [GaCl3(IMes)] (both C6D6), and the mesityl para-methyl 1H resonance is 0.08 ppm downfield of that for the same complex.[23] An analogous shift is not observed for compound 80, which exhibits [20] similar chemical shifts to those of [InClH2(IMes)] (2.13 and 2.17 ppm respectively,

80; 2.11 and 2.13 ppm) and those of [{InBr2(IMes)}2] (single broad resonance at 2.14 [13] ppm) (Table 8.1). Previous studies have shown that the imidazol-2-ylidene 4,5-C2H2 1H NMR resonance can provide a useful handle for the relative Lewis acidity of the [24] coordinated group 13 MX3 unit. Based on this measure, comparison of the 4,5-C2H2 [21,23] resonances of compounds 78-80 with those of [GaCl3(IMes)] (Table 8.1), and that predicted for [InCl3(IMes)] (predicted based on the trend in [InHnClm(IMes)] resonances) (Table 8.1),[20] indicates that tetrahalodigallane and -diindane possess similar Lewis acidities to those of their respective trihalides. It is noteworthy that the 1H and 13C NMR spectra of 79 do not contain more than one set of IMes resonances nor an imidazolium-2-CH resonance, as would be consistent with the ionic formulation of a + [19] related species reported by Jones and co-workers; [(IPrH) ][GaI2GaI3(IPr)]. All three compounds exhibit carbenic carbon resonances in the expected region (78; 139.5, 79; [22] 139.8, 80; 140.2 ppm, [GaCl2H(IMes)]; 140.3 ppm, also C6D6).

316 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

Complex o-CH3 p-CH3 4,5-C2H2 Dec. (°C) Reference

78 2.17 2.13 5.76 230 This work

79 2.19 2.13 5.70 216 This work

80 2.11 2.17 5.76 234 This work

[{InBr2(IMes)}2] 2.14 2.14 5,74 n/a [13]

[GaH3(IMes)] 2.02 2.05 6.04 214 [20]

[GaClH2(IMes)] 2.03 2.05 5.95 263 [24b]

[GaCl2H(IMes)] 2.02 2.05 5.84 274 [24b]

[GaCl3(IMes)] 2.00 2.05 5.77 176 [21,23]

[GaIH2(IMes)] 2.01 2.01 5.89 181 [25]

[InH3(IMes)] 2.29 2.38 6.35 115 [20]

[InClH2(IMes)] 2.13 2.17 6.09 119 [20]

1 Table 8.1 - Spectroscopic ( H NMR, C6D6) and physical data for the complexes reported herein and related literature compounds.

Cooling of a saturated toluene solution of 78 to -25 °C afforded colourless prisms suitable for single crystal X-ray diffraction structure determination. Compound 78 crystallises in the monoclinic space group P21 with one anti molecule in the asymmetric unit (Figure 8.5, pg. 318).

317 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

Figure 8.5 - Molecular structure of 78 (50% thermal ellipsoids), view normal to the Ga(1)-Ga(2) vector (left) and view down Ga(1)-Ga(2) vector (right) showing anti arrangement of ligands. All hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°): Ga(1)-Ga(2) 2.4243(17), Ga(1)-C(1) 2.047(11), Ga(2)-C(22) 2.062(13), Ga(1)-Cl(1) 2.241(4), Ga(1)-Cl(2) 2.212(4), Ga(2)-Cl(3) 2.237(3), Ga(2)-Cl(4) 2.248(3), C(1)-Ga(1)-Ga(2) 120.3(3), C(1)-Ga(1)-Cl(1) 104.7(3), C(1)-Ga(1)-Cl(2) 101.7(3), Cl(1)-Ga(1)-Ga(2) 102.07(11), Cl(1)-Ga(1)-Cl(2) 103.57(17), Cl(2)-Ga(1)-Ga(2) 122.17(11), N(1)-C(1)-N(2) 104.3(9), C(22)-Ga(2)-Ga(1) 121.3(3), C(22)-Ga(2)-Cl(3) 97.5(4), C(22)-Ga(2)-Cl(4) 105.8(4), Cl(3)-Ga(2)-Ga(1) 124.45(11), Cl(3)-Ga(2)-Cl(4) 102.33(12), Cl(4)-Ga(2)-Ga(1) 103.01(10), N(3)-C(22)-N(4) 104.4(12).

The bonds of 78 are expectedly longer than those of its trivalent analogue

[GaCl3(IMes)] (78; Ga-C 2.047(11) and 2.062(13) Å, Ga-Cl 2.212(4)-2.248(3) Å, [21] [GaCl3(IMes)]; 1.954(4) Å and 2.1674(8)-2.1910(8) Å respectively). Surprisingly, its bonding exhibits marked differences relative to the eight known structurally [26] characterised tetrachlorodigallanes [{GaCl2(L)}2] (L = Lewis base), of which seven exhibit an anti conformation. For instance, the Cl-Ga-Cl angles of 78 (103.57(17) and 102.33(12)°) are below the range described by the aforementioned complexes (104.8-110.2°),[26] the Ga-Cl bonds are extended (2.212(4)-2.248(3) Å) versus the mean average of [{GaCl2(L)}2] complexes (2.20 Å), and the Cl-Ga-Ga bonding evidences two distinct chloride environments at each gallium (viz. Cl(1)-Ga(1)-Ga(2) 102.33(12)° and Cl(4)-Ga(2)-Ga(1) 103.01(10)°, Cl(2)-Ga(1)-Ga(2) 122.17(11)° and Cl(3)-Ga(2)-Ga(1)

124.45(11)°, range of observed Cl-Ga-Ga angles for literature [{GaCl2(L)}2] species [26] 111.6-118.0°). Comparison of 78 with the (IPr)GaI2 fragment of the eclipsed anion of [19] [IPr·H][Ga2I5(IPr)] also indicates greater distortion despite the decreased size of the NHC herein. This can be seen in the Ga-Ga-I, I-Ga-I and C-Ga-I angles about the

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(IPr)GaI2 of the anion, which range from 103.24(4)-109.81(19)°, while the analogous Ga-Ga-Cl, Cl-Ga-Cl and C-Ga-Cl angles of 78 lie between 101.7(3) and 122.17(11)°. The Ga(1)-Ga(2) bond length in 78 (2.4243(17) Å) is in good agreement with the range observed for the aforementioned structurally characterised tetrachlorodigallanes (2.392-2.447 Å).[26]

8.3.2 NHC Complexes of Thallium(I)

A number of NHC complexes of thallium(III) have been reported (See Chapter Seven).[27] Very few NHC complexes of thallium(I) have been reported vide supra, which is surprising given the preference of thallium to exist in the +1 oxidation state. Work in this area has likely been stymied by the poor solubility of thallium(I) compounds in organic solvents. Indeed, the aforementioned thallium(I) NHC complexes (Figure 8.4) were prepared from TlOTf and TlCp respectively.[15-16]

To further examine the NHC chemistry of thallium, the reaction of TlOTf with IMes was investigated. Treatment of TlOTf in THF with one equivalent of IMes, also in THF, at -40 °C led to the immediate deposition of thallium metal.9 The same outcome was observed for IPr. 1H NMR spectra of the vacuum dried crude reaction mixtures display low field resonances consistent with protonation of the carbenic position indicating formation of imidazolium salts. These outcomes are consistent with the aforementioned poor thermal stability of the tris(NHC) thallium triflate complex vide supra.

Aldridge has reported the preparation of 2,6-dimesitylpyridine complexes of thallium(I) F using in situ prepared Tl[BAr 4] as a soluble source of thallium(I). The success of this F F route lead to the reaction of Tl[BAr 4] and IMes herein, however treatment of Tl[BAr 4] in toluene with one or two equivalents of IMes in toluene at -40 °C likewise resulted in the immediate formation of a black thallium containing precipitate. Concentration of the F filtered reaction mixture afforded the bis(NHC) proton complex [(IMes)2H][BAr 4] (81) as a colourless crystalline solid as determined by single crystal XRD structure determination. The molecular structure of 81 can be found in the appendix.

Krossing and Jones recently reported the preparation of bis(NHC) complexes of gallium(I) and indium(I) (Figure 8.3). In those instances, the weakly coordinating t F tetrakis(perfluoro-tert-butoxy)aluminate anion, [Al(O Bu )4], was employed to

9 As evidenced by a green flame test result. 319 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

solubilise and stabilise the low oxidation state metals. To build on this work, the t F synthesis and characterisation of Tl[Al(O Bu )4] was targeted. Sonication of t F Li[Al(O Bu )4] and TlCl in fluorobenzene at 50 °C overnight followed by layering of t F the filtered reaction mixture affords [Tl(C6H5F)2.5][Al(O Bu )4] (82) as colourless 19 prisms. The F NMR spectrum of 82 (C6H5F) displays a single resonance at -75.1 ppm, attributable to the tetrakis(perfluoro-tert-butoxy)aluminate anion. The 27Al NMR spectrum of 82 (C6H5F) displays a single resonance at 34.8 ppm, which is also attributable to the tetrakis(perfluoro-tert-butoxy)aluminate anion. Compound 82 crystallises in the monoclinic space group P2/c and is isomorphous to its gallium(I) [28] + congener. The asymmetric unit of 82 contains one half [Tl(C6H5F)2] cation (Figure + t F 8.6), one [Tl(C6H5F)3] cation (Figure 8.7, pg. 321) and one and a half [Al(O Bu )4] anions.

+ Figure 8.6 - Molecular structure of [Tl(C6H5F)2] cation in 82 (10% RvdW). All hydrogen atoms omitted for clarity. Symmetry operation used to generate # atoms: 1-x, y, ½-z. Tl(1A)-X6 2.80 Å.

+ The [Tl(C6H5F)2] cation adopts a bent sandwich structure with each arene ring η6-coordinated to the thallium centre. This coordination geometry was similarly [29] observed in [Tl(C6Me6)2][H2N{B(C6F5)3}2]. The distance between the thallium centre and the centroid of the arene ring (X6) is 2.80 Å, which is similar to those observed in + [29] [Tl(C6Me6)2] (2.789 and 2.855 Å).

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+ Figure 8.7 - Molecular structure of [Tl(C6H5F)3] cation in 82 (10% RvdW). All hydrogen atoms omitted for clarity. Tl(1A)-X6(1) 3.00 Å, Tl(1A)-X6(2) 3.52 Å, Tl(1A)-X6(3) 3.07 Å.

+ The [Tl(C6H5F)3] cation of 82 exhibits a bent sandwich structure with two η6-coordinated arenes. The thallium centre is further coordinated by a third arene ring 1 + through an η -arene interaction. The [Tl(C6H5F)3] cation of 82 represents only the second example of a tris(arene) adduct of thallium, the first being 6 [29] [Tl(C6H5Me)3][H2N{B(C6F5)3}2] in which three η -arene interactions are observed. The distances of the thallium centre to the centroids of the two η6-coordinated arene rings are 3.00 and 3.07 Å. These distances are longer than those in the Tl(C6H5F)2 + [29] cation and the range observed in [Tl(C6H5Me)3] (2.942-3.010 Å) reflecting the poorer π-donor character of fluorobenzene relative to toluene despite the reduced hapticity of the third donor.

The reaction of 82 with two equivalents of IMes or IPr at ambient temperature in fluorobenzene affords pale yellow solutions. Layering the filtered reaction mixtures t F with hexane affords colourless prisms of [Tl(IMes)2][Al(O Bu )4] (83) and t F 10 [Tl(IPr)2][Al(O Bu )4] (84) respectively in good yields (Scheme 8.4, pg. 322). Complexes 83 and 84 can be stored indefinitely at ambient temperature under an inert atmosphere in the dark, however, prolonged exposure to light results in photodissociation and the deposition of black solids.

10 Complex 84 was prepared by Dr Thomas A. Martin, as part of a joint project. 321 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

Scheme 8.4 - Preparation of bis(NHC) complexes of thallium(I)

The 1H NMR spectrum of 83 exhibits sharp signals attributable to a single IMes environment in solution. The chemical shifts of the IMes resonances are considerably [27] upfield shifted relative to those observed in [TlCl3(IMes)]. For example, the mesityl 1 ortho-methyl H resonance of 83 (1.65 ppm, C6H5F) is 0.46 ppm upfield of the 1 analogous resonance of [TlCl3(IMes)] (CD2Cl2) and the 4,5-C2H2 H NMR resonance (6.52 ppm) is 1.01 ppm upfield of that for the same complex. A similarly pronounced 1 t F upfield shift of the mesityl ortho-methyl H resonance for [Ga(IMes)2][Al(O Bu )4] [14] (1.79 ppm, C6H5F) was observed relative to that for [GaCl3(IMes)] (2.00 ppm, [21] 1 CDCl3). The H NMR spectrum of 84 exhibits sharp signals attributable to a single

IPr environment in solution with isopropyl methyl (0.81 and 0.99 ppm, C6H5F) and 1 methine (2.32 ppm, C6H5F) H resonances that are upfield shifted relative to those for [30] 13 [InBr3(IPr)] (1.10, 1.35 and 2.48 ppm, CDCl3). The C NMR spectra of 83 and 84 lack carbenic carbon resonances, presumably due to coupling to the two spin-active thallium isotopes (203Tl, 29%, I = ½; 205Tl, 71%, I = ½). It is noteworthy that no further evidence of thallium coupling was observed in the 1H and 13C NMR spectra of 83 and

84, this contrasts [TlCl3(IMes)] and [TlCl3(IPr*) (72), for which thallium coupling of the 4,5-protons and carbons is observed.[27]

Compound 83 crystallises in the triclinic space group P 1̅ with a disordered half molecule of fluorobenzene in the asymmetric unit. Compound 84 crystallises in the [14] monoclinic space group P21/n and is isomorphous to its indium congener. The molecular structures of the cations in 83 and 84 are depicted in Figures 8.8 and 8.9 respectively (pg. 323). Salient metrical parameters are listed in Table 8.2 (pg. 324).

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+ Figure 8.8 - Molecular structure of the [Tl(IMes)2] cation in 83 (50% thermal ellipsoids). All hydrogen atoms omitted and mesityl groups depicted as wireframes for clarity.

+ Figure 8.9 - Molecular structure of the [Tl(IPr)2] cation in 84 (50% thermal ellipsoids). All hydrogen atoms omitted and Dipp groups depicted as wireframes for clarity.

323 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

M-CNHC CNHC-M-CNHC θyaw θpitch

2.560(6) 14.3 17.3 83 (IMes) 100.66(17) 2.561(5) 16.3 16.1

2.189(3) 11.7 23.0 [Ga(IMes) ]+ 104.5(1) 2 2.196(3) 13.1 22.5

2.703(4) 19.8 12.5 84 (IPr) 122.45(12) 2.745(4) 16.5 17.4

2.287(3) 11.8 27.7 [Ga(IPr) ]+ 118.2(1) 2 2.288(4) 11.1 31.0

2.488(2) 10.5 34.3 [In(IPr) ]+ 120.36(7) 2 2.505(2) 12.5 31.3

Table 8.2 - Selected bond parameters of bis(NHC) complexes of group 13 metal(I) cations

It is noteworthy that the Tl-CNHC distances in 83 and 84 (Table 8.2) are considerably [27] longer than those observed in [TlCl3(IMes)] (2.179(9) Å). This reflects the decreased electrophilicity of the thallium(I) centre and the increased steric congestion in 83 and 84 relative to [TlCl3(IMes)] albeit with a reduced coordination number. The shorter

Tl-CNHC distances and considerably smaller CNHC-Tl-CNHC angle in 83 relative to 84 likely reflect the decreased steric demand of IMes relative to IPr, although electronic effects vide infra cannot be dismissed (Table 8.2).

In contrast to a majority of metal NHC complexes, the thallium centres in 83 and 84 do not lie in the plane of, nor the C2 axis of, either of the coordinated NHCs. Similar “tilted” NHC coordination was observed for the lighter group 13 metal(I) congeners [14] (viz. Figure 8.3). This tilt can be quantified by the offset angle of the M-CNHC bond to the C2 axis of the imidazole ring as a combination of yaw and pitch angles. The yaw angle describes the tilting in the plane of the heterocycle while the pitch angle describes the tilting out of the plane of the heterocycle (Figure 8.10, pg. 325).[31]

324 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

Figure 8.10 - NHC pitch and yaw angles taken from reference 31

Computational studies conducted by Jones and Krossing on the aforementioned gallium(I) and indium(I) complexes reveal that a non-zero pitch angle enables back donation of metal electron density from the metal based electron pair to the vacant p-orbital of the carbenic carbon (Figure 8.11).[14] It is likely that non-zero yaw angles arise from steric crowding invoked when the metal and the NHC manoeuvre to optimise σ- and π-bonding interactions.

Figure 8.11 - The postulated σ- π-bonding interactions of Jones and Krossing[14]

The pitch angles described in 83 and 84 are significantly smaller than those of their gallium and indium counterparts (Table 8.2). This is consistent with less back donation from the thallium(I) to the NHCs relative to the same interaction at gallium(I) and indium(I) and is consistent with the higher s-character of the metal based electron pair in 83 and 84.

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8.4 Conclusions

In summary, this chapter describes the preparation of NHC complexes of several low oxidation state group 13 metals. Bis(NHC) complexes of tetrahalodigallanes and terachlorodiindane have been reported. Complex 78 is the second NHC complex of gallium(II) to be crystallographically characterised.

The reactivity of NHCs with soluble sources of thallium(I) was investigated. Reactions F using TlOTf and Tl[BAr 4] resulted in the immediate deposition of black solids, presumably thallium, concurrent to imidazolium salt formation. The thallium complex of the weakly coordinating tetrakis(perfluoro-tert-butoxy)aluminate anion (82) was prepared. In contrast to the aforementioned soluble sources of thallium(I), bis(NHC) complexes of thallium(I) (83 and 84) can be prepared by the reaction of 82 with two equivalents of NHC in fluorobenzene at ambient temperature. Complexes 83 and 84 display good thermal stabilities in the solid and solution states, however photoinduced decomposition is observed in the solid-state. The preparations of 83 and 84 represent a doubling of the number of known thallium(I) NHC complexes viz. Figure 8.4.

The solid-state structures of 83 and 84 display tilted atypical coordination of the NHCs. The coordination of each NHC to the thallium centre has been characterised in terms of NHC pitch and yaw angles. The pitch angles measured in 83 and 84 are considerably less than those of their gallium and indium congeners. This has been rationalised by the high s-character of the metal based electron pair and is in keeping with expectations based on periodic trends.

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8.5 Future Directions

The bis(NHC) complexes of tetrahalodigallane (78 and 79) and tetrachlorodiindane (80) are attractive targets for functionalisation. It is conceivable that the reaction of 78 and 79 with hydride sources such as silanes will yield gallium(II) hydrides or lower oxidation state digallanes subsequent to H2 elimination. Both outcomes are currently unprecedented. It is noteworthy that a dihydrido aluminium(II) NHC complex; [11] [{AlH2(IPr)}2] (Figure 8.3), has been reported.

Aluminium(I) complexes of weakly coordinating anions remain unknown. Given the t F stability of Ga[Al(O Bu )4] with respect to disproportionation, it is conceivable that an analogous aluminium(I) compound may be isolable. To this end, it is possible that the t F [32] protoylsis of [{AlCp*}4] with four equivalents of [H(OEt2)2][Al(O Bu )4] or t F t F [32] t F [(MesH)H][( Bu O)3Al-F-Al(O Bu )3] could afford Al[Al(O Bu )4]. Indeed, the t F [33] protoylsis of [Zn2Cp*2] with two equivalents of [H(OEt2)2][Al(O Bu )4] or F [34] 2+ [H(OEt2)2][BAr 4] results in the isolation of solvated [Zn2] cations. Access to t F Al[Al(O Bu )4] would greatly facilitate the expansion of aluminium(I) coordination chemistry, possibly enabling aluminium(I) congeners of 83 and 84 to be prepared.

Complexes 83 and 84 will likely function as bis(NHC) transmetallation reagents for d-block NHC chemistry. The high lattice energy of thallium(I) halides may even promote the metathesis of the accompanying tetrakis(perfluoro-tert-butoxy)aluminate anion thus affording coordinatively unsaturated bis(NHC)complexes of d-block metals. As indicated at the outset of this chapter, bis(NHC) complexes of group 9[35] and 10[36] cations have proved to be a goldmine for small molecules activation.

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8.6 Experimental

8.6.1 General Synthetic Procedures

[37] [38] [38] F [39] t F [40] “GaI”, IMes·HCl, IPr·HCl, Tl[BAr ] and Li[Al(O Bu )4] were synthesised by literature procedures. IMes and IPr were prepared by the addition of nBuLi (1.0 equiv.) to IMes·HCl and IPr·HCl respectively (1.0 equiv.) in THF, followed by extraction into toluene and recrystallised from diethyl ether (IMes) or toluene (IPr).

For detailed information regarding the general handling of solvents, chemicals and characterisations please refer to the appendix.

8.6.2 Synthesis of [{GaCl2(IMes)}2] (78)

A solution of Ga[GaCl4] (209 mg, 1.49 mmol) in toluene (15 mL) was treated dropwise with a solution of IMes (434 mg, 1.43 mmol) in toluene (40 mL) at -78 °C. The resultant orange solution was allowed to warm to ambient temperature over several hours, during this period a yellow solution was obtained with a small amount of grey deposited solid. Filtration and concentration in vacuo, followed by slow cooling to -25 °C afforded colourless crystals (110 mg, 26%); m.p. 182-184 °C, (dec. 230-234 °C). 1H

NMR (400 MHz, C6D6) δ 2.13 (s, 6H, p-CH3), 2.17 (s, 12H, o-CH3), 5.76 (s, 2H, NCH), 13 6.75 (s, 4H, m-ArH). C NMR (100 MHz, C6D6) δ 18.6 (o-CH3), 21.2 (p-CH3), 123.6 (NCH), 129.3 (m-ArCH), 129.9, 134.5, 135.5 (ArC), 139.5 (NCN). IR (Nujol, cm-1) 1608 (w), 1539 (w), 1261 (w), 1230 (w), 1097 (br m), 1031 (br m), 854 (w), 800 (br w),

727 (w). Anal. Cal. for C42H48N4Ga2Cl4: C, 56.67; H, 5.44; N, 6.29. Found: C, 57.85; H, 6.06; N, 5.90%.

8.6.3 Synthesis of [{GaI2(IMes)}2] (79)

A solution of IMes (257 mg, 0.84 mmol) in toluene (40 mL) was added dropwise to a stirred slurry of “GaI” (0.84 mmol) in toluene (20 mL) at -78 °C. The resultant light brown mixture was allowed to warm to ambient temperature over several hours, during this period a yellow solution was obtained with a small amount of grey solid. Filtration, followed by solvent removal in vacuo, afforded a brown powder. Washing with diethyl ether (30 mL) gave an off white powder (180 mg, 34%); m.p. 216-220 °C, (dec. 1 300-320 °C). H NMR (300 MHz, C6D6) δ 2.13 (s, 6H, p-CH3), 2.29 (s, 12H, o-CH3), 13 5.70 (s, 2H, NCH), 6.75 (s, 4H, m-ArH). C NMR (76 MHz, C6D6) δ 18.1 (o-CH3), 328 References for this chapter begin on pg. 331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

21.2 (p-CH3), 124.4 (NCH), 129.3 (ArCH), 130.5, 135.0, 136.1 (ArC), 139.8 (NCN). IR (Nujol, cm-1) 1608 (w), 1261 (w), 1223 (w), 1112 (w), 1032 (br m), 929 (w), 857 (w), 800 (br m), 761 (w), 727 (br w).

8.6.4 Synthesis of [{InCl2(IMes)}2] (80)

In[InCl4] (302 mg, 1.63 mmol) was added to a solution of IMes (520 mg, 1.71 mmol) in toluene (30 mL) with stirring at room temperature. The reaction mixture was stirred for 16 h, upon which a white precipitate was observed. The precipitate was isolated by filtration and dried in vacuo to afford a white powder (620 mg, 64%); m.p. 234-238 °C 1 (dec.). H NMR (500 MHz, C6D6) δ 2.11 (s, 12H, o-CH3), 2.17 (s, 6H, p-CH3), 5.76 (s, 13 2H, NCH), 6.80 (s, 4H, m-ArH). C NMR (100 MHz, C6D6) 18.3 (o-CH3), 21.4

(p-CH3), 123.5 (NCH), 129.9 (m-ArCH), 130.2, 133.7, 135.1 (ArC), 140.2 (NCN). IR (Nujol, cm-1) 2277 (br w), 1608 (w), 1541 (w), 1231 (m), 1109 (w), 1035 (br w), 931

(w), 850 (m), 768 (m), 728 (w). Anal. Cal. for C22H48Cl4In2N4: C, 51.46; H, 4.94; N, 5.72. Found: C, 51.51; H, 5.11; N, 5.82%.

t F 8.6.5 Synthesis of [Tl(C6H5F)2.5][Al(O Bu )4] (82)

t F TlCl (1.00 g, 4.2 mmol) and Li[Al(O Bu )4] (3.66 g, 3.8 mmol) were suspended in fluorobenzene (20 mL). The resultant slurry was sonicated overnight at 50 °C. A colourless solution containing a colourless precipitate containing some metallic solids was afforded. The solution was filtered, concentrated and layered with hexane (40 mL). Placement at -20 °C overnight afforded large colourless blocks suitable for X-ray diffraction structure determination. The crystals were washed with hexane (3×10 mL) 19 and then dried under vacuum (4.39 g, 83%). F NMR (376 MHz, C6H5F)  -75.1 t F 27 (O Bu ). Al NMR (104 MHz, C6H5F) δ 34.9 (AlO4).

t F 8.6.6 Synthesis of [Tl(IMes)2][Al(O Bu )4] (83)

A schlenk flask was charged with 82 (345 mg, 0.21 mmol) and IMes (160 mg, 0.47 mmol). Fluorobenzene (20 mL) was then added and the resultant colourless solution was stirred at room temperature overnight with the exclusion of light. During this period a pale yellow solution was obtained with a small amount of colourless precipitate deposited. The solution was filtered and layered with hexane (40 mL). Large colourless

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blocks suitable for X-ray diffraction structure determination were obtained after 48 h standing at ambient temperature. The crystals were washed with hexane (3×10 mL) and 1 then dried under vacuum (295 mg, 71%). H NMR (400 MHz, C6H5F) δ 1.65 (s, 24H, o- 13 CH3), 2.24 (s, 12H, p-CH3), 6.52 (s, 4H, NCH), 6.74 (s, 8H, m-ArH). C NMR (100 1 MHz, C6D6) δ 16.6 (o-CH3), 20.5 (p-CH3), 122.1 (br q, JCF = 295 Hz, CF3), 122.7 (NCH), 129.5 (m-ArCH), 134.1 (ipso-ArC), 134.6 (o-ArC), 140.0 (p-ArC). 19F NMR t F 27 (376 MHz, C6H5F) δ -75.0 (O Bu ). Al NMR (104 MHz, C6H5F) δ 34.8 (AlO4).

t F 8.6.7 Synthesis of [Tl(IPr)2][Al(O Bu )4] (84)

A schlenk flask was charged with 82 (700 mg, 0.50 mmol) and IPr (390 mg, 1.00 mmol). Fluorobenzene (20 mL) was then added and the resultant colourless solution was stirred at room temperature overnight with the exclusion of light. During this period a pale yellow solution was obtained with a small amount of colourless precipitate deposited. The solution was filtered and layered with hexane (40 mL). Placement at -20 °C overnight afforded large yellow blocks suitable for X-ray diffraction structure determination. The crystals were washed with hexane (3×10 mL) and then dried under 1 3 vacuum (540 mg, 55%). H NMR (400 MHz, C6H5F) δ 0.81 (d, JHH = 7.0 Hz, 24H, 3 3 CH(CH3)2), 0.99 (d, JHH = 7.0 Hz, 24H, CH(CH3)2), 2.32 (sept, JHH = 7.0 Hz, 8H, 13 CH(CH3)2), 6.73 (s, 4H, NCH), 7.12-7.33 (m, 12H, m- and p-ArH). C NMR (100

MHz, C6H5F) δ 23.6, 24.0 (CH(CH3)2), 28.7 (CH(CH3)2), 124.4 (NCH), 129.3, 134.8, 19 t F 27 145.8 (ArC). F NMR (376 MHz, C6H5F) δ -75.0 (O Bu ). Al NMR (104 MHz,

C6H5F) δ 34.8 (AlO4).

330 References for this chapter begin on pg. 331

8.7 References

[1] de Fremont, P.; Marion, N.; Nolan, S. P., Coord. Chem. Rev. 2009, 253, 862- 892. [2] (a) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P., J. Am. Chem. Soc. 2005, 127, 3516-3526; (b) Arduengo, A. J.; Gamper, S. F.; Calabrese, J. C.; Davidson, F., J. Am. Chem. Soc. 1994, 116, 4391-4394; (c) Konnick, M. M.; Guzei, I. A.; Stahl, S. S., J. Am. Chem. Soc. 2004, 126, 10212- 10213; (d) Hruszkewycz, D. P.; Wu, J.; Hazari, N.; Incarvito, C. D., J. Am. Chem. Soc. 2011, 133, 3280-3283; (e) Fortman, G. C.; Scott, N. M.; Linden, A.; Stevens, E. D.; Dorta, R.; Nolan, S. P., Chem. Commun. 2010, 46, 1050-1052. [3] (a) Yamashita, M.; Goto, K.; Kawashima, T., J. Am. Chem. Soc. 2005, 127, 7294-7295; (b) Clement, N. D.; Cavell, K. J.; Jones, C.; Elsevier, C. J., Angew. Chem. Int. Ed. 2004, 43, 1277-1279. [4] Ghadwal, R. S.; Roesky, H. W.; Merkel, S.; Henn, J.; Stalke, D., Angew. Chem. Int. Ed. 2009, 48, 5683-5686. [5] (a) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F.; von R. Schleyer, P.; Robinson, G. H., Science 2008, 321, 1069-1071; (b) Sidiropoulos, A.; Jones, C.; Stasch, A.; Klein, S.; Frenking, G., Angew. Chem. Int. Ed. 2009, 48, 9701-9704; (c) Jones, C.; Sidiropoulos, A.; Holzmann, N.; Frenking, G.; Stasch, A., Chem. Commun. 2012, 48, 9855-9857; (d) Kinjo, R.; Donnadieu, B.; Bertrand, G., Angew. Chem. Int. Ed. 2010, 49, 5930-5933; (e) Wang, Y.; Xie, Y.; Wei, P.; King, R. B.; Schaefer, H. F.; Schleyer, P. v. R.; Robinson, G. H., J. Am. Chem. Soc. 2008, 130, 14970-14971; (f) Back, O.; Kuchenbeiser, G.; Donnadieu, B.; Bertrand, G., Angew. Chem. Int. Ed. 2009, 48, 5530-5533. [6] Dyker, C. A.; Lavallo, V.; Donnadieu, B.; Bertrand, G., Angew. Chem. Int. Ed. 2008, 47, 3206-3209. [7] Tonner, R.; Frenking, G., Organometallics 2009, 28, 3901-3905. [8] Wang, Y.; Quillian, B.; Wei, P.; Wannere, C. S.; Xie, Y.; King, R. B.; Schaefer, H. F.; Schleyer, P. v. R.; Robinson, G. H., J. Am. Chem. Soc. 2007, 129, 12412- 12413. [9] Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A., Science 2012, 336, 1420-1422.

331 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

[10] Fliedel, C.; Schnee, G.; Avilés, T.; Dagorne, S., Coord. Chem. Rev. 2014, 275, 63-86. [11] Bonyhady, S. J.; Collis, D.; Frenking, G.; Holzmann, N.; Jones, C.; Stasch, A., Nat. Chem. 2010, 2, 865-869. [12] Quillian, B.; Wei, P.; Wannere, C. S.; Schleyer, P. v. R.; Robinson, G. H., J. Am. Chem. Soc. 2009, 131, 3168-3169. [13] Baker, R. J.; Farley, R. D.; Jones, C.; Kloth, M.; Murphy, D. M., Chem. Commun. 2002, 1196-1197. [14] Higelin, A.; Keller, S.; Göhringer, C.; Jones, C.; Krossing, I., Angew. Chem. Int. Ed. 2013, 52, 4941-4944. [15] Nakai, H.; Tang, Y. J.; Gantzel, P.; Meyer, K., Chem. Commun. 2003, 24-25. [16] Arnold, P. L.; Scarisbrick, A. C., Organometallics 2004, 23, 2519-2521. [17] Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F., J. Am. Chem. Soc. 1992, 114, 9724-9725. [18] Nogai, S.; Schmidbaur, H., Inorg. Chem. 2002, 41, 4770-4774. [19] Baker, R. J.; Bettentrup, H.; Jones, C., Eur. J. Inorg. Chem. 2003, 2446-2451. [20] Abernethy, C. D.; Cole, M. L.; Jones, C., Organometallics 2000, 19, 4852-4857. [21] Marion, N.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Stevens, E. D.; Fensterbank, L.; Malacria, M.; Nolan, S. P., Organometallics 2007, 26, 3256- 3259. [22] Alexander, S. G.; Cole, M. L.; Forsyth, C. M.; Furfari, S. K.; Konstas, K., Dalton Trans. 2009, 2326-2336. [23] Cole, M. L.; Kloth, M., Unpublished data, University of New South Wales. [24] (a) Alexander, S. G.; Cole, M. L.; Forsyth, C. M., Chem. Eur. J. 2009, 15, 9201- 9214; (b) Cole, M. L.; Furfari, S. K.; Kloth, M., J. Organomet. Chem. 2009, 694, 2934-2940; (c) Ball, G. E.; Cole, M. L.; McKay, A. I., Dalton Trans. 2012, 41, 946-952. [25] Baker, R. J.; Jones, C., Appl. Organomet. Chem. 2003, 17, 807-808. [26] As determined by a survey of the Cambridge Structural Database v. 5.36 with updates for November 2014. [27] Cole, M. L.; Davies, A. J.; Jones, C., J. Chem. Soc., Dalton Trans. 2001, 2451- 2452.

332 Chapter Eight: NHC Complexes of Low Oxidation State Group 13 Metals

[28] Slattery, J. M.; Higelin, A.; Bayer, T.; Krossing, I., Angew. Chem. Int. Ed. 2010, 49, 3228-3231. [29] Sarazin, Y.; Hughes, D. L.; Kaltsoyannis, N.; Wright, J. A.; Bochmann, M., J. Am. Chem. Soc. 2007, 129, 881-894. [30] Baker, R. J.; Davies, A. J.; Jones, C.; Kloth, M., J. Organomet. Chem. 2002, 656, 203-210. [31] Fegler, W.; Spaniol, T. P.; Okuda, J., Dalton Trans. 2010, 39, 6774-6779. [32] Kraft, A.; Beck, J.; Steinfeld, G.; Scherer, H.; Himmel, D.; Krossing, I., Organometallics 2012, 31, 7485-7491. [33] Schulz, S.; Schuchmann, D.; Krossing, I.; Himmel, D.; Bläser, D.; Boese, R., Angew. Chem. Int. Ed. 2009, 48, 5748-5751. [34] Banh, H.; Gemel, C.; Seidel, R. W.; Fischer, R. A., Chem. Commun. 2015, 51, 2170-2172. [35] (a) Tang, C. Y.; Thompson, A. L.; Aldridge, S., J. Am. Chem. Soc. 2010, 132, 10578-10591; (b) Tang, C. Y.; Lednik, J.; Vidovic, D.; Thompson, A. L.; Aldridge, S., Chem. Commun. 2011, 47, 2523-2525; (c) Tang, C. Y.; Smith, W.; Thompson, A. L.; Vidovic, D.; Aldridge, S., Angew. Chem. Int. Ed. 2011, 50, 1359-1362; (d) Phillips, N.; Rowles, J.; Kelly, M. J.; Riddlestone, I.; Rees, N. H.; Dervisi, A.; Fallis, I. A.; Aldridge, S., Organometallics 2012, 31, 8075- 8078; (e) Phillips, N.; Treasure, L.; Rees, N. H.; Tirfoin, R.; McGrady, J. E.; Aldridge, S., Eur. J. Inorg. Chem. 2014, 4877-4885; (f) Phillips, N.; Tang, C. Y.; Tirfoin, R.; Kelly, M. J.; Thompson, A. L.; Gutmann, M. J.; Aldridge, S., Dalton Trans. 2014, 43, 12288-12298. [36] (a) Rivada-Wheelaghan, O.; Ortuño, M. A.; Díez, J.; García-Garrido, S. E.; Maya, C.; Lledós, A.; Conejero, S., J. Am. Chem. Soc. 2012, 134, 15261-15264; (b) Rivada-Wheelaghan, O.; Ortuño, M. A.; Díez, J.; Lledós, A.; Conejero, S., Angew. Chem. Int. Ed. 2012, 51, 3936-3939. [37] Green, M. L. H.; Mountford, P.; Smout, G. J.; Speel, S. R., Polyhedron 1990, 9, 2763-2765. [38] Hintermann, L., Beilstein J. Org. Chem. 2007, 3, 1-5. [39] Cullinane, J.; Jolleys, A.; Mair, F. S., Dalton Trans. 2013, 42, 11971-11975. [40] Krossing, I., Chem. Eur. J. 2001, 7, 490-502.

333

APPENDIX

Appendix One: General Procedures

A1.1 General Experimental Procedures

All synthetic manipulation were performed using standard Schlenk and glove box techniques under an atmosphere of either high purity argon or nitrogen, unless otherwise specified. All glassware was flame dried under vacuum to remove residual water prior to use.

All solvents required for air sensitive reactions were dried, degassed and stored for use under an inert gas atmosphere. Benzene, diethyl ether, DME, hexane, THF and toluene were distilled from sodium benzophenone ketyl. Methanol and ethanol were distilled from magnesium. Fluorobenzene was distilled from phosphorous pentoxide. Acetonitrile, dichloromethane and pentane were collected from an Innovative Technology MD-7 solvent purification system. Acetonitrile and dichloromethane were stored over 4 Å molecular sieves. Pentane was stored over a potassium mirror.

All reagents were purchased from commercial sources unless otherwise stated, and used as received unless otherwise stated. Air sensitive reagents were stored under an atmosphere of argon in a Saffron Scientific Alpha glove box. LiAlH4 was extracted into dry diethyl ether and the solvent was subsequently removed in vacuo and stored in a glove box. Organolithium reagents were decanted into J. Youngs tapped flasks under argon and were standardised according to literature procedures.[S1]

A1.2 Characterisations

A1.2.1 NMR Characterisations

1H, 2H, 7Li, 11B, 13C, 19F and 27Al NMR spectra were recorded on either a Bruker Avance DPX 200 (1H: 200.13 MHz and 13C: 50.32 MHz), Bruker Avance DPX 250 (1H: 250.13 MHz, 13C: 62.90 MHz), Bruker Avance DPX 300 (1H: 300.30 MHz, 13C: 75.52 MHz), Bruker Avance III 300 (1H: 300.17 MHz, 13C: 75.48 MHz), Bruker Avance III 400 (1H: 400.13 MHz, 7Li: 155.51 MHz, 11B: 128.38 MHz, 13C: 100.62 MHz, 19F: 376.44 MHz), Bruker Avance III 500 (1H: 500.13 MHz) or Bruker Avance III 600 (1H: 600.16 MHz, 2H: 92.13 MHz, 13C: 150.92 MHz) spectrometer at 298 K, unless otherwise stated. All spectra were recorded as solutions in either benzene-d6

(C6D6), chloroform-d (CDCl3), dichloromethane-d2 (CD2Cl2), dimethylsulfoxide-d6

(DMSO-d6), tetrahydrofuran-d8 (THF-d8) or toluene-d8 (C7D8) and the chemical shifts

S2 Appendix One: General Procedures

[S2] were referenced to residual non-deuterated solvent peaks. C6D6, C7D8 and THF-d8 were stored over sodium and freeze-thaw degassed prior to use. CD2Cl2 was dried over

CaH2, vacuum transferred and freeze-thaw degassed prior to use. Chemical shifts (δ) are reported in parts per million (ppm). Uncertainties in the chemical shifts were typically ± 1 19 13 n 0.01 ppm for H and F, ± 0.05 ppm for C. Coupling constants ( JXY) are reported in Hertz (Hz). Uncertainties in coupling constants are ± 0.05 Hz for 1H-1H, ± 0.5 Hz for 1H-205Tl, 1H-103Rh, 13C-103Rh, 13C-203Tl and 13C-205Tl couplings. Multiplicities are denoted as singlet (s), doublet (d), triplet (t), quartet (q), septet (sept) or multiplet (m) and prefixed broad (br) where applicable.

The following two-dimensional NMR techniques were routinely used for the assignment of organic and organometallic compounds: COSY (Correlation Spectroscopy), TOCSY (Total Correlation Spectroscopy), NOESY (Nuclear Overhauser Effect Spectroscopy), HSQC (Heteronuclear Single Quantum Coherence) and HMBC (Heteronuclear Multiple Bond Correlation). All NMR spectra were processed using Bruker Topspin 3.1.

A1.2.2 Vibrational Characterisations

Infrared spectra (4,000 to 400 cm-1) of compounds 28, 29, 40, 41 and 52 were recorded on a Bruker Alpha FTIR spectrometer under inert atmosphere in a glove box using the attenuated total reflection sampling method. Infrared spectra of compounds 1-27, 30-40, 42-51 and 52-80 were prepared as Nujol mulls on sodium chloride crystal windows and the spectra (4,000 to 400 cm-1) were recorded on a Nicolet Avatar 320 FTIR spectrometer. Absorbances are reported in wavenumbers (cm-1) and the intensity of the absorbance is denoted as very strong (vs), strong (s), medium (m) or weak (w) and prefixed broad (br) or sharp (sh) where applicable.

A1.2.3 Single Crystal X-ray Diffraction (XRD) Studies

Crystalline samples of 1-18, 20-27, 30-49, 50-61, 64-67, 69, 71-72, 76-78, 81 and 82-84 were mounted on MiTeGen micromounts in type NVH immersion oil at 150(2) K unless otherwise stated. A summary of crystallographic data can be found in Appendix Two. Data from compounds (32a, 40, 41, 44, 52b) were collected on an Oxford

Excalibur II diffractometer with a MoKα X-ray source ( = 0.71073 Å), and Sapphire2

S3 Appendix One: General Procedures

CCD detector. Data from all other compounds were collected on a Bruker APEX II diffractometer with a Bruker Quazar Multilayer Optics MoKα X-ray micro source ( = 0.71073 Å), and an Apex II CCD detector. All datasets were corrected for absorption using SADABS.[S3] Unit cell parameters were determined for collection employing software defaults and optimized upon completion of data collection using all collected frames. Structure solution and refinement was carried out using the SHELX suite of programs[S4] with the GUI X-Seed.[S5] All non-hydride hydrogen atoms were refined in calculated positions (riding model). The hydride ligands of complexes 53-56, 59-61, 64, 66, 67, 69, 71 and 76. Methine hydrogens of complexes 64-67, 69, 71 and 72 were located in difference maps and refined isotropically.

A1.2.4 Other Characterisation Techniques

Melting points of air sensitive compounds were determined in sealed glass capillaries under argon and are uncorrected. Microanalyses were conducted at the Campbell Microanalytical Laboratory, University of Otago, P.O. Box 56, Dunedin, New Zealand or the Microanalytical Unit, Research School of Chemistry, Australian National University, Canberra, Australia.

A1.3 Nomenclature and Atom Numbering

Terphenyl containing compounds were named according to the IUPAC nomenclature recommendations for symmetric terphenyls. The general atom number is shown in Figure A1.1 (below).

Figure A1.1 - Atom numbering in terphenyl moieties

S4 Appendix Two: Crystallographic Data

Figure A3.1 - Molecular structure of 2 (50% thermal ellipsoids).All hydrogen atoms excepting H(1) omitted for clarity

Figure A3.2 - Molecular structure of 5 (50% thermal ellipsoids) All hydrogen atoms omitted for clarity. Highest occupancy Cy ring displayed.

S5 Appendix Two: Crystallographic Data

1 2 3

Molecular Formula C48H51N3 C33H40N2 C37H47N2 Mol. Weight 669.92 464.67 519.77 Temperature, K 150(2) 173(2) 150(2)

Space Group P-1 P-1 P21/n a, Å 10.4832(7) 8.7630(18) 16.3108(6) b, Å 12.3273(7) 12.297(3) 10.5397(5) c, Å 15.6966(8) 12.746(3) 17.7238(8) α, deg 88.070(3) 77.04(3) 90 β, deg 84.174(3) 75.88(3) 90.373(2) γ, deg 86.051(2) 72.65(3) 90 Volume, Å3 2014.4(2) 1352.6(5) 3046.9(2) Z 2 2 4 Description Prism Plate Prism Colour Yellow Colourless Colourless -3 Dc, g cm 1.104 1.141 1.133 F(000) 720 504 1132 μ, mm-1 0.064 0.066 0.065 Reflections Collected 15495 15590 46211

Rσ 0.0537 0.0489 0.0650

Rint 0.0301 0.0401 0.0599 Unique Reflections 9123 6785 7995 Parameters Varied 481 327 362

R1 0.0518 0.0509 0.0612

wR2 (all data) 0.1428 0.1430 0.1992 GooF 1.028 1.013 1.072 Δρ/e Å3 0.247/-0.217 0.232/-0.224 0.336/-0.308

S6 Appendix Two: Crystallographic Data

Figure A3.3 - Molecular structure of 6 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Symmetry operation used to generate # atoms: 1-x, y, ½-z.

Figure A3.4 - Molecular structure of 7 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Symmetry operation used to generate # atoms: 1-x, y, ½-z.

S7 Appendix Two: Crystallographic Data

4 5 6

C35H45AlN2 Molecular Formula C50H56AlN3·0.5C6H14 C39H52AlN3 ·0.5C7H8 Mol. Weight 769.04 520.71 589.82 Temperature, K 150(2) 150(2) 150(2) Space Group P-1 P-1 Cc a, Å 10.837(2) 10.0544(4) 18.6872(8) b, Å 11.883(2) 10.9283(6) 11.7214(8) c, Å 19.695(4) 16.8478(9) 17.0577(11) α, deg 97.74(3) 91.823(2) 90 β, deg 96.64(3) 104.003(2) 114.652(3) γ, deg 111.73(3) 109.973(2) 90 Volume, Å3 2296.6(8) 1685.15(15) 3395.8(4) Z 2 2 4 Description Tabular plate Plate Octahedral Colour Yellow Colourless Colourless -3 Dc, g cm 1.112 1.026 1.154 F(000) 830 564 1280 μ, mm-1 0.082 0.083 0.091 Reflections Collected 24643 29079 25688

Rσ 1.0877 0.0600 0.0421

Rint 0.3985 0.0532 0.0468 Unique Reflections 11823 9085 7186 Parameters Varied 538 447 387

R1 0.0994 0.0554 0.393

wR2 (all data) 0.3357 0.1795 0.1184 GooF 0.803 1.042 1.043 Δρ/e Å3 0.264/-0.252 0.375/-0.312 0.251/-0.306

S8 Appendix Two: Crystallographic Data

Figure A3.5 - Molecular structure of 8 (50% thermal ellipsoids). All hydrogen atoms omitted and Cy groups depicted as wireframes for clarity.

Figure A3.6 - Molecular structure of 9 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S9 Appendix Two: Crystallographic Data

7 8 9

Molecular Formula C26H40AlN3 C39H62AlN3 C37H59AlN2 Mol. Weight 421.59 599.89 558.84 Temperature, K 173(2) 150(2) 152(2)

Space Group C2/c P21/n P21/n a, Å 17.6571(7) 13.2187(9) 12.510(2) b, Å 8.9969(3) 17.6327(13) 18.884(4) c, Å 16.5011(4) 15.7818(10) 15.799(3) α, deg 90 90 90 β, deg 92.050(3) 95.395(3) 107.278(6) γ, deg 90 90 90 Volume, Å3 2619.67(15) 3662.1(4) 3563.8(12) Z 4 4 4 Description Block Block Block Colour Colourless Colourless Colourless -3 Dc, g cm 1.069 1.088 1.042 F(000) 920 1320 1232 μ, mm-1 0.093 0.085 0.082 Reflections Collected 25534 55403 38300

Rσ 0.0326 0.0399 0.1088

Rint 0.0551 0.0634 0.1236 Unique Reflections 4010 8073 9677 Parameters Varied 142 398 377

R1 0.0444 0.0462 0.0709

wR2 (all data) 0.1336 0.1386 0.2373 GooF 1.027 1.075 1.073 Δρ/e Å3 0.370/-0.305 0.239/-0.414 0.622/-0.505

S10 Appendix Two: Crystallographic Data

Figure A3.7 - Molecular structure of 10 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Highest occupancy Me groups displayed.

Figure A3.8 - Molecular structure of 12 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S11 Appendix Two: Crystallographic Data

10 11 12

Molecular C50H50RhN3O2 C28H34AlN2 C31H34RhN2O2 Formula ·C48H51N3 Mol. Weight 434.62 827.84 578.58 Temperature, K 152(2) 152(2) 152(2)

Space Group P21/n P21/n P-1 a, Å 13.321(7) 11.1757(4) 10.2807(4) b, Å 14.394(8) 16.1731(7) 10.9865(4) c, Å 14.679(7) 45.4418(18) 14.6713(5) α, deg 90 90 70.8800(11) β, deg 94.30(3) 94.131(2) 79.7465(13) γ, deg 90 90 74.6877(15) Volume, Å3 2807(3) 8192.1(6) 1502.48(10) Z 4 4 2 Description Parallelepiped Plate Plate Colour Colourless Orange Yellow -3 Dc, g cm 1.029 1.342 1.279 F(000) 952 3456 608 μ, mm-1 0.088 0.461 0.596 Reflections 42132 122651 21911 Collected

Rσ 0.0706 0.1332 0.0354

Rint 0.0893 0.1392 0.0424 Unique 6188 18080 5886 Reflections Parameters 312 992 336 Varied

R1 0.0613 0.0692 0.0253

wR2 (all data) 0.2129 0.2246 0.0724 GooF 1.046 0.996 1.136 Δρ/e Å3 0.246/-0.397 0.863/-1.087 0.588/-0.377

S12 Appendix Two: Crystallographic Data

Figure A3.9 - Molecular structure of 13 (50% thermal ellipsoids). All hydrogen atoms omitted and Cy groups depicted as wireframes for clarity.

Figure A3.10 - Molecular structure of 14 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S13 Appendix Two: Crystallographic Data

13 14 15 Molecular C H RhN O C H RhN O C H Rh N O Formula 39 56 3 2 37 53 2 2 52 64 2 6 4 Mol. Weight 701.77 660.72 1042.91 Temperature, K 152(2) 153(2) 150(2)

Space Group P21/n P21/n P-1 a, Å 9.4904(4) 19.2923(12) 13.2722(5) b, Å 18.2900(8) 9.6687(7) 13.4363(5) c, Å 20.8209(7) 20.0830(13) 15.3662(7) α, deg 90 90 81.307(2) β, deg 99.416(2) 110.009(3) 74.676(2) γ, deg 90 90 77.731(2) Volume, Å3 3565.4(2) 3520.0(4) 2565.68(18) Z 4 4 2 Description Prism Block Rhombohedron Colour Yellow Yellow Orange -3 Dc, g cm 1.307 1.247 1.350 F(000) 1488 1400 1080 μ, mm-1 0.516 0.517 0.691 Reflections 27967 28496 39809 Collected

Rσ 0.0411 0.0464 0.0771

Rint 0.0431 0.0435 0.0623 Unique 7768 7676 11205 Reflections Parameters 414 393 593 Varied

R1 0.0284 0.0374 0.0418

wR2 (all data) 0.0873 0.1028 0.1120 GooF 1.094 1.060 1.029 Δρ/e Å3 0.435/-0.574 0.412/-0.577 0.740/-0.730

S14 Appendix Two: Crystallographic Data

Figure A3.11 - Molecular structure of 17 (20% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S15 Appendix Two: Crystallographic Data

16 17 18

Molecular Formula C105H161Rh3N6O6LiCl C33H47RhN2 C32H46RhN3 Mol. Weight 1954.51 574.63 575.63 Temperature, K 153(2) 152(2) 150(2) Space Group C2/c P-1 Cc a, Å 34.876(3) 10.5092(6) 17.240(8) b, Å 26.438(3) 11.2966(6) 8.861(5) c, Å 22.979(2) 14.1488(7) 18.770(8) α, deg 90 93.648(2) 90 β, deg 115.098(5) 102.187(2) 94.05(2) γ, deg 90 113.466(2) 90 Volume, Å3 19187(3) 1485.51(14) 2860(2) Z 8 2 4 Description Block Prism Prism Colour Orange Yellow Red -3 Dc, g cm 1.115 1.285 1.337 F(000) 6688 608 1216 μ, mm-1 0.582 0.598 0.622 Reflections Collected 142218 22607 11032

Rσ 0.2038 0.0757 0.0443

Rint 0.2109 0.0676 0.0362 Unique Reflections 21203 6540 4908 Parameters Varied 907 349 333

R1 0.0695 0.0487 0.0268

wR2 (all data) 0.2103 0.1439 0.0666 GooF 0.855 1.060 1.063 Δρ/e Å3 0.716/-1.407 0.699/-1.750 0.331/-0.418

S16 Appendix Two: Crystallographic Data

21 22 23

Molecular Formula C41H59LiN2O2·0.5C7H8 C45H63LiN2O2 C89H118Li2N4O2 Mol. Weight 660.88 670.91 1289.75 Temperature, K 150(2) 150(2) 150(2)

Space Group P21/n P21/n P21/n a, Å 10.266(2) 10.876(8) 13.0976(12) b, Å 15.815(3) 20.258(15) 27.836(3) c, Å 23.371(5) 18.401(13) 20.729(2) α, deg 90 90 90 β, deg 101.79(3) 96.13(3) 102.540(4) γ, deg 90 90 90 Volume, Å3 3714.5(13) 4031(5) 7377.2(13) Z 4 4 4 Description Plate Block Prism Colour Colourless Colourless Colourless -3 Dc, g cm 1.182 1.105 1.161 F(000) 1436 1464 2808 μ, mm-1 0.071 0.066 0.068 Reflections 30788 59608 105594 Collected

Rσ 0.6625 0.0776 0.4536

Rint 0.3348 0.0800 0.2570 Unique Reflections 9957 11388 20154 Parameters Varied 429 541 779

R1 0.0983 0.0684 0.0960

wR2 (all data) 0.2170 0.2292 0.2807 GooF 0.843 1.033 0.801 Δρ/e Å3 0.174/-0.206 0.254/-0.229 0.270/-0.292

S17 Appendix Two: Crystallographic Data

Figure A3.12 - Molecular structure of 24 (50% thermal ellipsoids). All hydrogen atoms omitted and THF molecules excepting O atoms depicted as wireframes for clarity.

Figure A3.13 - Molecular structure of 26 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S18 Appendix Two: Crystallographic Data

24 25 26

C56H66LiN3O2 Molecular Formula C32H50LiN3O2 C32H54LiN3O2 ·C4H8O Mol. Weight 515.69 892.16 519.72 Temperature, K 150(2) 150(2) 150(2)

Space Group P21/c P21/c P21/c a, Å 18.8982(15) 11.9251(4) 16.5643(18) b, Å 18.6119(15) 17.6801(5) 11.0730(8) c, Å 19.5461(16) 24.5711(7) 19.0048(19) α, deg 90 90 90 β, deg 111.056(3) 97.2130(10) 104.858(3) γ, deg 90 90 90 Volume, Å3 6415.9(9) 5139.5(3) 3369.2(6) Z 8 4 4 Description Square slab Prism Prism Colour Yellow Yellow Colourless -3 Dc, g cm 1.068 1.153 1.025 F(000) 2256 1928 1144 μ, mm-1 0.065 0.070 0.063 Reflections Collected 65900 43158 8451

Rσ 0.3280 0.0799 0.1655

Rint 0.1698 0.0588 0.0522 Unique Reflections 18170 13342 5889 Parameters Varied 740 616 366

R1 0.0968 0.0636 0.0751

wR2 (all data) 0.2543 0.1797 0.2364 GooF 0.936 1.020 0.964 Δρ/e Å3 0.287/-0.236 0.642/-0.552 0.275/-0.254

S19 Appendix Two: Crystallographic Data

Figure A3.14 - Molecular structure of 27 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.15 - Molecular structure of 30 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S20 Appendix Two: Crystallographic Data

27 30 31 Molecular C H LiN O C H LiN C H NaN Formula 52 60 3 48 50 3 48 50 3 Mol. Weight 749.97 675.85 691.90 Temperature, K 150(2) 156(2) 150(2)

Space Group P21/c P21/c P21/n a, Å 12.6496(9) 10.6536(9) 14.2522(19) b, Å 13.9682(10) 22.3187(17) 19.794(3) c, Å 25.7416(17) 17.0499(12) 14.8684(18) α, deg 90 90 90 β, deg 91.733(3) 92.052(3) 109.082(6) γ, deg 90 90 90 Volume, Å3 4546.3(5) 4051.4(5) 3964.1(9) Z 4 4 4 Description Prism Prism Octahedral Colour Yellow Yellow Yellow -3 Dc, g cm 1.096 1.108 1.159 F(000) 1616 1448 1480 μ, mm-1 0.064 0.064 0.076 Reflections 62275 33486 67132 Collected

Rσ 0.0885 0.0678 0.0728

Rint 0.1007 0.0735 0.0766 Unique Reflections 9308 8932 11394 Parameters Varied 528 481 481

R1 0.0645 0.0597 0.0587

wR2 (all data) 0.2000 0.1967 0.2074 GooF 1.039 1.076 1.027 Δρ/e Å3 0.253/-0.278 0.247/-0/259 0.297/-0.329

S21 Appendix Two: Crystallographic Data

Figure A3.16 - Molecular structure of 32a (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.17 - Molecular structure of 32·C6H14 (30% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S22 Appendix Two: Crystallographic Data

32a 32b 32·C6H14

Molecular Formula C48H50KN3 C48H50KN3 C48H50KN3 C6H14 Mol. Weight 708.01 708.01 708.01 Temperature, K 173(2) 154(2) 153(2)

Space Group P21/n P21 Pca21 a, Å 14.0211(4) 10.6705(4) 17.870(9) b, Å 19.9427(5) 15.6826(8) 12.905(6) c, Å 14.7220(4) 12.3438(7) 20.797(9) α, deg 90 90 90 β, deg 107.917(3) 93.288(2) 90 γ, deg 90 90 90 Volume, Å3 3916.91(19) 2062.23(18) 4796(4) Z 4 2 4 Description Octahedral Prism Rod Colour Yellow Yellow Yellow -3 Dc, g cm 1.201 1.140 0.981 F(000) 1512 756 1512 μ, mm-1 0.173 0.164 0.141 Reflections Collected 38060 17394 36432

Rσ 0.0720 0.0940 0.1903

Rint 0.0673 0.0574 0.1431 Unique Reflections 9311 8593 9084 Parameters Varied 481 481 515

R1 0.0546 0.0575 0.0931

wR2 (all data) 0.1205 0.1680 0.3382 GooF 1.015 1.066 0.897 Δρ/e Å3 0.316/-0.305 0.371/-0.445 0.425/-0.339

S23 Appendix Two: Crystallographic Data

Figure A3.18 - Molecular structure of 33 (35% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.19 - Molecular structure of 34 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S24 Appendix Two: Crystallographic Data

33 34 35 Molecular C H RbN C H CsN C H K N Formula 48 50 3 48 50 3 75 83 2 4 Mol. Weight 754.38 801.82 1118.65 Temperature, K 151(2) 150(2) 150(2)

Space Group P21 P21 P21/n a, Å 11.1579(18) 11.0720(4) 13.7833(11) b, Å 15.707(2) 15.5491(5) 22.120(2) c, Å 11.9335(18) 12.1161(5) 21.3958(16) α, deg 90 90 90 β, deg 100.237(7) 99.4860(10) 107.050(3) γ, deg 90 90 90 Volume, Å3 2058.2(5) 2057.38(13) 6236.5(9) Z 2 2 4 Description Prism Prism Plate Colour Yellow Yellow Yellow -3 Dc, g cm 1.217 1.294 1.191 F(000) 792 828 2396 μ, mm-1 1.238 0.935 0.198 Reflections 29570 15813 93779 Collected

Rσ 0.0964 0.0575 0.1404

Rint 0.0670 0.0470 0.1485 Unique Reflections 8396 7603 13843 Parameters Varied 481 481 750

R1 0.0847 0.0289 0.0712

wR2 (all data) 0.1036 0.1054 0.2583 GooF 0.992 1.167 1.014 Δρ/e Å3 0.345/-0.511 0.531/-0.670 0.726/-0.722

S25 Appendix Two: Crystallographic Data

Figure A3.20 - Molecular structure of 37 (20% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.21 - Molecular structure of 39 (20% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S26 Appendix Two: Crystallographic Data

36 37 38 Molecular C H LiN C H IGaN C H GaIN Formula 52 59 3 48 68 6 24 34 3 Mol. Weight 739.90 925.70 561.16 Temperature, K 152(2) 150(2) 150(2)

Space Group P21/n P21/c P-1 a, Å 11.4916(4) 14.464(2) 10.764(3) b, Å 30.8596(12) 16.600(2) 11.169(3) c, Å 30.8596(12) 21.284(3) 12.729(5) α, deg 90 90 96.760(17) β, deg 110.931(2) 109.052(6) 114.864(10) γ, deg 90 90 105.707(12) Volume, Å3 4420.4(3) 4830.5(12) 1288.8(7) Z 4 4 2 Description Prism Block Prism Colour Yellow Pale Yellow Colourless -3 Dc, g cm 1.112 1.591 1.446 F(000) 1592 2410 566 μ, mm-1 0.063 1.557 2.279 Reflections 65312 65034 13343 Collected

Rσ 0.0547 0.0987 0.2474

Rint 0.0688 0.0772 0.1192 Unique Reflections 9771 13258 5642 Parameters Varied 581 521 270

R1 0.0571 0.1474 0.0973

wR2 (all data) 0.1728 0.4773 0.2872 GooF 1.046 1.548 1.002 Δρ/e Å3 0.339/-0.268 3.216/-4.567 1.782/-2.096

S27 Appendix Two: Crystallographic Data

Figure A3.22 - Molecular structure of 42 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S28 Appendix Two: Crystallographic Data

39 40 41 Molecular C H ClGaN C H ClInN C H IInN Formula 48 68 6 48 68 6 48 68 6 Mol. Weight 834.25 879.35 970.80 Temperature, K 150(2) 173(2) 150(2)

Space Group P21/c P21/c P21/c a, Å 14.315(3) 14.5014(4) 14.375(3) b, Å 16.444(3) 16.4263(4) 16.586(3) c, Å 21.068(4) 21.0903(6) 21.259(4) α, deg 90 90 90 β, deg 109.614(9) 109.584(3) 109.19(3) γ, deg 90 90 90 Volume, Å3 4671.6(17) 4733.2(2) 4786.8(19) Z 4 4 4 Description Cube Cube Cube Colour Colourless Colourless Colourless -3 Dc, g cm 1.186 1.234 1.347 F(000) 1784 1856 2000 μ, mm-1 0.684 0.593 1.176 Reflections 45713 61574 32439 Collected

Rσ 0.1494 0.0309 0.1963

Rint 0.0988 0.0390 0.1357 Unique Reflections 13896 11395 11242 Parameters Varied 521 521 553

R1 0.0625 0.0303 0.0972

wR2 (all data) 0.1828 0.0804 0.2936 GooF 1.016 1.021 1.038 Δρ/e Å3 0.796/-0.655 0.827/-0.422 2.846/-2.108

S29 Appendix Two: Crystallographic Data

42 43 44 Molecular C H N Tl C H Ga N C H InN Formula 96 136 12 4 51.5 54.34 0.66 3 51.5 54 3 Mol. Weight 2275.65 784.70 829.80 Temperature, K 180(2) 150(2) 150(2)

Space Group P212121 P-1 P-1 a, Å 13.5767(5) 10.454(5) 10.4601(5) b, Å 20.2026(7) 11.495(6) 11.3940(6) c, Å 35.6666(11) 19.835(11) 19.9439(9) α, deg 90 103.568(13) 103.975(4) β, deg 90 93.883(16) 95.003(4) γ, deg 90 110.470(18) 110.046(5) Volume, Å3 9782.8(6) 2141.3(19) 2128.86(18) Z 4 2 2 Description Orange Orange Orange Colour Prism Prism Prism -3 Dc, g cm 1.545 1.217 1.295 F(000) 4480 830 866 μ, mm-1 6.617 0.680 0.593 Reflections 50362 15895 19419 Collected

Rσ 0.0790 0.6349 0.1273

Rint 0.0348 0.2001 0.0911 Unique Reflections 25777 9000 9663 Parameters Varied 1041 527 526

R1 0.0481 0.0891 0.0954

wR2 (all data) 0.1131 0.2671 0.2893 GooF 0.942 0.859 1.040 Δρ/e Å3 1.286/-2.128 0.571/-0.230 1.580/-2.043

S30 Appendix Two: Crystallographic Data

Figure A3.23 - Molecular structure of 46 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.24 - Molecular structure of 47 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S31 Appendix Two: Crystallographic Data

45 46 47 Molecular C H TlN C H Cl AlN C H Cl GaN Formula 51 57 3 48 50 2 3 48 50 2 3 Mol. Weight 916.37 766.79 809.53 Temperature, K 150(2) 152(2) 150(2) Space Group P-1 P-1 P-1 a, Å 10.5812(4) 10.7290(7) 11.3360(14) b, Å 11.4066(4) 11.7522(8) 12.840(2) c, Å 20.4438(8) 19.8810(14) 18.301(3) α, deg 98.587(2) 100.490(3) 87.195(8) β, deg 100.828(2) 95.000(3) 78.733(8) γ, deg 111.878(2) 111.394(2) 76.500(8) Volume, Å3 2182.92(14) 2262.5(3) 2540.2(6) Z 2 2 2 Description Orange Prism Prism Colour Prism Yellow Yellow -3 Dc, g cm 1.394 1.126 1.058 F(000) 930 812 848 μ, mm-1 3.736 0.197 0.677 Reflections 34139 32899 20402 Collected

Rσ 0.0960 0.0608 0.4682

Rint 0.0584 0.0515 0.0959 Unique Reflections 11063 9468 12682 Parameters Varied 509 526 499

R1 0.0621 0.0898 0.0839

wR2 (all data) 0.1666 0.2998 0.2247 GooF 1.057 1.044 0.715 Δρ/e Å3 3.607/-3.685 0.787/-1.940 0.644/-0.847

S32 Appendix Two: Crystallographic Data

Figure A3.25 - Molecular structure of 50 (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

S33 Appendix Two: Crystallographic Data

48 50 51 Molecular C H Br InN O C H GaN C H In N Formula 50 55 2 3 0.5 53 63 3 100 112 2 6 Mol. Weight 980.61 811.78 1627.59 Temperature, K 150(2) 155(2) 150(2)

Space Group P-1 P-1 P21/n a, Å 11.0858(9) 10.8007(6) 10.5238(4) b, Å 11.1952(9) 11.8461(7) 15.7425(5) c, Å 19.8902(13) 19.6602(11) 51.9642(19) α, deg 80.214(3) 97.282(3) 90 β, deg 78.334(3) 96.972(3) 93.140(2) γ, deg 70.584(3) 111.686(2) 90 Volume, Å3 2265.9(3) 2279.6(2) 8596.0(5) Z 2 2 4 Description Prism Plate Rod Colour Yellow Yellow Yellow -3 Dc, g cm 1.437 1.183 1.258 F(000) 998 866 3408 μ, mm-1 2.323 0.641 0.586 Reflections 32891 35322 69250 Collected

Rσ 0.0601 0.0356 0.0801

Rint 0.0435 0.0396 0.0785 Unique Reflections 11324 9999 18847 Parameters Varied 513 520 1001

R1 0.0412 0.0488 0.0484

wR2 (all data) 0.1070 0.1621 0.1467 GooF 1.003 1.072 1.052 Δρ/e Å3 0.791/-0.728 1.373/-0.720 0.604/-0.672

S34 Appendix Two: Crystallographic Data

Figure A3.26 - Molecular structure of 52a (50% thermal ellipsoids). All hydrogen atoms omitted for clarity.

Figure A3.27 - Molecular structure of 52b (50% thermal ellipsoids). All hydrogen atoms omitted for clarity. Symmetry operation used to generate # atoms: x, ½-y, 1-z.

S35 Appendix Two: Crystallographic Data

52a 52b 53

Molecular Formula C100H112Tl2N6 C50H56TlN3 C73H96AlN4O Mol. Weight 1806.69 903.34 1072.52 Temperature, K 153(2) 173(2) 150(2)

Space Group P21/n Pbna P21/n a, Å 10.5327(8) 18.3042(4) 12.8648(7) b, Å 15.7020(12) 16.0286(3) 40.718(2) c, Å 51.888(4) 16.1071(4) 13.0579(6) α, deg 90 90 90 β, deg 93.222(3) 90 111.988(2) γ, deg 90 90 90 Volume, Å3 8567.9(11) 4725.67(18) 6342.6(5) Z 4 8 4 Description Prism Prism Block Colour Yellow Yellow Colourless -3 Dc, g cm 1.401 2.539 1.123 F(000) 3664 3664 2332 μ, mm-1 3.807 6.902 0.078 Reflections Collected 59775 37229 43870

Rσ 0.1084 0.0376 0.0744

Rint 0.0918 0.0555 0.0446 Unique Reflections 18936 5837 18527 Parameters Varied 1001 264 723

R1 0.0558 0.0552 0.0788

wR2 (all data) 0.1576 0.1406 0.2320 GooF 1.003 1.241 1.080 Δρ/e Å3 1.897/-1.558 3.024/-1.517 0.330/-0.413

S36 Appendix Two: Crystallographic Data

Figure A3.28 - Molecular structure of 54 (50% thermal ellipsoids). All hydrogen atoms excepting H(1) omitted and Dipp groups depicted as wireframes for clarity.

Figure A3.29 - Molecular structure of 55 (50% thermal ellipsoids). All hydrogen atoms excepting H(1) omitted and Dipp groups depicted as wireframes for clarity.

S37 Appendix Two: Crystallographic Data

54 55 56

Molecular Formula C48H69AlN6 C48H69GaN6 C48H69InN6 Mol. Weight 757.07 799.81 844.91 Temperature, K 150(2) 150(2) 150(2)

Space Group P21/n P21/c P21/c a, Å 14.5823(7) 14.6502(6) 14.667(5) b, Å 16.1625(8) 16.1245(6) 16.510(6) c, Å 20.9200(11) 20.9328(8) 21.164(6) α, deg 90 90 90 β, deg 109.972(2) 110.465(2) 109.752(11) γ, deg 90 90 90 Volume, Å3 4634.0(4) 4632.8(3) 4823(3) Z 4 4 4 Description Cube Cube Cube Colour Colourless Colourless Colourless -3 Dc, g cm 1.085 1.147 1.163 F(000) 1648 1720 1792 μ, mm-1 0.081 0.631 0.526 Reflections Collected 46969 38422 54321

Rσ 0.1377 0.0564 0.0522

Rint 0.0857 0.0512 0.0440 Unique Reflections 14012 9451 13381 Parameters Varied 558 537 516

R1 0.0681 0.0563 0.0400

wR2 (all data) 0.2123 0.1788 0.1272 GooF 1.021 1.029 0.988 Δρ/e Å3 0.429/-0.486 1.576/-0.652 0.640/-0.073

S38 Appendix Two: Crystallographic Data

Figure A3.30 - Molecular structure of 58 (50% thermal ellipsoids). All hydrogen atoms omitted and Dipp groups depicted as wireframes for clarity.

Figure A3.31 - Molecular structure of 59 (50% thermal ellipsoids). All hydrogen atoms excepting H(1) and H(2) omitted for clarity.

S39 Appendix Two: Crystallographic Data

57 58 59

Molecular Formula C48H68TlClN6 C48H68TlBrN6 C48H52AlN3 Mol. Weight 968.90 1013.36 697.91 Temperature, K 150(2) 173(2) 150(2)

Space Group P21/c P21/c P-1 a, Å 14.6044(6) 14.570(3) 10.440(2) b, Å 16.5465(9) 16.835(3) 12.331(3) c, Å 21.0726(11) 21.235(4) 15.978(3) α, deg 90 90 89.95(2) β, deg 109.055(2) 108.21(3) 82.91(2) γ, deg 90 90 85.68(2) Volume, Å3 4813.2(4) 4947.6(19) 2035.5(7) Z 4 4 2 Description Cube Cube Prism Colour Orange Orange Yellow -3 Dc, g cm 1.337 1.360 1.139 F(000) 1984 2056 748 μ, mm-1 3.448 4.108 0.086 Reflections Collected 86204 37529 19527

Rσ 0.0393 0.1350 0.0950

Rint 0.0631 0.0657 0.0515 Unique Reflections 10521 13550 9735 Parameters Varied 521 521 489

R1 0.0253 0.0669 0.0553

wR2 (all data) 0.0674 0.2047 0.1464 GooF 1.122 1.004 1.015 Δρ/e Å3 0.557/-0.883 0.957/-1.277 0.258/-0.357

S40 Appendix Two: Crystallographic Data

60 61 64

Molecular Formula C51H59GaN3 C5H11AlN2 C29H45GaN2 Mol. Weight 783.73 126.14 491.39 Temperature, K 152(2) 173(2) 150(2)

Space Group P-1 P21/m C2/c a, Å 10.4624(5) 7.5728(15) 17.0085(7) b, Å 11.3645(5) 7.0904(14) 9.0804(5) c, Å 20.0930(8) 7.9026(16) 17.7985(9) α, deg 103.836(2) 90 90 β, deg 94.296(2) 107.19(3) 92.882(2) γ, deg 110.472(2) 90 90 Volume, Å3 2139.96(17) 405.37(15) 2745.4(2) Z 2 2 4 Description Prism Needle Octahedron Colour Yellow Colourless Colourless -3 Dc, g cm 1.216 1.033 1.189 F(000) 834 136 1056 μ, mm-1 0.681 0.164 1.020 Reflections Collected 30986 - 15454

Rσ 0.0525 - 0.0529

Rint 0.0415 0.0258 0.0358 Unique Reflections 9330 1151 2682 Parameters Varied 525 58 209

R1 0.0482 0.0434 0.0341

wR2 (all data) 0.1464 0.1405 0.0947 GooF 1.054 1.034 1.082 Δρ/e Å3 1.126/-0.812 0.383/-0.193 0.352/-0.316

S41 Appendix Two: Crystallographic Data

65 66 67

Molecular Formula C33H50Br3InN2O C27H39InN2 C27H39GaN2 Mol. Weight 845.30 506.42 461.32 Temperature, K 150(2) 150(2) 153(2)

Space Group Pbca P-1 P21/c a, Å 15.8412(7) 12.591(4) 10.4897(4) b, Å 18.6259(7) 15.893(5) 17.9539(8) c, Å 23.2271(12) 15.980(6) 14.3571(5) α, deg 90 119.048(13) 90 β, deg 90 90.951(17) 97.212(2) γ, deg 90 92.806(17) 90 Volume, Å3 6853.3(5) 2789.1(17) 2682.49(18) Z 8 4 4 Description Rod Prism Block Colour Colourless Colourless Colourless -3 Dc, g cm 1.639 1.206 1.142 F(000) 3392 1056 984 μ, mm-1 4.215 0.861 1.040 Reflections Collected 110495 50927 21746

Rσ 0.0713 0.0550 0.0512

Rint 0.0519 0.0528 0.0541 Unique Reflections 10034 15187 5904 Parameters Varied 369 667 291

R1 0.0309 0.0465 0.0373

wR2 (all data) 0.0526 0.1542 0.1271 GooF 1.004 1.019 1.090 Δρ/e Å3 0.528/-0.453 1.248/-1.323 0.493/-0.290

S42 Appendix Two: Crystallographic Data

Figure A3.32 - Molecular structure of 67 (40% thermal ellipsoids). All hydrogen atoms excepting H(1A), H(1B) and H(1C) omitted for clarity.

Figure A3.33 - Molecular structure of 71 (50% thermal ellipsoids). All hydrogen atoms excepting H(1), H(2) and H(3) omitted and phenyl groups depicted as wireframes for clarity.

S43 Appendix Two: Crystallographic Data

69 71 72

Molecular Formula C69H59InN2 C69H59GaN2·C7H8 C69H56TlCl3N2 Mol. Weight 1031.00 1078.03 1223.87 Temperature, K 150(2) 150(2) 152(2)

Space Group P21/n P-1 P21/n a, Å 14.9002(3) 11.1381(13) 11.7532(7) b, Å 18.1635(4) 13.611(2) 19.9463(12) c, Å 19.6091(4) 21.508(3) 23.9631(14) α, deg 90 71.898(7) 90 β, deg 90.2050(10) 80.314(7) 96.329(3) γ, deg 90 70.521(7) 90 Volume, Å3 5306.97(19) 2914.4(7) 5583.5(6) Z 4 2 4 Parallelogramic Description Prism Prism Plate Colour Colourless Colourless Colourless -3 Dc, g cm 1.290 1.228 1.456 F(000) 2144 1136 2464 μ, mm-1 0.490 0.518 3.081 Reflections Collected 91429 39745 87192

Rσ 0.0512 0.1210 0.1224

Rint 0.0277 0.1709 0.2675 Unique Reflections 10851 11842 12323 Parameters Varied 679 744 678

R1 0.0364 0.0742 0.0493

wR2 (all data) 0.1179 0.2462 0.1472 GooF 1.108 1.022 0.996 Δρ/e Å3 0.456/-0.717 0.675/-0.738 1.154/-2.567

S44 Appendix Two: Crystallographic Data

76 77 78

Molecular Formula C37H45GaMoN2O4 C46H50In2MoN4O4 C42H48Cl4Ga2N4 Mol. Weight 747.41 1048.48 890.08 Temperature, K 155(2) 155(2) 173(2)

Space Group P-1 P-1 P21 a, Å 10.347(3) 11.239(2) 10.345(2) b, Å 12.911(3) 11.714(3) 14.917(3) c, Å 15.362(4) 20.444(5) 14.442(3) α, deg 67.692(12) 100.061(13) 90 β, deg 84.730(14) 101.521(11) 14.442(3) γ, deg 84.465(14) 104.468(10) 90 Volume, Å3 1886.3(9) 2481.1(10) 2160.0(8) Z 2 2 2 Description Rectangular Plate Plate Prism Colour Pale Yellow Yellow Colourless -3 Dc, g cm 1.316 1.403 1.369 F(000) 772 1052 916 μ, mm-1 1.084 1.211 1.528 Reflections Collected 24676 9971 18728

Rσ 0.2342 0.2245 0.2639

Rint 0.2275 - 0.1327 Unique Reflections 6436 9971 9453 Parameters Varied 427 526 501

R1 0.0755 0.1685 0.0906

wR2 (all data) 0.2166 0.4527 0.2289 GooF 0.911 1.043 0.983 Δρ/e Å3 1.097/-0.856 3.619/-3.848 1.329/-2.181

S45 Appendix Two: Crystallographic Data

Figure A3.34 - Molecular structure of the cation in 81 (50% thermal ellipsoids). All hydrogen atoms except H(12) omitted for clarity.

S46 Appendix Two: Crystallographic Data

81 83 84

Molecular Formula C73H60BF24N4 C61H50.5AlF36.5N4O4Tl C70H72AlF36N4O4Tl Mol. Weight 1460.06 1828.40 1948.66 Temperature, K 155(2) 150(2) 150(2)

Space Group P-1 P-1 P21/n a, Å 12.5809(5) 10.7926(6) 15.2839(5) b, Å 17.3178(7) 17.7974(9) 28.9544(10) c, Å 17.6631(7) 19.1300(11) 18.4627(7) α, deg 91.456(2) 92.060(3) 90 β, deg 110.080(2) 94.732(3) 91.3414(15) γ, deg 90.621(2) 101.645(2) 90 Volume, Å3 3612.4(3) 3581.4(3) 8168.2(5) Z 2 2 4 Description Prism Block Prism Colour Colourless Colourless Pale Yellow -3 Dc, g cm 1.342 1.696 1.585 F(000) 1494 1798 3880 μ, mm-1 0.122 2.410 2.118 Reflections 55914 48841 178391 Collected

Rσ 0.0480 0.0658 0.0506

Rint 0.0419 0.0464 0.0527 Unique Reflections 15783 15258 22943 Parameters Varied 1086 985 1045

R1 0.0516 0.0593 0.0653

wR2 (all data) 0.1749 0.1741 0.2046 GooF 1.019 1.055 1.030 Δρ/e Å3 0.900/-0.524 1.744/-0.886 1.970/-2.177

S47 Appendix Three: Revised Steric Parameters

Ligand V Ligand V

MeACy 29.3 iPrGiso 39.4

Menacnac 29.5 tBuAiso 39.7

Me2pip N3Dipp2 32.2 Giso 40.0

Fiso 33.5 C6F5nacnac 40.0

tBuACy 33.8 MeGiso 40.0

MeAiso 34.0 DippBIAN 40.0

p-tolnacnac 35.4 tBunacnac 40.3

tBuAAd 35.8 CyGiso 41.7

tBuAtBu 36.0 Xynacnac 42.1

MesPhACy 36.6 Dippnacnac 44.4

DitopACy 37.8 DippTAPDPh 46.4

Dmp ACy 37.9 N3Dmp2 46.7

Ph Aiso 39.2 P(NMes*)2 49.1

CyAiso 35.8 DippnacnactBu 49.5

pipGiso 36.0 DippBIPMPh 50.3

Table A3.1 - V parameters for various monoanionic bidentate N,N'-ligands calculated using the dimethylaluminium probe and a sphere of radius 4.0 Å

S48 Appendix Four: Assignment of M-π-arene Hapticities

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 2.866 105.7 X6 2.761 90.8

X5 2.804 100.3 X5 2.771 85.0

X4 2.773 94.6 X4 2.812 79.4

X3 2.763 86.9 X3 2.890 72.3

X2 2.814 82.1 X2 2.981 68.4

Table A4.1 - Assignment of the hapticities of intramolecular sodium π-arene interactions in 31

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 2.850 97.4 X6 2.895 94.6

X5 2.828 91.8 X5 2.886 89.0

X4 2.842 86.2 X4 2.918 83.4

Table A4.2 - Assignment of the hapticities of intramolecular potassium π-arene interactions in 32a

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 3.008 98.89 X6 3.059 101.71

X5 2.978 93.67 X5 3.015 96.61

X4 2.977 88.48 X4 2.985 91.92

X3 3.007 81.26 X3 3.007 84.40

Table A4.3 - Assignment of the hapticities of intramolecular potassium π-arene interactions in 32b

S49 Appendix Four: Assignment of M-π-arene Hapticities

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X3 3.241 94.2 X3 3.295 103.6

X2 3.284 89.4 X2 3.381 97.3

X1 3.238 85.9 X1 3.218 95.7

Table A4.4 - Assignment of the hapticities of intramolecular potassium π-arene

interactions in 32·C6H14

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 3.244 97.2 X6 3.280 93.2

X5 3.221 92.3 X5 3.276 88.4

X4 3.220 87.6 X4 3.306 84.4

X3 3.257 81.9 X3 3.366 77.0

Table A4.5 - Assignment of the hapticities of intramolecular rubidium π-arene interactions in 33

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 3.370 98.0 X6 3.370 89.4

X5 3.343 93.2 X5 3.384 84.8

X4 3.327 89.1 X4 3.431 80.0

X3 3.369 82.2 X3 3.506 74.0

Table A4.6 - Assignment of the hapticities of intramolecular caesium π-arene interactions in 34

S50 Appendix Four: Assignment of M-π-arene Hapticities

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X6 2.490 112.2 X6 2.522 113.3

X5 2.398 105.9 X5 2.424 107.2

X4 2.362 98.8 X4 2.360 101.0

X3 2.310 90.1 X3 2.319 91.6

X2 2.387 83.9 X2 2.351 86.3

X1 2.361 78.5 X1 2.352 80.0

Table A4.7 - Assignment of the hapticities of intramolecular lithium π-arene interactions in 36

Xn d (Å) α (°) Xnʹ d (Å) α (°)

X4 3.353 99.0 X4 3.265 96.1

X3 3.337 91.8 X3 3.321 92.6

X2 3.314 88.8 X2 3.264 85.8

X1 3.351 83.8 X1 3.377 80.1

Table A4.8 - Assignment of the hapticities of intramolecular thallium π-arene interactions in 45

S51 Appendix Five: Publications, Oral and Poster Presentations

A5.1 Publications in Support of this Thesis

(I) Low Valent and Hydride Complexes of NHC Coordinated Gallium and Indium, Graham E. Ball; Marcus L. Cole and Alasdair I. McKay, Dalton Trans. 2012, 41, 946-952.

(II) The Stabilization of Gallane and Indane by a Ring Expanded Carbene, Anthony R. Leverett; Alasdair I. McKay and Marcus L. Cole, Dalton Trans. 2015, 44, 498-500.

A5.2 Oral Presentations in Support of this Thesis

(I) Preparation of Thallium Hydride Complexes, 20th Reactive Organometallics Symposium (ROMS 20), University of New South Wales, 7th November 2011.

(II) Quantification of Ligand Steric Character, 23rd Reactive Organometallics Symposium (ROMS 23), Australian National University, 21st June 2013.

(III) Quantification of the Steric Character of Multidentate Ligands, A Crystallographic Approach, Crystallography at the Cutting Edge Symposium, University of New South Wales, 7th November 2014.

(IV) A Mechanistic Study of the Decomposition of NHC Complexes of Indane (InH3), 26th Reactive Organometallics Symposium (ROMS 26), University of New South Wales, 21st November 2014.

A5.3 Conference Papers in Support of this Thesis

(I) Photochemical NMR Spectroscopy Studies of Group 13 Halohydrides, 5th Australasian Organometallics Meeting (OZOM 5), University of New South Wales, 17-20th January 2010.

(II) Low Valent Group 13 Complexes of Bulky Triazenides, 6th Australasian Organometallics Meeting (OZOM 6), University of Tasmania, 17-20th January 2011.

(III) Low Valent Group 13 Complexes of Bulky Triazenides, 19th EuCHEMS Conference on organometallic Chemistry (EuCOMC), Université Toulouse III - Paul Sabatier, 3-7th July 2011.

S52 Appendix Five: Publications, Oral and Poster Presentations

(IV) Bulky Triazenide Complexes of the Heavy Group 13 Metals, New Zealand Institute of Chemistry Conference (NZIC), University of Waikato, 27th November-1st December 2011.

(V) Bulky Triazenide Complexes of the Heavy Group 13 Metals, Royal Australian Institute of Chemistry Inorganic Chemistry Conference (IC’11), University of Western Australia, 4-8th December 2011.

S53 References for Appendix

[S1] (a) Burchat, A. F.; Chong, J. M.; Nielsen, N., J. Organomet. Chem. 1997, 542, 281-283; (b) Hoye, T. R.; Eklov, B. M.; Voloshin, M., Org. Lett. 2004, 6, 2567- 2570. [S2] Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I., Organometallics 2010, 29, 2176- 2179. [S3] Sheldrick, G. M., SADABS, A program for area detector absorption correction, Bruker Analytical X-Ray-Division Madison Wisconsin, USA, 2008. [S4] Sheldrick, G. M., Acta Crystallogr., Sect. A 2008, 64, 112-122. [S5] Barbour, L. J., J. Supramol. Chem. 2001, 1, 189-191.

S54