Copyright by John David Gorden 2001

The Dissertation Committee for John David Gorden Certifies that this is the approved version of the following dissertation:

Low Valent and Mixed Valent Cyclopentadienyl

Complexes of the Group 13 Elements

Committee:

Alan H. Cowley, Supervisor

Richard A. Jones

Richard J. Lagow

John G. Ekerdt

Jason B. Shear

Low Valent and Mixed Valent Cyclopentadienyl

Complexes of the Group 13 Elements

by

John David Gorden, B.S.

Dissertation

Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

The University of Texas at Austin December, 2001

For Anne

Your love will always be my greatest discovery. Acknowledgements

First of all I would like to thank my supervising professor, Dr. Alan H. Cowley. I am extremely grateful for all of his intellectual guidance, support, and for the risk he took with this academically suspect student. I wish to express my appreciation to Dr. Charles Macdonald for helping me find focus in my work. His infectious enthusiasm for all areas chemistry has encouraged us all. I would also like to thank Dr. Richard Jones for his help throughout my time here. Special thanks go out to my generation of the Cowley research group for their help, friendship, and tolerance. A collective thanks to Dr. Andreas Voigt, Rob Wiacek, Jeff Pietryga, Piyush Shukla, Jamie Jones, Dr. Jason Clyburne, Dr. Colin Abernethy, Dr. Brian McBurnett, Dr. Vivianna Lomelli, Joel Silverman. I would like to also thank Dr. Vincent Lynch for his help with some of the X-ray work presented here. My heartfelt gratitude to Julie Campos for keeping everything running smoothly and for always providing a willing ear I needed to vent. I would like to express deep appreciation for the love and support of my parents, family, and in-laws, without which none of this would have been possible. I wish to thank the Dorothy Banks Charitable Trust for their financial support in the form of a Graduate Research Fellowship as well as the National Science Foundation, the Robert A. Welch Foundation and the National Academy of Sciences through Sigma Xi. Finally, and most of all, I would like to thank my wife Anne for her never- ending love, support and understanding. She has endured too much time alone, and too many long distance conversations during the course of these studies.

v Low Valent and Mixed Valent Cyclopentadienyl

Complexes of the Group 13 elements

Publication No.______

John David Gorden, Ph.D. The University of Texas at Austin, 2001

Supervisor: Alan H. Cowley

A variety of low-coordinate bonding environments that feature group 13 elements have been explored. The highlights in this area include the isolation and structural characterization of the decamethylborocenium cation, the most tightly squeezed and the first compound to adopt a s/p geometry in the solid state, the synthesis of the first gallocenium cation, the first examples of main group constrained geometry compounds, and the first examples of multidecker p-block cations.

The reactivities of monovalent group 13 pentamethylcyclopentadienide compounds with conjugated systems and electron-deficient tris(perfluorophenyl) compounds has also been explored. It has been found that [(C5Me5)M]n (M = Al,

Ga) fragments will undergo oxidative addition to diazabutadienes, resulting in the formation of monomeric five-membered ring systems. Furthermore, it has been vi shown that the reactions of [(C5Me5)M]n clusters (M = Al, Ga) with (C6F5)3M (M =

B, Al, Ga, In) yield the first examples of group 13 M(I)-M(III) donor-acceptor complexes, the first valence isomer of a dialane, and a unique inverse sandwich complex featuring p-bonding to perfluorophenyl ligands.

It has further been found that the reactions of (C5Me5)2AlMe and

(C5Me5)3Ga with tetramethylimidazol-2-ylidene yield unprecedented (C5Me5)2MH carbene complexes and tetramethylfulvene.

vii Table of Contents

List of Tables...... x

List of Figures ...... xiv

Chapter 1. General Introduction...... 1 Introduction...... 1 References and Notes ...... 12

Chapter 2. Synthesis and Structure of Group 13 Cations ...... 15 Introduction...... 15 Section 2.1 Metallocenium Cation Precursors...... 22 Section 2.2 Borocenium Cations...... 36 Section 2.3 Aluminocenium Cations...... 42 Section 2.4 Gallocenium Cations...... 51 Section 2.5 Constrained Geometry Complexes ...... 66 Section 2.6 Multidecker Cations...... 75 Experimental...... 83 Tables of Crystallographic and Theoretical Data ...... 100 References and Notes ...... 151

Chapter 3. Reactions with Monovalent Group 13 Cyclopentadienides...... 159 Introduction...... 159 Section 3.1 Cycloadditions ...... 167 Section 3.2 Al(I) Donor-Acceptor Complexes ...... 178 Section 3.3 Ga(I) Donor-Acceptor Complexes...... 189 Section 3.4 In(I) Complexes ...... 197 Experimental...... 203 Tables of Crystallographic and Theoretical Data ...... 213 References and Notes ...... 232

viii

Chapter 4. Reactions of Group 13 Cyclopentadienides with a Nucleophilic Carbene...... 241 Introduction...... 241 Results and Discussion...... 167 Experimental...... 249 Tables of Crystallographic Data ...... 254 References and Notes ...... 261

Appendix. Listing of Compound Numbers by Chapters...... 263

Vita ...... 265

ix List of Tables

Table 1.1. Selected Properties of the Group 13 Elements………………………3 Table 1.2. Electronegativities and Radii of Non-Group 13 Elements…………..3 Table 1.3 Selected Thermodynamic Properties of Group 13 Elements………..4 1 Table 2.1. Crystal Data and Structure Refinement for (h -C5Me5)2BBr……. 102 1 Table 2.2. Selected Bond Lengths [Å] for (h -C5Me5)2BBr………………… 103 1 Table 2.3. Selected Bond Angles [°] for (h -C5Me5)2BBr………………….. 103 1 Table 2.4. Crystal Data and Structure Refinement for (h -C5Me5)2BMe…… 105 1 Table 2.5. Selected Bond Lengths [Å] for (h -C5Me5)2BMe……………….. 106 1 Table 2.6. Selected Bond Angles [°] for (h -C5Me5)2BMe…………………. 106 1 Table 2.7. Crystal Data and Structure Refinement for (h -C5Me5)2GaCl….. 108 1 Table 2.8. Selected Bond Lengths for (h -C5Me5)2GaCl…………………… 109 1 Table 2.9. Selected Bond Angles [°] for (h -C5Me5)2GaCl………………… 109 Table 2.10. Crystal Data and Structure Refinement for 1 2 (h -C5Me5)(h -5Me5)2GaMe…………………………………….. 111 1 2 Table 2.11. Selected Bond Lengths for (h -C5Me5)(h -C5Me5)GaMe……….. 112 1 2 Table 2.12. Selected Bond Angles [°] for (h -C5Me5)(h -C5Me5)GaMe…….. 112 Table 2.13. Crystal Data and Structure Refinement for 1 5 + - [(h -C5Me5)(h -C5Me5)B] [AlCl4] ……………………...………. 114 Table 2.14. Selected Bond Lengths [Å] for 1 5 + - [(h -C5Me5)(h -C5Me5)B] [AlCl4] …………….……………….. 115 Table 2.15. Selected Bond Angles [°] for 1 5 + - [(h -C5Me5)(h -C5Me5)B] [AlCl4] ……………………………… 115 + Table 2.16. Selected BP86 Calculation Results for [(h-C5H5)2B] Cations….. 116 Table 2.17. Crystal Data and Structure Refinement for 5 [(h -C5Me5)(C6F5)AlCl]2………………………………………… 118 5 Table 2.18. Selected Bond Lengths [Å] for [(h -C5Me5)(C6F5)AlCl]2………. 119 5 Table 2.19. Selected Bond Angles [°] for [(h -C5Me5)(C6F5)AlCl]2………… 119

x Table 2.20. Crystal Data and Structure Refinement for 5 + - [(h -C5Me5)2Al] [AlCl4] ………………………………………… 121 Table 2.21. Selected Bond Lengths [Å] for 5 + - [(h -C5Me5)2Al] [AlCl4] ………………………………………… 122 5 + - Table 2.22. Selected Bond Angles [°] for [(h -C5Me5)2Al] [AlCl4] ………… 122 Table 2.23. Crystal Data and Structure Refinement for 3 [(h -C5Me5)(C6F5)GaCl]2………………………………………... 124 3 Table 2.24. Selected Bond Lengths [Å] for [(h -C5Me5)(C6F5)GaCl]2………. 125 3 Table 2.25. Selected Bond Angles [°] for [(h -C5Me5)(C6F5)GaCl]2………… 125 Table 2.26. Crystal Data and Structure Refinement for 1 1 (h - C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)…………………………. 127 Table 2.27. Selected Bond Lengths [Å] for 1 1 (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)…………………………. 128 Table 2.28. Selected Bond Angles [°] for 1 1 (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)…………………………. 128 Table 2.29. Crystal Data and Structure Refinement for 1 2 (h -C5Me5)(h -5Me5)GaC6F5…………………………………….. 130 1 2 Table 2.30. Selected Bond Lengths [Å] for (h -C5Me5)(h -C5Me5)GaC6F5…. 131 Table 2.31. Selected Bond lengths Angles [°] for 1 2 (h -C5Me5)(h -C5Me5)GaC6F5…………………………………... 131 Table 2.32. Crystal Data and Structure Refinement for 1 3 + - [(h -C5Me5)(h -C5Me5)Ga] [BF4] ………………………………. 133 Table 2.33. Selected Bond Lengths [Å] for 1 3 + - [(h -C5Me5)(h -C5Me5)Ga] [BF4] ………………………………. 134 Table 2.34. Selected Bond Angles [°] for 1 3 + - [(h -C5Me5)(h -C5Me5)Ga] [BF4] ………………………………. 134

Table 2.35. Optimized [(h-C5H5)Ga] cations…………………………………...62 Table 2.36. Crystal Data and Structure Refinement for 1 5 + - [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] ……………………………. 136 Table 2.37. Selected Bond Lengths [Å] for 1 5 + - [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] …………………………….. 137

xi Table 2.38. Selected Bond Angles [°] for 1 5 + - [(h -C5Me5)(h -C5Me5)2Ga] [AlCl4] …………………………… 137 Table 2.39. Crystal Data and Structure Refinement for CGCAlMe·THF…….139 Table 2.40. Selected Bond Lengths [Å] for CGCAlMe·THF…………………140 Table 2.41. Selected Bond Angles [°] for CGCAlMe·THF…………………...140 Table 2.42. Crystal Data and Structure Refinement for CGCAlMe·Carbene…142 Table 2.43. Selected Bond Lengths [Å] for for CGCAlMe·Carbene………… 143 Table 2.44. Selected Bond Angles [°] for CGCAlMe·Carbene……………….143

Table 2.45. Crystal Data and Structure Refinement for CGCAlCl·Et2O……..145

Table 2.46. Selected Bond Lengths [Å] for CGCAlCl·Et2O………...………..146

Table 2.47. Selected Bond Angles [°] for CGCAlCl·Et2O……………………146 Table 2.48. Crystal Data and Structure Refinement for 6 5 6 + - [(h -C7H8)In(h -C5Me5)In(h -C7H8)] [(C6F5)3BO(H)B(C6F5)3] .. 148 Table 2.49. Selected Bond Lengths [Å] for 6 5 6 + - [(h -C7H8)In(h -C5Me5)In(h -C7H8)] [C6F5)3BO(H)B(C6F5)3] … 149 Table 2.50. Selected Bond Angles [°] for 6 5 6 + - [(h -C7H8)In(h -C5Me5)In(h -C7H8)] [(C6F5)3BO(H)B(C6F5)3] ...149 Table 2.51. CpSn Calculations at the B3LYP/A Level of Theory…………… 150

Table 2.52. CpIn and C6H6In Calculations at the BP86/A Level of Theory…. 150 Table 3.1. Crystal Data and Structure Refinement for 5 (Mes2DAB)Al(h -C5Me5)……………………………………….. 214 5 Table 3.2. Selected Bond Lengths [Å] for (Mes2DAB)Al(h -C5Me5)……… 215

Table 3.3. Selected Bond Angles [°] for (Mes2DAB)Al(C5Me5)…………… 215

Table 3.4. Crystal Data and Structure Refinement for Mes2DAB………….. 216

Table 3.5. Selected Bond Lengths [Å] for Mes2DAB………………………. 217

Table 3.6. Selected Bond Angles [°] for Mes2DAB………………………… 217 Table 3.7. Crystal data and Structure Refinement for 5 (h -C5Me5)AlB(C6F5)3…………………………………...……… 218 5 Table 3.8. Selected Bond Lengths [Å] for (h -C5Me5)AlB(C6F5)3…………. 219 5 Table 3.9. Selected Bond Angles [°] for (h -C5Me5)AlB(C6F5)3…………… 220 Table 3.10. Summary of Theoretical Calculations for……………………….. 220 xii Table 3.11. Crystal Data and Structure Refinement for 5 (h -C5Me5)AlAl(C6F5)3………………………………………….. 221 5 Table 3.12. Selected Bond Lengths [Å] for (h -C5Me5)AlAl(C6F5)3………… 222 5 Table 3.13. Selected Bond Angles [°] for (h -C5Me5)AlAl(C6F5)3………….. 222 5 Table 3.14. Crystal Data and Structure Refinement for (h -C5Me5)Al(C6F5)2..223 3 Table 3.15. Selected Bond Lengths [Å] for (h -C5Me5)Al(C6F5)2…………… 224 3 Table 3.16. Selected Bond Angles [°] for (h -C5Me5)Al(C6F5)2……………... 224 Table 3.17. Crystal Data and Structure Refinement 5 For (h C5Me5)GaB(C6F5)3……………………………………….. 225 5 Table 3.18. Bond Lengths [Å] for (h -C5Me5)GaB(C6F5)3…………………... 226 5 Table 3.19. Selected Bond Angles [°] for (h -C5Me5)GaB(C6F5)3…………… 226 Table 3.20. Crystal Data and Structure Refinement for 5 (h -C5Me5)GaAl(C6F5)3…………………………………………..227 5 Table 3.21. Selected Bond Lengths [Å] for (h -C5Me5)GaAl(C6F5)3………… 228 5 Table 3.22. Selected Bond Angles [°] for (h -C5Me5)GaAl(C6F5)3………….. 228 Table 3.23. Crystal Data and Structure Refinement for 5 + - [(h -C5Me5)In2] [B(C6F5)4] ………………………………………230 5 + - Table 3.24. Selected Bond Lengths [Å] for [(h -C5Me5)In2] [B(C6F5)4] ……. 231 5 + - Table 3.25. Selected Bond :Angles [°] for [(h -C5Me5)In2] [B(C6F5)4] ……... 231 Table 4.1. Crystal Data and Structure Refinement for 1 (h -C5Me5)2GaH·Carbene………………………………………..256 1 Table 4.2. Selected Bond Lengths [Å] for (h -C5Me5)2GaH·Carbene………257 1 Table 4.3. Selected Bond Angles [°] for (h -C5Me5)2GaH·Carbene……….. 257 Table 4.4. Crystal Data and Structure Refinement for 1 (h -C5Me5)2AlH·Carbene…………………………………………259 1 Table 4.5. Bond Lengths [Å] for (h -C5Me5)2AlH·Carbene…………………260 1 Table 4.6. Bond Angles [°] for (h -C5Me5)2AlH·Carbene…………………..260

xiii List of Figures

Figure 1.1. Sterically Demanding Substituents……………………………...…...7 1 Figure 2.1. Molecular structure of (h (s)-C5Me5))2BBr showing the slipped nature of the C5Me5 rings………………………………23 1 Figure 2.2. Molecular structure of [h (s)-C5Me5]2BMe………………………..25 2 Figure 2.3. Solid-state structure of (h -C5Me5)2AlMe………………………….29 1 Figure 2.4. Molecular structure of [(h (s)-C5Me5)2GaCl]2…………………….31 1 2 Figure 2.5. Molecular structure of (h (p)-C5Me5)(h -C5Me5)GaMe……...33, 110 1 5 + Figure 2.6. Molecular structure of [(h -C5Me5)(h -C5Me5)B] showing the atom numbering scheme……………………………...39 5 Figure 2.7. Molecular structure of [(h -C5Me5)(C6F5)AlCl]2…………………..45 5 + - Figure 2.8. Molecular structure of a cation in [(h -C5Me5)2Al] [AlCl4] ………49 3 Figure 2.9. Molecular structure of [(h -C5Me5)(C6F5)GaCl]2 showing the atom numbering scheme…………………………………..53, 123 1 1 Figure 2.10. Molecular structure of (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5) showing the atom numbering scheme………………………...54, 126 1 2 Figure 2.11. Molecular structure of (h (p)-C5Me5)(h -C5Me5)GaC6F5 showing the atom numbering scheme………………………...56, 129 1 3 + - Figure 2.12. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [BF4] showing the atom numbering scheme………………………...58, 132 1 3 + - Figure 2.13. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] showing the atom numbering scheme………………………...63, 135 1 Figure 2.14. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe THF showing the atom numbering scheme…………………...69, 138 1 Figure 2.15. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe carbene showing the atom numbering scheme………………..70, 141 1 Figure 2.16. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlCl×OEt2 showing the atom numbering scheme………………………...73, 144 Figure 2.17. Molecular structure of 5 5 5 + - [(h -C5Me5)Sn(m-h -C5Me5)Sn(h -C5Me5)] [Ga(C6F5)4] ………...77

xiv Figure 2.18. Molecular structure of 6 5 6 + - [(h -C7H8)In(m-h -C5Me5)In(h C7H8)] [HOB2(C6F5)6] …………..80 1 Figure 2.19. Molecular structure of (h -C5Me5)2BBr showing the atom numbering scheme………………………………………………...101 1 Figure 2.20. Molecular structure of (h -C5Me5)2BMe showing the atom numbering scheme………………………………………………...104 1 Figure 2.21. Molecular structure of [(h -C5Me5)2GaCl]2 showing the atom numbering scheme………………………………………………...107 1 5 + - Figure 2.22. Molecular structure of [(h -C5Me5)(h -C5Me5)B] [AlCl4] showing the atom numbering scheme…………………………….113 1 5 + - Figure 2.23. Molecular structure of [(h -C5Me5)(h -C5Me5)B] [AlCl4] showing both crystallographically independent units…………….113 5 Figure 2.24. Molecular structure of (h -C5Me5)(C6F5)AlCl showing the atom numbering scheme………………………………………117 5 + - Figure 2.25. Molecular structure of [(h -C5Me5)2Al] [AlCl4] showing the atom numbering scheme………………………………………120 5 + - Figure 2.26. Molecular structure of [(h -C5Me5)2Al] [AlCl4] showing both crystallographically independent units………………………120 1 3 + - Figure 2.27. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [BF4] - showing [BF4] bridged dimer…………………………………….132 6 5 6 + Figure 2.28. Molecular structure of [(h -C7H8)In(m-h -C5Me5)In(h -C7H8)] - [HOB2(C6F5)6] showing the unit cell contents…………………...147 6 5 6 + Figure 2.29. Molecular structure of [(h -C7H8)In(m-h -C5Me5)In(h -C7H8)] showing the C5Me5 numbering scheme and the bent geometry…..147 5 Figure 3.1. Molecular structure of [(h -C5Me5)In]6 showing the octahedral In6 core………………………………………………...163 Figure 3.2. Three dimensional representation of lone pair molecular 5 orbital of (h -C5H5)Al…………………………………………….164 5 Figure 3.3. Molecular structure of (Mes2DAB)Al(h -C5Me5) showing the numbering scheme……………………………………….172, 215 Figure 3.4. Molecular structure of 1,4-bis(2,4,6-trimethylphenyl)- 1,4-diazabuta-1,3-diene showing the atom numbering scheme……………………………………………………….173, 217

xv 5 Figure 3.5. Molecular structure of (h -C5Me5)Al®B(C6F5)3 showing the atom numbering scheme…………………………………182, 219 5 Figure 3.6. Molecular structure of (h -C5Me5)Al®B(C6F5)3 showing the atom numbering scheme…………………………………185, 222 3 Figure 3.7. Molecular structure of (h -C5Me5)Al(C6F5)2 showing the atom numbering scheme…………………………………187, 224 Figure 3.8. Molecular structure of one of the two crystallographically independent molecules of (Dipp2nacnac)Ga®B(C6F5)3………….192 5 Figure 3.9. Molecular structure of (h -C5Me5)Ga®B(C6F5)3 showing atom-labeling scheme………………………………………..193, 226 5 Figure 3.10. Molecular structure of (h -C5Me5)Ga®Al(C6F5)3 featuring both crystallographically independent molecules…………...195, 228 5 + 5 Figure 3.11. The central core of [In2(h -C5Me5)] featuring an h -bonded In atom on each face of the (m-C5Me5) group as well as 6 - h -capping by adjacent C6F5 groups from [B(C6F5)4] ………201, 229 5 + - Figure 3.12. Molecular structure of [In2(h -C5Me5)] [B(C6F5)4] showing the atom numbering scheme………………………………………229 1 Figure 4.1. Molecular structure of (h -C5Me5)2GaH carbene complex showing the atom numbering scheme………………………247, 255 1 Figure 4.2. Molecular structure of (h -C5Me5)2AlH·carbene complex showing the atom numbering scheme……………………….243, 258

xvi

CHAPTER 1

General Introduction

Few families of elements vary as widely in properties and behavior as those that compose group 13. The five elements, boron, aluminum, gallium, indium, and thallium, each have a ground state in which the valence electrons are in the configuration ns2np1.1 This is the root of many of the similarities between these elements, including the dominance of the +III oxidation state for all of the members of the group, excluding thallium, and the acceptor properties of many of the resulting compounds. Unlike the other elements comprising group 13, the +I oxidation state of Tl is preferred to the +III oxidation state by a small margin due to several factors that are discussed below. While their similarities may be numerous, it is their non-conformity to periodic trends that makes these elements interesting and challenging to work with.

The goals of this dissertation, in a general sense, are to obtain a better understanding of the in bonding and electronic properties of group 13 compounds.

A more specific aim of this work is to gain an enhanced understanding of the bonding in and reactivities of compounds containing group 13 elements in low

1 oxidation states or electron-deficient environments. The major themes that will be addressed are (i) the isolation and characterization of the bonding in group 13 cations, (ii) examination of the donor properties of monovalent pentamethylcyclopentadienyl metal fragments (C5Me5M), and (iii) studies of the reactivities of strongly Lewis basic Arduengo-type carbenes with group 13 pentamethylcyclopentadienides.

Due to the variety of projects that will be described within this dissertation, each chapter contains a brief introductory section to acquaint the reader with the appropriate background information to the research contained therein. The general information listed below pertains to the individual group 13 elements, some aspects of their bonding, and a brief introduction to the chemistry of low-coordinate compounds. The nomenclature of compounds used throughout this dissertation conforms to that commonly used in the literature, and does not necessarily follow the conventions of IUPAC. Important compounds are numbered in each chapter and specific syntheses and characterizational data are described at the end of each chapter.

General Properties

Some general information about each of the group 13 elements and other selected elements relevant to this dissertation are listed in Tables 1.1 and 1.2, respectively.

2 Table 1.1. Selected Properties of the Group 13 Elements

Element Z/Effective Atomic Van der Covalent Electronegativity2 Isotopes2 Spin6 nuclear mass3 Waals radius5 (Pauling) (%) (I) charge, Z*2 (g/mol) radius4 (Å) (Clementi) (Å)

B 5 /2.42 10.811 2.08 0.88 2.04 10B (19.82) 3 11B (80.18) 3/2 Al 13 /4.07 26.982 2.05 1.25 1.61 27Al (100.0) 5/2 Ga 31 /6.22 69.723 1.90 1.25 1.81 69Ga (60.11) 3/2 71Ga (39.89) 3/2 In 49 /8.47 114.82 1.90 1.50 1.78 113In (4.33) 9/2 115In (95.67) 9/2 Tl 81 /12.25 204.383 2.00 1.55 1.62 (Tl)I 203Tl (29.52) 1/2 2.04 (Tl)III 205Tl (70.48) 1/2

Table 1.2. Electronegativities and Radii of Non-Group 13 Elements

Electronegativity2 van der Waals Covalent Element (Pauling) radius4 (Å) radius5 (Å) H 2.20 1.30 0.37 C 2.55 1.70 0.77 Si 1.90 2.10 1.18 N 3.04 1.55 0.75 O 3.44 1.50 0.73 F 3.98 1.55 0.71 Cl 3.16 1.80 0.99

Bonding

All of the members of the group 3A (group 13) are metals, except for boron, which is a metalloid. Boron stands out from the other members of the family because the relatively tight binding of the valence electrons, as reflected by the relatively large first ionization energy, the small size of the atom due to being on the second row of the periodic table, and an electronegativity closer to that of carbon and hydrogen. Boron is too electronegative to be considered a metal and instead

3 forms more localized covalent bonds resulting in metalloid characteristics. As a result of the electron deficiency of boron, many of the B-B bonds are of the multicenter type rather than the more usual 2-center-2-electron bonds found for elements that are further to the right in the periodic table. The small ns np promotion energy (Table 1.3) and the closeness in energy of the valence s and p orbitals favor a major contribution from the 2s orbital to the bonding of boron compounds. Because of these factors, the univalent state of boron is rarely

7 encountered except in the case of tightly bound cluster complexes such as [t-BuB]4 and ‘high temperature’ species like BF and BCl.8,9 The univalent state for the other members of group 13 becomes more favorable with increasing atomic number, due to several factors which are discussed below.

Table 1.3 Selected Thermodynamic Properties of Group 13 Elements

Property B Al Ga In Tl

Ionization Energies2,5 (kcal/mol) M M+ 191.3 138.0 138.3 133.4 140.8 M+ M2+ 580.1 434.2 473.0 435.1 471.1 M2+ M3+ 874.8 656.0 708.2 646.3 687.9 Total (M M3+) 1646.2 1228.2 1319.5 1214.8 1299.8 Electron Affinity1011 5.50 10.52 8.640 8.13 7.17 (kcal/mol) Promotion Energy1 ns2np1 ns1np2 82.5 82.9 108.5 99.9 129.3 kcal/mol

4 Oxidation States and the Inert Pair Effect

In group 13, the common oxidation states are +III and +I. The former oxidation state results from the formal loss of the three valence electrons ns2np1, leaving a +III center with a noble gas core. While the +III state is observed for all of the elements in this group, the +I state, which results from the removal of only the single valence p electron, is common only for the heavier congeners. This tendency for the heavier members of a group to adopt an oxidation state of two less than the group maximum is commonly referred to as the inert pair effect.1

The relatively large effective nuclear charges for the heavier elements, particularly thallium, result from the presence of poorly shielding f and d electrons.

This factor, coupled with relativistic effects, leads to substantial stabilization of the pair of valence electrons in the s orbital. Furthermore, the weak covalent bonds formed by indium and thallium do not necessarily offset the high promotion energies required to achieve the +III oxidation state.9 The use of sterically demanding and strongly electron donating substituents has only recently permitted the study of the monovalent state of the lighter group 13 elements.12

Electron-deficient Environments

The majority of the work described within this dissertation is concerned with compounds that are electron-deficient, i.e. they lack the number of valence electrons required to fill all of the valence orbitals. The compounds of interest fall

5 into three categories, namely cationic species of the general type 1.1, where the central metal is low-coordinate (M = +III), highly reactive monovalent M(I) fragments, 1.2, analogous to carbenes 1.3, and strongly electron-deficient perfluorophenyl derivatives, 1.4. Low-coordinate and electron-deficient species are

+ R R Rf

M R M : C: Rf M

f R R R

1.1 1.2 1.3 1.4 f (M = B, Al, Ga, In; R = alkyl, C5H5, C5Me5; R = C6F5) of interest for a variety of reasons including, their sometimes unique structure and bonding,13 their ability to undergo addition reactions (e.g. cycloadditions, donor acceptor complex formation),14,15 and their propensity to abstract halide and methanide groups and thus serve as initiators for polymerization reactions.16 Group

13 cations are also attracting interest as catalysts for olefin polymerization reactions.17

Sterically Demanding Substituents

The stabilization of many low-coordinate and electron-deficient group 13 species is accomplished by the use of sterically demanding and often electronically stabilizing substituents. The term “sterically demanding” typically refers to a ligand with a relatively large number of atoms fixed in a position close to the nucleus of

6 interest. Some commonly employed ligands for the stabilization of low valent and electron-deficient species are shown in Figure 1.1.

TMS TMS

E E Si E C TMS E C H E TMS TMS i-Pr t-Bu TMS Trisyl Disyl

_ E E E

- Mes Mes* Dipp [C5Me5]

Figure 1.1. Sterically Demanding Substituents.

One of the most widely used bulky substituents is the pentamethyl-

- cyclopentadienyl ligand [C5Me5] , which is used extensively in the present work.

The C5Me5 ligand can adjust effectively to the electronic situation at the center to which it is bonded due to the wide range of bonding modes available, which encompasses hapticities from h1 to h5. In conjunction with this bonding flexibility, the bulky nature of the s- or p- bound C5Me5 group thus allows for both the kinetic and thermodynamic stabilization of otherwise highly reactive species. While complexes using the cyclopentadienide anion have been investigated in detail with 7 regard to the f-block and d-block elements, it has only been recently that analogous complexes of main group elements have begun to be studied in detail. The range of electronegativities of the main group elements is the principal factor that is responsible for the highly varied nature of C5H5-main group element interactions and the interested reader is referred to several recent reviews on this subject.13, 18

Characterization

Several characterization techniques have been utilized in the work described in the present dissertation. High-resolution mass spectral (HRMS) and low- resolution mass spectral data (MS) have been used extensively to determine the exact masses, molecular formulas, and fragmentation patterns of the new compounds. Although chemical ionization (CI) is one of the softer ionization techniques, many of the molecules that will be discussed do not retain their integrity following ionization.

Nuclear magnetic resonance spectroscopy (NMR) is one of the most valuable spectroscopic techniques available to the synthetic chemist, permitting not only the identification of new species, but also serving as a diagnostic tool for purity assessment as well as allowing the progress of reactions to be monitored. Apart from 1H and 13C NMR spectroscopy, which have been used routinely in the present work, 11B, 19F, and 27Al NMR spectroscopy have also proved to be extremely useful. The high isotopic abundance and very large chemical shift ranges make

8 group 13 nuclei very sensitive probes for chemical studies. The spectral linewidths, which depend upon e.g. the geometry of the substituents attached to a given nucleus, can vary from 3 to over 6000 Hz. Although the 27Al nucleus possesses a quadrupole moment, narrow lines in the NMR spectra can sometimes be observed. For

3+ - example, octahedrally solvated Al , tetrahedral AlX4 , and dimers of the type Al2R6

(R = halogen, alkyl) all exhibit high symmetry about the 27Al nucleus; consequently the electric field gradient (EFG) at this nucleus will be small, and relatively narrow lines are observed.6 In the case of many of the aluminum species that will be discussed here, particularly the trigonal species, the linewidths are much broader because of the large EFG about the 27Al nucleus.

The most valuable diagnostic tool that has been utilized in the present work is single crystal X-ray diffraction. The spectroscopic methods of characterization described above often do not provide definitive structural information, particularly in regard to determination of the hapticities p-bonded C5H5 and C5Me5 ligands.

However, it is recognized that the structures in the solid state and solution can sometimes differ and in such cases there is a useful complementarity between NMR spectroscopy and X-ray crystallography. A similar comment applies to structures that are fluxional on the NMR time scale. Specific experimental details and tables of pertinent crystallographic data will be included at the end of each chapter.

9 Dissertation Overview

The next three chapters of the dissertation describe studies of a variety of low-coordinate bonding environments that feature group 13 elements. Chapter 2 features a discussion of the generation of group 13 cations that involve the cyclopentadienyl ligands. The highlights in this area include the isolation and structural characterization of the decamethylborocenium cation,19 the most tightly squeezed metallocene and the first compound to adopt a s/p geometry in the solid state, the synthesis of the first gallocenium cation,20 the first examples of main group constrained geometry compounds,21 and the first examples of multidecker p- block cations.22

Chapter 3 represents a synthetic study of the reactivities of monovalent group 13 pentamethylcyclopentadienide compounds with conjugated systems and electron-deficient tris(perfluorophenyl) compounds. It has been found that

[(C5Me5)M]n (M = Al, Ga) fragments will undergo oxidative addition to diazabutadienes, resulting in the formation of monomeric five-membered ring

14 systems. Furthermore, it has been shown that the reactions of [(C5Me5)M]n clusters (M = Al, Ga) with (C6F5)3M (M = B, Al, Ga, In) yield the first examples of group 13 M(I)-M(III) donor-acceptor complexes,15a the first valence isomer of a dialane,15b and a unique inverse sandwich complex featuring p-bonding to perfluorophenyl ligands. A number of interesting decomposition products that provide insights into the chemistry of these species is also discussed.

10 Chapter 4 focuses on the reactivities of strongly Lewis basic Arduengo-type carbenes with group 13 pentamethylcyclopentadienides. It has been found that the reactions of (C5Me5)2AlMe and (C5Me5)3Ga with tetramethylimidazol-2-ylidene

23 yield unprecedented (C5Me5)2MH carbene complexes and tetramethylfulvene.

11 References and Notes

(1) Downs, A. J. Chemistry of Aluminum, Gallium, Indium and Thallium;

Blackie Academic and Professional: Glasgow, 1993, and references therein.

(2) Emsley, J. The Elements 2nd ed.; Clarendon Press: Oxford, 1991.

(3) IUPAC, Inorganic Chemistry Division, Commission on Atomic Weights and

Isotopic Abundances, Pure Appl. Chem., 1991, 63, 975.

(4) Dean, J. A., Ed. Lange’s Handbook of Chemistry, 13th ed.; McGraw-Hill:

New York, 1985.

(5) Lide, D. R., Editor-in-Chief Handbook of Chemistry and Physics, 73rd ed.;

CRC Press: Boca Raton, FL, 1992-1993.

(6) Harris, R. K., Ed. NMR and the Periodic Table; Academic press: New York,

1978.

(7) Hartmut, K.; Armin, B. J. Organomet. Chem. 1982, 234(2), C17.

(8) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon Press:

Oxford, 1984.

(9) Cotton, F. A.; Wilkinson, G.; Murillo, C.; Bochman, M. Advanced

Inorganic Chemistry, 6th ed.; Wiley: New York, 1999.

(10) Norman, N. C. Periodicity and the s- and p-Block Elements, Oxford

University Press: New York, 1997.

(11) Hotop, H.; Lineberger, W. C. J. Phys. Chem. Ref. Data 1985, 14, 731.

12

(12) Loos, D.; Baum, E.; Ecker, A.; Schnöckel, H. Angew. Chem., Int. Ed. Engl.,

1997, 36, 860.

(13) For recent reviews, see: Jutzi, P.; Burford, N. Chem. Rev. 1999, 99, 969;

Shapiro, P. J. Coord. Chem. Rev. 1999, 189, 1.

(14) Cowley, A. H.; Gorden, J. D.; Abernethy, C. D.; Clyburne, J. A.; McBurnett,

B. G.; J. Chem. Soc., Dalton Trans. 1998, 1937.

(15) (a) Gorden, J. D.; Voigt, A.; Macdonald, C. L. B.; Silverman, J. S.; Cowley,

A. H. J. Am. Chem. Soc. 2000, 122, 950; (b) Gorden, J. D.; Macdonald, C.

L. B.; Cowley, A. H. Chem. Commun., 2001, 75.

(16) For an extensive review, see: Piers, W. E.; Chivers, T. Chem. Soc. Rev.

1997, 26, 345.

(17) Bochmann, M.; Dawson, D. M. Angew. Chem., Int. Ed. Engl. 1996, 35,

2226.

(18) Jutzi, P; Reumann, G. J. Chem. Soc., Dalton Trans. 2000, 2237; Beswick,

M. A.; Palmer, J. S.; Wright, S. Chem. Soc. Rev. 1998, 27, 225; Jutzi, P.;

Burford, N. in : Synthesis, Reactivity, and Applications, 1st ed.,

1998, p 3-59 and references therein.

(19) Voigt, A.; Filipponi, S.; Macdonald, C. L. B.; Gorden, J. D.; Cowley, A. H.

Chem. Commun. 2000, 11, 911-912.

(20) Macdonald, C. L. B.; Gorden, J. D.; Voigt, A.; Cowley, A.H. J. Am. Chem.

Soc., 2000 122, 11725-11726.

13

(21) Pietryga, J. M.; Gorden, J. D.; Macdonald, C. L. B.; Voigt, A.; Wiacek R. J.;

Cowley, A. H. J. Am. Chem. Soc., 2001, 123, 7713.

(22) Cowley, A. H.; Macdonald, C. L. B.; Silverman, J. S.; Gorden, J. D.; Voigt,

A. Chem. Commun., 2001, 2, 175-176.

(23) Gorden, J. G.; Macdonald, C. L. B.; Cowley, A. H. J. Organomet. Chem., Accepted.

14

CHAPTER 2

Synthesis and Structure of Group 13 Cations

Introduction Traditionally in , the word “metallocene” has been confined to (bis-cyclopentadienyl)metal derivatives; however, the scope of the definition has now been expanded to include half-sandwich, multidecker, and polymeric cyclopentadiene species.1 The cyclopentadienyl ligand itself has attracted the attention of the main group chemist for many years due to its tendency for ring slippage and fluxionality. Moreover, the bulky pentamethylcyclopentadienyl, C5Me5, ligand has proved to be effective for the stabilization of highly reactive species by adjusting to slight changes in the electronic properties of the element center, while also possessing enough steric encumbrance to provide effective kinetic stabilization.2 The six possible bonding modes for the C5Me5 ligand are shown in Scheme 2.1. Due to the hapticity changes, the C5Me5 ligand is able to adjust its effective electron contribution to the element center.

15 Scheme 2.1. The six possible bonding modes for C5Me5 E E E E E E

h1(s) h1(p) h3 h5 h4 h2

Another important facet of the cyclopentadienyl family of ligands is their facile migratory behavior. Such behavior is particularly evident in dynamic NMR studies, which show that for many C5Me5 species there is an equivalence of for all proton and all C and Me carbon resonances. This process is accomplished by 1,2- sigmatropic shifts as illustrated in Scheme 2.2.2

E E C

C

E

C TS E E

C

C

E

Scheme 2.2. Degenerate sigmatropic rearrangements in C5Me5-E compounds where C designates a given C-atom in the ring

16 Polymerization Catalysis

Traditional Ziegler-Natta type metallocene catalysis involves a cocatalyst, such as an aluminum alkyl or methylalumoxane (MAO). In the generally accepted mechanism the active species is most commonly generated by treating a metallocene dichloride with MAO, which acts both as an alkylating agent and as a Lewis acidic acceptor for a methanide ligand, to produce the catalytically

+ 3 active 14- electron [(C5H5)2MR] species. (Scheme 2.3).

Me-MAO

Cl Zr Zr + MAO Me Cl

Scheme 2.3. Treatment of a zirconocenedichloride with methylalumoxane

Independently, Marks et al.4 and Ewen et al.5 were the first to recognize the ability of B(C6F5)3 to replace methylalumoxane as the polymerization initiator.

(Scheme 2.4). The methanide abstraction process is more complete in the case of

- B(C6F5)3 due to the lower coordinative ability of the [MeB(C6F5)3] anion. Several papers have appeared in the literature describing methanide abstraction reactions of organometallic complexes of titanium,6 hafnium,6 platinum,7 and yttrium8 that give catalytically active species. Furthermore, a nickel olefin polymerization catalyst has

9 been prepared by B(C6F5)3 promoted fluoride ion abstraction. Investigations of the reactivities of B(C6F5)3 with substituted cyclopentadienyl transition metal 17 compounds have been shown that this Lewis acid is capable of abstracting a number of other ligand types from the metal center, including benzyl, amide, and hydride anions.6

Me Me

Zr + B(C6F5)3 Zr Me Me

B(C6F5)3

Scheme 2.4. Methanide abstraction from dimethylzirconocene using B(C6F5)3

Attention has now turned to the use of cationic main group species as olefin polymerization catalysts. Thus the parent cationic aluminocenium salts

+ - [(C5H5)2Al] [X] , which were also prepared by B(C6F5)3-promoted methanide abstraction, have been shown to be effective for the polymerization of isobutene.10

However, these aluminocenium salts are only stable at low temperatures and have not yet been structurally characterized (Scheme 2.5). However, recently Shapiro et al. have been able to isolate and structurally characterize the analogous

5 + - pentamethylcyclopentadienyl derivative, [(h -C5Me5)2Al] [MeB(C6F5)3] , which

2 11 was obtained via the reaction of (h -C5Me5)2AlMe with B(C6F5)3. The use of anions with decreased coordinating ability and the replacement of the

18 cyclopentadiene ligands with more bulky C5Me5 ligands stabilizes such complexes and allows for ambient temperature structural investigations.

Al Me B(C F ) Me + B(C6F5)3 Al 6 5 3

Scheme 2.5. Synthesis of the aluminocenium cation by methanide abstraction

The past decade has witnessed an upsurge of interest in the chemistry of main group metallocenes.12 Apart from the fact that much less is known about s- and p-block metallocenes than their d- and f-block counterparts, interest in the main group metallocenes has been stimulated by structure and bonding considerations,12 their utility as reagents and chemical vapor deposition sources,13 and, as mentioned above, the possibility that cationic species might serve as useful catalysts for alkene polymerization.10,11 In the context of group 13 metallocenium cations, prior to the work presented here, only one such cation had been structurally authenticated,

14 + namely the decamethylaluminocenium cation. Although the salt [(h-C5Me5)2B]

- 15 [BCl4] had been described by Jutzi et al. a number of years ago, it had only been characterized on the basis of 1H and 11B NMR spectroscopy. Definitive structural data were needed e.g. to distinguish between the h1(p)/h5 and h1(s)/h5 ground state structures.

19 In principle, the synthesis of bis(pentamethylcyclopentadienyl)group 13 cations can be accomplished by a number of methods including (i) methanide abstraction from (h-C5Me5)2MMe (M = B, Al, Ga) with a Lewis acid, LA, (ii) metathesis with the salt of a non-coordinating anion such as LiB(C6F5)3, and (iii) halide abstraction from bis(pentamethylcyclopentadienyl)group 13 halides. These three processes are summarized in Scheme 2.6.

M X + A M LAX

1. X = Me A = B(C6F5)3 LAX = MeB(C6F5)3 2. X = Cl, Br A = LiB(C6F5)4 LAX = B(C6F5)4 3. X = Cl A = B(C6F5)3, AlCl3 LAX = ClB(C6F5)3, AlCl4

Scheme 2.6. Synthesis of metallocenium cations

The present chapter is divided into six sections which detail the results of numerous investigations that provide for a more complete understanding of this unparalleled series of metallocenium sandwich compounds. The first section is concerned with the bonding and reactivity of group 13 metallocenium precursors, which provide many insights into the nature of the cations formed. The second section focuses on the decamethylborocenium cation, which possesses an 20 unprecedented “tightly squeezed” h5/h1 structure. The third and fourth sections are devoted to the decamethylaluminocenium cation and the only reported gallocenium cation, which features a unique h1/h3 bonding arrangement. The final two sections will cover the syntheses of the first constrained geometry main group compounds and the first examples of triple-decker main group cations.

21

Section 2.1

Metallocenium Cation Precursors

Introduction

The structures, bonding arrangements and reactivity patterns of the precursors to the metallocenium cations provide many useful insights into the nature of the actual cations that are formed, hence a thorough examination of these materials is an important component of the present work.

Results and Discussion

Synthesis and Characterization of (h-C5Me5)2BX (X = Cl, Br)

Typically, bis(pentamethylcyclopentadienyl)haloboranes are conveniently synthesized in high yields by treatment of BX3 (X = Cl 1, Br 2) with two

15 1 equivalents of Li(C5Me5). The H NMR spectrum of each of these group 13 halogens exhibits only a single signal for the protons on the C5Me5 ring. Likewise, the 13C NMR spectra show only two resonances, one for the methyl carbons and one for the ring carbons. The equivalence of the ipso, a, and b positions of the C5Me5 substituents in the NMR spectra is typical of p-block metallocenes and is usually 22 attributed to rapid 1,2-sigmatropic rearrangements. The ionization of 1 and 2 appears to be favorable judging from the fact that the positive ion chemical

+ ionization (CI) mass spectra show a peak at m/e 281 [(h-C5Me5)2B] .

1 Figure 2.1. Molecular structure of (h (s)-C5Me5))2BBr (2) showing the slipped nature of the C5Me5 rings.

Recrystallization of 1 and 2 from hexane solution provided block-shaped crystals that were suitable for X-ray diffraction experiments. Details of the data collection, structure solution and refinement are compiled in Table 2.1 and selected metrical parameters are listed in Tables 2.2 and 2.3. The molecular structures of 1 23 15 and 2 (and (h-C5Me5)2BF ) are virtually identical but exhibit significant differences from those of their heavier congeners (vide infra). As illustrated in Figure 2.1, each haloborane possesses a monomeric structure of approximate C2 symmetry about the

B-X axis. For example, in compound 2, each C5Me5 ring is sigma-bonded to the boron atom, as evidenced by the Cmethyl-Cipso-B bond angles of 111.5(9)° and

115.2(9)°, and the localized bis-diene structure of the cyclopentadienyl rings. Thus, the average Cipso-Ca distance of 1.536(14) Å, is characteristic of a single bond and the average Ca-Cb distance of 1.352(15) Å, is characteristic of a double bond. The most intriguing feature of the haloborane structures is the unprecedented arrangement of the C5Me5 substituent which shows a twisting about the Cipso-B bonds. This canted nature of the C5Me5 ligands can be attributed to repulsion of the p-electron clouds on the C5Me5 rings, a subject which will be discussed further in

Section 2.

1 Synthesis and Characterization of (h (s)-C5Me5)2BMe

1 A high yield of [h (s)-C5Me5]2BMe (3) was realized by methylation of the bis-(pentamethylcyclopentadienyl)haloboranes 1 and 2 with MeLi and subsequent purification by sublimation. Again, the 1H NMR spectrum shows only a single signal for the protons in the C5Me5 ring, and the B-Me resonance falls in a shielded position at d 0.39. Likewise, the 13C NMR spectrum shows only two resonances, one for the methyl carbons and one for the ring carbons. The chemical ionization

24 (CI) mass spectrum comprises peaks attributable to both the parent compound as

+ + well as to the cations [(h-C5Me5)2B] (m/e = 281) and [(h-C5Me5)BMe] (m/e =

161).

1 Figure 2.2. Molecular structure of [h (s)-C5Me5]2BMe (3).

Recrystallization of 3 from hexane solution provided block-shaped crystals that were suitable for X-ray diffraction experiments. Details of the data collection, structure solution and refinement are compiled in Table 2.4 and selected metrical parameters are listed in Tables 2.5 and 2.6. As illustrated in Figure 2.2, both

C5Me5 rings of 3 are sigma-bonded to the boron atom, as evidenced by the Cmethyl- 25 Cipso-B bond angles in the range 121.0(3) and 114.2(3) and the localized diene structure of the cyclopentadienyl ring. The molecular structure of 3 is distinctly different both from those of the haloboranes and those of the heavier congeneric methyl compounds (vide infra). Thus compound 3 possesses a monomeric structure of C1 symmetry due to the canted nature of the s-C5Me5 rings. In contrast to the haloborane structures 1 and 2, the C5Me5 rings on the methyl analogue are almost

1 perpendicular to each other. Moreover, unlike [h (s)-C5Me5]2BBr, the arrangement of these C5Me5 rings is not due to a high degree of p-cloud repulsion caused by their close proximity to each other. Instead, this type of structure is adopted because the boron center no longer has the p electron contribution originating from halogen back bonding. The requisite p-donation into the vacant boron orbital is therefore provided by the C5Me5 substituents.

Analysis of “(h-C5Me5)2AlCl”

As monitored by 1H and 27Al NMR spectroscopy, all attempts to synthesize

(h-C5Me5)2AlCl (4) by treatment of E(C5Me5) ( E = Li, Na, K) with AlCl3 afforded a mixture of products that could not be separated. Analysis of the 27Al NMR spectra showed three resonances, one corresponding to the desired product (d -10) as well as two additional resonances at d –115 and d 40. The mass of the reaction mixture

5 + exhibited peaks attributable to [(h -C5Me5)2Al] and a variety of C5Me5- and Cl- derived counter anions; however, it was impossible to detect a peak corresponding 26 to the molecular ion, regardless of the ionization technique employed. Shapiro and co-workers11 independently corroborated these observations while attempting to

27 synthesize (h-C5Me5)3Al. Moreover, these authors showed that the Al resonance signal at d –115 corresponded to decamethylaluminocenium cation [(h5-

+ C5Me5)2Al] . The intensity of this signal was found to be dependent on the temperature and polarity of the solvent, thus suggesting that an equilibrium process was occurring (Scheme 2.7). The redox behavior and the migratory nature of

5 C5Me5 ligands in [(h -C5Me5)Al]4 are well documented and, in fact, the decamethylaluminocenium cation was first synthesized by the addition of equimolar

Cl Cl Al Al Al Al Cl Cl

Scheme 2.7. Equilibrium formation of the decamethylaluminocenium cation

5 14a 5 amounts of (h -C5Me5)Al(I) to AlCl3 , Scheme 2.8. The formation of [(h -

+ C5Me5)2Al] appears to be a thermodynamic sink for many reactions involving aluminum compounds bearing C5Me5 substituents. Further support for such a conclusion comes from results recently reported by Jutzi and co-workers16 in which

5 + - the decamethylaluminocenium salts [(h -C5Me5)2Al] [AlX4] were isolated as the

27 5 exclusive products from the reactions of decamethylsilocene, [(h -C5Me5)2Si] with

AlX3 (X = Cl, Br).

Al 3 + AlCl3 Al Cp*-AlCl3 + 2Al(0)

Scheme 2.8. Reaction of (h5-pentamethylcyclopentadienyl)aluminum with aluminum trichloride

Synthesis and Characterization of (h-C5Me5)2AlMe

The reaction of MeAlCl2 with two equivalents of KC5Me5 in toluene solution afforded (h-C5Me5)2AlMe (5) in high yield. The identity of 5 was established by the 1H NMR spectrum, which showed only a single signal for the

C5Me5 protons in the expected region at d 1.88 and a resonance at d -1.62 attributable to the methyl group on Al. Likewise, the 13C NMR spectra exhibited only two resonances, namely one for the C5Me5-methyl carbons (d 11.05) and one

10 13 for the C5Me5-ring carbons (d 115.68). As in the case of (C5H5)2AlMe, a C signal for the Al-methyl group was not observed, presumably due to extreme signal broadening by the quadrupolar Al nucleus (I = 5/2). The chemical ionization (CI) mass spectrum of 5 comprised peaks attributable to both the parent compound and

5 + 5 + also to the cations [(h -C5Me5)2Al] and [(h -C5Me5)AlMe] .

28 Large colorless rods of 5 were obtained by filtration and concentration of the filtrate of the original reaction mixture. Although the data from X-ray diffraction studies confirmed the connectivity and composition of 5, the structure is of poor

5 quality due to a high degree of disorder about the h -C5Me5 rings which could not be modeled satisfactorily (Figure 2.3). In a subsequent study, Shapiro and co-

11 workers published a similar synthesis of 5 using NaC5Me5 instead of KC5Me5.

These authors were able to grow X-ray quality crystals of 5 by slow cooling of a hexamethyl disiloxane solution. The disorder of the rings appears to be driven by

2 Figure 2.3. Solid-state structure of (h -C5Me5)2AlMe (5).

29 steric factors arising from nonbonding interactions between the C5Me5-methyl groups closest to the Al-Me moiety, that cause a degree of bending away from the ring plane. Previously, theoretical calculations at the RHF/3-21G(*) level of theory had shown that for cyclopentadienyl complexes of aluminum the preference for an h2 structure is very slight, and indicated that slippage of the cyclopentadienyl ring to other hapticities should be extremely facile, with a barrier of between 2 and 6 kcal/mol.17 Supportive of such a conclusion is the fact that other

5 3 1 peralkylcyclopentadienyl aluminum(III) compounds exhibit h , h , and h ring coordination geometries both in the crystalline state18,19 and in solution.20

Synthesis and Characterization of (h-C5Me5)2GaCl

The bis(pentamethylcyclopentadienyl)halogallanes, (h-C5Me5)2GaX (X = Cl

21 6, Br 7), are conveniently synthesized in high yield by treatment of GaX3 with two

1 equivalents of LiC5Me5. The H NMR spectrum of each of these group 13 halides

13 exhibits only a single signal for the protons on the C5Me5 ring. Likewise, the C

NMR spectra show only two resonances, namely one for the methyl carbons and one for the ring carbons. The formation of cations from 6 and 7 appears to be favorable since the positive ion chemical ionization (CI) mass spectra show peaks

+ attributable to [(h-C5Me5)2Ga] .

30

1 Figure 2.4. Molecular structure of [(h (s)-C5Me5)2GaCl]2 (6).

Recrystallization of 6 from hexane solution provided colorless block-shaped crystals that were suitable for X-ray diffraction experiments. Compound 6 crystallizes in the triclinic space group P-1 with 1.5 crystallographically independent molecules of approximately C2v symmetry in the asymmetric unit,

(Figure 2.4). There are no unusually short intermolecular contacts and the metrical parameters for both species are very similar and hence only one set of data will be discussed. Details of the data collection, structure solution and refinement are compiled in Table 2.7 and selected metrical parameters are listed in Tables 2.8 and

2.9. In contrast to (h-C5Me5)2BX (X = Cl, Br), which is monomeric in the

5 crystalline state, and (h-C5Me5)2AlCl, which tends toward autoionization into [(h -

+ - C5Me5)2Al] and [(h-C5Me5)2AlCl2] , the gallium analogue 6 dimerizes by means of

31 1 chloride bridges. Each C5Me5 ring is attached to gallium in an h fashion as indicated by the localized bonding within the ring (av Cipso-Ca = 1.498(6) Å; Ca-Cb

= 1.350(6) Å). The Ga-C bond length of 2.001(4) Å is similar to that reported22 for

1 (h -C5Me5)3Ga (2.038(4) Å).

Synthesis and Characterization of (h-C5Me5)2GaMe

A high yield of (h-C5Me5)2GaMe (8) was realized by the treatment MeGaCl2 with two equivalents of LiC5Me5. As in the case of the other compounds discussed

1 in this section, the H NMR spectrum shows only a single signal for the C5Me5 ring protons, and the Ga-Me resonance appears in a highly shielded position at d -1.29.

Likewise, the 13C NMR spectra of 8 shows only three resonances, namely one for the Ga-methyl group (d 1.27) and one each for C5Me5-methyl (d 11.81) and C5Me5- ring carbons (d 119.90). The chemical ionization (CI) mass spectrum exhibits peaks

+ attributable to both the molecular ion and to the cations [(h-C5Me5)2Ga] and [(h-

+ C5Me5)GaMe] .

32

1 2 Figure 2.5. Molecular structure of (h (p)-C5Me5)(h -C5Me5)GaMe (8).

Recrystallization of 8 from hexane solution provided colorless block-shaped crystals that were suitable for X-ray diffraction experiments. Details of the data collection, structure solution and refinement are compiled in Table 2.10 and selected metrical parameters are listed in Tables 2.11 and 2.12. The molecular structure of 8 is very similar to that of the lighter group 13 methyl derivatives that feature two C5Me5 ligands. One of the C5Me5 rings of 8 is attached to gallium in an h1 fashion as indicated by the localized p system [C(21)-C(22) = 1.47(2) Å, C(21)-

C(25) = 1.50(2) Å, C(22)-C(23) = 1.39(2) Å, C(23)-C(24) = 1.38(2) Å, C(24)-C(25)

= 1.38(2) Å], and a large differences in the Ga-C distances: Ga-C(21) (2.059(11) Å),

Ga-C(22) (2.630(11) Å), and Ga-C(25) (2.662(9) Å). The other ring is bonded in an 33 h2 fashion as evidenced by the fact that two of the Ga-C distances, (2.210(11) Å to

C(11) and 2.172(9) Å to C(12)) are considerably shorter than the other three:

(2.778(9) Å to C(13), 2.773(11) Å to C(15) and 3.059(12) Å to C(14)). The ipso methyl carbon atom C(211) lies 0.362 Å out of the least squares plane of the C5 ring, compared to 0.171 Å for C(121) and 0.134 Å for C(111). The C5Me5 rings of 8 are planar within experimental error, which distinguishes this compound from the

2 aluminum analogue, [(h -C5Me5)2AlMe], that features distortions from ring planarity due to folding of the ring carbons away from the Al-Me region. Unlike the halogallane 6, the C5Me5 rings of the methyl analogue 8 are not parallel, but instead adopt a bent conformation in which the C5Me5 rings have an average Cipso-Ga-Cipso bond angle of 119.5º.

Conclusions

Due to the small covalent radius of boron, the bonding in the bis(pentamethylcyclopentadienyl)-substituted boron precursors is largely defined by repulsions between the p-clouds of the C5Me5 rings, Furthermore, there is a greater tendency for Al(III) to form p-interactions with its cyclopentadienyl rings, as

5 + evidenced by the ease of (h -C5Me5)2Al formation, as compared with Ga(III), which exhibits a preference for localized sigma-bonding and dimerization through halide bridges. This difference in bonding is undoubtedly associated with the greater electronegativity of Ga relative to that of Al (See Table 1.1). All of the

34 methyl compounds, (h-C5Me5)2MMe (M = B, Al, Ga), have structures that allow for donation of p-electron density into the electron-deficient metal atom, M. This

“proto metallocene” type of structure, that features bending of the rings above and below the M-Me (M = Al, Ga) region, is unique to group 13 cyclopentadienide complexes.11 Typically, the cyclopentadienyl ligand in transition metal cyclopentadienide complexes adopts a position such that it is directed away from the alkyl-metal region.23 Take collectively, all of these factors would suggest that the bonding and reactivities of the group 13 metallocenium cations should vary greatly, a surmise that will be discussed in later sections.

35

Section 2.2

Borocenium Cations

Introduction

The unusual structure of beryllocene, Be(h-C5H5)2 (9), has attracted the attention of chemists for several years.12 In both the solid and vapor states, 9 adopts a “slip-sandwich” structure in which the parallel cyclopentadienyl rings are attached to beryllium in an h1(p)/h5 fashion.24 In solution, 9 is fluxional due to rapid changes in ring hapticities,25 Scheme 2.9. The observed structure contrasts with the h1(s)/h5 structure predicted on the basis of numerous theoretical calculations.25,26

Be Be

Scheme 2.9. Fluxional behavior of Be(h-C5H5)2

+ The borocenium cation [B(h-C5H5)2] , which is isoelectronic with 9, is not known and unlikely to be stable at ambient temperature. Although the

36 + + 1 decamethylborocenium cation [(h-C5Me5)2B] , [10] , has been characterized by H and 11B NMR spectroscopy,27 such data cannot be used to distinguish between h1(p)/h5 and h1(s)/h5 structures. It was therefore necessary to perform an X-ray analysis of a suitable salt of [10]+.

Results and Discussion

+ Synthesis and Characterization of (h-C5Me5)2B

It was found by NMR spectroscopy that a variety of salts of [10]+ can be

1 27 generated by treatment of (h -C5Me5)2BCl with e.g. LiB(C6F5)4, GaCl3, or AlCl3.

However, from the standpoint of single crystal growth, the best reaction was that

1 between equimolar amounts of (h -C5Me5)2BCl and AlCl3 in CH2Cl2/C6D6 solution

+ - + - which afforded an 86% yield of [10] [AlCl4] . The crystalline state of [10] [AlCl4] consists of an array of two independent cations and anions. Details of the data collection, structure solution and refinement are compiled in Table 2.13 and selected metrical parameters are listed in Tables 2.14 and 2.15. There are no unusually short interionic contacts and the metrical parameters for the independent cations are very similar, hence only one set of data is discussed here. The decamethylborocenium cation [10]+ features one h5-bonded and one h1(s)-bonded

C5Me5 substituent, both of which feature planar C5 rings within experimental error

(Figure 2.6). Such an arrangement for a main group metallocene had been predicted theoretically but never observed experimentally in the crystalline state.26

37 5 5 The boron-(h -C5Me5) ring centroid distance (1.290(5) Å) and the C(1)-B(1)-(h -

C5Me5) ring centroid arrangement is nearly linear (177.9(5)°) and the boron-carbon

1 distance for the h -bonded C5Me5 ring, B(1)-C(1), (1.582(6) Å) is considerably

5 longer than the boron-(h -C5Me5) ring centroid distance (1.269(5) Å). The C5Me5 rings of [10]+ are non-parallel as indicated, for example, by the 114.4(5)° tilt angle

1 between the B(1)-C(1) bond and the least squares plane of the h -C5Me5 ring. A further differentiating feature is that the h1-attached ring of [10]+ exhibits a typical localized structure with average Ca-Cb and Cb-Cb bond distances of 1.339(5) and

1.476(6) Å, respectively.

It has been shown theoretically that a difference of only 2.6 kcal/mol exists among several model structures for beryllocene28 and a compression of 0.02 Å of

5 the metal-ring distances from equilibrium in a compound like [(h -C5H5)2Mg] has been estimated to require only 0.17 kcal/mol.29 It is not surprising therefore that, while an h1/h5 parallel-ring structure is prevalent for beryllocene in the solid,30,31 in

32 the solution and gas phases (h-C5Me5)2Be adopts an approximate D5d structure. It appears that if one of the C5Me5 rings forms a sufficiently strong (s-C5Me5)-Be

5 1 5 bond, it prevails over the somewhat weaker (h -C5Me5)-Be binding, and the h /h

1 5 structure results. While (C5Me4H)2Be still adopts a h /h conformation for the tetramethylcyclopentadienide rings,32 the alternative slip-sandwich observed for the

38 C5Me5 analogue could be due to destabilization by van der Waals repulsions between the Me groups on the C5Me5 ring.

1 5 + + Figure 2.6. Molecular structure of [(h -C5Me5)(h -C5Me5)B] [10] showing the atom numbering scheme.

The structure of [10]+ also contrasts with that of the isovalent

5 decamethylaluminocenium cation, which adopts a staggered bis(h -C5Me5) -like geometry.33 To provide insight into the reason(s) for this structural

+ + difference, DFT calculations were performed on [B(h-C5Me5)2] , [B(h-C5H5)2] ,

+ + 34 and [Al(h-C5H5)2] . The optimization of [10] at the BP86/A level of theory ,

Table 2.16, provides excellent agreement with the experimental structure. Thus, the global minimum is the observed h1(s)/h5 structure with calculated B(1)-C(1) and

5 B(1)-(h -C5Me5) ring centroid distances of 1.593 and 1.291 Å, respectively, a C(1)-

39 5 1 B(1)-(h -C5Me5) ring centroid angle of 179°, and an h -C5Me5 ring tilt angle of

123°. Moreover, calculation of the 11B chemical shift for this structure using the

GIAO method35 (d 43.1) is in excellent agreement with the experimental value (d

27 5 + 41.5). The staggered bis-h (D5d) structure of [10] is computed to be 48.95 kcal/mol higher in energy than the h1/h5 structure, thus confirming that the observed geometry is not caused by crystal packing forces. Examination of space-filling

5 + models reveals the existence of pronounced steric congestion in [(h -C5Me5)2B] which is relieved somewhat in proceeding to the h1/h5 structure. However, traditional steric effects are not responsible for the observed geometry of [10]+ since

+ DFT calculations on the unsubstituted borocenium cation, [(h-C5H5)2B] reveal that the ground state geometry is also h1/h5 and remarkably similar to that of [10]+.

More importantly, the difference in energy between the h1/h5 and bis-h5 structures is essentially the same for both the C5Me5- and C5H5-substituted cations (45.39 kcal/mol for the latter) therefore, the presence of the methyl groups on the cyclopentadienyl ring is not a factor in determining the preferred conformation.

+ Surprisingly, the D5d [(h-C5H5)2B] structure is not even a true minimum (Nimag = 4) on the potential energy surface (PES). Conversely, no h1/h5 minimum is found for

+ [(h-C5H5)2Al] ; geometry optimization on the Cs symmetry PES proceeds smoothly

5 to the bis-h (D5h) structure instead. The difference in bonding modes is attributable to the higher electronegativity of boron and greater strength (and lower ionicity) of

40 B-C vs. Al-C bonding. The smaller size and greater effective nuclear charge of boron is also important, especially in comparison to Be(h-C5H5)2, because the putative D5d structure is rendered much less stable due to the increased repulsion between the p-clouds on the cyclopentadienyl ligands, which would be closer than the C-C interlayer separation in graphite, 2.58 Å vs. 3.35 Å36 respectively.

1 5 Adoption of the h (p)/h “slipped-sandwich” structure by Be(h-C5H5)2 relieves this

+ strain energy sufficiently, but the closer ligand proximity in [(h-C5H5)2B] mandates the non-parallel, p-localized h1(s)/h5 alternative. In effect, the change from Be to

B+ results in a much steeper PES which more clearly favors the h1(s)/h5 structure.

Conclusions

The structure of and bonding in the first authentic example of an h1(s)/h5

+ metallocene have been established. The potential energy surface for [(h-C5H5)2B] is much steeper than that for Be(h-C5H5)2 in the ring centroid-element-ring centroid region, thus favoring a s,p over a p,p type bonding arrangement. Furthermore,

+ DFT calculations on the [B(h-C5H5)2] show that the LUMO is present on the cyclopentadienyl ring rather than the boron center therefore the borocenium cation will not catalyze olefin polymerizations. Because of the small size, combined with the high effective nuclear charge of the cationic boron(III) center, the isolation of a more tightly sandwiched metallocene is not anticipated.

41

Section 2.3

Aluminocenium Cations

Introduction

The decamethylaluminocenium cation was first synthesized by by Schnöckel

14a 5 et al. by the addition of equimolar amounts of (h -C5Me5)Al(I) to AlCl3, as summarized in Scheme 2.10. Note that this reaction is somewhat complex in that it involves the disproportionation of Al(+I) to Al(+III) and Al(0) as well as the transfer of C5Me5 groups. An effort was therefore made to develop a simpler method of preparation of the decamethylaluminocenium cation. In light of the

- - facile elimination of Cl and Me anions from the bis(h-C5Me5) derivatives 4 and 5, respectively, as evidenced by mass spectral data, attempts were made to convert 4 and 5 into the aluminocenium cation [11]+ by treatment with an appropriate Lewis

37 5 + acid. Since Chien and Rausch were able to synthesize the (h -C5Me5)Sn cation by the addition of LiB(C6F5)3 to a solution of (h-C5Me5)SnCl it seemed reasonable to attempt this approach using “(h-C5Me5)2AlCl”. As an alternative method, it was decided to treat the chloroalane with B(C6F5)3 since this Lewis acid is known to abstract halide anions.9 Given that crystallographically characterizable material was desirable, non-coordinating anions of comparable sizes were selected in order to 42 maximize the lattice energies of the product. Of the various methods employed, the addition of AlCl3 to “(h-C5Me5)2AlCl” was the most successful in terms of producing a crystalline sample of the desired salt of the decamethylaluminocenium cation, [11]+. The tetrachloroaluminate salt of [11]+ has been examined by X-ray crystallography, as has a C6F5 exchange product produced by the reaction of

B(C6F5)3 with “(h-C5Me5)2AlCl”.

Cp*

Al + AlCl 0 3 Al + 2Al 3/4 Cl Al Al Al Al Cl Cp* Cl Cp* Cp*

+ 5 Scheme 2.10. Generation of [11] from (h -C5Me5)Al(I) and AlCl3

Results and Discussion

Reactions with “(h-C5Me5)2AlCl”

As pointed out above, an obvious approach to the synthesis of the decamethylaluminocenium cation was via the metathetical reaction of (h-

C5Me5)2AlCl (4) with LiB(C6F5)4 in dichloromethane solution at room temperature.

5 + 27 In fact, the formation of the desired cation, [(h -C5Me5)2Al] , was indicated by Al

NMR spectroscopic assay; however, a multitude of proton signals were evident in the 1H NMR spectrum of the reaction mixture thus indicating the formation of

43 several (unidentified) decomposition products. Moreover, upon storage of the sample at room temperature, a steady decrease in the concentration of [11]+ was observed to take place over a number of days, as evidenced by a steady diminution in signal intensity of the 27Al NMR peak at d –102.

Similar results were obtained when 4 was treated with B(C6F5)3, namely the initial detection of the desired cation, followed by the evolution of decomposition products. However, in this case, concentration and storage of the filtrate from the reaction mixture at – 20 °C resulted in the isolation of a crop of colorless crystals in low yield. A single crystal X-ray diffraction study of this material revealed its

5 identity as [(h -C5Me5)(C6F5)AlCl]2 (12). Presumably this surprising product arose

- from [C5Me5] abstraction from 4 by B(C6F5)3, followed by C6F5 back-transfer.

X-Ray Crystal Structure of 12

The crystalline state structure of 12 comprises an array of chloride-bridged dimers with of approximate Ci symmetry. (Figure 2.7) There are 1.5 crystallographically independent molecules in the asymmetric unit. The metrical parameters for both species are very similar hence only one set of data will be discussed; there are no unusually short intermolecular contacts. Details of the data collection, structure solution and refinement are compiled in Table 2.17 and selected metrical parameters are listed in Tables 2.18 and 2.19. Within

5 experimental error the C5Me5 ligands are planar and are h bonded to Al with all Al-

44 C distances of similar lengths (2.115(4) Å to C(13), 2.215(5) Å to C(14), 2.365(6) Å

5 to C(15), 2.374(6) Å to C(16) and 2.218(5) Å to C(17)). The average h -C5Me5 ring centroid distance in 7 (1.916(5) Å) is considerably longer than those in the

11,14 decamethylaluminocenium cation (1.783(2) Å) and the average Al-(C6F5) bond distance is in excellent agreement (1.989(4) Å) with those reported for the toluene and benzene adducts of tris(perfluorophenyl)aluminum38 (1.984(14) Å, 1.979(7) Å).

5 Figure 2.7. Molecular structure of [(h -C5Me5)(C6F5)AlCl]2 (12).

45 2 Reactions with (h -C5Me5)2AlMe

Since methyl abstraction by B(C6F5)3 represents a well-established route to d-block metallocene cations,3 it seemed reasonable to explore the reaction of (h2-

+ - C5Me5)2AlMe (5) with B(C6F5)3 in the hope of preparing [11] [MeB(C6F5)3] . In view of the fact that the Al(III)-Me bond strength is less than that of the Al(III)-Cl bond, it was assumed that abstraction of a methanide anion with B(C6F5)3 would be

2 more facile and less prone to side-product formation for (h -C5Me5)2AlMe than for

(h-C5Me5)2AlCl. Treatment of 5 with B(C6F5)3 in toluene solution at room temperature produced an amber oil that yielded an off-white powder after repeated washing with hexane. The initial formation of the desired product in CH2Cl2

5 + - solution was evident from the detection of [(h -C5Me5)2Al] and [MeB(C6F5)3] ions on the basis of multinuclear NMR experiments; however, all attempts at crystallization of the product from toluene and CH2Cl2 solution were unsuccessful

+ - and resulted in decomposition even at 0 °C. Apparently, [11] [MeB(C6F5)] is unstable with respect to C6F5 back-transfer from B(C6F5)3.

Underscoring the sensitivity of these systems to reaction conditions, while the present work was in progress Shapiro and co-workers11 reported the isolation of

+ - [11] [MeB(C6F5)] by slow diffusion of pentane into a CH2Cl2 solution of this salt at

+ - -78 °C. Interestingly, it was found that [11] [MeB(C6F5)3] can be stored for months at –17 °C under an inert atmosphere with no apparent decomposition. As

1 + - monitored by H NMR spectroscopy, the decomposition of [11] [MeB(C6F5)3]

46 occurs at room temperature over a period of a few days via elimination of C5Me5H.

Furthermore, these authors reported that CDCl3 solutions of this salt appeared to be stable for months at room temperature with only minor discoloration of the sample.

+ - The foregoing work implies that the thermal stability of [11] [MeB(C6F5)3] is highly solvent dependent and highlights the need to search for an appropriate solvent for the generation of such compounds.

The reaction of “(h-C5Me5)2AlCl” with AlCl3

Realizing the tendency of perfluorophenyl-based Lewis acids to produce decomposition products and recognizing the propensity of 4 to generate the decamethylaluminocenium cation spontaneously by C5Me5 rearrangement, it was believed that the addition of a stoichiometric amount of AlCl3 would shift equilibrium of “(h-C5Me5)2AlCl” (4) toward the formation of the aluminocenium

- salt. This belief was also based on the fact that AlCl3 has been shown to abstract Cl

1 5 from (h-C5Me5)2BCl to form the decamethylborocenium salt, [(h -C5Me5)(h -

+ - C5Me5)2B] [AlCl4] .

It was discovered that the addition of an equimolar quantity of AlCl3 to 4 in

+ - CH2Cl2 solution resulted in a 93% yield of colorless crystalline [11] [AlCl4] . The

+ - HRMS data for [11] [AlCl4] were in satisfactory accord with the calculated m/e

+ - + - values for both [11] and [AlCl4] . The presence of both [11] and [AlCl4] in

27 CD2Cl2 solution was established on the basis of the detection of Al NMR signals

47 at d -102 and d 115 respectively. In agreement with Shapiro et al. the 1H and 13C

NMR spectra for [11]+ were found to exhibit singlet resonances for the methyl groups and ring carbon atoms. However, an X-ray crystal structure was considered desirable in order to establish C5Me5 ring hapticities and to determine the degree of

+ - anion/cation interactions. The salt [11] [AlCl4] appears to be thermally stable when heated to 100 °C in toluene solution for several hours. Moreover, this material can be stored under an inert atmosphere for several months, both in solution and in the crystalline state, and only slight discoloration is apparent upon slow heating of the solid up to its melting point of 123 °C.

+ - X-Ray Crystal Structure of [11] [AlCl4]

+ - The X-ray crystallographic data for [11] [AlCl4] are listed in Table 2.20, and selected bond lengths and angles are compiled in Tables 2.21 and 2.22.

+ - Compound [11] [AlCl4] crystallizes in triclinic space group P1 and the asymmetric unit consists of two independent cations and anions. There are no unusually short interionic contacts and the metrical parameters for the independent cations are very similar and hence only one set of data is discussed here. The structure of the decamethylaluminocenium cation is ferrocene-like and has (ring-centroid)-Al-(ring- centroid) angle of 180°. The C5Me5 rings adopt a staggered arrangement with an angle of 36° between them. A similar conformation has been reported for [11]+[(h1-

-14a + - 11 C5Me5)AlCl3] and [11] [MeB(C6F5)3] . There is no evidence for residual

48 Al···Cl interactions in the structure, as demonstrated by the fact that the closest such contact is 5.835 Å. Moreover, there is essentially no distortion about any of the tetrahedral Al centers. The average Al-C5Me5 ring centroid distance (1.773(5) Å) is

+ - 11 in excellent accord with that reported for [11] [MeB(C6F5)3] (1.783(2) Å).

16 + - Recently Jutzi et al. have been able to isolate [11] [AlCl4] from the reaction of decamethylsilicocene with AlCl3. Evidently, this reaction, which was monitored by

27 Al NMR spectroscopy, involves a double C5Me5 group transfer from silicon to aluminum.

5 + - + Figure 2.8. Molecular structure of a cation in [(h -C5Me5)2Al] [AlCl4] (11 ).

49 Conclusions

The synthesis of decamethylaluminocenium cation can be accomplished by the abstraction of a Cl- anions from a precursor chloride using a variety of perfluorophenyl-substituted Lewis Acids. While B(C6F5)3 has been shown to be an excellent methanide abstracting agent in the context of transition metal chemistry, this is not the case in aluminum chemistry because of C6F5 back-transfer ligand

+ - redistribution reactions. The best synthesis of [11] [AlCl4] was carried out by halide abstraction using AlCl3 and, once formed in a pure state this compound was found to exhibit remarkable thermal stability with respect to ligand rearrangement.

+ - However, the thermal stability of [11] [ MeB(C6F5)3] is highly dependent upon the choice of solvent.

5 Compound 12, [(h -C5Me5)(C6F5)AlCl]2, was formed either by the initial formation of [11]+ and subsequent ligand rearrangement or, more likely, by the

- direct abstraction of a [C5Me5] anion by B(C6F5)3 and subsequent C6F5 exchange to give (h-C5Me5)B(C6F5)2 and 12, (Scheme 2.11). However, no conclusive evidence for either proposal was found by spectroscopic analysis of the mother liquor.

F F + F F FAST Cl - F Cl 2 B(C6F5)3 2 [Cp*B(C6F5)3] Al Al F Al Al 2 Cl Cl Al F F

Cl F F

Scheme 2.11. Proposed reaction of “(h-C5Me5)2AlCl” with B(C6F5)3

50

Section 2.4

Gallocenium Cations

Introduction

In the context of group 13 metallocenes, two structurally authenticated cations, namely the decamethylborocenium cation [10]+13,39 and the decamethylaluminocenium cation [11]+14 have been discussed in earlier sections, along with a survey of some of the decomposition products that originate from these cations. While cation [10]+ features an unprecedented “tightly squeezed” h5/h1

+ structure, [11] possesses a ferrocene-like structure, with D5d symmetry. The present section is devoted to a discussion of the approaches that have been taken for the synthesis of the decamethylgallocenium cation [13]+. Methanide or chloride abstraction from gallium-methyl or gallium-chloride precursors produced a number of decomposition products that have been isolated and studied by X-ray crystallography. Of the various methods employed, protonolysis or Lewis acid

1 abstraction of a C5Me5 ligand from (h -C5Me5)3Ga proved to be the most successful methods for preparing the desired cation, [13]+. The tetrafluoroborate and tetrachloroaluminate salts of [13]+ have been examined by X-ray crystallography and further insights into their electronic and molecular structures have been gained

51 from DFT calculations that were performed on the parent gallocenium cation, [(h-

+ C5H5)2Ga] .

Results and Discussion

1 Reactions with (h -C5Me5)2GaX (X = Cl, Br)

On the basis of 1H and 11B NMR spectroscopy it was found that the reaction

1 of (h -C5Me5)2GaX (6, X = Cl, 7, X = Br) with B(C6F5)3 resulted in a mixture of products. However, concentration of the reaction mixture afforded two very interesting crystalline decomposition products in low yields. By means of single crystal X-ray diffraction it was determined that the isolated crystals correspond to

3 1 two unique exchange products [(h -C5Me5)(C6F5)GaCl]2 (14), and (h -

1 C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)(15).

X-Ray Crystal Structure of 14

The crystalline state of 14 comprises an array of centrosymmetric chloride- bridged dimers as shown in Figure 2.9. Details of the data collection, structure solution and refinement are compiled in Table 2.23 and selected metrical parameters are listed in Tables 2.24 and 2.25. There are no unusually short

3 intermolecular contacts. The C5Me5 ligands are bonded to gallium in an h fashion as evidenced by the fact that three of the Ga-C distances (2.019(4) Å to C(11),

2.516(6) Å to C(12), 2.499(6) Å to C(15)) are considerably shorter than the other

52 two (3.030(6) Å to C(13) and 3.045(5) Å to C(14). The ipso methyl carbon atom

(C(111)) lies 0.22 Å out of the least squares plane of the C5 ring, compared with

0.05 Å for (C(151)) and (C(121)). The average Ga-C6F5 bond distances in 14

(1.972(4) Å) are very similar to those in the THF adduct of

40 - 41 tris(perfluorophenyl)gallium (1.986(2) Å) and the [(C6F5)4Ga] anion (2.010(20)

Å).

3 Figure 2.9. Molecular structure of [(h -C5Me5)(C6F5)GaCl]2 (14) showing the atom numbering scheme.

X-Ray Crystal Structure of 15

Compound 15 crystallizes in the monoclinic space group P21/n and there are no unusually short intermolecular contacts between the chloride-bridged dimers

(Figure 2.10). Details of the data collection, structure solution and refinement are compiled in Table 2.26 and selected metrical parameters are listed in Tables 2.27

1 and 2.28. Each C5Me5 ring of 15 is attached to gallium in an h (s) fashion as 53 indicated by the localized bonding (av Ca-Cb = 1.354(7) Å; Cb-Cb = 1.454(7) Å).

Furthermore, the Ga-C bond lengths in 15 (Ga(1)-C(11) = 1.993(4) Å, Ga(1)-C(21)

= 1.992(4) Å, Ga(1)-C(31) = 2.006(4) Å) are only marginally shorter than those

22 1 reported for (h (s)-C5Me5)3Ga (2.038(4) Å). The Al-C6F5 bond distance (1.973(4)

Å) is in close agreement with previously published values for perfluorophenyl- substituted gallium compounds.

1 1 Figure 2.10. Molecular structure of (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)(15) showing the atom numbering scheme.

Overall, the most intriguing feature of 15 is the fact that the chemical properties are distinctly different from those of analogous aluminum compounds.

54 As mentioned previously, (h-C5Me5)2AlCl exhibits a high propensity toward the formation of the corresponding decamethylaluminocenium salt; conversely biscyclopentadienyl gallium halides tend to form covalent dimers. These different properties are undoubtedly associated with the greater electronegativity and increased effective nuclear charge of Ga(III) relative to that of Al(III).

Reaction of (h-C5Me5)2GaMe with B(C6F5)3

Since methyl abstraction by B(C6F5)3 represents a viable route to d-block metallocene cations,42 it seemed appropriate to investigate the reaction of (h1(p)-

2 C5Me5)(h -C5Me5)GaMe (8) with B(C6F5)3 in the hope of preparing [(h-

+ - C5Me5)2Ga] [MeB(C6F5)3] . The initial formation of the desired product in CH2Cl2

+ - solution was evident from the identification of [13] and [MeB(C6F5)3] ions on the basis of multinuclear NMR spectroscopic data. However, upon attempted recrystallization of this salt it was converted into (h-C5Me5)2GaC6F5 (16) via a

43 putative C6F5 back-transfer reaction. Interestingly, if the reaction of 8 with

B(C6F5)3 is carried out in Et2O solution, there is no evidence for the intermediacy of

+ - [(h-C5Me5)2Ga] [MeB(C6F5)3] . In view of the recent concern with the molecular structures of bis(cyclopentadienyl) compounds of aluminum,44,45 it was decided to investigate that of 16.

55

1 2 Figure 2.11. Molecular structure of (h (p)-C5Me5)(h -C5Me5)GaC6F5 (16) showing the atom numbering scheme.

X-ray Crystal Structure of 16

The crystalline state of 16 (Figure 2.11) consists of monomeric units with

1 2 the same h - and h -bonding mode as that found for (h-C5Me5)2GaMe (8). Details of the data collection, structure solution and structure refinement are compiled in

Table 2.29 and selected metrical parameters are listed in Tables 2.30 and 2.31. The

2 h -bonded C5Me5 ring in 16 was modeled in two positions; however, only the major contributor is shown in Figure 2.11. One of the C5Me5 rings of 16 is attached to

1 gallium in an h (p) fashion as indicated by the localized p system (av Cipso-Ca =

56 1.472(3) Å, av Ca-Cb = 1.373(3) Å, av Cb-Cb = 1.432(4) Å), and a large increase in the average Ga-C distances from Ga-Cipso (2.043(2) Å) to Ga-Ca (2.584(4) Å) and

2 Ga-Cb (3.149(4) Å). The other ring is bonded in an h fashion as evidenced by the fact that two of the Ga-C distances (2.183(5) Å to C(11), 2.17(2) Å to C(12)) are considerably shorter than the other three (2.722(5) Å to C(13), 2.792(15) Å to C(15) and 3.055(15) Å to C(15)). As in the case of the aluminum derivatives, (h-

23 11 C5R5)2AlMe (R = H , Me ), the faces of the cyclopentadienyl rings are located above and below the metal center. Within experimental error the Ga-Cipso distance

1 for the h -bonded C5Me5 group in 16 (Ga-C(21) 2.043(2) Å) is the same as that in the parent compound (h-C5Me5)2GaMe (8) (Ga-C(21) 2.059(11) Å). Compounds 8 and 16 represent the first crystallographically characterized examples of gallium

1 2 compounds in which the C5Me5 rings are h - and h -bonded to the group 13 element. Finally, the average Ga-C6F5 bond distance in 16 (1.973(4) Å) is indistinguishable from those in the THF adduct of tris(perfluorophenyl)gallium40

(1.981(2) Å), and compounds 14 (1.972(4) Å) and 15 (1.973(4) Å).

+ - Synthesis and Characterization of [(h-C5Me5)2Ga] [BF4]

Of the various synthetic methods employed, the most successful in terms of

1 the isolation of crystalline material was protonolysis of (h -C5Me5)3Ga with HBF4 in CH2Cl2 solution which resulted in a 56% yield of pale yellow crystalline

+ - + - [13] [BF4] . The HRMS data for [13] [BF4] were in satisfactory accord with the 57 + - calculated m/e values for both [13] and the BF4 anion and the presence of the latter

11 19 in CD2Cl2 solution was established on the basis of B and F NMR spectroscopy.

1 13 + The H and C NMR spectra for [13] exhibited only singlet resonances for the CH3 groups and ring carbon atoms down to –70 °C. However, given the fluxional behavior in solution, an X-ray crystal structure was desirable.

1 3 + - Figure 2.12. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [BF4] + - ([13] [BF4] ) showing the atom numbering scheme.

+ - X-ray Crystal Structure of [13] [BF4]

+ - The crystalline state structure of [13] [BF4] comprises pairs of

- decamethylgallocenium cations that are connected by two bridging BF4 anions such that the symmetry of each dimeric unit is C2 (Figure 2.12). Details of the data collection, structure solution and refinement are compiled in Table 2.32 and

58 selected metrical parameters are listed in Tables 2.33 and 2.34. In contrast to the

+ decamethylborocenium cation, the C5Me5 rings of [13] are almost parallel (1.8° angle between the normals to the least squares planes). One ring is attached to

1 gallium in an h fashion as indicated by the localized bonding (av Ca-Cb = 1.348(4)

Å; av Cb- Cb = 1.475(4) Å). Furthermore, the Ga-C(21) bond length of 1.971(2) Å

22 1 is somewhat shorter than that reported for (h -C5Me5)3Ga (2.038 Å). The other ring is bonded in an h3 fashion as evidenced by the fact that three of the Ga-C distances (2.001(3) Å to C(11), 2.352(3) Å to C(12), and 2.353(3) Å to C(15)) are considerably shorter than the other two (2.735(3) Å to C(13) and 2.741(3) Å to

3 C(14). The bonding in the h -bonded ring is much more delocalized (av Ca-Cb =

1.381(4) Å; Cb-Cb = 1.415(4) Å); however, the ipso methyl carbon atom (C(111)) lies 0.43 Å out of the least squares plane of the C5 ring. The interactions between

- the decamethylgallocenium cations and BF4 anions are manifested by the Ga × × F contacts (Ga(1)-F(11) = 2.186(2) Å; Ga(1)-F(21) = 2.174(2) Å) and disparities in the B-F bond lengths (e.g. B(1) – F(12) = 1.358(3) Å; B(1) – F(11) = 1.419(3) Å).

The structure of [13]+ is clearly different from that of the cognate boron and aluminum cations. The structure of [10]+ has been interpreted earlier on the basis of

5 39 repulsions between the p clouds of the h -C5Me5 rings. It was anticipated that such repulsions would be negligible in the case of [13]+ because of the larger ionic radius of Ga3+ and that consequently, like [11]+, it would possess a ferrocene-like

59 structure. Some insights into this structural question have been gleaned from DFT

34 + + calculations on the model cations [(h-C5H5)2Ga] and [(h-C5H5)2Al] .

Summary of Theoretical Results for [(C5H5)2Ga].

All calculations were performed with the Gaussian 94 package46 of programs by Dr. Charles Macdonald at The University of Texas at Austin. Each cation in

Table 2.35 was fully optimized in the indicated symmetry at the BP8634/A47 level of theory. The haptotropic search summarized below was accomplished by fixing the

1 parameters of the (h -C5H5)Ga fragment in the geometry obtained by the complete optimization above. The (p-C5H5) ring was constrained to be planar, then a series of single point calculations were performed with the (C5H5)2Ga fragment translated along the mirror plane a distance (Dist in Å) away from the position of the centroid of (p-C5H5) ring, Scheme 2.12.. The bending of the angle at Ga (defined by the

3 normal to the plane of (p-C5H5)-Ga-Cipso was examined with Dist = 0.8 (h -C5H5) in a similar manner. These calculations were then repeated with the addition of two negative point charges fixed in the positions of F(11) and F(21) (as found in the X- ray crystal structure of the decamethyl analogue).

60 H

H

Angle Ga

H H

Dist 1 Scheme 2.12. Theoretical modeling of (h -C5H5)Ga fragment

The global minimum for the gallocenium cation corresponds to the [(h1(p)-

5 + 5 + C5H5)(h -C5H5)Ga] geometry with Cs symmetry. The [(h -C5H5)2Ga] structure is

+ higher in energy by 8.81 kcal/mol (c.f. [(h-C5H5)2B] where the energy difference is

45 kcal/mol)39 and there is only 0.09 kcal/mol difference in energy between the staggered (D5d) and eclipsed (D5h) conformations. It is important to note that the

D5d and D5h structures are not minima on the potential energy surface (Nimag = 2 for each). Each pair of doubly degenerate imaginary frequencies corresponds to a ring slippage that lowers the symmetry to Cs. In contrast, the global minimum for

+ 5 + [(C5H5)2Al] is the D5d [(h -C5H5)2Al] ferrocene-like structure and there is no stationary point corresponding to the Cs geometry. A haptotropic search across the p-bonded cyclopentadienyl ring reveals a very shallow potential with respect to deformation of the (p-C5H5)-Ga bond (see Table 2.35 for full details). In summary, the unique bonding mode observed in gallocenium cation [13]+ appears to be a consequence of three factors, namely (i) the p-cloud repulsion effect is

61 insignificant compared with that in the tightly-bonded borocenium cation, [10]+ (ii)

+ the ionic character of the C5Me5-metal bonding in [13] is less than that in the aluminocenium cation [11]+ due to the lower electronegativity of aluminum, and

(iii) the shallow potential of the (p)C5Me5-Ga bonding, which allows for perturbation of the cation structure by the accompanying anions.

Table 2.35. Optimized [(h-C5H5)Ga] cations

Symmetry Energy Relative Nimag ZPVE E + ZPVE Relative Energy Energy (kcal/mol) (kcal/mol) D5d -2309.793789 8.81 1 (2deg) 0.161223 -2309.632566 8.28 D5h -2309.793645 8.90 1 (2deg) 0.161263 -2309.632382 8.40 Cs -2309.807833 0.00 0 0.162069 -2309.645764 0.00 † Cs -2309.796298 7.24 2 0.178234 -2309.618064 17.38 † C5H5 ring substituents constrained to be planar and rings constrained to be parallel.

+ - Synthesis and Characterization of [(h-C5Me5)2Ga] [AlCl4] (17)

Since the theoretical study of the isolated model gallocenium cation

+ 1 5 [(C5H5)2Ga] indicated that the ground state geometry generally is h -h , it was decided to explore the consequences of changing the counteranion of the

1 decamethylgallocenium cation. The reaction of (h -C5Me5)3Ga with AlCl3 in

1 CH2Cl2 solution resulted in the isolation of needle-shaped crystals of (h -

C5Me5)2GaCl (ca. 85% w/w) and bright yellow blocks of a second product (ca. 15% w/w) following concentration of the filtrate from the reaction mixture and storage at

1 5 –20 °C. The second product was identified as [(h (s)-C5Me5)(h -

+ - C5Me5)Ga] [AlCl4] (17) on the basis of X-ray crystallography.

62

1 3 + - Figure 2.13. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] (17) showing the atom numbering scheme.

1 5 + - X-ray Crystal Structure of [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] (17)

Compound 17 crystallizes in the monoclinic space group P21/c. Details of the data collection, structure solution and refinement are compiled in Table 2.36 and selected metrical parameters are listed in Tables 2.37 and 2.38. The crystalline state of 17 consists of anion-cation pairs as shown in Figure 2.13 with approximate

Cs symmetry about the Ga-C(21)-Al plane. The decamethylgallocenium cation

+ 1 [17] features one h (s)-bonded C5Me5 substituent as indicated by the localized ring bonding (av Ca-Cb = 1.348(4) Å; Cb- Cb = 1.475(4) Å). The other ring is bonded in a distorted fashion, with a hapticity between h3 and h5, as shown by the fact that all

63 the C-Ga distances are of similar length (Ga-C(21) = 2.097(3) Å, Ga-C(22) =

2.192(3) Å, Ga-C(23) = 2.385(3) Å, Ga-C(24) = 2.395(3) Å, Ga-C(25) = 2.219(3)

Å) and the C5Me5 ring features delocalized C-C bonding. The Ga-C(11) bond

5 length of 1.996(3) Å considerably longer than the gallium-(h -C5Me5) ring centroid

22 1 distance (1.906(5) Å) and is similar to that reported for (h -C5Me5)3Ga (2.038 Å).

- The interactions between the decamethylgallocenium cation and the [AlCl4] anion are manifested by the Ga × × × Cl contacts (Ga-Cl(2) = 3.160 Å; Ga-Cl(3) =

3.000 Å). These contacts are considerably longer than the Ga × × × F contacts found

+ - in [13] [BF4] (av Ga-F = 2.180 Å ) and the Ga-Cl distance in the covalent compound [(h-C5Me5)2GaCl]2 (av Ga-Cl = 2.4111(13) Å ). Furthermore, the

- AlCl4 anion is only slightly distorted from tetrahedral geometry (Cl(2)-Al-Cl(3) =

103.83°). While the degree of interaction between the cations and anions in

+ - + - [17] [AlCl4] is considerably less than that found in [13] [BF4] the energies required to go from h5 to h3 are very modest, and therefore that other factors, such as crystal packing, could contribute to the observed hapticity preference.

Conclusions

1 3 + - 1 In summary, the salts [(h -C5Me5)(h -C5Me5)Ga] [BF4] and [(h -

5 + - C5Me5)(h -C5Me5)Ga] [AlCl4] have been prepared and represent the first examples of structurally characterized gallocenium cations. There is a small difference in

3 5 energy between the h and h modes of attachment of the C5Me5 ligand to gallium 64 in these decamethylgallocenium salts and, as a consequence, the structures are sensitive to the subtleties of anion interactions and lattice packing effects. The structure of the gallocenium cation is quite different from that of the analogous boron and aluminum cations, and furthermore this species exhibits only marginal stability, particularly with respect to C6F5 back-transfer reactions. The decamethylgallocenium salts also exhibit a dramatically increased reactivity toward elemental oxygen, and other adventitious impurities when compared with the lighter group 13 analogues.

65

Section 2.5

Constrained Geometry Complexes

Introduction

2- The bridged amidocyclopentadienide ligand [Me2Si(C5Me4)(N-t-Bu)]

(CGC, 18), which was developed originally in the context of single-component scandium catalysts,48 has also resulted in some exciting developments in group 4 transition metal chemistry.49 As evidenced by the patent literature,50 these so-called

“constrained geometry complexes” have proved to be inter alia highly effective olefin polymerization catalysts. It is interesting therefore that, apart from a

(presumably non-chelated) bis(Grignard) reagent,51 ligand 18 has not been employed in main group chemistry. Herein the syntheses of the first constrained geometry complexes of aluminum are described and compared with the first such gallium complexes synthesized by Jeffrey Pietryga in our research group.

66 Me 2-

Me Me

Me Me Si

Me N

Me Me Me

18

The motivation to prepare the constrained geometry complexes stemmed from the analogy between these half-sandwich complexes and the corresponding metallocenes,52 the current interest in the structures and bonding in cyclopentadienyl/main group compounds,10,12,55 and the fact that aluminocenium cations function as olefin polymerization catalysts. From the standpoint of the trends observed for transition metal derivatives, it was anticipated that the constrained geometry group 13 cations might exhibit higher reactivities than those of the corresponding metallocenium cations.

Results and Discussion

1 Synthesis and Characterization of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×THF

1 The complex [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×THF (19) was prepared by

51 treatment of the di-, [Me2Si(C5Me4)(N-t-Bu)](MgCl)2×THF, with

MeAlCl2 in THF solution. The compound was isolated as a THF adduct, and

67 characterized by X-ray crystallography. (Figure 2.14) Although 19 crystallizes in

1 different space group, the molecular structure is very similar to that of [Me2Si(h -

C5Me4)(N-t-Bu)]GaMe×THF (20).

Me

Me Me

Me Me Si M THF Me N Me

Me Me Me

19, 20 (M = Al, Ga)

In contrast to d- and f-block constrained geometry complexes,48,49 19 and 20 feature s- rather than p-bonding interactions with the C5Me4 ring due to the lack of appropriate acceptor orbitals on aluminum or gallium and the presence of a coordinated Lewis base. The Me4C5 ring possesses a localized diene structure and the s-attachment of the group 13 element occurs at an a position with respect to the m-SiMe2 group since this affords a five-membered M-C-C-Si-N ring. As reflected by the sums of angles, the geometries are very close to trigonal planar in both compounds. Details of the data collection, structure solution and refinement are compiled in Table 2.39 and selected metrical parameters are listed in Tables

2.40 and 2.41.

68

1 Figure 2.14. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×THF (19) showing the atom numbering scheme.

Although the group 13 element geometries are nominally tetrahedral, there is a wide departure of bond angles from the ideal values, particularly in the case of 19.

The M-Me substituent is arranged in an exo fashion with respect to the tethered ligand and the THF molecule is located in the “wedge” between the face of the cyclopentadienyl moiety and the N-t-Bu group. The 13C and 1H NMR spectra for 19 and 20 indicate that on a time averaged basis the molecular symmetry is Cs rather than the C1 structure determined by X-ray diffraction. Thus only two types of ring

Me resonances are detected rather than four, and the methyl groups on the SiMe2 fragment are equivalent. A plausible fluxional process involves rapid 69 dissociation/re-association of the THF molecule in concert with the reversible migration of the group 13 element between C(12) and C(15) (Figure 2.14) in the

3 53 base-free complexes, [Me2Si(h -C5Me4)(N-t-Bu)MMe] (M = Al, Ga). Such a suggestion receives support from the observation that the treatment of 19 with tetramethylimadazol-2-ylidene54 results in elimination of THF and quantitative

1 10,11 formation of the adduct [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×carbene (21). In turn,

1 13 the H and C NMR spectra for 21 is indicative of a static C1 structure as a consequence of the superior donor strength of carbene vs. THF.

1 Figure 2.15. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×carbene (21) showing the atom numbering scheme.

70 As determined by X-ray analysis, the overall structural features of 21

(Figure 2.15) are similar to those of the THF adducts 19 and 20. Details of the data collection, structure solution and refinement are compiled in Table 2.42 and selected metrical parameters are listed in Tables 2.43 and 2.44. Thus, the carbene ligand is located between the cyclopentadienyl and t–Bu groups and the Al-Me substituent lies outside the “bite” of the chelate ligand. The Al-Ccarbene (2.041(3) Å) and Ga-Ccarbene (2.074(3) Å) bond distances are similar to those reported for

13a 13b (carbene)AlR3 (2.124(6) Å) adducts (R = H, Me; carbene = 1,3-diisopropyl-

2,4-dimethylimidazol-2-ylidene).

Me H

Me Me H H

Me Me H H Si Si M M H Me N N

Me Me H H Me H

22 23

The mass spectrum of 19 exhibits a peak at m/e 276, which corresponds to the cation 22. Accordingly, the model cation 23 was investigated by means of BP86

DFT calculations.34 Geometry optimization together with frequency calculations indicate that the ground state geometry of 23 possesses C1 symmetry, but is very

71 close to Cs symmetry. The cyclopentadienyl group is attached to aluminum in a pentahapto fashion and the computed Al-ring centroid and Al-N distances are 1.762

Å and 1.795 Å, respectively. Of particular import is the morphology of the LUMO, which in each case is a primarily metal-based orbital having a symmetry suitable for coordination by olefins. For 23 the energy of the LUMO (-0.30412 au) is 55.8

+ kcal/mol lower than the LUMO energy calculated for [(h-C5H5)2Al] (-0.21255 au) which has been shown to be an effective a-olefin polymerization catalyst.10,11 The presence of a lower energy LUMO suggests that, as observed for group 4 transition metals,49 the constrained geometry aluminum cation is likely to be a more active olefin polymerization catalyst than is its metallocene analogue.

Methanide abstraction from 21 by B(C6F5)3 in toluene solution has been

- 1 19 attempted. Judging from the detection of the [MeB(C6F5)3] anion by H, F, and

11B NMR spectroscopy, this process evidently occurs. However, thus far it has not proved possible to isolate crystalline material suitable for X-ray diffraction. Noting this result, and recognizing that chloride abstraction from (h-C5Me5)2MCl (M = B,

Al, Ga) by AlCl3 is a viable synthetic route to the formation and isolation of

1 metallocenium salts, the synthesis of the complex [Me2Si(h -C5Me4)(N-t-

Bu)]AlCl×Et2O (24) was undertaken by treatment of the di-Grignard reagent,

51 [Me2Si(C5Me4)(N-t-Bu)](MgCl)2×THF, with AlCl3 in Et2O solution. The compound was isolated as an Et2O adduct, and characterized by X-ray crystallography.

72 While the THF adducts 19 and 20 exhibit 1H and 13C NMR spectra consistent with a complex of Cs symmetry, suggesting either complete Lewis base dissociation or a dissociation and re-association process that is rapid on the NMR timescale, the NMR spectra of the Et2O adduct 24, presumably a stronger Lewis acid, are consistent with an intact acid-base complex of C1 symmetry. Although complex 24 crystallizes in a very different space group, the molecular structure of each Et2O adduct is quite similar to those of the THF adducts (Figure 2.16). Details of the data collection, structure solution and refinement are compiled in Table 2.45 and selected metrical parameters are, listed in Tables 2.46 and 2.47. However, the latter data are unexceptional and not worthy of extensive commentary. A preliminary spectroscopic study of the abstraction of the chloride ion from 24 have thus far given inconclusive results.

1 Figure 2.16. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlCl×OEt2 (24) showing the atom numbering scheme.

73 Conclusions

In conclusion, the first examples of aluminum-containing constrained geometry complexes have been prepared and isolated as either THF, Et2O or

1 carbene adducts. Preliminary experiments indicate that [Me2Si(h -C5Me4)(N-t-

Bu)]AlMe ×carbene undergoes methanide abstraction when treated with B(C6F5)3.

DFT calculations on a model constrained geometry aluminum cation suggest that such cations will be more active than the corresponding aluminocenium cations.

74

Section 2.6

Multidecker Cations

Introduction

An elegant approach to the formation of multidecker, sandwich-type anions of the heavier main group elements consists of the addition of cyclopentadienide anions to neutral metallocenes in the presence of weakly coordinating cations.55,56

However, judging from a literature survey, the inverse of this approach had not been reported prior to the present work,57 viz. the synthesis of homonuclear multidecker p-block cations by the addition of positively charged fragments to neutral metallocenes in the presence of appropriate anions. Two different but complementary reactions were undertaken to demonstrate the viability of the latter approach.

In Sn

In Sn

25 26 75 Results and Discussion

58 5 Since it is known that the reaction of Sn(h -C5Me5)2 with a variety of

5 + acidic reagents results in salts of [Sn(h -C5Me5)] , it was reasoned that, in principle,

5 this cation should be able to add to Sn(h -C5Me5)2 to afford the desired triple decker

5 5 5 + + cation, [(h -C5Me5)Sn(m-h -C5Me5)Sn(h -C5Me5)] [25] . Moreover, it was recognized that the choice of the gegenion would be important, bearing in mind that

(i) the anion should be weakly coordinating, and (ii) the chance of obtaining a crystalline product would be maximized if the anion and cation were of comparable

5 59 size. The addition of a toluene solution of Sn(h -C5Me5)2 to a solution of

Ga(C6F5)3 in the same solvent at 0 ºC resulted in a yellow precipitate which was

+ - recrystallized from hot toluene solution to afford [25] [Ga(C6F5)4] in 74.5% yield

(Scheme 2.13).

Ga(C6F5)4

Sn Toluene 2 (Cp*)2Sn + Ga(C6F5)3 + Cp*Ga(C6F5)2 0 oC

Sn

5 Scheme 2.13. Reaction of (h -C5Me5)2Sn with Ga(C6F5)3

76 + - The positive and negative CI mass spectra for [25] [Ga(C6F5)4] revealed the

+ - 1 13 119 presence of [25] and [Ga(C6F5)4] ions, respectively. The H, C, and Sn NMR spectra evidenced only one type of C5Me5 group and a unique Sn center thus

+ 5 5 + suggesting reversible dissociation of [25] into Sn(h -C5Me5)2 and [Sn(h -C5Me5)] .

Definitive structural information was provided by a low-temperature X-ray crystal structure.

5 5 5 + Figure 2.17. Molecular structure of [(h -C5Me5)Sn(m-h -C5Me5)Sn(h -C5Me5)] - [Ga(C6F5)4] .

As shown in Figure 2.17, the crystalline state consists of [25]+ and

- [Ga(C6F5)4] ions and there are no unusually short interionic contacts. Presumably,

- - the initially formed anion is [Ga(C6F5)3(C5Me5)] however, since [B(C6F5)nR4-n] anions are known to undergo facile redistribution reactions,60 a similar process can

- be postulated to explain the formation of [Ga(C6F5)4] . The structures of the

77 - - [Ga(C6F5)4] and [C6F5)3BO(H)B(C6F5)3] anions are similar to those reported in the

61 + literature The structure of [25] is such that a pentahapto C5Me5 ring serves as a

5 bridging group for two Sn(h -C5Me5) units. Within experimental error, the two Sn

5 atoms are located equidistantly from the ring centroid (X(1C)) of the m-(h -C5Me5) group (2.644(19) Å) and the Sn(1)-X(1C)-Sn(2) angle is close to 180° (174.9(4)°).

The average distance from the Sn atoms to the ring centroids of the two terminal

5 5 (h -C5Me5) rings, X(1A) and X(1B), is shorter than that to the bridging (h -C5Me5)

5 moiety (2.246(18) Å) and lies between the values reported for Sn(h -C5Me5)2 (2.396

58c 5 + 3c Å) and [Sn(h -C5Me5)] (2.157 Å). The X(1A)-Sn-X(1C) and X(1B)-Sn-X(1C) angles of 154.6(7) and 151.8(7)º, respectively are very similar to the values reported

5 58c for Sn(h -C5Me5)2 (av 154.9º). An intriguing feature of the overall structure is

+ 5 - that [25] adopts a cis-type geometry while the triple-decker anions [(h -C5H5)3Tl2]

5 - 55b, 56 and [(h -C5H5)Cs2] possess transoid arrangements.

Sn In In

5 + 6 + Scheme 2.14. The isolobal relationships between [Sn(h -C5H5)] , [In(h -C6H6)] 5 and [In(h -C5H5)]

A second method of triple-decker cation synthesis recognized the isolobal

5 + 6 + 5 relationship between [Sn(h -C5H5)] , [In(h -C6H6)] and [In(h -C5H5)] (Scheme

6 + 5 2.14), thus suggesting that [In(h -C6H6)] should add to In(h -C5Me5) units to form 78 a triple decker cation. Pentamethyl(cyclopentadienyl)indium(I) is a weakly held hexamer in the crystalline state that undergoes facile dissociation to the monomer in

21 5 solution and in the vapor phase. Since protolytic cleavage of In(h -C5Me5) in the presence of an arene solvent represented a potential source of [In(arene)]+ cations,

5 6,62 In(h -C5Me5) was treated with equimolar quantities of B(C6F5)3 and the

63 Brønsted acid H2O·B(C6F5)3 in toluene solution at 0 °C, Scheme 2.15. The reaction mixture afforded colorless crystals upon storage at -30°C for several days.

Since the product could not be characterized unambiguously on the basis of spectroscopic data, an X-ray crystallographic study was undertaken.

In In

2 + H2O-B(C6F5)3 + B(C6F5)3 Toluene HO-(B(C6F5)3)2

In

5 Scheme 2.15. Protolytic cleavage of In(h -C5Me5) with H2O·B(C6F5)3 to give + - [26] [(C6F5)3BO(H)B(C6F5)3]

Details of the data collection, structure solution and refinement are compiled in Table 2.48 and selected metrical parameters are listed in Tables 2.49 and 2.50.

6 5 6 The crystalline state (Figure 2.18) consists of [(h -C7H8)In(m-h -C5Me5)In(h -

+ + - 8 C7H8)] [26] and [(C6F5)3BO(H)B(C6F5)3] ions with 1.5 additional toluene molecules per asymmetric unit. There are no unusually short interionic contacts.

The central core of [26]+ features an h5-bonded In atom on each face of the (m-

79 C5Me5) group. The In-ring centroid (X(1A)) distances of 2.528(4) and 2.435(4) Å for In(1) and In(2), respectively are longer than those reported21 for monomeric

5 + (2.288(4) Å) and hexameric (2.302(4) Å) In(h -C5Me5). As in the case of [25] , the metal-X-metal angle in [26]+ is close to linear (176.0(4)º). The triple-decker structure of [26]+ is completed by capping h6-bonded toluene molecules. The In- ring centroid (X(1B) and X(1C)) distances of 3.490(4) and 3.325(4) Å for In(1) and

In(2), respectively are considerably longer than those reported for

[In(I)·2mesitylene]+ (2.83 and 2.89 Å).64 Nevertheless, it is interesting to note that,

+ akin to [26] , the toluene-(m-C5Me5)-toluene moieties are distinctly bent (124.4(4) and 130.3(4)° for X(1A)-In(1)-X(1B) and X(1A)-In(2-X(1C), respectively) and that the overall cationic geometry is cisoid.

6 5 6 + Figure 2.18. Molecular structure of [(h -C7H8)In(m-h -C5Me5)In(h C7H8)] - + [HOB2(C6F5)6] [26] .

80 Part of the reason for the long arene distances in [26]+ may relate to the fact that the net +1 charge is delocalized over two In centers. However, the bonding in

[26]+ can be interpreted in two different ways, namely (i) as a triple-decker sandwich cation or (ii) a base-stabilized inverse sandwich cation. Density functional theory calculations were therefore undertaken in an effort determine which bonding model is more accurate.

Summary of Theoretical Results

All calculations were performed with the Gaussian 9446 package of programs. Each molecule/ion was fully optimized in the indicated symmetry.

(Bond lengths in Å, angles in degrees, Xt is the centroid of a terminal aromatic ring,

Xb is the centroid of the bridging aromatic ring and the dihedral is defined as the angle between the two planes defined by the points (Xt,n, Mn, and Xb) for n=1 and n=2 (0° = cisoid, 180° = transoid), Tables 2.51 and 2.52.) Density functional theory

5 + (DFT) optimization of the model system [In(m-h -C5H5)In] predicts a D5h symmetric structure with a computed In-X distance of 2.515 Å that is close to the value observed experimentally for [26]+. Moreover, the h6-coordination of two

+ benzene molecules to the [In(m-C5H5)In] moiety causes only a slight perturbation of the core thus lending credence to model (ii), the base-stabilized inverse sandwich structure. Furthermore, the benzene-In bond dissociation energies (6.6 kcal/mol)

5 suggest a very weak interaction. In sharp contrast, calculations on [(h -C5H5)Sn(m-

81 5 5 + + h -C5H5)Sn(h -C5H5)] as a model for 25 predict a much more tightly bonded triple-decker sandwich environment – the weakest bond (36.6 kcal/mol) being that

5 5 5 + between the [(h -C5H5)Sn(h -C5H5)] and [Sn(h -C5H5)] fragments.

Conclusions

The syntheses of the first main group triple-decker cations, namely, [(h5-

5 5 + 6 5 6 C5Me5)Sn(m-h -C5Me5)Sn(h -C5Me5)] and [(h -C7H8)In(m-h -C5Me5)In(h -

+ 5 C7H8)] have been achieved. The former was isolated as the salt [(h -C5Me5)Sn(m-

5 5 + - 5 h -C5Me5)Sn(h -C5Me5)] [Ga(C6F5)4] from the reaction of Sn(h -C5Me5)2 with

6 5 6 Ga(C6F5)3, while the latter was prepared as the salt [(h -C7H8)In(m-h -C5Me5)In(h -

+ - 5 C7H8)] [(C6F5)3BO(H)B(C6F5)3] from treatment of [In(h -C5Me5)]6 with an equimolar mixture of B(C6F5)3 and H2O·B(C6F5)3. Both salts were characterized by

X-ray crystallography. It is anticipated that the C5Me5 acidolysis methodology will prove to be very useful for the preparation of isolobally-related compounds with very different properties.

82

Chapter 2

Experimental

General procedures

All solvents (diethylether, THF, benzene, toluene, hexane, pentane), were distilled from sodium benzophenone ketyl or CaH2 (CH2Cl2) and degassed prior to use. Solid reactants were handled in a VAC Vacuum Atmospheres or M-Braun -filled drybox. All reactions were performed under a dry oxygen-free argon atmosphere or under vacuum using standard Schlenk or drybox techniques; all glassware was oven-dried before use.

5 The group 13 trihalides, MeLi, HBF4, and [(h -C5Me5)In]6 were purchased from a commercial source and used without further purification.

Bromopentafluorobenzene was purchased from a commercial source and distilled at

40 °C/0.01 torr prior to use. Tris(pentafluorophenyl)borane and C5Me5H were prepared according to literature procedures65 or purchased from a commercial

1 15 source and used without further purification. The compounds (h -C5Me5)2BCl,

1 22 38 MeGaCl2, E(C5Me5) (E = Li, Na, K), (h -C5Me5)3Ga, Al(C6F5)3·toluene,

40 54 Ga(C6F5)3, Li(BC6F5)4, tetramethylimadazol-2-ylidene, [Me2Si(h-C5Me4)(N-t-

83 - 5 59 63 Bu)][MgCl]2 ·THF, (h -C5Me5)2Sn, H2O B(C6F5), were prepared according to literature procedures.

Physical Measurements

Low-resolution EI mass spectra were obtained on a Bell and Howell 21-491 instrument; low-resolution CI mass spectra were run on a Finnigan MAT TSQ-700; and high-resolution mass spectra were measured on a VG Analytical ZAB-VE sector instrument. Solution-phase NMR spectra were recorded at 295 K, unless otherwise noted, on a GE QE-300 instrument (1H, 300 MHz; 11B, 96 MHz; 13C, 75

MHz; 19F, 282 MHz; 27Al, 78.21 MHz) or a Varian Inova-500 spectrometer (1H, 500

MHz; 11B, 160 MHz; 13C, 125 MHz; 19F, 470 MHz; 27Al, 130 MHz). All NMR samples were flame-sealed or run immediately following removal from the drybox.

Benzene-d6 was dried over sodium-potassium alloy and distilled prior to use.

8 Toluene-d and CD2Cl2 were obtained in sealed vials from a commercial source and used without further purification. 1H and 13C NMR spectra are reported relative to tetramethyl silane (d 0.00) and are referenced to solvent. 11B chemical shifts are

19 reported relative to BF3(Et2O) (d 0.00), F chemical shifts are reported relative to

27 3+ C6F6 (d -162.9), and Al chemical shifts are reported relative to [Al(D2O)6] (d

0.00). All 13C spectra were obtained under conditions of broad band proton decoupling unless otherwise noted. Variable-temperature (VT) NMR studies utilized equilibration times of ten minutes at each temperature. Melting points were obtained in sealed capillaries under argon (1 atm) on a Fisher-Johns apparatus and 84 are uncorrected. Elemental analyses were performed by Atlantic Microlab, Inc.,

Northcross, GA.

X-Ray Crystallography

Suitable single crystals were covered with perfluorinated polyether oil and the X-ray data were collected on either a Nonius Kappa CCD diffractometer or a

Siemens P4 diffractometer. Structure determinations and refinements were performed Dr. Charles Macdonald, Dr. Andreas Voigt, or Dr. Brian McBurnett at

The University of Texas at Austin. All structures were solved by direct methods and refined by full-matrix least squares on F2 using the Siemens SHELX PLUS 5.0

(PC) software package.66 All non-hydrogen atoms were allowed anisotropic thermal motion and hydrogen atoms, which were included at calculated positions

(C-H 0.96 Å), were refined using a riding model and a general isotropic thermal parameter. The total number of reflections, collection ranges, and final R values are listed in the appropriate tables for each molecule.

Data from the Siemens P4 diffractometer were collected at 213 K using graphite-monochromated Mo Ka radiation (l = 0.71073 Å). Accurate unit cell parameters were determined by recentering 25 optimal high angle reflections. A correction was applied for Lorentz-polarization. Three standard reflections were measured every 1800 seconds during each data collection, and no decreases in intensities were observed.

85 Data from the Nonius-Kappa CCD diffractometer were collected at 153 K using an Oxford Cryostream low-temperature device and graphite monochromated

Mo Ka radiation (l = 0.71073 Å). A correction was applied for Lorentz- polarization. A total of 105 frames of data were collected using w-scans with a scan range of 1.9 and a counting time of 482 seconds per frame.

1 Preparation of (h -C5Me5)2BCl (1)

To a suspension of LiC5Me5 (4.26 g, 30.0 mmol) in hexane was added 15 mL of BCl3 (3.76 g, 15 mmol) at –50 °C. The resulting reaction mixture was allowed to warm slowly to room temperature over several hours, then refluxed overnight. The reaction mixture was filtered at room temperature, and the filtrate was concentrated and cooled to –20 °C to afford yellow crystals of the desired

1 13 1 product, 2.0 g, 42% yield, mp 89-90 °C. H NMR (C6D6): d 1.95 (s, Cp*); C-{ H}

11 NMR (C6D6): d 123.73 (s, Cp*-ring), 13.85 (s, Cp*-Me); B NMR (C6D6): d 74.7

½ (w = 370 Hz); HRMS (CI, CH4): calcd for C20H30BCl, 316.2129; found,

316.2130.

1 Preparation of [(h -C5Me5)2BBr]2 (2)

Neat BBr3 (3.76 g, 15 mmol) was added to a suspension of LiC5Me5 (4.26 g,

30.0 mmol) in hexane at –50 °C. The resulting reaction mixture was allowed to warm slowly to room temperature over several hours, then refluxed overnight. The

86 reaction mixture was filtered at room temperature, and the filtrate was concentrated and cooled to –20 °C to afford yellow crystals of the desired product in 35% yield.

1 11 H NMR (C6D6): d 1.60 (s, Cp*); B NMR (C6D6): d 77.8.

1 Preparation of (h -C5Me5)2BMe (3)

A solution of MeLi in Et2O (1.4 M in Et2O, 6.4 mmol) was added to a

1 solution of (h -C5Me5)2BCl (2.03 g, 6.4 mmol) in Et2O at –40 °C. The resulting pale yellow reaction mixture was stirred overnight. The volatiles were removed in vacuo, and the resulting white powder was extracted with consecutive portions of hexane and dried under vacuum. The desired product was obtained by sublimation of the remaining white residue at 45 °C and 0.04 torr, 1.65 g, 87% yield, mp 57-58

1 13 1 °C. H NMR (C6D6): d 0.39 (s, BMe), 1.60 (s, Cp*); C{ H} NMR (C6D6): d

11 13.44 (s, Cp*-Me), 124.44 (s, Cp*-ring); B NMR (C6D6): d 85.6; HRMS (CI,

CH4): calcd for C21H33B, 296.2675; found, 296.2687.

Preparation of (h-C5Me5)2AlCl (4)

To a suspension of KC5Me5 (2.63 g, 15 mmol) in toluene (100 mL) was added AlCl3 (1.0 g, 7.5 mmol) at –76 °C. The resulting reaction mixture was allowed to warm slowly to room temperature over several hours, then refluxed overnight. The reaction mixture was filtered at room temperature, and the filtrate was concentrated and cooled to –20 °C to afford a yellow powder of the desired

87 1 13 1 product, 2.0 g, 80% yield. H NMR (C6D6): d 1.82 (s, Cp*); C-{ H} NMR

27 (C6D6): d 119.50 (s, Cp*-Me), 13.85 (s, Cp*-ring); Al NMR (C6D6): d -10; HRMS

(CI, CH4): calcd for C20H30Al, 297.2163; found, 297.2169.

2 Preparation of (h -C5Me5)2AlMe (5)

A solution of MeAlCl2 in hexanes (5.0 ml, 1 M, 5.0 mmol) was added to a slurry of KC5Me5 (1.75 g, 10.0 mmol) ) in toluene (60 mL) at –76 °C. The reaction mixture was allowed to warm to room temperature then refluxed for approximately

4 h. The volatiles were removed in vacuo and the resulting white powder was extracted with consecutive portions of hexane and filtered through Celite®. The resulting pale yellow solution was concentrated and cooled to –20 °C, to afford large colorless rod shaped crystals over a period of a few weeks, 1.25 g, 4.0 mmol,

1 13 1 81% yield. H NMR (C6D6): d -1.63 (s, AlMe), 1.89 (s, Cp*); C{ H} NMR

(C6D6): d 11.05 (s, Cp*-Me), 115.68 (s, Cp*-ring); HRMS (CI, CH4): calcd for

C20H30Al 312.2512; found, 312.2519; calcd for C21H32Al, 297.2163; found,

297.2166.

1 Preparation of (h -C5Me5)2GaBr (7)

A solution of GaBr3 (1.65 g, 5.3 mmol) in diethylether (100 mL) was added to a slurry of LiC5Me5 (1.51 g, 10.6 mmol) in diethylether (100 mL) at room temperature. The reaction mixture was allowed to stir for 48 h, then all volatiles

88 were removed in vacuo. Hexanes were added to the remaining pale yellow solid mixture and the resulting slurry was filtered through Celite®. The filtrate was concentrated to the point of incipient crystallization then cooled to -20 °C overnight to afford a crop of colorless needle-shaped crystals; typical yield (first crop of crystals) 0.50 g, 1.1 mmol, 22 % (the yield can be increased by subsequent cycles of concentration and recrystallization); mp 129-130 °C. MS (CI, CH4): 418 to 422

(M+) 30%, 339 and 341 (M-Br)+ 100%, 283 to 287 (M-Cp*)+ 30%; HRMS (CI,

1 CH4): calcd for C20H30GaBr, 418.0787; found, 418.072. H NMR (C6D6): d 1.75 (s,

13 1 Cp*); C{ H} NMR (C6D6): d 12.28 (s, Cp*-Me), 121.53 (s, Cp*-ring).

1 2 Preparation of (h -C5Me5)(h -C5Me5)2GaMe (8)

A solution of MeGaCl2 in Et2O (1.49 g, 9.6 mmol) was added to a slurry of

LiC5Me5 (2.74 g, 19.3 mmol) ) in Et2O at room temperature. The reaction mixture was allowed to stir for approximately 48 h, following which the volatiles were removed in vacuo. The resulting white powder was extracted with consecutive portions of hexane and filtered through Celite®. The pale yellow filtrate was concentrated and cooled to –20 °C to afford a crop of colorless crystals over a

1 period of days, 2.15 g, 6.0 mmol, 64% yield. H NMR (C6D6): d -1.29 (s, GaMe),

13 1 1.89 (s, Cp*); C{ H} NMR (C6D6): d 1.27 (s, GaMe), 11.81 (s, Cp*-Me), 119.90

+ (s, C5Me-ring); HRMS (CI, CH4): calcd for C21H32Ga (M -H) , 353.175982; found,

+ 353.177003; calcd for C21H30Ga (M –Me) , 339.160332; found, 339.159934.

89 1 NMR Scale Reaction of (h -C5Me5)2BCl with B(C6F5)3

1 In a drybox, a solution was formed by the addition of (h -C5Me5)2BCl

(0.100 g, 0.316 mmol) and B(C6F5)3 (0.162 g, 0.316 mmol) to 3 mL of C6D6.

Agitation of the reaction mixture for 20 min resulted in the formation of a yellow- slightly brown solution that was analyzed by 11B NMR spectroscopy. A 11B

+ resonance corresponding to the formation of the desired product, [(h-C5Me5)2B] , was detected at d -42.1. However, the intensity of this peak was less than those of

1 (h -C5Me5)2BCl (d 74.4) and B(C6F5)3 (d 59.0). A small quantity of an unidentified exchange product was detected at d 43.2. A steady decrease in the

+ concentration of the [(h-C5Me5)2B] cation was evident over a number of hours as

11 monitored by the intensity of the d –42.1 resonance. B NMR (C6D6): d -42.1 (br,

+ ½ ½ ½ [(Cp*)2B] , w = 210 Hz), 43.2 (br, w = 420 Hz), 59.0 (br, (C6F5)3B, w = 845

½ Hz) 74.2 (br, (Cp*)2BCl, w = 380 Hz).

1 NMR Scale Reaction of (h -C5Me5)2BCl with LiB(C6F5)4

1 In a drybox, (h -C5Me5)2BCl (0.124 g, 0.392 mmol) and LiB(C6F5)4 (0.269 g, 0.392 mmol) were dissolved in 3 mL of C6D6. Agitation of the reaction mixture for 10 min resulted in the formation of a yellow-slightly brown solution that contained traces of a white precipitate. The filtrate was analyzed by 1H and 11B

NMR spectroscopy. Initially, the 11B NMR spectrum featured resonances

+ corresponding to the desired cation [(h-C5Me5)2B] (d -41.9), together with 90 - 1 resonances at d -12.6, and 74.4 corresponding to [(C6F5)4B] and (h -C5Me5)2BCl, respectively. Two additional (unassigned) resonances were detected -1.0 and 42.6.

Following storage at room temperature for seven days, the 11B NMR spectrum of

+ the solution showed a substantial increase in the intensity for the [(h-C5Me5)2B]

1 cation and a concomitant decrease in the intensity of the (h -C5Me5)2BCl peak.

- During the same time period, the resonance corresponding to [(C6F5)4B] disappeared while whose at -1.0 and 42.6 increased, thus suggesting the formation

1 11 of exchange products. H NMR (C6D6): d 1.58 (s, Cp*). B NMR (C6D6): d -41.9

+ ½ - ½ (br, [(Cp*)2B] , w = 170 Hz), -12.6 (s, [C6F5]4B] ), -1.0 (br, w = 855 Hz), 42.6

½ ½ (br, w = 1120 Hz), 74.4 (br, (Cp*)2BCl, w = 370 Hz).

1 5 + - Preparation of [(h -C5Me5)(h -C5Me5)B] [AlCl4] (10)

1 Equimolar quantities of (h -C5Me5)2BCl and AlCl3 were combined in a 50%

CH2Cl2/d6-benzene solution. Removal of the solvent slowly under reduced pressure

1 5 + - at room temperature afforded an 86% yield of [(h -C5Me5)(h -C5Me5)B] [AlCl4] ,

1 mp ~60 °C (dec). H NMR (C6D6): d 1.65 (s, 15H, Cp* -Me), 1.49 (s, 3H, Cp* ipso-Me), 1.63 (s, 6H, Cp* a-Me), 1.69 (s, 6H, Cp* b-Me). 13C{1H} NMR (75.48

5 MHz, 295 K, C6D6): d 9.13 (h -Me), 112.93 (Cp* ring C), 15.48 (Cp* ipso-Me),

51.79 (Cp* ipso ring C), 10.63 (Cp* a-Me), 136.36 (Cp* a ring C), 12.17 (Cp* b-

11 27 Me), 138.10 (Cp* b ring C). B NMR (C6D6): d -41.5 (s). Al NMR (C6D6): d

100 (s). 91 Reaction of “(h-C5Me5)2AlCl” with B(C6F5)3

In a drybox, “(h-C5Me5)2AlCl” (0.105 g, 0.316 mmol) and B(C6F5)3 (0.162 g, 0.316 mmol) were dissolved in 3 mL of C6D6. Agitation of the reaction mixture for 20 min resulted in the formation of a yellow-slightly brown solution that was analyzed by 27Al NMR spectroscopy. The 27Al NMR spectrum of this solution exhibited a resonance at d -102 indicating the formation of the desired cation, [(h-

+ C5Me5)2Al] in moderate yield. However, the resonance for the starting material (h-

C5Me5)2AlCl (d -10) remained the dominant peak and was accompanied by a small

+ amount of a potential exchange product at d 45. The signal for [(h-C5Me5)2Al] decreased steadily with time and after prolonged storage of the sample and after concentration of the solution and prolonged storage at – 20 °C, colorless crystals were deposited in a very low yield. Single crystal X-ray diffraction revealed that

5 these crystals are the exchange product [(h -C5Me5)(C6F5)AlCl]2 (12).

2 Reaction of (h -C5Me5)2AlMe with B(C6F5)3

2 In a drybox, (h -C5Me5)2AlMe (0.094 g, 0.300 mmol) and B(C6F5)3 (0.154 g, 0.300 mmol) were dissolved in to 3 mL of CD2Cl2. Agitation of the reaction mixture for 20 min resulted in the formation of a yellow-slightly brown solution that was analyzed by 11B and 27Al NMR spectroscopy. 11B NMR spectroscopic assay of

- the solution revealed the presence of the desired [MeB(C6F5)3] anion (d -11.2) in

+ 27 high yield, and the [(h-C5Me5)2Al] cation at was detected by Al NMR 92 11 spectroscopy (d –102). Some starting material, B(C6F5)3, was also detected by B

NMR spectroscopy (d 61.0) and was accompanied by a minor quantity of an

+ apparent exchange product (d 44.0). The intensities of the [(h-C5Me5)2Al] and

- 1 [MeB(C6F5)3] resonances decreased steadily with time. H NMR (CD2Cl2): d 2.15

- 11 - (s, Cp*), 0.56 (s, [MeB(C6F5)3] ); B NMR (CD2Cl2): d -12.2 (br, [MeB(C6F5)3] );

½ 27 + 43.2 (br, w = 420 Hz); Al NMR (CD2Cl2): d -102 (s, [Cp*2Al] ). Scaling up of the above reaction was unsuccessful and no new products were isolated.

5 + - + Preparation of [(h -C5Me5)2Al] [AlCl4] [11]

A suspension of Al2Cl6 (0.40 g, 1.50 mmol) in CH2Cl2 (40 mL) was added to a stirred pale yellow solution of “(h-C5Me5)2AlCl” (1.00 g, 3.00 mmol) in CH2Cl2

(40 mL) at -78°C. After warming to room temperature, the resulting amber colored solution was allowed to stir for 14 h. The solution was concentrated to a volume of

10 mL and cooled slowly to -20°C to afford a crop of colorless blocks, 1.3 g, 2.78 mmol, 92.8 % yield, mp 123-124°C (dec). HRMS (CI, CH4): calcd for

C20H30Al2Cl4, 464.0732; found, 464.0743; HRMS (CI, CH4): calcd for C20H30Al

1 27 297.2163; found, 297.2166; H NMR (CD2Cl2): d 2.18 (s, Cp*); Al NMR

+ - (CD2Cl2): d -102 (s, [Cp*2Al] ) , d 115 (s, AlCl4 ).

93 1 3 Preparation of (h -C5Me5)(h -C5Me5)(C6F5)Ga (16)

A solution of B(C6F5)3 (0.325 g, 0.92 mmol) in Et2O (20 mL) was added to a

1 2 stirred pale yellow solution of (h -C5Me5)(h -C5Me5)GaMe (0.468, 0.92 mmol) in

Et2O (20 mL) at room temperature. After the pale yellow reaction mixture had been stirred for 48 h, the solution was concentrated to a volume of 5 mL and cooled to –

20 °C to afford a crop of colorless crystals, 0.4 g, 78% yield, mp 145 °C (dec).

1 HRMS (CI, CH4): calcd for C26H31F5Ga 507.1602; found, 507.1627; H NMR

13 1 (C6D6): d 1.73 (s, Cp*); C{ H} NMR (C6D6): d 121.00 (s, Cp*), 14.30 (s, Cp*);

19 F NMR (C6D6): d -92.5 (s, o-C6F5) , -118.8 (s, p-C6F5), -123.7 (s, m-C6F5).

1 3 + - Preparation of [(h -C5Me5)(h -C5Me5)2Ga] [BF4]

A solution of HBF4 (54% solution in Et2O, 1.1 mmol) in CH2Cl2 (20 mL)

1 was added to a stirred pale yellow solution of (h -C5Me5)3Ga (0.377 g, 0.79 mmol) in CH2Cl2 (20 mL) at room temperature. After the dark yellow reaction mixture had been stirred for 48 h, the volatiles were removed under reduced pressure, and the resulting pale yellow powder was recrystallized from CH2Cl2 to afford a crop of yellow plates, 0.19 g, 56% yield, mp 170-171 °C. HRMS (CI, CH4): calcd for

1 11 C20H30Ga 339.1603; found, 339.1597; H NMR (CD2Cl2): d 1.80 (s, Cp*); B

13 1 NMR (CD2Cl2): d 0.8 (sharp s, BF4); C{ H} NMR (CD2Cl2): d 120.4 (s,

+ + [(Cp*)2Ga] ) , 11.5 (s, [(Cp*)2Ga] ).

94 1 5 + - Preparation of [(h -C5Me5)(h -C5Me5)2Ga] [AlCl4] (17)

1 A pale yellow solution of (h -C5Me5)3Ga (0.399 g, 0.84 mmol) in CH2Cl2

(20 mL) was added to a stirred slurry of AlCl3 (0.116 g, 0.87 mmol) in CH2Cl2 (20 mL) at room temperature. The bright yellow reaction mixture was stirred until the

AlCl3 had fully dissolved/reacted (approximately 3-4 d), then the solution was concentrated to a volume of ca. 5 mL by removing the volatiles under reduced pressure. The concentrated solution was cooled to -20 °C for 24 h, resulting in a crop of colorless needle-shaped crystals of (h-C5Me5)2GaCl (ca. 85% w/w, identified by X-ray crystallography). After standing for a week at –20 °C, a crop of

1 5 + - large bright yellow blocks of [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] (ca. 15% w/w, identified by X-ray crystallography) was deposited; total yield 0.23 g. For [(h1-

5 + - C5Me5)(h -C5Me5)Ga] [AlCl4] : mp 115-117 °C (dec). HRMS (CI, CH4): calcd for

C20H30Ga, 339.1603; found, 339.1592; calcd for AlCl4, 166.8570; found, 166.8571.

1 H NMR (CD2Cl2): d 1.80 (s, Cp*); 13C{1H} NMR (CD2Cl2): d 120.4 (s,

+ + [Cp*2Ga] ) , 11.5 (s, [Cp*2Ga] ).

Preparation of (CGC)AlMe THF (19)

A colorless hexane solution of MeAlCl2 (2.3 mL of 1.0 M solution, 2.3 mmol) was syringed slowly into a stirred pale yellow solution of

[(CGC)(MgCl)2.THF] (1.0 g, 2.3 mmol) in 75 mL THF at -78°C. The reaction mixture was allowed to warm to room temperature, then stirred for 12 h. The

95 solvent and volatiles were removed under reduced pressure and the resulting pale yellow solid was extracted with 50 mL of toluene and filtered through Celite® to afford a yellow solution. Storage of the concentrated solution at ambient temperature afforded a crop of colorless cube-shaped crystals (0.54 g, 65% yield);

+ mp. 102–5 °C. MS (CI , CH4): m/z 363 [M, 100 %]; 348 [M -CH3, 32.90 %]; 292

+ + [M -THF, 26.70 %]; 276 [(CGC)Al , 16.77 %]; HRMS (CI , CH4) calcd for

C20H38AlNOSi, 363.2538; found, 363.2526; calcd for C16H30AlNSi, 291.1963;

1 found, 291.1957. H NMR (C6D6): d 3.27 (m, THF, 4H), 2.19 (s, C5Me2, 6H); 2.06

(broad s, C5Me2, 6H); 1.36 (s, NCMe3, 9H); 0.98 (m, THF, 4H); 0.65 (s, SiMe2,

13 1 6H); -0.48 (s, AlMe, 3H); C{ H} NMR (C6D6): d 130.73 (s, Cp-ring), 130.21 (s,

Cp-ring), 126.85 (s, Cp-ring), 71.43 (s, THF), 51.47 (s, NCMe3), 33.13 (s, NCMe3),

24.76 (s, THF), 14.41 (s, C5Me2), 11.43 (s, C5Me2), 6.65 (s, SiMe2), -9.73 (s,

27 1 AlMe); Al NMR (C6D6): d 130 (Br, w1/2 = 2890 Hz). H NMR (500.00 MHz, 213

K, toluene-d8): d 3.02 (m, THF, 2H), 2.89 (m, THF, 2H), 2.15 (s, C5Me2, 6H), 2.10

(s, C5Me, 3H), 1.92 (s, C5Me, 3H), 1.33 (s, NCMe3, 9H), 0.70 (s, SiMe, 3H), 0.68

(m, THF, 4H), 0.60 (s, SiMe, 3H); -0.45 (s, AlMe, 3H).

Preparation of (CGC)AlMe·(tetramethylimadazol-2-ylidene) (21)

A dark yellow solution of tetramethylimadazol-2-ylidene (0.35 g, 2.8 mmol) in toluene (25 mL) was added dropwise to a stirred pale yellow solution of

[(CGC)AlMe THF] (1.0 g, 2.8 mmol) in THF (50 mL) at –78 °C. The reaction

96 mixture was allowed to warm to room temperature, then stirred overnight.

Concentration of the solution in vacuo produced a pale yellow solution from which colorless cube-shaped crystals of (CGC)AlMe carbene were obtained after storage

+ at room temperature, 1.1 g, 95 % yield, mp 100 °C (dec). MS (CI , CH4): m/z 415

[M, 100 %]; 400 [M -Me, 90.70 %]; 291 [M –Carbene, 1.42 %]; 276 [(CGC)Al+,

+ 2.58 %]; HRMS (CI , CH4) calcd for C23H42AlN3Si, 415.2963; found, 415.2965;

1 calcd for C22H39Al1N3Si1, 400.2729; found, 400.2723. H NMR (C7D8): d 3.09

(broad, N(1,3)-Me, 6H), 2.53 (s, C5Me, 3H); 2.23 (s, C5Me, 3H); 1.88 (s, C5Me,

3H); 1.64 (s, C5Me, 3H); 1.48 (s, NCMe3, 9H); 1.25 (s, C(4,5)-Me, 6H), 0.67 (s,

13 1 SiMe, 3H); 0.62 (s, SiMe, 3H); -0.28 (s, AlMe, 3H); C{ H} NMR (CD2Cl2): d

130.73 (s, Cp-ring), 130.21 (s, Cp-ring), 126.85 (s, Cp-ring), 71.43 (s, THF), 51.47

(s, NCMe3), 33.13 (s, NCMe3), 24.76 (s, THF), 14.41 (s, C5Me2), 11.43 (s, C5Me2),

27 6.65 (s, SiMe2), -9.73 (s, AlMe); Al NMR (CD2Cl2): d 125 (Br, w1/2 = 2410 Hz).

Preparation of (CGC)AlCl Et2O (24)

A colorless solution of AlCl3 (0.31 g, 2.3 mmol) in Et2O (30 mL) was added dropwise to a stirred pale yellow suspension of [(CGC)(MgCl)2 THF] (1.0 g, 2.3 mmol) in Et2O (150 mL) at –78 °C. The reaction mixture was allowed to warm to room temperature then stirred overnight. The volatiles were removed in vacuo and the resulting pale yellow solid was extracted with toluene (50 mL) and filtered through Celite® to afford a yellow solution. Concentration of this solution in vacuo

97 produced a pale yellow solution from which colorless rod-shaped crystals of

(CGC)AlCl Et2O were obtained after storage at –20 °C, 0.65 g, 73 % yield, mp 100-

+ 115 °C (dec). MS (CI , CH4): m/z 384 [M, 100 %]; 349 [M -Cl, 44.10 %]; 311 [M –

1 Et2O, 69.63 %]; H NMR (300.00 MHz, 295 K, C6D6): d 3.49 (m, Et2O, 4H), 2.14

(s, C5Me, 3H); 2.11 (s, C5Me, 3H); 2.05 (s, C5Me, 3H); 1.93 (s, C5Me, 3H); 1.45 (s,

27 NCMe3, 9H); 0.65 (s, SiMe2, 6H); 0.61 (s, SiMe2, 6H); Al NMR (C7D8): d 105

(Br, w1/2 = 3100 Hz).

5 + - Preparation of [(h -C5Me5)2In] [(C6F5)3BO(H)B(C6F5)3] (26)

5 A solution of In(h -C5Me5) (0.1 g, 0.4 mmol) in toluene (40 mL) was treated with equimolar quantities (0.195 mmol each) of B(C6F5)3 and the Brønsted acid

H2O·B(C6F5)3 in toluene solution (40 mL) at 0 °C. The reaction mixture afforded colorless crystals (0.25 g, 70.4% yield) following concentration (ca. 10 mL) and storage at -30°C for several days. HRMS: calcd for C10H15In, 364.925; found,

1 364.924. H NMR (300.00 MHz, 295 K, C6D6) d 1.49 (s, 15H, Cp*), 2.09 (s, 6H,

Ph-Me), 6.9-7.0 (m, 8H, free o-Tol and m-Tol), 7.02-7.04 (m, 2H, free p-Tol), d

7.09-7.12 (m, 8H, bound o-Tol and m-Tol), 7.12-7.13 (m, 2H, bound p-Tol);

13 1 C{ H} NMR (CD2Cl2): d 9.63 (s, Cp*), 21.36 (s, Ph(Me)), d 116.72 (s, Cp*), d

125.64 (s, p-Tol), d 128.51 (s, m-Tol), 129.28 (s, o-Tol), 137.85 (s, ipso-Tol); 19F

2 2 NMR (C6D6): d -134.35 (d, JF-F 17.4 Hz, p-C6F5), -158.16 (“t”, JF-F 20.9 Hz, p-

98 11 C6F5), (m, m-C6F5). B NMR (96.28 MHz, 295 K, C6F5): d -9.9. Elemental analysis calcd for C70.5H44B2F30In2O: C, 48.99; H, 2.57. Found: C, 49.66; H, 2.86.

99

Chapter 2

Tables of Crystallographic and

Theoretical Data

100

1 Figure 2.19. Molecular structure of (h -C5Me5)2BBr (2) showing the atom numbering scheme.

101

1 Table 2.1. Crystal Data and Structure Refinement for (h -C5Me5)2BBr (2)

Identification code s

Empirical formula C20 H30 B Br Formula weight 361.16 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 7.7070(15) Å a= 90°. b = 15.777(3) Å b= 90.00(3)°. c = 16.096(3) Å g = 90°. Volume 1957.2(7) Å3 Z 4 Density (calculated) 1.226 Mg/m3 Absorption coefficient 2.096 mm-1 F(000) 760 Crystal size 0.2 x 0.2 x 0.2 mm3 Theta range for data collection 2.94 to 28.12°. Index ranges -7<=h<=10, -20<=k<=20, -20<=l<=19 Reflections collected 12964 Independent reflections 4513 [R(int) = 0.0731] Completeness to theta = 28.12° 94.4 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4513 / 0 / 199 Goodness-of-fit on F2 3.002 Final R indices [I>2sigma(I)] R1 = 0.1873, wR2 = 0.4750 R indices (all data) R1 = 0.2249, wR2 = 0.4818 Largest diff. peak and hole 2.485 and -2.518 e.Å-3

102 1 Table 2.2. Selected Bond Lengths [Å] for (h -C5Me5)2BBr (2)

Br(1)-B 1.987(11) B-C(12) 1.550(14) C(1)-C(15) 1.367(15) C(3)-C(10) 1.341(16) C(1)-C(9) 1.471(15) C(3)-C(19) 1.470(16) C(1)-C(16) 1.512(15) C(3)-C(5) 1.469(15) C(2)-C(9) 1.339(14) C(19)-C(13) 1.359(15) C(2)-C(8) 1.510(13) C(19)-C(20) 1.523(17) C(2)-C(7) 1.518(13) C(13)-C(12) 1.540(14) C(7)-C(14) 1.554(14) C(13)-C(6) 1.479(14) C(7)-C(15) 1.556(14) C(12)-C(11) 1.555(15) C(7)-B 1.585(14) C(12)-C(10) 1.535(16) C(9)-C(18) 1.516(16) C(10)-C(4) 1.523(18) C(15)-C(17) 1.493(16)

1 Table 2.3. Selected Bond Angles [°] for (h -C5Me5)2BBr (2)

C(15)-C(1)-C(9) 110.4(9) C(7)-B-Br(1) 114.1(7) C(9)-C(2)-C(7) 113.6(9) C(13)-C(19)-C(3) 109.0(10) C(8)-C(2)-C(7) 119.2(9) C(19)-C(13)-C(12) 108.5(9) C(2)-C(7)-C(14) 111.5(9) C(19)-C(13)-C(6) 126.5(10) C(2)-C(7)-C(15) 99.5(8) C(12)-C(13)-C(6) 124.9(10) C(14)-C(7)-C(15) 110.7(8) C(13)-C(12)-C(11) 107.9(9) C(2)-C(7)-B 117.0(8) C(13)-C(12)-B 117.3(8) C(14)-C(7)-B 115.2(9) C(11)-C(12)-B 111.5(9) C(15)-C(7)-B 100.9(8) C(13)-C(12)-C(10) 103.1(9) C(2)-C(9)-C(1) 107.3(9) C(11)-C(12)-C(10) 112.7(9) C(1)-C(15)-C(7) 109.2(8) B-C(12)-C(10) 104.1(9) C(17)-C(15)-C(7) 123.1(10) C(3)-C(10)-C(12) 107.8(9) C(12)-B-C(7) 127.9(9) C(4)-C(10)-C(12) 122.5(13) C(12)-B-Br(1) 117.8(7)

103

1 Figure 2.20. Molecular structure of (h -C5Me5)2BMe (3) showing the atom numbering scheme.

104 1 Table 2.4. Crystal Data and Structure Refinement for (h -C5Me5)2BMe (3)

Identification code d

Empirical formula C21 H33 B Formula weight 296.28 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Orthorhombic

Space group P212121 Unit cell dimensions a = 7.5688(15) Å a= 90°. b = 17.863(4) Å b= 90°. c = 27.857(6) Å g = 90°. Volume 3766.4(13) Å3 Z 8 Density (calculated) 1.045 Mg/m3 Absorption coefficient 0.057 mm-1 F(000) 1312 Crystal size 0.4 x 0.4 x 0.2 mm3 Theta range for data collection 2.92 to 27.48°. Index ranges -9<=h<=9, -23<=k<=23, -36<=l<=35 Reflections collected 7702 Independent reflections 7702 [R(int) = 0.0000] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7702 / 0 / 419 Goodness-of-fit on F2 1.017 Final R indices [I>2sigma(I)] R1 = 0.0696, wR2 = 0.1416 R indices (all data) R1 = 0.1413, wR2 = 0.1783 Absolute structure parameter 5.21(845) Largest diff. peak and hole 0.189 and -0.255 e.Å-3

105 1 Table 2.5. Selected Bond Lengths [Å] for (h -C5Me5)2BMe (3)

C(1)-B(1) 1.591(5) C(18)-C(19) 1.462(5) C(2)-B(2) 1.598(5) C(20)-C(29) 1.353(5) C(10)-C(19) 1.339(4) C(20)-C(26) 1.514(5) C(10)-C(16) 1.515(4) C(21)-C(22) 1.499(5) C(11)-C(15) 1.500(5) C(21)-C(25) 1.516(5) C(11)-C(12) 1.525(5) C(21)-B(2) 1.627(5) C(11)-B(1) 1.614(5) C(22)-C(23) 1.348(5) C(12)-C(13) 1.352(5) C(23)-C(24) 1.457(5) C(13)-C(14) 1.454(4) C(24)-C(25) 1.361(5) C(14)-C(15) 1.345(5) C(26)-C(27) 1.523(5) C(16)-C(17) 1.515(5) C(27)-C(28) 1.353(5) C(26)-B(2) 1.606(5) C(28)-C(29) 1.463(5) C(16)-B(1) 1.609(6) C(28)-C(29) 1.463(5) C(17)-C(18) 1.354(5)

1 Table 2.6. Selected Bond Angles [°] for (h -C5Me5)2BMe (3)

C(19)-C(10)-C(16) 110.3(3) C(17)-C(16)-B(1) 108.2(3) C(101)-C(10)-C(16) 122.1(3) C(161)-C(16)-B(1) 121.0(3) C(15)-C(11)-C(12) 102.0(3) C(18)-C(17)-C(16) 109.4(3) C(15)-C(11)-B(1) 114.2(3) C(17)-C(18)-C(19) 109.4(3) C(12)-C(11)-B(1) 99.5(3) C(10)-C(19)-C(18) 109.1(3) C(111)-C(11)-B(1) 114.2(3) C(29)-C(20)-C(26) 109.7(3) C(13)-C(12)-C(11) 108.6(3) C(201)-C(20)-C(26) 123.0(3) C(121)-C(12)-C(11) 123.6(3) C(22)-C(21)-C(25) 102.7(3) C(12)-C(13)-C(14) 109.9(3) C(22)-C(21)-B(2) 114.2(3) C(15)-C(14)-C(13) 108.8(3) C(25)-C(21)-B(2) 100.1(3) C(14)-C(15)-C(11) 110.4(3) C(23)-C(22)-C(21) 109.7(3) C(10)-C(16)-C(17) 101.7(3) C(22)-C(23)-C(24) 109.6(3) C(10)-C(16)-B(1) 105.6(3) C(25)-C(24)-C(23) 109.1(3)

106

1 Figure 2.21. Molecular structure of [(h -C5Me5)2GaCl]2 (6) showing the atom numbering scheme.

107 1 Table 2.7. Crystal Data and Structure Refinement for (h -C5Me5)2GaCl (6)

Identification code p1b

Empirical formula C20 H30 Cl Ga Formula weight 375.61 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 8.672(2) Å a= 80.23(3)°. b = 14.309(3) Å b= 85.84(3)°. c = 23.345(5) Å g = 84.53(3)°. Volume 2837.4(10) Å3 Z 6 Density (calculated) 1.319 Mg/m3 Absorption coefficient 1.592 mm-1 F(000) 1188 Crystal size 0.3 x 0.1 x 0.1 mm3 Theta range for data collection 2.98 to 27.56°. Index ranges -9<=h<=11, -17<=k<=18, -29<=l<=30 Reflections collected 45374 Independent reflections 12490 [R(int) = 0.0807] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 12486 / 0 / 625 Goodness-of-fit on F2 1.059 Final R indices [I>2sigma(I)] R1 = 0.0555, wR2 = 0.1273 R indices (all data) R1 = 0.0905, wR2 = 0.1452 Largest diff. peak and hole 1.145 and -0.673 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x+2,-y+1,-z ; -x, -y, -z

108 1 Table 2.8. Selected Bond Lengths for (h -C5Me5)2GaCl (6)

C(11)-C(15) 1.493(6) Cl(1)-Ga(1) 2.4313(12) C(11)-C(12) 1.500(6) Cl(1)-Ga(2) 2.4429(12) C(11)-Ga(1) 2.005(4) Cl(2)-Ga(2) 2.4243(12) C(12)-C(13) 1.354(6) Cl(2)-Ga(1) 2.4422(11) C(13)-C(14) 1.458(6) C(21)-Ga(1) 2.010(4) C(14)-C(15) 1.352(6) C(22)-C(23) 1.354(6) C(21)-C(22) 1.484(6) C(23)-C(24) 1.456(6) C(21)-C(25) 1.494(6) C(24)-C(25) 1.351(6)

1 Table 2.9. Selected Bond Angles [°] for (h -C5Me5)2GaCl (6)

C(15)-C(11)-C(12) 103.1(3) C(22)-C(23)-C(24) 109.1(4) C(15)-C(11)-Ga(1) 112.1(3) C(25)-C(24)-C(23) 109.4(4) C(12)-C(11)-Ga(1) 109.4(3) C(24)-C(25)-C(21) 108.5(4) C(13)-C(12)-C(11) 109.2(3) Ga(1)-Cl(1)-Ga(2) 96.73(4) C(12)-C(13)-C(14) 109.0(3) Ga(2)-Cl(2)-Ga(1) 96.94(4) C(15)-C(14)-C(13) 109.2(3) C(11)-Ga(1)-C(21) 129.2(2) C(14)-C(15)-C(11) 109.4(3) C(11)-Ga(1)-Cl(1) 111.36(12) C(22)-C(21)-C(25) 104.0(3) C(21)-Ga(1)-Cl(1) 106.76(12) C(22)-C(21)-Ga(1) 100.5(3) C(11)-Ga(1)-Cl(2) 104.19(12) C(25)-C(21)-Ga(1) 98.0(3) C(21)-Ga(1)-Cl(2) 112.63(12) C(211)-C(21)-Ga(1) 117.6(3) Cl(1)-Ga(1)-Cl(2) 83.10(4) C(23)-C(22)-C(21) 108.9(4) Cl(2)-Ga(2)-Cl(1) 83.23(4)

109

1 2 Figure 2.5. Molecular structure of (h -C5Me5)(h -C5Me5)GaMe (8) showing the atom numbering scheme.

110 1 2 Table 2.10. Crystal Data and Structure Refinement for (h -C5Me5)(h - C5Me5)2GaMe (8)

Identification code shelx

Empirical formula C21 H33 Ga Formula weight 355.19 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21 Unit cell dimensions a = 7.8112(4) Å a= 90°. b = 11.2335(4) Å b= 93.797(3)°. c = 11.1606(6) Å g = 90°. Volume 977.16(8) Å3 Z 2 Density (calculated) 1.207 Mg/m3 Absorption coefficient 1.404 mm-1 F(000) 380 Crystal size 0.2 x 0.2 x 0.2 mm3 Theta range for data collection 3.29 to 27.51°. Index ranges -7<=h<=10, -14<=k<=12, -14<=l<=14 Reflections collected 12166 Independent reflections 4098 [R(int) = 0.0800] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4098 / 1 / 200 Goodness-of-fit on F2 1.077 Final R indices [I>2sigma(I)] R1 = 0.1168, wR2 = 0.3063 R indices (all data) R1 = 0.1236, wR2 = 0.3148 Absolute structure parameter 0.11(5) Largest diff. peak and hole 4.976 and -1.623 e.Å-3 ______

111 1 2 Table 2.11. Selected Bond Lengths for (h -C5Me5)(h -C5Me5)GaMe (8)

Ga(01)-C(1) 1.952(10) C(15)-C(11) 1.44(2) Ga(01)-C(21) 2.059(11) C(15)-C(151) 1.49(2) Ga(01)-C(12) 2.172(9) C(13)-C(14) 1.37(2) Ga(01)-C(11) 2.210(11) C(13)-C(12) 1.43(2) C(24)-C(23) 1.38(2) C(13)-C(131) 1.53(2) C(24)-C(25) 1.38(2) C(11)-C(12) 1.44(2) C(24)-C(241) 1.50(2) C(11)-C(111) 1.50(2) C(22)-C(23) 1.39(2) C(121)-C(12) 1.50(2) C(22)-C(21) 1.47(2) C(25)-C(21) 1.50(2) C(22)-C(221) 1.50(2) C(25)-C(251) 1.50(2) C(23)-C(231) 1.52(2) C(14)-C(141) 1.53(2) C(15)-C(14) 1.40(2) C(21)-C(211) 1.519(14)

1 2 Table 2.12. Selected Bond Angles [°] for (h -C5Me5)(h -C5Me5)GaMe (8)

C(1)-Ga(01)-C(21) 120.1(4) C(15)-C(11)-C(111) 125.1(12) C(1)-Ga(01)-C(12) 120.7(4) C(12)-C(11)-Ga(01) 69.4(6) C(21)-Ga(01)-C(12) 116.6(4) C(15)-C(11)-Ga(01) 96.5(7) C(1)-Ga(01)-C(11) 116.4(5) C(111)-C(11)-Ga(01) 114.4(8) C(21)-Ga(01)-C(11) 118.7(4) C(24)-C(25)-C(21) 107.8(10) C(12)-Ga(01)-C(11) 38.4(5) C(13)-C(12)-C(11) 105.7(10) C(23)-C(24)-C(25) 109.5(10) C(13)-C(12)-C(121) 124.0(11) C(23)-C(22)-C(21) 107.4(10) C(11)-C(12)-C(121) 125.0(11) C(24)-C(23)-C(22) 110.9(9) C(13)-C(12)-Ga(01) 98.9(7) C(14)-C(15)-C(11) 107.1(11) C(11)-C(12)-Ga(01) 72.2(6) C(14)-C(13)-C(12) 110.0(11) C(121)-C(12)-Ga(01) 116.7(8) C(12)-C(11)-C(15) 107.5(10) C(13)-C(14)-C(15) 109.6(11) C(12)-C(11)-C(111) 125.2(11) C(22)-C(21)-C(25) 104.2(9) C(25)-C(21)-C(211) 117.5(12) C(22)-C(21)-C(211) 120.3(12) C(22)-C(21)-Ga(01) 94.9(7) C(211)-C(21)-Ga(01) 119.4(8) 112

1 5 + - Figure 2.22. Molecular structure of [(h -C5Me5)(h -C5Me5)B] [AlCl4] showing the atom numbering scheme.

1 5 + - Figure 2.23. Molecular structure of [(h -C5Me5)(h -C5Me5)B] [AlCl4] showing both crystallographically independent units.

113 1 5 Table 2.13. Crystal Data and Structure Refinement for [(h -C5Me5)(h - + - C5Me5)B] [AlCl4]

Identification code chuck

Empirical formula C40 H60 Al2 B2 Cl8 Formula weight 900.06 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 17.133(3) Å a= 90°. b = 13.611(3) Å b= 90.30(3)°. c = 20.493(4) Å g = 90°. Volume 4778.8(16) Å3 Z 4 Density (calculated) 1.251 Mg/m3 Absorption coefficient 0.535 mm-1 F(000) 1888 Crystal size 0.2 x 0.18 x 0.16 mm3 Theta range for data collection 2.98 to 27.49°. Index ranges -22<=h<=22, -17<=k<=17, -26<=l<=26 Reflections collected 19718 Independent reflections 10898 [R(int) = 0.0376] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 10898 / 0 / 469 Goodness-of-fit on F2 1.539 Final R indices [I>2sigma(I)] R1 = 0.0718, wR2 = 0.2090 R indices (all data) R1 = 0.1136, wR2 = 0.2254 Largest diff. peak and hole 0.828 and -0.494 e.Å-3

114 1 5 + - Table 2.14. Selected Bond Lengths [Å] for [(h -C5Me5)(h -C5Me5)B] [AlCl4]

Cl(1)-Al(1) 2.1255(14) C(1)-C(2) 1.511(5) Cl(2)-Al(1) 2.126(2) C(1)-C(6) 1.534(5) Al(1)-Cl(4) 2.127(2) C(2)-C(3) 1.345(5) Al(1)-Cl(3) 2.150(2) C(2)-C(7) 1.504(5) C(13)-C(14) 1.420(5) C(15)-C(11) 1.428(5) C(13)-C(12) 1.424(5) C(15)-C(14) 1.430(5) C(13)-B(1) 1.787(5) C(15)-C(20) 1.494(5) C(5)-C(4) 1.337(5) C(12)-C(11) 1.431(5) C(5)-C(10) 1.483(5) C(4)-C(3) 1.469(6) C(5)-C(1) 1.534(4) C(4)-C(9) 1.500(5) B(1)-C(1) 1.580(5) C(3)-C(8) 1.505(5) B(1)-C(14) 1.756(5) B(1)-C(12) 1.779(5) B(1)-C(15) 1.760(5) B(1)-C(11) 1.791(5)

1 5 + - Table 2.15. Selected Bond Angles [°] for [(h -C5Me5)(h -C5Me5)B] [AlCl4]

Cl(1)-Al(1)-Cl(2) 109.97(6) C(13)-C(12)-C(11) 107.9(3) Cl(1)-Al(1)-Cl(4) 109.68(7) C(5)-C(4)-C(3) 109.8(3) Cl(2)-Al(1)-Cl(4) 110.87(7) C(2)-C(3)-C(4) 109.4(3) Cl(1)-Al(1)-Cl(3) 107.33(7) C(2)-C(1)-C(5) 102.1(3) Cl(2)-Al(1)-Cl(3) 109.44(7) C(2)-C(1)-C(6) 114.5(3) C(14)-C(13)-C(12) 108.3(3) C(5)-C(1)-C(6) 114.2(3) C(4)-C(5)-C(1) 108.9(3) C(2)-C(1)-B(1) 106.5(3) C(1)-B(1)-C(14) 134.4(3) C(5)-C(1)-B(1) 106.2(3) C(1)-B(1)-C(12) 138.5(3) C(6)-C(1)-B(1) 112.4(3) C(14)-B(1)-C(12) 81.4(2) C(3)-C(2)-C(1) 109.4(3) C(1)-B(1)-C(13) 136.8(3) C(14)-B(1)-C(11) 81.3(2) C(1)-B(1)-C(11) 138.7(3) C(13)-B(1)-C(11) 80.3(2)

115 + Table 2.16. Selected BP86 Calculation Results for [(h-C5H5)2B] Cations

Energy Rel. Energy NBO q(B) GIAO N imag Dipole (kcal/mol) d(11B)* Moment D5d -411.5408073 45.39 0.56022 n/d 4 0 D5h -411.5395324 46.19 0.56069 n/d 5 0 5 1 Cs (h , h ) -411.6131451 0.00 0.73063 n/d 0 4.4351

5 1 Cs (h ,h ) -411.6023611 6.77 n/d n/d n/d 3.7576 parallel† 5 1 Cs (h ,h ) -411.5802912 20.62 0.68811 n/d 0 3.9679 parallel‡

(h-C5Me5)2B Cations 5 1 Cs (h , h ) -804.78389 0.00 n/d -43.1116 n/d 4.6984 5 5 D5d (h , h ) -804.70588 48.95 n/d -51.9602 n/d 0

* Referenced with respect to F3B·OMe2, calculated at the same level of theory and assumed to have d(11B) = 0 ppm. † 1 The h -C5H5 ring was not confined to planarity. ‡ 1 The h -C5H5 ring was restricted to remain planar.

116

5 Figure 2.24. Molecular structure of (h -C5Me5)(C6F5)AlCl (12) showing the atom numbering scheme.

117 5 Table 2.17. Crystal Data and Structure Refinement for [(h -C5Me5)(C6F5)AlCl]2 (12)

Identification code l

Empirical formula C48 H45 Al3 Cl3 F15 Formula weight 1094.13 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/c Unit cell dimensions a = 11.3045(8) Å a= 90°. b = 29.205(3) Å b= 108.299(4)°. c = 15.4522(10) Å g = 90°. Volume 4843.6(7) Å3 Z 4 Density (calculated) 1.500 Mg/m3 Absorption coefficient 0.336 mm-1 F(000) 2232 Crystal size 0.2 x 0.15 x 0.15 mm3 Theta range for data collection 1.55 to 22.50°. Index ranges -1<=h<=12, -1<=k<=28, -16<=l<=16 Reflections collected 6350 Independent reflections 5253 [R(int) = 0.0246] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 5253 / 0 / 622 Goodness-of-fit on F2 0.984 Final R indices [I>2sigma(I)] R1 = 0.0421, wR2 = 0.1069 R indices (all data) R1 = 0.0661, wR2 = 0.1266 Largest diff. peak and hole 0.327 and -0.303 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x+1,-y+1,-z+2 118 5 Table 2.18. Selected Bond Lengths [Å] for [(h -C5Me5)(C6F5)AlCl]2 (12)

Cl(1)-Al(4) 2.339(2) C(1)-C(2) 1.382(5) Cl(1)-Al(5) 2.349(2) C(15)-C(14) 1.409(7) Cl(2)-Al(5) 2.337(2) C(15)-C(16) 1.408(6) Cl(2)-Al(4) 2.360(2) C(2)-C(3) 1.370(6) Al(4)-C(1) 1.987(4) C(3)-C(4) 1.373(6) Al(4)-C(13) 2.115(4) C(5)-C(4) 1.367(6) Al(4)-C(17) 2.218(5) C(13)-C(14) 1.431(6) Al(4)-C(14) 2.215(5) Al(5)-C(21) 2.362(6) Al(4)-C(15) 2.365(6) Al(5)-C(20) 2.396(6) Al(4)-C(16) 2.374(6) C(17)-C(16) 1.411(7) Al(5)-C(18) 2.118(5) C(17)-C(13) 1.433(6) Al(5)-C(22) 2.212(5) C(6)-C(1) 1.374(6) Al(5)-C(19) 2.241(5) C(6)-C(5) 1.377(6)

5 Table 2.19. Selected Bond Angles [°] for [(h -C5Me5)(C6F5)AlCl]2 (12)

Al(4)-Cl(1)-Al(5) 96.09(6) C(15)-C(14)-C(13) 108.4(4) Al(5)-Cl(2)-Al(4) 95.83(6) C(15)-C(14)-C(141) 126.5(5) C(13)-Al(4)-C(14) 38.5(2) C(13)-C(14)-C(141) 124.9(5) C(17)-Al(4)-C(14) 62.4(2) C(141)-C(14)-Al(4) 124.4(4) C(13)-Al(4)-Cl(1) 103.70(13) C(3)-C(2)-C(1) 123.9(4) C(17)-Al(4)-Cl(1) 141.21(13) C(4)-C(3)-C(2) 118.9(4) C(14)-Al(4)-Cl(1) 93.57(14) C(21)-C(22)-C(18) 108.5(4) C(13)-Al(4)-Cl(2) 98.66(13) C(4)-C(5)-C(6) 118.9(4) C(17)-Al(4)-Cl(2) 92.64(13) C(11)-C(12)-C(7) 123.5(4) C(1)-Al(4)-C(16) 90.5(2) C(11)-C(10)-C(9) 119.7(4) C(17)-Al(4)-C(16) 35.6(2) C(19)-C(20)-C(21) 108.0(4) C(14)-Al(4)-C(16) 59.6(2) C(6)-C(1)-Al(4) 123.0(3) Cl(1)-Al(4)-C(16) 151.87(13) C(2)-C(1)-Al(4) 122.5(3) Cl(2)-Al(4)-C(16) 120.35(13) 119

5 + - Figure 2.25. Molecular structure of [(h -C5Me5)2Al] [AlCl4] showing the atom numbering scheme.

5 + - Figure 2.26. Molecular structure of [(h -C5Me5)2Al] [AlCl4] showing both crystallographically independent units.

120 5 + - Table 2.20. Crystal Data and Structure Refinement for [(h -C5Me5)2Al] [AlCl4]

Identification code shelx

Empirical formula C20 H30 Al2 Cl4 Formula weight 466.20 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 7.755(5) Å a= 85.710(5)°. b = 17.375(5) Å b= 83.601(5)°. c = 18.081(5) Å g = 84.788(5)°. Volume 2405.9(18) Å3 Z 4 Density (calculated) 1.287 Mg/m3 Absorption coefficient 0.568 mm-1 F(000) 976 Crystal size 0.4 x 0.4 x 0.3 mm3 Theta range for data collection 2.99 to 25.06°. Index ranges -9<=h<=9, -18<=k<=20, -21<=l<=20 Reflections collected 32448 Independent reflections 8499 [R(int) = 0.0411] Absorption correction N/a Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 8499 / 0 / 489 Goodness-of-fit on F2 1.021 Final R indices [I>2sigma(I)] R1 = 0.0466, wR2 = 0.1097 R indices (all data) R1 = 0.0703, wR2 = 0.1228 Extinction coefficient n/a Largest diff. peak and hole 0.969 and -0.745 e.Å-3

121 5 + - Table 2.21. Selected Bond Lengths [Å] for [(h -C5Me5)2Al] [AlCl4]

C(10)-C(19) 1.435(4) Al(3)-Cl(31) 2.1219(15) C(10)-C(16) 1.439(4) Al(3)-Cl(33) 2.1309(14) C(10)-Al(1) 2.145(3) Al(3)-Cl(32) 2.133(2) C(11)-C(12) 1.430(4) Al(3)-Cl(34) 2.1394(13) C(11)-C(15) 1.432(4) C(14)-Al(1) 2.148(3) C(11)-Al(1) 2.147(3) C(15)-Al(1) 2.141(3) C(12)-C(13) 1.432(4) C(16)-C(17) 1.436(4) C(12)-Al(1) 2.146(3) C(16)-Al(1) 2.150(3) C(13)-C(14) 1.434(4) C(17)-C(18) 1.431(4) C(13)-Al(1) 2.148(3) C(17)-Al(1) 2.156(3) C(14)-C(15) 1.435(4) C(18)-C(19) 1.432(4) C(19)-Al(1) 2.147(3) C(18)-Al(1) 2.154(3)

5 + - Table 2.22. Selected Bond Angles [°] for [(h -C5Me5)2Al] [AlCl4]

C(12)-C(11)-C(15) 108.1(2) C(28)-C(29)-C(20) 108.1(2) C(12)-C(11)-C(111) 126.4(3) C(15)-Al(1)-C(10) 179.39(11) C(15)-C(11)-C(111) 125.5(2) C(10)-Al(1)-C(12) 114.72(11) C(111)-C(11)-Al(1) 125.9(2) C(10)-Al(1)-C(11) 141.45(11) C(11)-C(12)-C(13) 107.9(2) C(10)-Al(1)-C(13) 114.37(11) C(11)-C(12)-C(121) 126.9(3) C(10)-Al(1)-C(14) 140.33(11) C(13)-C(12)-C(121) 125.1(2) C(141)-C(14)-Al(1) 125.4(2) C(121)-C(12)-Al(1) 125.5(2) C(11)-C(15)-C(14) 108.2(2) C(12)-C(13)-C(14) 108.3(2) C(11)-C(15)-C(151) 125.9(3) C(12)-C(13)-C(131) 124.5(2) C(14)-C(15)-C(151) 125.8(3) C(14)-C(13)-C(131) 127.2(3) C(151)-C(15)-Al(1) 126.1(2) C(131)-C(13)-Al(1) 125.3(2) C(13)-C(14)-C(141) 126.3(2) C(13)-C(14)-C(15) 107.5(2) C(15)-C(14)-C(141) 126.2(2)

122

3 Figure 2.9. Molecular structure of [(h -C5Me5)(C6F5)GaCl]2 (14) showing the atom numbering scheme.

123 3 Table 2.23. Crystal Data and Structure Refinement for [(h -C5Me5)(C6F5)GaCl]2 (14)

Identification code shelx

Empirical formula C36 H45 Cl2 F5 Ga2 Formula weight 783.06 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 16.844(5) Å a= 90.000(5)°. b = 13.772(5) Å b= 118.039(5)°. c = 17.627(5) Å g = 90.000(5)°. Volume 3609.1(20) Å3 Z 4 Density (calculated) 1.441 Mg/m3 Absorption coefficient 1.691 mm-1 F(000) 1608 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data collection 2.96 to 27.53°. Index ranges -21<=h<=17, -15<=k<=17, -19<=l<=22 Reflections collected 18562 Independent reflections 8235 [R(int) = 0.1238] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 8235 / 0 / 421 Goodness-of-fit on F2 1.028 Final R indices [I>2sigma(I)] R1 = 0.0539, wR2 = 0.0969 R indices (all data) R1 = 0.1134, wR2 = 0.1206 Largest diff. peak and hole 0.587 and -0.623 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x, -y, -z

124 3 Table 2.24. Selected Bond Lengths [Å] for [(h -C5Me5)(C6F5)GaCl]2 (14)

C(11)-C(12) 1.473(6) Cl(1)-Ga(1) 2.5070(12) C(11)-C(15) 1.479(6) C(21)-C(22) 1.507(6) C(11)-C(111) 1.527(6) Cl(2)-Ga(1) 2.4632(12) C(11)-Ga(1) 1.993(4) C(21)-C(211) 1.531(6) C(12)-C(13) 1.356(6) C(21)-Ga(1) 1.992(4) C(12)-C(121) 1.511(7) C(22)-C(23) 1.350(6) C(13)-C(14) 1.451(7) C(22)-C(221) 1.495(6) C(13)-C(131) 1.493(7) C(23)-C(24) 1.469(6) C(14)-C(15) 1.359(6) C(23)-C(231) 1.502(6) C(14)-C(141) 1.506(7) C(24)-C(25) 1.340(6) C(15)-C(151) 1.496(7) C(24)-C(241) 1.513(6) C(21)-C(25) 1.498(5) C(25)-C(251) 1.508(6)

3 Table 2.25. Selected Bond Angles [°] for [(h -C5Me5)(C6F5)GaCl]2 (14)

C(12)-C(11)-C(15) 104.5(4) C(24)-C(25)-C(21) 109.4(3) C(12)-C(11)-Ga(1) 94.4(3) C(35)-C(31)-C(32) 105.0(4) C(15)-C(11)-Ga(1) 97.6(3) Ga(2)-Cl(1)-Ga(1) 93.26(4) C(111)-C(11)-Ga(1) 115.6(3) Ga(2)-Cl(2)-Ga(1) 94.27(4) C(13)-C(12)-C(11) 109.2(4) C(21)-Ga(1)-Cl(2) 107.24(12) C(12)-C(13)-C(14) 108.3(4) C(11)-Ga(1)-Cl(2) 101.90(13) C(15)-C(14)-C(13) 109.6(4) C(21)-Ga(1)-Cl(1) 103.69(12) C(31)-Ga(2)-Cl(2) 113.70(12) C(11)-Ga(1)-Cl(1) 105.90(14) Cl(1)-Ga(2)-Cl(2) 89.28(4) Cl(2)-Ga(1)-Cl(1) 82.72(4) C(25)-C(24)-C(23) 109.6(4) C(32)-C(33)-C(34) 108.9(4) C(32)-C(31)-Ga(2) 94.7(2) C(35)-C(34)-C(33) 110.4(4) C(33)-C(32)-C(31) 108.3(4) C(14)-C(15)-C(11) 108.1(4) C(22)-C(21)-Ga(1) 109.2(3) C(25)-C(21)-C(22) 103.0(3) C(23)-C(22)-C(21) 109.2(4) C(25)-C(21)-Ga(1) 107.4(3) C(22)-C(23)-C(24) 108.7(4) 125

1 1 Figure 2.10. Molecular structure of (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5) (15) showing the atom numbering scheme.

126 Table 2.26. Crystal Data and Structure Refinement for 1 1 (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5)(15)

Identification code shelx

Empirical formula C36 H45 Cl2 F5 Ga2 Formula weight 783.06 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 16.844(5) Å a = 90.000(5)°. b = 13.772(5) Å b = 118.039(5)°. c = 17.627(5) Å g = 90.000(5)°. Volume 3609.1(20) Å3 Z 4 Density (calculated) 1.441 Mg/m3 Absorption coefficient 1.691 mm-1 F(000) 1608 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data collection 2.96 to 27.53°. Index ranges -21<=h<=17, -15<=k<=17, -19<=l<=22 Reflections collected 18562 Independent reflections 8235 [R(int) = 0.1238] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 8235 / 0 / 421 Goodness-of-fit on F2 1.028 Final R indices [I>2sigma(I)] R1 = 0.0539, wR2 = 0.0969 R indices (all data) R1 = 0.1134, wR2 = 0.1206 Largest diff. peak and hole 0.587 and -0.623 e.Å-3

127 1 1 Table 2.27. Selected Bond Lengths [Å] for (h -C5Me5)2GaCl2Ga(C6F5)(h - C5Me5)(15)

C(11)-C(12) 1.473(6) C(31)-Ga(2) 2.006(4) C(11)-C(15) 1.479(6) C(32)-C(33) 1.359(6) C(11)-Ga(1) 1.993(4) C(34)-C(35) 1.361(7) C(12)-C(13) 1.356(6) C(41)-Ga(2) 1.973(4) C(13)-C(14) 1.451(7) Cl(1)-Ga(2) 2.3344(11) C(14)-C(15) 1.359(6) Cl(1)-Ga(1) 2.5070(12) C(21)-C(25) 1.498(5) Cl(2)-Ga(2) 2.3399(12) C(21)-C(22) 1.507(6) C(24)-C(25) 1.340(6) C(21)-Ga(1) 1.992(4) C(31)-C(35) 1.487(6) C(22)-C(23) 1.350(6) C(31)-C(32) 1.483(6) C(23)-C(24) 1.469(6) Cl(2)-Ga(1) 2.4632(12)

1 1 Table 2.28. Selected Bond Angles [°] for (h -C5Me5)2GaCl2Ga(C6F5)(h - C5Me5)(15)

C(12)-C(11)-C(111) 120.5(4) C(42)-C(41)-Ga(2) 122.6(3) C(15)-C(11)-C(111) 119.4(4) C(46)-C(41)-Ga(2) 122.7(3) C(12)-C(11)-Ga(1) 94.4(3) Ga(2)-Cl(1)-Ga(1) 93.26(4) C(15)-C(11)-Ga(1) 97.6(3) Ga(2)-Cl(2)-Ga(1) 94.27(4) C(111)-C(11)-Ga(1) 115.6(3) C(21)-Ga(1)-C(11) 140.5(2) C(25)-C(21)-C(211) 113.9(3) C(21)-Ga(1)-Cl(2) 107.24(12) C(22)-C(21)-C(211) 112.9(4) C(11)-Ga(1)-Cl(2) 101.90(13) C(25)-C(21)-Ga(1) 107.4(3) C(21)-Ga(1)-Cl(1) 103.69(12) C(211)-C(21)-Ga(1) 110.1(3) Cl(2)-Ga(1)-Cl(1) 82.72(4) C(35)-C(31)-C(311) 120.9(4) C(41)-Ga(2)-C(31) 122.5(2) C(32)-C(31)-C(311) 121.0(4) C(41)-Ga(2)-Cl(1) 111.01(11) C(35)-C(31)-Ga(2) 94.7(3) C(31)-Ga(2)-Cl(1) 110.12(12) C(32)-C(31)-Ga(2) 94.7(2) C(41)-Ga(2)-Cl(2) 105.15(12) C(311)-C(31)-Ga(2) 114.6(3) C(31)-Ga(2)-Cl(2) 113.70(12)

128

1 2 Figure 2.11. Molecular structure of (h -C5Me5)(h -C5Me5)GaC6F5 (16) showing the atom numbering scheme.

129 1 2 Table 2.29. Crystal Data and Structure Refinement for (h -C5Me5)(h - C5Me5)GaC6F5 (16)

Identification code split2 Empirical formula C26 H30 F5 Ga Formula weight 507.22 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 9.7661(2) Å a= 90°. b = 16.3514(4) Å b= 95.3840(13)°. c = 15.2095(4) Å g = 90°. Volume 2418.08(10) Å3 Z 4 Density (calculated) 1.393 Mg/m3 Absorption coefficient 1.187 mm-1 F(000) 1048 Crystal size 0.20 x 0.20 x 0.10 mm3 Theta range for data collection 2.96 to 27.48°. Index ranges -11<=h<=12, -19<=k<=21, -19<=l<=19 Reflections collected 33064 Independent reflections 5518 [R(int) = 0.0479] Absorption correction None Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 5518 / 0 / 385 Goodness-of-fit on F2 1.035 Final R indices [I>2sigma(I)] R1 = 0.0396, wR2 = 0.0721 R indices (all data) R1 = 0.0625, wR2 = 0.0835 Largest diff. peak and hole 0.428 and -0.503 e.Å-3

130 1 2 Table 2.30. Selected Bond Lengths [Å] for (h -C5Me5)(h -C5Me5)GaC6F5 (16)

Ga-C(31) 1.985(2) C(21)-C(25) 1.470(3) Ga-C(41) 2.091(10) C(21)-C(22) 1.473(3) Ga-C(21) 2.043(2) C(22)-C(23) 1.371(3) Ga-C(12) 2.17(2) C(23)-C(24) 1.432(4) Ga-C(11) 2.183(5) C(24)-C(25) 1.373(3) Ga-C(42) 2.29(2) C(12)-C(13) 1.406(10) C(11)-C(15) 1.451(13) C(13)-C(14) 1.403(12) C(11)-C(12) 1.50(2) C(14)-C(15) 1.38(2)

1 2 Table 2.31. Selected Bond lengths Angles [°] for (h -C5Me5)(h -C5Me5)GaC6F5 (16)

C(31)-Ga-C(41) 120.4(3) C(25)-C(21)-Ga 91.38(15) C(31)-Ga-C(21) 117.14(9) C(22)-C(21)-Ga 95.14(15) C(41)-Ga-C(21) 121.6(3) C(211)-C(21)-Ga 117.3(2) C(31)-Ga-C(12) 117.6(3) C(36)-C(31)-Ga 122.9(2) C(21)-Ga-C(12) 119.3(3) C(32)-C(31)-Ga 121.5(2) C(31)-Ga-C(11) 116.7(2) C(13)-C(12)-Ga 96.8(8) C(21)-Ga-C(11) 123.4(2) C(121)-C(12)-Ga 116.0(7) C(12)-Ga-C(11) 40.4(5) C(11)-C(12)-Ga 70.2(6) C(31)-Ga-C(42) 105.5(5) C(42)-C(41)-Ga 78.6(9) C(41)-Ga-C(42) 37.7(6) C(45)-C(41)-Ga 97.7(13) C(21)-Ga-C(42) 129.7(4) C(411)-C(41)-Ga 117.5(9) C(111)-C(11)-Ga 115.9(6) C(41)-C(42)-Ga 63.7(8) C(15)-C(11)-Ga 98.4(7) C(43)-C(42)-Ga 102.1(11) C(12)-C(11)-Ga 69.4(6) C(421)-C(42)-Ga 106.6(10)

131

1 3 + - Figure 2.12. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [BF4] showing the atom numbering scheme.

1 3 + - Figure 2.27. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [BF4] showing - [BF4] bridged dimer. 132 1 3 Table 2.32. Crystal Data and Structure Refinement for [(h -C5Me5)(h - + - + - C5Me5)Ga] [BF4] , [13] [BF4]

Identification code pbcn

Empirical formula C20 H30 B F4 Ga Formula weight 426.97 Temperature 133(2) K Wavelength 0.71073 Å Crystal system Orthorhombic Space group Pbcn Unit cell dimensions a = 11.972(2) Å a= 90°. b = 16.481(3) Å b= 90°. c = 20.449(4) Å g = 90°. Volume 4034.7(14) Å3 Z 8 Density (calculated) 1.406 g/cm3 Absorption coefficient 1.400 mm-1 F(000) 1776 Crystal size 0.25 x 0.2 x 0.05 mm3 Theta range for data collection 3.16 to 27.47°. Index ranges -13<=h<=15, -21<=k<=19, -26<=l<=24 Reflections collected 24914 Independent reflections 4539 [R(int) = 0.0736] Absorption correction None Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4538 / 0 / 246 Goodness-of-fit on F2 1.228 Final R indices [I>2sigma(I)] R1 = 0.0478, wR2 = 0.0836 R indices (all data) R1 = 0.0952, wR2 = 0.0935 Largest diff. peak and hole 0.737 and -0.511 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x,y,-z+1/2 133 1 3 + - Table 2.33. Selected Bond Lengths [Å] for [(h -C5Me5)(h -C5Me5)Ga] [BF4] , + - [13] [BF4]

Ga(1)-C(21) 1.971(2) C(23)-C(24) 1.475(4) Ga(1)-C(11) 2.001(3) C(24)-C(25) 1.346(4) Ga(1)-F(21) 2.174(2) C(14)-C(15) 1.382(4) Ga(1)-F(11) 2.186(2) C(14)-C(13) 1.415(4) Ga(1)-C(12) 2.352(3) C(13)-C(12) 1.380(4) Ga(1)-C(15) 2.353(3) C(21)-C(25) 1.508(3) C(11)-C(15) 1.463(3) C(21)-C(22) 1.511(3) C(11)-C(12) 1.467(4) C(23)-C(22) 1.350(4)

1 3 + - Table 2.34. Selected Bond Angles [°] for [(h -C5Me5)(h -C5Me5)Ga] [BF4] , + - [13] [BF4]

C(21)-Ga(1)-C(11) 157.46(11) F(22)-B(2)-F(21) 108.51(10) C(21)-Ga(1)-F(21) 100.35(9) C(14)-C(15)-Ga(1) 90.6(2) C(11)-Ga(1)-F(21) 98.32(9) C(11)-C(15)-Ga(1) 57.76(13) C(21)-Ga(1)-F(11) 99.78(9) C(151)-C(15)-Ga(1) 119.2(2) C(11)-Ga(1)-F(11) 95.73(9) C(13)-C(12)-Ga(1) 90.4(2) F(21)-Ga(1)-F(11) 80.18(7) C(11)-C(12)-Ga(1) 57.79(14) C(21)-Ga(1)-C(12) 123.17(10) C(121)-C(12)-Ga(1) 117.5(2) C(11)-Ga(1)-C(12) 38.32(10) C(12)-C(11)-Ga(1) 83.9(2) F(21)-Ga(1)-C(12) 136.22(8) C(111)-C(11)-Ga(1) 119.7(2) F(11)-Ga(1)-C(12) 95.59(9) B(2)-F(21)-Ga(1) 166.94(12) C(21)-Ga(1)-C(15) 128.60(10) C(25)-C(21)-Ga(1) 109.1(2) C(11)-Ga(1)-C(15) 38.20(9) C(22)-C(21)-Ga(1) 109.2(2) F(21)-Ga(1)-C(15) 91.16(8) C(211)-C(21)-Ga(1) 109.5(2) F(11)-Ga(1)-C(15) 131.60(8) F(22)-B(2)-F(22)#1 114.3(3) C(12)-Ga(1)-C(15) 59.34(9) F(12)-B(1)-F(11) 109.20(10) B(1)-F(11)-Ga(1) 169.38(13) F(12)#1-B(1)-F(11) 108.68(10) C(15)-C(11)-Ga(1) 84.0(2) F(11)#1-B(1)-F(11) 106.9(3)

134

1 5 + - Figure 2.13. Molecular structure of [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] (17) showing the atom numbering scheme.

135 1 5 Table 2.36. Crystal Data and Structure Refinement for [(h -C5Me5)(h - + - C5Me5)Ga] [AlCl4] (17)

Identification code shelx

Empirical formula C20 H30 Al Cl4 Ga Formula weight 508.94 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Monoclinic

Space group P21/c Unit cell dimensions a = 13.3800(7) Å a= 90°. b = 11.5016(7) Å b= 99.449(3)°. c = 15.8623(8) Å g = 90°. Volume 2408.0(2) Å3 Z 4 Density (calculated) 1.404 Mg/m3 Absorption coefficient 1.626 mm-1 F(000) 1048 Crystal size 0.5 x 0.5 x 0.5 mm3 Theta range for data collection 3.15 to 27.46°. Index ranges -17<=h<=17, -13<=k<=14, -20<=l<=17 Reflections collected 22788 Independent reflections 5470 [R(int) = 0.0881] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 5470 / 0 / 245 Goodness-of-fit on F2 1.025 Final R indices [I>2sigma(I)] R1 = 0.0499, wR2 = 0.0872 R indices (all data) R1 = 0.1024, wR2 = 0.1032 Largest diff. peak and hole 0.343 and -0.448 e.Å-3 ______

136 1 5 + - Table 2.37. Selected Bond Lengths [Å] for [(h -C5Me5)(h -C5Me5)Ga] [AlCl4] (17)

C(11)-C(15) 1.500(4) C(22)-C(23) 1.430(5) C(11)-C(12) 1.506(4) C(22)-Ga(1) 2.192(3) C(11)-Ga(1) 1.996(3) C(23)-C(24) 1.417(4) C(12)-C(13) 1.344(4) C(23)-Ga(1) 2.385(3) C(13)-C(14) 1.475(4) C(24)-C(25) 1.420(4) C(14)-C(15) 1.351(4) C(24)-Ga(1) 2.395(3) C(21)-C(25) 1.451(4) C(25)-Ga(1) 2.219(3) C(21)-C(22) 1.447(5) C(21)-Ga(1) 2.097(3)

1 5 + - Table 2.38. Selected Bond Angles [°] for [(h -C5Me5)(h -C5Me5)2Ga] [AlCl4] (17)

C(15)-C(11)-C(12) 103.9(3) C(231)-C(23)-Ga(1) 128.7(2) C(15)-C(11)-C(111) 114.1(3) C(23)-C(24)-Ga(1) 72.4(2) C(12)-C(11)-C(111) 114.9(2) C(25)-C(24)-Ga(1) 65.4(2) C(15)-C(11)-Ga(1) 103.8(2) C(241)-C(24)-Ga(1) 129.5(2) C(12)-C(11)-Ga(1) 104.2(2) C(24)-C(25)-Ga(1) 79.0(2) C(111)-C(11)-Ga(1) 114.5(2) C(21)-C(25)-Ga(1) 65.9(2) C(25)-C(21)-Ga(1) 75.0(2) C(251)-C(25)-Ga(1) 124.8(2) C(22)-C(21)-Ga(1) 73.9(2) Cl(1)-Al-Cl(4) 112.06(6) C(211)-C(21)-Ga(1) 125.4(2) Cl(1)-Al-Cl(2) 110.66(6) C(23)-C(22)-Ga(1) 79.3(2) Cl(1)-Al-Cl(3) 110.04(5) C(21)-C(22)-Ga(1) 66.8(2) C(11)-Ga(1)-C(21) 174.20(12)

137

1 Figure 2.14. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×THF (19) showing the atom numbering scheme.

138 Table 2.39. Crystal Data and Structure Refinement for CGCAlMe·THF (19)

Identification code z

Empirical formula C20 H38Al N O Si Formula weight 363.25 Temperature 213(2) K Wavelength 0.71073 Å Crystal system Orthorhombic Space group Fdd2 Unit cell dimensions a = 33.429(10) Å a= 90°. b = 34.035(9) Å b= 90°. c = 7.939(2) Å g = 90°. Volume 9033.0(43) Å3 Z 20 Density (calculated) 1.069 Mg/m3 Absorption coefficient 0.150 mm-1 F(000) 3200 Crystal size 0.08 x 0.15 x 0.15 mm3 Theta range for data collection 1.71 to 27.51°. Index ranges -42<=h<=42, -42<=k<=34, -10<=l<=5 Reflections collected 13902 Independent reflections 3879 [R(int) = 0.0504] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3879 / 1 / 267 Goodness-of-fit on F2 0.900 Final R indices [I>2sigma(I)] R1 = 0.0367, wR2 = 0.0741 R indices (all data) R1 = 0.0652, wR2 = 0.0791 Absolute structure parameter 0.89(14) Extinction coefficient 0.00001(3) Largest diff. peak and hole 0.231 and -0.174 e.Å-3 ______

139 Table 2.40. Selected Bond Lengths [Å] for CGCAlMe·THF (19)

Si(1)-N(1) 1.734(2) C(2)-C(1) 1.484(3) Si(1)-C(2) 1.876(3) C(1)-C(5) 1.451(3) Al(1)-N(1) 1.838(2) C(1)-C(9) 1.538(4) Al(1)-O(1) 1.891(2) C(3)-C(4) 1.439(4) Al(1)-C(16) 1.988(3) C(5)-C(4) 1.370(4) Al(1)-C(1) 2.071(3) N(1)-C(12) 1.474(3) Al(1)-C(2) 2.495(3)

Table 2.41. Selected Bond Angles [°] for CGCAlMe·THF (19)

N(1)-Si(1)-C(2) 97.36(10) C(3)-C(2)-Si(1) 132.4(2) C(10)-Si(1)-C(2) 112.83(12) C(1)-C(2)-Si(1) 118.4(2) N(1)-Al(1)-O(1) 107.60(9) C(3)-C(2)-Al(1) 114.8(2) N(1)-Al(1)-C(16) 124.06(11) C(1)-C(2)-Al(1) 56.04(12) O(1)-Al(1)-C(16) 101.98(12) Si(1)-C(2)-Al(1) 80.37(9) N(1)-Al(1)-C(1) 102.46(10) C(5)-C(1)-C(9) 120.1(2) O(1)-Al(1)-C(1) 110.46(10) C(2)-C(1)-C(9) 122.8(2) C(16)-Al(1)-C(1) 110.09(12) C(5)-C(1)-Al(1) 112.6(2) N(1)-Al(1)-C(2) 75.85(9) C(2)-C(1)-Al(1) 87.50(15) O(1)-Al(1)-C(2) 95.43(9) C(9)-C(1)-Al(1) 102.3(2) C(16)-Al(1)-C(2) 146.51(11) C(12)-N(1)-Al(1) 126.4(2) C(1)-Al(1)-C(2) 36.46(9) Si(1)-N(1)-Al(1) 106.36(11) C(12)-N(1)-Si(1) 126.74(15) C(18)-C(19)-C(20) 107.5(4) C(19)-C(18)-C(17) 106.9(3)

140

1 Figure 2.15. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlMe·carbene (21) showing the atom numbering scheme.

141 Table 2.42. Crystal Data and Structure Refinement for CGCAlMe·Carbene (21)

Identification code shelx

Empirical formula C23 H42 Al N3 Si Formula weight 415.67 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Orthorhombic

Space group Pc21b Unit cell dimensions a = 8.886(5) Å a= 90.000(5)°. b = 14.301(5) Å b= 90.000(5)°. c = 19.386(5) Å g = 90.000(5)°. Volume 2463.5(18) Å3 Z 4 Density (calculated) 1.121 Mg/m3 Absorption coefficient 0.144 mm-1 F(000) 912 Crystal size 0.3 x 0.3 x 0.2 mm3 Theta range for data collection 3.11 to 30.46°. Index ranges -11<=h<=12, -18<=k<=18, -26<=l<=25 Reflections collected 21560 Independent reflections 6378 [R(int) = 0.0779] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6378 / 1 / 262 Goodness-of-fit on F2 1.123 Final R indices [I>2sigma(I)] R1 = 0.0833, wR2 = 0.1222 R indices (all data) R1 = 0.1177, wR2 = 0.1327 Absolute structure parameter 0.12(16) Largest diff. peak and hole 0.502 and -0.352e.Å-3 ______

142 Table 2.43. Selected Bond Lengths [Å] for for CGCAlMe·Carbene (21)

C(1)-Al 2.041(3) C(41)-Al 2.053(3) C(11)-C(15) 1.410(5) N(1)-Si 1.737(3) C(11)-C(12) 1.478(4) N(1)-Al 1.853(3) C(11)-Si 1.872(3) C(12)-Al 2.166(3) C(11)-Al 2.390(3) C(13)-C(14) 1.381(5) C(12)-C(13) 1.439(4) C(14)-C(15) 1.422(4) C(31)-N(1) 1.482(4)

Table 2.44. Selected Bond Angles [°] for CGCAlMe·Carbene (21)

C(15)-C(11)-C(12) 106.5(3) C(31)-N(1)-Si 126.4(2) C(15)-C(11)-Si 132.2(2) C(31)-N(1)-Al 128.5(2) C(12)-C(11)-Si 119.1(2) Si-N(1)-Al 103.97(13) C(15)-C(11)-Al 108.2(2) N(1)-Al-C(1) 115.92(12) C(12)-C(11)-Al 63.1(2) N(1)-Al-C(41) 113.11(13) Si-C(11)-Al 82.22(12) C(1)-Al-C(41) 107.19(13) C(13)-C(12)-C(11) 106.2(3) N(1)-Al-C(12) 103.34(12) C(13)-C(12)-C(121) 122.9(3) C(1)-Al-C(12) 105.60(11) C(11)-C(12)-C(121) 125.8(3) C(41)-Al-C(12) 111.43(13) C(13)-C(12)-Al 107.8(2) N(1)-Al-C(11) 77.32(11) C(11)-C(12)-Al 79.5(2) C(1)-Al-C(11) 142.09(11) C(121)-C(12)-Al 103.7(2) C(41)-Al-C(11) 98.06(13) C(14)-C(13)-C(12) 109.2(3) C(12)-Al-C(11) 37.45(11) C(13)-C(14)-C(15) 108.9(3) N(1)-Si-C(11) 96.00(13) C(11)-C(15)-C(14) 109.2(3)

143

1 Figure 2.16. Molecular structure of [Me2Si(h -C5Me4)(N-t-Bu)]AlCl·OEt2 (24) showing the atom numbering scheme.

144

Table 2.45. Crystal Data and Structure Refinement for CGCAlCl·Et2O (25)

Identification code avjoh08

Empirical formula C19 H37 Al Cl N O Si Formula weight 386.02 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Orthorhombic Space group Pbca Unit cell dimensions a = 15.5558(9) Å a= 90°. b = 16.5146(12) Å b= 90°. c = 17.6755(9) Å g = 90°. Volume 4540.8(5) Å3 Z 8 Density (calculated) 1.129 Mg/m3 Absorption coefficient 0.266 mm-1 F(000) 1680 Crystal size 0.5 x 0.3 x 0.3 mm3 Theta range for data collection 2.14 to 25.00°. Index ranges -1<=h<=18, -1<=k<=19, -1<=l<=21 Reflections collected 4924 Independent reflections 3992 [R(int) = 0.0518] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3990 / 0 / 218 Goodness-of-fit on F2 1.098 Final R indices [I>2sigma(I)] R1 = 0.0802, wR2 = 0.2008 R indices (all data) R1 = 0.1655, wR2 = 0.2847 Extinction coefficient 0.0064(11) Largest diff. peak and hole 0.452 and -0.452 e.Å-3

145 Table 2.46. Selected Bond Lengths [Å] for CGCAlCl·Et2O (25)

Al(1)-N(1) 1.806(5) C(3)-C(4) 1.433(9) Al(1)-O(1) 1.873(5) C(5)-C(4) 1.358(9) Al(1)-C(1) 2.037(7) Si(1)-C(2) 1.869(6) Al(1)-Cl(1) 2.162(3) C(1)-C(5) 1.442(8) Al(1)-C(2) 2.448(6) C(1)-C(2) 1.487(8) Si(1)-N(1) 1.727(5) C(2)-C(3) 1.393(8)

Table 2.47. Selected Bond Angles [°] for CGCAlCl·Et2O (25)

N(1)-Al(1)-O(1) 112.1(2) C(11)-C(1)-Al(1) 104.4(4) N(1)-Al(1)-C(1) 104.8(2) C(3)-C(2)-Al(1) 115.6(4) O(1)-Al(1)-C(1) 113.5(2) C(1)-C(2)-Al(1) 56.2(3) N(1)-Al(1)-Cl(1) 117.0(2) Si(1)-C(2)-Al(1) 80.4(2) O(1)-Al(1)-Cl(1) 100.0(2) C(5)-C(4)-C(3) 109.1(6) C(1)-Al(1)-Cl(1) 109.6(2) Si(1)-N(1)-Al(1) 105.9(3) N(1)-Al(1)-C(2) 76.8(2) C(12)-Si(1)-Al(1) 129.7(3) O(1)-Al(1)-C(2) 102.9(2) C(5)-C(1)-C(11) 120.2(6) C(1)-Al(1)-C(2) 37.3(2) C(2)-C(1)-C(11) 121.4(5) Cl(1)-Al(1)-C(2) 145.8(2) C(5)-C(1)-Al(1) 113.4(4) N(1)-Si(1)-C(2) 96.7(2) C(2)-C(1)-Al(1) 86.5(4) C(12)-Si(1)-C(2) 112.3(3)

146

6 5 6 + Figure 2.28. Molecular structure of [(h -C7H8)In(m-h -C5Me5)In(h -C7H8)] - [HOB2(C6F5)6] (26) showing the unit cell contents. The fluorine atoms not shown.

6 5 6 + + Figure 2.29. Molecular structure of [(h -C7H8)In(m-h -C5Me5)In(h -C7H8)] [26] showing the C5Me5 numbering scheme and the bent geometry.

147 6 5 Table 2.48. Crystal Data and Structure Refinement for [(h -C7H8)In(m-h - 6 + - C5Me5)In(h -C7H8)] [(C6F5)3BO(H)B(C6F5)3] (27) Identification code d

Empirical formula C69.50 H40 B2 F30 In2 O Formula weight 1712.28 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/c Unit cell dimensions a = 16.042(3) Å a= 90°. b = 20.771(4) Å b= 107.74(3)°. c = 21.165(4) Å g = 90°. Volume 6716.6(23) Å3 Z 4 Density (calculated) 1.693 Mg/m3 Absorption coefficient 0.814 mm-1 F(000) 3372 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data collection 2.91 to 27.48°. Index ranges -20<=h<=20, -26<=k<=26, -27<=l<=27 Reflections collected 25963 Independent reflections 15133 [R(int) = 0.0259] Absorption correction None Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 15127 / 0 / 973 Goodness-of-fit on F2 1.395 Final R indices [I>2sigma(I)] R1 = 0.0417, wR2 = 0.1150 R indices (all data) R1 = 0.0590, wR2 = 0.1268 Extinction coefficient none Largest diff. peak and hole 1.147 and -0.844 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x,-y+2,-z 148 6 5 6 Table 2.49. Selected Bond Lengths [Å] for [(h -C7H8)In(m-h -C5Me5)In(h - + - C7H8)] [C6F5)3BO(H)B(C6F5)3] (27)

2 In(1)-C(h -C5Me5) av 2.807(3) In(1)-X(Tol1) 2.528(4)

In(1)-C(Tol1) av 3.752(3) In(1)-X(C5Me5) 3.490(4)

In(2)-C(C5Me5) av 2.722(3) In(2)-X(C5Me5) 2.435(4) In(2)-C(Tol2) av 3.598(3) In(2)-X(Tol2) 3.325(4) B-C av 1.646(4) .B-O av 1.559(4)

6 5 6 Table 2.50. Selected Bond Angles [°] for [(h -C7H8)In(m-h -C5Me5)In(h - + - C7H8)] [(C6F5)3BO(H)B(C6F5)3] (27)

X(1A)-In(1)-X(1B) 124.4(4) In(1)-X(1A)-In(2) 176.0(4) X(1A)-In(2)-X(1C) 130.3(4) B(1)-O-B(2) 141.1(2)

149 Table 2.51. CpSn Calculations at the B3LYP34/A67,68 Level of Theory

Symmetry Energy (au) M-X t M-X b M-X b -M X t-M-X b Dihedral + CpSn C5v -196.6881022 2.196 Cp2Sn C2v -390.4229961 2.504 149.9 + [CpSnCpSnCp] C1 -587.1545468 2.331 2.773 178.0 148.9 61.0

DH (kcal/mol) + + CpSn + Cp2Sn ® [Cp3Sn2] -27.26

Average Bond (kcal/mol) Energies

[CpSnCp-SnCp]+ 36.63 [CpSnCpSn-Cp]+ 265.32 † Cp = cyclopentadienyl, C5H5

69 67, 68 Table 2.52. CpIn and C6H6In Calculations at the BP86 /A Level of Theory

Symmetry Energy (au) M-X t M-X b M-X b -M X t-M-X b Dihedral In+ -1.6620558 † CpIn C5v -195.4527391 2.328 + [InCpIn] D5h -197.1866895 2.515 180

DH (kcal/mol) CpIn + In+ ® [InCpIn]+ -45.11

Symmetry Energy (au) M-X t M-X b M-X b -M X t-M-X b Dihedral C6H6 D6h -232.2333777 + [(C6H6)In] C6v -233.9481026 2.621

DH (kcal/mol) + + C6H6 + In ® [C6H6-In] -33.05

Symmetry Energy (au) M-X t M-X b M-X b -M X t-M-X b Dihedral [(C6H6)InCpI C1 -661.685627 3.069 2.591 176.3 143.3 23.5 + n(C6H6)]

DH (kcal/mol) 2 C6H6 + [(C6H6)InC -20.19 + + [InCpIn] ® pIn(C6H6)] (kcal/mol) Average (kcal/mol) Bond Energies

[(C6H6)InCpI 6.64 + n-(C6H6)] [(C6H6)InCp- 42.36 + In(C6H6)] † Cp = cyclopentadienyl, C5H5

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154

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A. Chem. Commun., 2001, 2, 175-176.

(42) See, for example: Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345.

(43) For a discussion of C6F5 transfer reactions, see e.g. Dioumaev, V. K.;

Harrod, J. F. Organometallics. 1997, 16, 2798.

(44) Shapiro, P. J.; Burns, C. T. Abstract INOR 329, 218th ACS National

Meeting, New Orleans, LA August 22-26, 1999.

(45) Fisher, J. D.; Wei, M.-Y.; Willett, R.; Shapiro, P. J. Organometallics 1994,

13, 3324.

(46) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson, B. G.;

Robb, M. A.; Cheeseman, J. R.; Keith, T. A.; Petersson, G. A.; Montgomery,

J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrewski, V. G.; Ortiz, J. V.;

Foresman, J. B.; Cioslowski, J.; Stefanow, B. B.; Nanayakkara, A.;

Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;

Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;

Binkley, J. S.; DeFrees, D. J.; Baker, J.; Stewart, J. P.; Head-Gordon, M.;

Gonzalez, C.; Pople, J. A. GAUSSIAN 94 (Revision B.2) (Gaussian, Inc.;

Pittsburgh PA, 1995).

(47) Basis sets: 6-31G* for C and H, 6-31+G* for Al.

155

(48) Shapiro, P. J.; Bunel, E. E.; Schaefer, W. P.; Bercaw, J. E. Organometallics

1990, 9, 867; Shapiro, P. J.; Cotter, W. D.; Schaefer, W. P.; Labinger, J.;

Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623.

(49) See, for example, Chen, Y.-X.; Stern, C. L.; Yang, S.; Marks, T. J. J. Am.

Chem. Soc. 1996, 118, 12451; Chen, Y.-X.; Marks, T. J. Organometallics

1997, 16 , 3649; Woo, T. K.; Margl, P. M.; Lohrenz, J. C. W.; Blochl, P. E.;

Ziegler, T. J. Am. Chem. Soc. 1996, 118, 13021.

(50) Canich, J. M.; Hlatky, G. G.; Turner, H. W. PCT Appl. WO 92-00333, 1992;

Canich, J. M. Eur. Patent Appl. EP 420 436-Al 1991; Stevens, J. C.

Timmers, F. J.; Wilson, D. R. Schmidt, G. F.; Nickias, P. N.; Rosen, R. K.;

Knight, G. W.; Lai, S. Eur. Patent Appl. EP 416 815-A2, 1991.

(51) Strickler; J. R; Power; J. M.; U.S. Patent 5,359,105, 1994.

(52) Okuda, J.; Eberle, T. Chapter 7 in Metallocenes; Togni, A.; Halterman, R. L.

Eds., Wiley-VCH, 1997.

(53) DFT calculations indicate that the geometry-optimized structures involve

ç3-attachment of the cyclopentadienyl ring.

(54) Kuhn, N.; Kratz, T. Synthesis 1993, 561.

(55) (a) Beswick, M. A.; Gornitzka, H.; Kärcher, J.; Mosquera, M. E. G.; Palmer,

J. S.; Raithby, P. R.; Russell, C. A.; Stalke, D.; Steiner A.; Wright, D. S.

Organometallics, 1999, 18, 1148, and references therein. (b) Armstrong, D.

R.; Edwards, A. J.; Moncrieff, D.; Paver, M. A.; Raithby, P. R.; Rennie, M.-

156

A.; Russell C. A.; Wright, D. S. J. Chem. Soc., Chem. Commun., 1995, 927.

(c) Beswick, M. A.; Palmer J. S.; Wright, D. S. Chem. Soc. Rev., 1998, 27,

225.

(56) Harder S.; Prosenc, M. H. Angew. Chem., Int. Ed. Engl., 1996, 35, 97.

(57) Cowley, A. H.; Macdonald, C. L. B.; Silverman, J. S.; Gorden, J. D.; Voigt,

A. Chem. Commun., 2001, 175.

(58) (a) Dory T. S.; Zuckerman, J. J. J. Organomet. Chem., 1985, 281, C1; (b)

Kohl, F. X.; Jutzi, P. Chem. Ber., 1981, 114, 488; (c) Jutzi, P.; Kohl, F.;

Hofmann, P.; Krüger, C.; Tsay, Y.-H. Chem. Ber., 1980, 113, 757.

(59) Jutzi, P.; Hielscher, B. Organometallics, 1986, 5, 1201.

(60) Dioumaev, V. K; Harrod, J. F. Organometallics, 1997, 16, 2798.

(61) (a) Tebbe, K.-F.; Gilles, T; Conrad F.; Tyrra, W. Acta Cryst. C., 1996, C 52,

1663, (b) Danopoulos, A. A.; Galsworthy, J. R.; Green, M. L. H.; Cafferkey,

S.; Doerrer, L. H.; Hursthouse, M. B. Chem. Comm., 1998, 2529.

(62) (a) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc. London

1963, 212; (b) Massey, A. G.; Park, A. J. J. Organomet. Chem., 1964, 2,

245; (c) Massey, A. G.; Park, A. J. J. Organomet. Chem., 1966, 5, 218.

(63) Doerrer, L. H.; Green, M. L. H. J. Chem. Soc., Dalton Trans., 1999, 4325.

(64) (a) Ebenhöch, J.; Müller, G.; Riede, J.; Schmidbaur, H. Angew. Chem. Int.

Ed. Engl., 1984, 23, 386; (b) Schmidbaur, H. Angew. Chem., Int. Ed. Engl.,

1985, 24, 893.

157

(65) Quindt, V.; Saurenz, D.; Schmitt, O.; Schlär, M.; Dezember, T.;

Wolmershäuser, G.; Sitzmann, H. J. Organomet. Chem. 1999, 579, 376.

(66) Sheldrick, G. M., SHELXTL PC Version 5.0, Siemens Analytical X-ray

Instruments, Inc., 1994.

(67) 6-31G* for C and H, E(h-C5H5) and (3s3p1d) basis sets of for In and Sn.

(68) Bergner, A.; Dolg, M.; Kuechle, W.; Stoll, H.; Preuss, H. Mol. Phys., 1993,

80, 1431.

(69) (a) Becke, A. D. J. Chem. Phys., 1993, 98, 5648. (b) Becke, A. D. Phys. Rev.

A, 1988, 38, 3098. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B, 1988, 37,

785. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys., 1980, 58, 1200.

158

CHAPTER 3

Reactions with Monovalent Group 13 Cyclopentadienides

Introduction

The most common oxidation state of the group 13 elements is +III, although others are possible, including +I and +II. Consistent with periodic trends, the lower oxidation state +I, is favored for the heavier elements (In, Tl), whereas the chemistry of the lighter elements is dominated by the higher oxidation state +III.

For this reason M(I) compounds (M = B, Al, Ga) are rare.1

It has been well established that for thallium the +I oxidation state is predominant both solution and solid state.2 For example, the monohalides of thallium are prepared by oxidation of Tl metal with aqueous HX because, under these conditions, Tl(I) is stable with regard to disproportionation to Tl(III) and

Tl(0).3 In contrast, the monohalides of the lighter homologues (Al, Ga) are oxidized under these conditions, producing H2 and the corresponding oxide/hydroxide.

While there are no aluminum monohalides that are stable at room temperature, recent developments have led to the isolation of the first solvent-stabilized complexes.4 Although such species have been identified in the gas phase or via matrix isolation,1 the lack of room temperature stable aluminum(I) species can be 159 attributed to their instability with respect to disproportionation.

While there are many possible ways to produce monovalent metal halides of aluminum (Schemes 3.1-3.3), these reactions require synthesis temperatures in excess of 800 °C in order to suppress the formation of the thermodynamically favored trihalide. The gaseous monovalent metal halides are stabilized by quenching and co-condensing with a suitable non-reactive donor solvent such as

M + HX MX + 1/2 H Scheme 3.1 2 2M + X 2MX Scheme 3.2 2 2M + MX 3MX Scheme 3.3 3

Et2O or NEt3 at 77K. This synthetic method led to the formation of [Al4Br4(NEt3)4], the first monovalent aluminum halide complex to be structurally characterized by

X-ray diffraction methods.5 The production of these monohalides is of particular importance because they can be used as precursors for the synthesis of other novel low-valent aluminum compounds.6

In general, the synthesis of organometallic M(I) compounds of aluminum and gallium has been accomplished by two methods: (i) metathetical reactions of dissolved M(I) halides, and (ii) by the reduction of suitable M(III) precursors.4

While the substitution reactions of dissolved monovalent halides can be carried out under mild conditions, complex experimental procedures are necessary to effect purification of the products. Processes based on the reduction of M(III) compounds, while not requiring specialized equipment, are best carried out at elevated 160 temperatures, which makes this method unsuitable for the synthesis of thermally sensitive molecules.6

Cp*

Al toluene Cp* 4[AlCl] + 4[MgCp*2] Al Al + 2[MgClCp*(Et2O)]2 Al Et2O Cp* Cp* 1 5 Scheme 3.4. Synthesis [(h -C5Me5)2Al]4 from monovalent AlCl and decamethyl- magnesocene

In 1991 the first example of an Al(I) organometallic compound stable at room temperature was produced via reaction of the monohalide complex

5 7 [AlCl·Et2O]4 with [Mg(h -C5Me5)2] in toluene solution. (Scheme 3.4) The

5 structure of [(h -C5Me5)Al]4 was determined by X-ray diffraction and shown to be tetrameric in the crystalline state. Individual molecules consist of Al4 tetrahedra and each aluminum is bonded to a pentamethylcyclopentadienyl group in a pentahapto fashion (1). An alternative synthetic method for 1 that involves the potassium metal reduction of [AlCl2(h-C5Me5)]2 (Scheme 3.5) was published two years later by

Roesky et al.8 This method, which does not require the use of specialized apparatus, made this interesting compound more readily available for use by the organometallic chemist. Even so, the method suffers from some impurity contamination and low yields (~20%) due to the fact that a temperature of 100°C is needed for the reduction reaction. More recently, Jutzi et al.9 have reported higher yields of 1 by using AlI3 in place of Al2Cl6 and by sonication of the resulting Al(h- 161 C5Me5)I2 with molten potassium in toluene solution. The Jutzi et al. method can also be employed for the synthesis of the analogous gallium(I) compound, [(h5-

C5Me5)Ga]6.

Cp*

Al -4ClSiMe 3 +8K/-8KCl Al Al Cp* 2Al2Cl6 + 4Cp*SiMe3 2[AlCl2Cp*]2 Cp* Al hexanes toluene 1 Cp* 5 Scheme 3.5. Synthesis [(h -C5Me5)Al]4 by the alkali metal reduction method

27 5 Dynamic Al NMR studies indicate that [(h -C5Me5)Al]4 undergoes

5 reversible dissociation to the corresponding monomer, [(h -C5Me5)Al], in toluene solution.10 Raising the temperature from 40°C to 120°C results in a progressive decrease in the signal at d 80 due to the tetramer and the emergence and concomitant increase of signal at d 150 that is attributable to the monomer. The foregoing spectral changes are reversible, leading to the conclusion that the tetramer-monomer dissociation process is reversible. Comparable experiments with

5 the analogous gallium and indium hexamers, [(h -C5Me5)M]6, reveal that they are also weakly bonded and undergo reversible dissociation in solution (Figure 3.1).

This tendency for pentamethylcyclopentadienyl-substituted clusters of the

5 type [(h -C5Me5)M]n (M = Al, Ga, In) to undergo dissociation into stable monomers under mild conditions renders them unique among other monovalent group 13 species. Thus, the cyclopentadienyl-substituted tetramer, [(C5H5)Al]4 is extremely unstable and undergoes disproportionation at temperatures above -60°C within a 162 10 few seconds. On the other hand, the boron tetramer, [t-BuB]4 does not undergo conversion to the corresponding monomer due to the presence of strong boron- boron bonds.11

5 Figure 3.1. Molecular structure of [(h -C5Me5)In]6 showing the octahedral In6 core.

5 In the crystalline state, [(h -C5Me5)Al]4 is relatively unreactive toward dry air because the tetrameric metal core is well shielded by the

5 pentamethylcyclopentadienyl ligands. In solution however, [(h -C5Me5)Al] is readily oxidized upon exposure to air, and complete decomposition occurs within

5 minutes. Furthermore, toluene solutions of [(h -C5Me5)Al]4 are stable up to 110°C

(although disproportionation occurs after several days at this temperature).12 The

5 forgoing properties make [(h -C5Me5)Al]4 an extremely valuable starting material 163 for the synthesis and study of new organoaluminum compounds and other low valent aluminum species. Furthermore, recent theoretical studies13 indicate the RM fragments (R = C5H5; M = B, Al, Ga) are analogous to phosphines, singlet carbenes12, and borylenes14 in the sense that they possess pyramidal geometries and exhibit distinctly lone pair (s-type) character, (Figure 3.2). It is not surprising then, given their similarities to singlet carbenes, that group 13 monomers of the type [(h5-

5 C5Me5)M] will undergo similar insertion reactions. The most explored area of [(h -

C5Me5)M]n chemistry has been its reactions with the Group 15 and 16 elements.

5 15 For example, when [(h -C5Me5)Al] (1) is treated with P4, 2 is produced and heterocubanes [(C5Me5Al)4E4] (3) are formed when 1 is combined with elemental

S,6 Se,8 or Te.8 Furthermore, the corresponding reactions with elemental As and Sb have been shown to yield heteropolyhederal structures of type 4. 16,17

Figure 3.2. Three dimensional representation of lone pair molecular orbital of 5 (h -C5H5)Al.

164 Cp* Cp* E Al Cp* E Al P AlCp* Al E AlCp* P Cp* Al E Cp*Al Cp*Al AlCp* Cp*Al P E Al Cp*Al P Al Cp* E Cp* (E = S, Se, Te) (E = As, Sb) 2 3 4

Four general methods have been developed for the synthesis of organoaluminum compounds: (i) metathetical reactions of metal alkyls and aluminum halides (Scheme 3.6), (ii) mercury displacement reactions (Scheme 3.7),

(iii) hydroalumination of unsaturated hydrocarbons (Scheme 3.8), and (iv) dehalogenation of organoaluminum sesquihalides (Scheme 3.9).3 It is interesting however, that only the first of these methods involves a univalent aluminum reagent.

5 Clearly, the synthetic potential of such species in general, and [(h -C5Me5)Al]4 in particular, has been under-utilized and therefore represents an area of challenge.

This comment applies equally well to the chemistry of the heavier congeneric

5 5 pentamethylcyclopentadienyl clusters [(h -C5Me5)Ga]6 and [(h -C5Me5)In]6.

3RM + AlX3 AlR3 + 3MX Scheme 3.6

2Al + 3R2Hg 2AlR3 + 3Hg Scheme 3.7

2Al + 3H2 + 6CH2=CR2 2Al(CH2CR2)3 Scheme 3.8

Na 3RX + 2Al R2AlX + RAlX2 2AlR3 + Al Scheme 3.9 -NaCl

165 The present chapter is divided into four sections, each of which is concerned with the synthesis and study of a different type of [(C5Me5)M] chemistry. In the first section, theresults obtained in the area of [4+2] cycloaddition chemistry will be

5 discussed. The second section is devoted to the study of [(h -C5Me5)Al] donor- acceptor complexes, while the third section addresses the corresponding donor-

5 acceptor complexes derived from [(h -C5Me5)Ga]. The final section is concerned

5 with the preliminary results of a study of the reaction of [(h -C5Me5)In]6 with

5 B(C6F5)3 and the consequent formation of the [(h -C5Me5)In2][B(C6F5)4], a pentamethylcyclopentadienyl half- featuring the first example

6 - of h -bonding to the perfluorophenyl groups of [B(C6F5)4] .

166

Section 3.1

Cycloadditions

Introduction

As pointed out above, low valent aluminum and gallium compounds are of current interest, and the most readily available aluminum(I) and gallium(I) compounds are (h5-pentamethylcyclopentadienyl)aluminum and –gallium analogue, which in the crystalline state are tetrameric and hexameric, respectively. The use of

5 5 [(h -C5Me5)Al]4 and [(h -C5Me5)Ga]6 as precursors for the preparation of novel organometallic complexes has only received scant attention.6,18 The objective of this section is to discuss the oxidative addition reactions of these compounds, which resulted in the formation of new three-coordinate organometallic species. To this

5 5 end, [(h -C5Me5)Al]4 and [(h -C5Me5)Ga]6 were allowed to react with a series of conjugated organic substrates, including 1,3-dienes, ortho-quinones, and diazabutadienes.19

167 R R Al N N + Cp*Al

N N

R R 1 5 6

Results and Discussion

It has been known for several years that N-heterocyclic carbenes will add to conjugated organic systems to form cyclic products. Since monovalent [(h5-

5 C5Me5)Al] and [(h -C5Me5)Ga] are isolobal with a singlet carbene it was therefore anticipated that similar reactivities toward conjugated systems will be observed.

Indeed, studies by Schnöckel et al.,10 have shown that 1 reacts quantitively with 2,3- dimethyl-1,3-butadiene to produce compound 7 (Scheme 3.10). However, 7 was not suitable for X-ray analysis and the proposed structure was based solely on NMR spectroscopic data.

Cp*

Al toluene Al Al Cp* 4[Cp*Al] Cp*Al Cp* Al 1 Cp* 7 5 Scheme 3.10. Cycloaddition of 2,3 dimethyl-1,3-butadiene to [(h -C5Me5)Al]

In the present work, clean reactions with 1 were observed only in the case of diazabutadienes. Interest in group 13 diazabutadiene (DAB) complexes of the

168 general type 8 has been stimulated largely by their isoelectronic relationship to the corresponding silylenes20 and germylenes21 (9). Since both 8 and 9 feature six p- electrons, important questions arise regarding delocalization and possible aromatic character. Previous examples of type 8 (M = Al, Ga) have been stabilized by either dimerization or by intramolecular Lewis base intervention.22,23 The preceding examples were the products of metathetical processes based on the reaction of the dilithio derivatives of DAB with group 13 trihalides or organodihalides.23,24

Dimerization can be further avoided by providing an additional donor function to the organoaluminum or organogallium unit.23 The availability of stable organometallic compounds with a group 13 element in the formal oxidation state +I

5 led to a new synthetic approach, namely the oxidative addition of [(h -C5Me5)Al]

5 and [(h -C5Me5)Ga] species to diazabutadienes.

R R

N N

M R' M:

N N

R R

8 (M = Al, Ga) 9 (M = Si, Ge)

5 When t-BuN=CH-CH=Nt-Bu (t-BuDAB) was treated with [(h -C5Me5)Al]4 in toluene solution, the sole isolated product was the known free radical complex

[Al(t-BuDAB)2], 10, which was isolated as dark green crystals in 85% yield. Cloke,

169 Raston, and coworkers first isolated compound 10 by co-condensation of aluminum vapor and t-BuDAB or by treatment of t-BuDAB with a lithium aluminum hydride- aluminum powder mixture.25 Both approaches led to the formation of the homoleptic complex [Al(t-BuDAB)2] in moderate (~20%) yields. The formation of

10 most likely involves the reaction pathway shown in Scheme 3.11. The first step is a formal [4+2] cycloaddition leading to the oxidative addition product, 6. The

t-Bu t-Bu

Al N N + Al N N

t-Bu t-Bu

1 6

t-Bu t-Bu t-Bu N N N - Cp* Al +

N N N

t-Bu t-Bu t-Bu 10

5 Scheme 3.11. Cycloaddition of t-BuDAB using [(h -C5Me5)Al] yielding the known (t-BuDAB)2Al radical

170 · elimination of the [C5Me5] radical in the second step is facilitated by the high nucleophilicity of the nitrogen atoms of the t-BuDAB ligand augmented by the

· inductive effect of the t-butyl groups. The tendency for a [C5Me5] radical to behave

26 - as a leaving group has been well documented in the literature. The [C5Me5] anion

· and [C5Me5] radical are rather stable entities that can be eliminated easily under the

· appropriate conditions. In a single-electron reduction process, the [C5Me5] radical is eliminated, which then dimerizes to (C5Me5)2 or reacts via hydrogen transfer to

27 give C5Me5H and tetramethylfulvene. It was reasoned that the replacement of the tert-butyl substituents with electron-withdrawing phenyl groups would decrease the tendency toward C5Me5 elimination. Moreover, it was thought that the methyl groups of the bulky 1,4-bis(2,4,6-trimethylphenyl)-1,4-diazabuta-1,3-diene,

(Mes2DAB, 11), would afford a measure of kinetic stabilization. The reaction of

Mes Mes N N Mes N Al Toluene + 1/4 [Al(C5Me5)]4 25 ºC N 1

Mes 11 12 5 Scheme 3.12. Cycloaddition reaction of Mes2DAB using [(h -C5Me5)Al]

5 [(h -C5Me5)Al]4 with Mes2DAB takes place at 60°C in toluene solution and affords, upon work-up, yellow crystals of 12 (Scheme 3.12), isolated in 39% yield.

171 Elemental analysis and HRMS data for 12 correspond to the formula above. The 1H and 13C NMR spectra are consistent with the formation of a symmetrical ring and the development of a double bond between the ring carbon atoms. The equivalence

5 of the C5Me5 methyl groups down to -80 ºC is indicative of an h -bonding mode to aluminum. The 27Al NMR spectrum of 12 exhibits a single broad resonance at d =

45 which is within the region anticipated for tri-coordinate aluminum.28 However, for confirmation of the structure of 12, it was necessary to appeal to X-ray crystallography. (Figure 3.3)

5 Figure 3.3. Molecular structure of (Mes2DAB)Al(h -C5Me5) showing the numbering scheme.

X-ray Crystal Structure of 12

Compound 12 crystallizes in the monoclinic space group P21/n with four molecules in the unit cell. Figure 3.3 shows the molecular geometry together with

172 the numbering scheme. Details of the data collection, structure solution and refinement are compiled in Table 3.1 and selected metrical parameters are listed in

Tables 3.2 and 3.3. There are no unusually short contacts between individual molecules, thereby making 12 the first monomeric aluminum DAB compound. The pentamethylcyclopentadienyl group is h5-bonded to aluminum, as reflected by the near equivalence of the Al-C distances, and the fact that the AlN2C2 ring is essentially planar. Based on the C5Me5 ring centroid, the sum of angles at aluminum is approximately 360º. The nitrogen atoms also adopt a trigonal planar geometry and the mesityl rings are arranged such that they are approximately parallel to the C5Me5 ring.

Figure 3.4. Molecular structure of 1,4-bis(2,4,6-trimethylphenyl)-1,4-diazabuta- 1,3-diene (11) showing the atom numbering scheme.

The diazabutadiene, 11, crystallizes in the monoclinic space group P21/c with two molecules in the unit cell. Figure 3.4 shows the molecular geometry together with the numbering scheme. Details of the data collection, structure solution and refinement are compiled in Table 3.4 and selected metrical parameters are listed in Tables 3.5 and 3.6. In 11, the average carbon-nitrogen bond distance is

173 1.274(5) Å and the carbon-carbon bond distance is 1.467(7) Å. As illustrated in

Figure 3.4, the N-C-C-N backbone for compound 11 adopts a trans-type arrangement; while in 12 (Figure 3.3) the N-C-C-N backbone adopts a cis-type arrangement. In 12, the carbon-carbon bond distance of 1.331(2) Å and the average carbon-nitrogen bond distance of 1.406(2) Å, corresponding to bond orders of two and one, respectively. Furthermore, the average aluminum-nitrogen distance of

1.827(1) Å falls within the range anticipated for a single bond.29 The observed pattern of bond distances therefore points toward a relatively localized electronic structure.

The next logical step was to determine whether the heavier monovalent

5 group 13 species, namely [(h -C5Me5)Ga], would react with a diazabutadiene in a

5 similar fashion . When Mes2DAB was treated with [(h -C5Me5)Ga]6 under virtually identical conditions to those described above, the desired product 13 was formed

(Scheme 3.13). Unfortunately, despite several attempts, it was not possible to obtain crystals suitable for X-ray analysis. However, the 1H NMR and 13C NMR spectral data are similar to those for compound 12, demonstrating equivalence of the

Cp*-Me groups at room temperature, and a galladiazacyclopentene ring with a localized bond between the ring carbon atoms. Without a crystal structure, the hapticity of the C5Me5 ring could be determined due to rapid migratory processes involving the C5Me5 ring.

174 Mes Mes N N Mes N Ga Toluene + 1/6 [Ga(C5Me5)]6 25 ºC N

Mes 11 13 5 Scheme 3.13. Cycloaddition of Mes2DAB using [(h -C5Me5)Al]

Since the completion of the present work, Jutzi et al.30 have reported an X-

5 ray crystal structure for the product of the reaction of [(h -C5Me5)Ga]6 with 1,4- bis(2,6-diisopropylphenyl)-1,4-diazabuta-1,3-diene (DipDAB). In contrast to the h5 aluminum compound, 12, the C5Me5 ring of the Jutzi et al. product was found to be bonded to gallium in an h1(s) fashion. However, as in the case of 12, a localized electronic structure was observed for the DAB moiety. These authors also reported

5 that the reaction of t-BuDAB with [(h -C5Me5)Ga] resulted in formation of the

· known free radical [Ga[t-BuDAB]2] in high yields. Furthermore, the reactions of

5 1,4-bis(2,6-dimethylphenyl)DAB and 1,4-diisopropylDAB with [(h -C5Me5)Ga] resulted in the formation of red oils and only by the incorporation of isopropyl substituents on the phenyl rings were X-ray characterizable materials obtained.

175 Conclusions

The availability of stable organometallic compounds with a group 13 element in the formal oxidation state of +I has led to a new synthetic approach,

5 namely the oxidative addition of [(h -C5Me5)Al] to diazabutadienes. This approach resulted in the first example of a monomeric aluminum-containing heterocycle of the DAB type. Recently, this synthetic approach has been broadened to include the

5 gallium analogue, [(h -C5Me5)Ga]. X-ray crystal structure analysis revealed that the bonding within these new metallocycles can best be described as localized with respect to the N-C=C-N backbone. Previous examples of group 13 DAB complexes were stabilized by Lewis base interactions or by dimerizations involving the metal center.23,24 Consequently, localized bonding in the DAB moiety could be due to the absence of a properly oriented Al orbital to participate in ring delocalization. While the current examples are monomeric, with no extra donor function bound to the metal center, the aluminum atom appears to be planar and 3-coordinate when only the pentamethylcyclopentadienyl ring centroid is considered. While it is easy to visualize an empty aluminum p-orbital orthogonal to the metallocyclic plane, the

C5Me5 ring is indeed pentahapto and occupies the equivalent of three coordination sites. Most likely the putative empty p-orbital is rehybridized and becomes involved in s-bonding to the C5Me5 ring in much the same way as all Al valence s- and p-orbitals are used in s-bonding in the previous cases. Therefore, this overlap

176 of C5Me5 orbitals with the empty orbital on the group 13 metal centers makes aromaticicty unlikely.

5 The reactivity of DAB toward [(h -C5Me5)M] fragments is strongly dependent on the substituents on the nitrogen atoms. Furthermore, the reaction of

5 [(h -C5Me5)M] units with other isoelectronic species such as phenanthrenequinone and 3,5-di-tert-butyl-o-benzoquinone, under similar reaction conditions, failed to

5 give identifiable products. The reaction of [(h -C5Me5)Al] with t-BuDAB resulted

· in the formation of the known radical [Al[t-BuDAB]2] in high yield, thus providing an alternative synthetic method to the co-condensation technique used previously.

177

Section 3.2

Al(I) Donor-Acceptor Complexes

Introduction

5 5 Pentamethylcyclopentadienylaluminum and gallium ([(h -C5Me5)Al], [(h -

C5Me5)Ga]) were first prepared nearly a decade ago by Schnöckel et al. using metastable solutions of Al(I)Cl and Ga(I)Cl.4,7 It was not until the method based on

8 the reduction of (C5Me5)AlCl2 was developed by Roesky and coworkers, and later refinement of this process utilizing ultrasonic metal activation,9 that these species have become generally available to the synthetic chemist. Typically, RM species tend to aggregate into weakly bound tetrameric or hexameric entities; however, if a sufficient steric blockade is deployed, it is possible to isolate the monomeric derivatives. In solution, the resulting monomeric, carbene-like [(C5Me5)M] fragments have been shown to react with elemental P, S, Sb, Se and Te to form interesting cage compounds. Furthermore, these group 13 fragments will to add to transition metal multiple bonds as bridging ligands, displace other ligands from the coordination sphere to form strong group 13 element/transition metal bonds, and to undergo cycloaddition with conjugated organic molecules.

178 Theoretical studies of free and tetracarbonyliron-complexed group 13 diyls indicate that, regardless of the nature of the substituent R, the ground state of each four-valence-electron RM-(I) species is a singlet. In the particular case of [(h5-

C5Me5)Al], the DFT-calculated singlet-triplet energy gap lies between 67.6 and 70.9

5 kcal/mol, while for [(h -C5Me5)Ga] it is between 66.9 and 69.8 kcal/mol, depending

13 on the basis set employed. Accordingly, [(C5Me5)M] fragments are anticipated to exhibit Lewis base behavior due to the presence of a lone pair of electrons on the group 13 element center. However, while the reactivity of these fragments toward transition metal derivatives and the bonding in the resulting group 13/transition metal compounds have been investigated in some detail, such complexes do not exemplify pure Lewis base behavior due to the possibility of varying degrees of back donation on the part of the d-block element. This section is concerned with the synthesis and characterization of the first examples of compounds with group 13- group 13 donor-acceptor bonds.

Al + AlCl3 Al Cp*-AlCl3

5 Scheme 3.14. The reaction of [(h -C5Me5)Al] with halogenated Lewis acids

179 Results and Discussion

31 5 Previously, it has been reported that the reaction [(h -C5Me5)Al]4 with halogenated Lewis acids results in the formation of the aluminocenium cation via a

C5Me5 transfer reaction (Scheme 3.14). Accordingly, it was clear that it would be necessary to replace the halogens on the Lewis acid by more electronegative, less

32 labile substituents. Given the well-documented acceptor behavior of B(C6F5)3 this compound appeared to an ideal Lewis acid candidate.

Ar Ar Ar B Al

+ B(C6F5)3 Al

14 5 Scheme 3.15. Reaction of [(h -C5Me5)Al] with B(C6F5)3

5 Synthesis and characterization of (h -C5Me5)Al®B(C6F5)3 (14)

5 33 The reaction of [Al(h -C5Me5)]4 with B(C6F5)3 in a 1:4 mole ratio in toluene solution resulted, after workup, in a 40% yield of a colorless crystalline product of with a mass spectrum that corresponded to the composition (h5-

11 C5Me5)Al®B(C6F5)3 (Scheme 3.15). Moreover, the B NMR chemical shift for 14 fell in the tetracoordinate boron region and the 19F chemical shifts of the

(equivalent) C6F5 groups were similar to those observed for other Lewis base 180 34 27 complexes of B(C6F5)3. The Al NMR chemical shift of the broad singlet resonance of 14 (d -59) was reasonably close to the value of d -71.5 computed by the GIAO method35 and the equivalence of the methyl protons was suggestive of h5-

27 attachment of the Me5C5 group to aluminum. For comparison, the Al chemical

5 5 shifts for uncoordinated monomeric [(h -C5Me5)Al] and tetrameric [(h -C5Me5)Al]4 are d 80 and -150, respectively.6 The foregoing spectroscopic conclusions were confirmed by X-ray crystallography.

Compound 14 crystallizes in the P-1 space group with Z = 2; the crystalline state consists of individual molecules of the Lewis acid-base adduct (Figure 3.5) and there are no unusually short intermolecular contacts. Details of the data collection, structure solution and refinement are compiled in Table 3.7 and selected metrical parameters are listed in Tables 3.8 and 3.9. The C5Me5 group is attached to aluminum in an h5 fashion and the ring centroid-Al-B moiety is essentially linear

(172.9(1)°). The average Al-C distance of 2.171(3) Å is considerably shorter than

5 9 5 those determined for [(h -C5Me5)Al] (2.388(7) Å) and [(h -C5Me5)Al]4 (2.344(4)

Å).36 Such shortening is anticipated as the aluminum lone pair is transformed into the donor-acceptor bond with the concomitant development of partial positive and negative charges on aluminum and boron, respectively.

There is a very little information in the literature with which to compare the

Al-B bond distance of 14 (2.169(3) Å). In the hydride-bridged complexes

2 37 5 2 38 Me3NAl(h -H2BH2)3 and [h -C5H5)Ti(m2-H)2]2Al(h -H2BH2) the average Al-B

181 separations are 2.18(2) to 2.27(3) Å, respectively, while in a variety of aluminum- substituted carboranes, these distances range from ~2.13 to 2.24 Å.39 A DFT

40 5 calculation on the model compound (h -C5Me5)AlBH3 revealed that the global minimum possesses a “staggered” Cs geometry similar to that observed for 1 with a computed Al-B bond distance of 2.127 Å. As a consequence of donor action on the part of the alanediyl, the geometry of B(C6F5)3 changes from trigonal planar to distorted tetrahedral. The sum of bond angles at boron is 339.8(2)° and, to the extent that this geometrical change is a measure of the strength of the donor- acceptor interactions, it is interesting to note an almost identical sum of bond angles

34f in (C6H5)3PB(C6F5)3.

5 Figure 3.5. Molecular structure of (h -C5Me5)Al®B(C6F5)3 (14) showing the atom numbering scheme.

5 Synthesis and characterization of (h -C5Me5)Al®Al(C6F5)3 (16)

Compounds with aluminum-aluminum bonds are attracting considerable recent attention. The simplest such compounds are the dialanes, R2AlAlR2, and a 182 number of these have now been structurally authenticated.41 It therefore seemed reasonable that valence isomers of dialanes, viz. RAl®AlR3, might be capable of existence if the appropriate substituents were employed. DFT calculations42 on the prototypical dialane, H2AlAlH2, revealed that the valence isomer HAl®AlH3 (15), is less stable than H2AlAlH2 by 9.17 kcal/mol. (Scheme 3.16) However, replacement of one of the dialane hydride substituents by cyclopentadienide

5 2 inverted this order and (h -C5H5)Al®AlH3 (15) is more stable than the dialane (h -

C5H5)(H)Al®AlH2 by 10.8 kal/mol (Scheme 3.17). A summary of the theoretical calculations is presented in Table 3.10.

H H H Al Al H Al Al Scheme 3.16 H H H H DH = 9.2 kcal/mol

H H Al Al H H Al Al Scheme 3.17 H 15 H

DH = -10.8 kcal/mol

5 In view of the foregoing, [(h -C5Me5)Al]4 was treated with Al(C6F5)3

×toluene43 in a 1:4 mole ratio in toluene solution at 25 °C. Following workup and

5 recrystallization, an 80% yield of yellow crystalline (h -C5Me5)Al®Al(C6F5)3 was obtained. The mass spectral data for 16 were consistent with the proposed dialane

5 isomer formulation. Moreover, the presence of the [(h -C5Me5)Al] and Al(C6F5)3 183 moieties in 16 was evident from the 1H, 13C, and 19F NMR spectroscopic data, noting of course, that the equivalence of the C5Me5 ring carbon and Me resonances could be due to the well-known fluxional behavior of cyclopentadienyl-aluminum systems.44 The 27Al NMR spectrum of 16 comprised singlet resonances at d -115 and 106. Given that the 27Al chemical shifts for the model compound 15, as

35,42b 5 computed by the GIAO method, are d –107 and 109 for the [(h - C5Me5)Al] and AlH3 centers, respectively, analogous assignments have been made for 16.

Further support for the proposed assignments stems from the experimentally

27 5 6 observed Al chemical shifts for monomeric [(h - C5Me5)Al] (d -150) and

43 27 Al(C6F5)3•arene (d 52 (benzene); d 61 (toluene)). The overall trend of Al chemical shifts is consistent with the transfer of electron density from the alanediyl to the Al(C6F5)3 fragment upon formation of the Al®Al donor-acceptor bond of 16.

The above spectroscopic conclusions were confirmed by X-ray crystallography. Compound 16 crystallizes in the C2/c space group with Z = 8; the crystalline state consists of individual molecules of the dialane isomer (Figure 3.6) and there are no unusually short intermolecular contacts. Details of the data collection, structure solution and refinement are compiled in Table 3.11 and selected metrical parameters are listed in Tables 3.12 and 3.13. The pentamethylcyclopentadienyl substituent is attached to aluminum in an h5 fashion and the ring centroid-Al-Al moiety deviates only modestly from linearity

(170.1(3)°). The Al-Al bond length in 2 (2.591(3)Å) is shorter than those in the

184 35a i 35b dialanes {(Me3Si)2CH}4Al2 (2.660(1)Å), {2,4,6- Pr3C6H2}4Al2 (2.647(3)Å),

35c and {t-Bu3Si}4Al2 (2.751(2)Å but identical to that in [RIAl-AlClR] (R =

35d [(Me3Si)2C(Ph)C(Me3Si)N]) (2.593(2) Å) within experimental error. The average

Al(1)-C bond length of 2.178(7) Å (Al-centroid: 1.810 (8) Å) is considerably shorter

5 45 5 than those reported for [(h -C5Me5)Al] (2.388(7) Å) and [(h -C5Me5)Al]4 (2.344

Å, av Al-centroid: 2.011 Å).6 Such a shortening is anticipated as the partially

5 antibonding aluminum “lone pair” orbital of [(h -C5Me5)Al] is transformed into the donor-acceptor bond with the concomitant development of positive and negative charges on the aluminum centers.13 The same trend is evident for other group 13

5 46 (h -C5Me5)M®acceptor complexes and is true for both main-group and transition element acceptors.

5 Figure 3.6. Molecular structure of (h -C5Me5)Al®B(C6F5)3 (16) showing the atom numbering scheme.

185 3 Synthesis and characterization of (C6F5)2Al(h -C5Me5)

5 Interestingly, when [Al(h -C5Me5)]4 was treated with In(C6F5)3 using the same procedure as that described above for the B(C6F5)3 reaction, the product was

3 colorless, crystalline (C6F5)2Al(h -C5Me5) (17). It is possible that 17 was produced

5 via C6F5 transfer from the adduct (h -C5Me5)Al®In(C6F5)3. (Scheme 3.18) Such a view would be consistent with the modest In-C bond energy and the relative stability of the In(I) oxidation state. The proposed formulation for 17 was consistent with mass spectral data and the presence of C6F5 and C5Me5 groups was evident from 19F and 1H NMR spectroscopic data; however, to establish e.g. the hapticity of the cyclopentadienyl ring it was necessary to perform an X-ray crystal structure analysis.

Ar Ar Al Al + In(C6F5)3 + "In(C6F5)"

5 Scheme 3.18. Reaction of (h -C5Me5)Al with In(C6F5)3

Individual molecules of 17 crystallize in the orthorhombic space group Pnma with

Z = 4; there are no unusually short intermolecular contacts (Figure 3.7). Details of the data collection, structure solution and refinement are compiled in Table 3.14 and selected metrical parameters are listed in Tables 3.15 and 3.16. The C5Me5 group is attached to aluminum in an h3 fashion, a coordination mode that has been

3 reported previously only in the case of the dimers [(h -C5Me5)(R)Al-h-Cl]2 (R =

186 Me, i-Pr).47 The Al-C(11) and Al-C(12) bond distances are 1.672(3) and 2.067(3)

Å, respectively while the Al(1)-C(13) distance is 2.687 Å. The Al-C(1) distance of

2.018(3) Å in 17 is slightly longer than those in the THF (1.995(3) Å),48 benzene

43 43 (1.979(7) Å), and toluene (1.984(2) Å) complexes of Al(C6F5)3. Preliminary

3 spectroscopic evidence suggests that (h C5Me5)Al(C6F5)2 is the dominant product in

5 the reaction of [(h -C5Me5)Al] with Ga(C6F5)3.

3 Figure 3.7. Molecular structure of (h -C5Me5)Al(C6F5)2 (17) showing the atom numbering scheme.

Conclusions

The present results have a bearing on the current debate49 concerning the nature of the bonding between group 13 univalent ligands, RM, and transition metal carbonyl fragments, M'(CO)n. Much of the discussion has centered on whether the

187 bonding is of the donor-acceptor type, viz. RM®M'(CO)n, or whether M' to M back bonding is important as reflected by the canonical forms RMDM'(CO)n and RM

M'(CO)n. The isolation of 14 and 16 proves that an alanediyl can function as a pure donor ligand because there is no question of back bonding in these particular cases.

Moreover, the experimental structural parameters and the DFT-computed charge distribution and orbital occupancy for the alanediyl fragment3 are very similar to

5 those for the terminal alanediyl transition metal complexes (h -C5Me5)AlFe(CO)4

50 5 36 (av Al-C = 2.147(8) Å) and (h -C5Me5)AlCr(CO)5 (av Al-C = 2.183(2) Å) , thus suggesting the existence of the same donor-acceptor bonding mode in both cases.

5 Finally, it is noteworthy that (h -C5Me5)AlB(C6F5)3 (14) represents the first

5 example of an aluminum(I)-boron donor-acceptor bond and (h -C5Me5)AlAl(C6F5)3

(15) is the first valence isomer of a dialane to be reported.

188

Section 3.3

Ga(I) Donor-Acceptor Complexes

Introduction

Although most of the organometallic chemistry of gallium features this element in the +III oxidation state, the recent literature reflects an emerging interest in gallium(I) derivatives. Typically, RGa species tend to aggregate into weakly bound tetrameric51 or hexameric52 clusters; however, if a sufficient steric blockade is deployed, it is possible to isolate monomeric derivatives.53,54 Thus, for example,

(Dipp2nacnac)Ga (18) [HC{MeC(2,6-i-Pr2C6H3)N}2]Ga) is monomeric in the

54 5 55 crystalline state while [(h -C5Me5)Ga] (19) is monomeric in the vapor state.

Molecular orbital calculations on 1856 and 1913 indicate that both molecules adopt a singlet ground state. Accordingly, 18 and 19 are anticipated to exhibit Lewis base behavior due to the presence of a lone pair of electrons on the gallium atom.

Indeed, it has been shown that 19 displays ligative behavior toward transition metal moieties26 but, as in the case of alanediyls, such complexes do not exhibit pure

Lewis base behavior because of the possibility of varying degrees of back donation on the part of the d-block element. This section addresses the preparation and

189 characterization of the first examples of gallium-group 13 donor-acceptor bonds.

Part of this work was performed in collaboration with the research group of

Professor Philip P. Power of the University of California, Davis.57

Results and Discussion

5 (Dipp2nacnac)Ga®B(C6F5)3 and (h -C5Me5)Ga®B(C6F5)3

The borane complexes [HC{MeC(2,6-i-Pr2C6H3)N}2]Ga®B(C6F5)3 (20) and

5 (h -C5Me5)Ga®B(C6F5)3 (21) were obtained by treatment of 18 and 19,

11 respectively, with B(C6F5)3 in toluene solution. (Scheme 3.19) The B NMR spectra of 20 and 21 comprise broad singlets at d –20.3 and –7.9, respectively, which fall in the tetracoordinate boron region and the 19F chemical shifts of the equivalent C6F5 groups are similar to those reported for other Lewis base complexes

34f 1 of B(C6F5)3. In the H NMR spectrum of 18 the Dipp2nacnac ligand resonances displays a symmetric pattern thus implying syn h2 bonding of the b-diketiminate group to gallium, while in the case of 19 the equivalence of the methyl protons is

5 suggestive of h -C5Me5 ring attachment.

Ar Dip Ar Ar N B

Ga + B(C6F5)3 N Dip Ga Dip N N Dip

18 20

Scheme 3.19. Reaction of (HC{MeC(2,6-i-Pr2C6H3)N}2)Ga with B(C6F5)3 190 The foregoing spectroscopic indications were confirmed by means of X-ray crystallography. The crystalline states of both complexes consist of individual molecules of 20 and 21 and there are no unusually short intermolecular contacts.

Details of the data collection, structure solution and refinement for compound 21 are compiled in Table 3.17 and selected metrical parameters are listed in Tables 3.18 and 3.19. In complex 20, which crystallizes as two crystallographically independent but chemically identical monomeric complexes (Figure 3.8), the gallium atoms possess trigonal planar geometry with an average Ga-N bond distance of 1.942(6)

Å. The latter distance is considerably shorter than the Ga-N bond distances (av

2.054(2) Å) in the precursor 18.54 This observation is consistent with a decrease in the partial antibonding character of these bonds upon conversion of the gallium lone pair into a gallium-boron donor-acceptor bond, and the concomitant development of positive and negative charges on the gallium and boron atoms, respectively. The

C3N2Ga array of the b-diketiminate ring is essentially planar with C-C and C-N distances that are indicative of delocalization of the p-electrons. As is apparent from Figure 3.8, the B-Ga-N angles differ slightly (by ca. 5°) which is a result of the differing steric interactions caused by the orientation of the C6F5 rings relative to the C6H3-2,6-i-Pr2 substituents.

191

Figure 3.8. Molecular structure of one of the two crystallographically independent molecules of (Dipp2nacnac)Ga®B(C6F5)3. H and F atoms are not shown.

5 The C5Me5 group of 21 is attached to gallium in an h fashion (Figure 3.9) and the ring centroid-Ga-B moiety is essentially linear (176.65(6)º). While the average Ga-C distance of 2.228(2) Å is considerably shorter than those reported for

5 55 5 45 [(h -C5Me5)Ga] (2.405(4) Å) and [(h -C5Me5)Ga]6 (2.380(9) Å) , they are in good agreement with those reported for the transition metal derivatives (h5-

5 26 C5Me5)GaFe(CO)4 (2.226(2) Å) and (h -C5Me5)GaCr(CO)5 (2.260(3) Å). The cause of this Ga-C bond shortening upon coordination is similar to that described above for the Ga-N bond shortening of 20. The Ga-B bond distances in 20

(2.142(3)Å, Ga(2)–B(2) and 2.156(3)Å, Ga(1)–B(1)) and 21 (2.160(2) Å) are slightly longer than that predicted for a single bond from the sum of the covalent radii of Ga (1.25Å) and B (0.85Å). These bond distances may be compared with the

192 average Ga-B distances reported for a variety of gallium-substituted carboranes

(2.14 to 2.33 Å).39,58

5 Figure 3.9. Molecular structure of (h -C5Me5)Ga®B(C6F5)3 (21) showing atom- labeling scheme. Hydrogen and fluorine atoms have been removed for clarity.

5 Synthesis and characterization of (h -C5Me5)Ga®Al(C6F5)3

Utilizing the same methodology as that described for the synthesis of the

5 5 dialane isomer, (h -C5Me5)Ga®Al(C6F5)3 was prepared from [(h -C5Me5)Ga] (18)

27 and Al(C6F5)3·toluene. The Al NMR chemical shift for 22 fell in the

19 tetracoordinate aluminum region and the F chemical shifts of the (equivalent) C6F5 groups were similar to those observed for other Lewis base complexes of

34 5 B(C6F5)3. The equivalence of the methyl protons was suggestive of h -attachment

193 of the C5Me5 group to the gallium atom. The foregoing spectroscopic conclusions were confirmed by X-ray crystallography. Compound 21 crystallizes in the P-1 space group with Z = 4 with one molecule of toluene per asymmetric unit; the crystalline state consists of two crystallographically independent molecules of the

Lewis acid-base complex (Figure 3.10) and there are no unusually short intermolecular contacts. Details of the data collection, structure solution and refinement are compiled in Table 3.20 and selected metrical parameters are listed in

5 Tables 3.21 and 3.22. The C5Me5 group is attached to gallium in an h fashion and the ring centroid-Ga-B angle is 160.68(6)°. While the average Ga-C distance of

5 2.225(2) Å is considerably shorter than those reported for [(h -C5Me5)Ga] (2.405(4)

55 5 52 Å) and [(h -C5Me5)Ga]6 (2.380(9) Å), they are in good agreement with those

5 reported for the transition metal derivatives (h -C5Me5)GaFe(CO)4 (2.226(2) Å) and

5 45 (h -C5Me5)GaCr(CO)5 (2.260(3) Å).

194

5 Figure 3.10. Molecular structure of (h -C5Me5)Ga®Al(C6F5)3 (22) featuring both crystallographically independent molecules. Hydrogen and fluorine atoms have been eliminated for clarity.

5 Due to the donor action of the (Dipp2nacnac)Ga and [(h -C5Me5)Ga] fragments, the geometry of B(C6F5)3 changes from trigonal planar to distorted tetrahedral upon formation of the Ga B dative bond. The extent of the geometrical change from trigonal planar toward tetrahedral of B(C6F5)3 has been taken to be an indication of the strength of the donor-acceptor interactions.34f The sums of the C–

B–C bond angles at boron in compound 21 (334.3(2), B(1); 332.8(2)°, B(2)) and 22

(342.2(2) Å) may be compared with the 339.8(2)° reported previously46 for (h5-

5 C5Me5)Al®B(C6F5)3, suggesting that [(h -C5Me5)Ga] is a slightly weaker Lewis

5 base than [(h -C5Me5)Al] whereas (Dipp2nacnac)Ga appears to be a slightly stronger one than either molecule. Furthermore, it is interesting to note that the

195 sums of bond angles at boron reported for H3CC N B(C6F5)3 and the p-O2N-

C6H4-C N B(C6F5)3 are nearly identical to that of compound 4, thus implying

5 34f similar donor strengths to that of [(h -C5Me5)Ga]. Due to the nature of the weak interactions, it is difficult to compare the sums of bond angles for (h5-

C5Me5)Ga®Al(C6F5)3 with other species due the packing effects caused by the extra molecule of toluene present within the crystal lattice. It remains to be seen if this is an accurate measure of the Lewis basicity of (Dipp2nacnac)Ga where high steric effects may also play a role.

Conclusions:

It has been demonstrated that gallanediyls, RGa, can function as donors toward strong Lewis acids as well as serving as ligands for transition metals. The

5 donor-acceptor complexes (Dipp2nacnac)Ga B(C6F5)3 (20) and (h -C5Me5)Ga

B(C6F5)3 (21), that were prepared via the reaction of the corresponding gallanediyls with B(C6F5)3, represent the first examples of compounds with gallium(I) boron donor-acceptor bonds. The gallanediyl (Dipp2nacnac)Ga appears to be slightly

5 more Lewis basic than [(h -C5Me5)Ga] and complex 20 is somewhat more thermally stable than 21. An analogous donor-acceptor complex (h5-

C5Me5)Ga Al(C6F5)3 (22) is the first example of a compound with a gallium(I) aluminum donor acceptor bond.

196

Section 3.4

In(I) Complexes

Introduction

Due to the so-called “inert pair” effect, the +I oxidation state is more stable for indium than for the lighter group 13 elements aluminum and gallium. In terms of organometallic chemistry, this is reflected by the fact that [(C5H5)In], the unsubstituted cyclopentadienyl derivative of indium(I), can be prepared by disproportionation of the indium(III) species, (C5H5)3In, (Scheme 3.19). Moreover,

[CpIn], which possesses a polymeric zig-zag structure in the crystalline state, is a sublimable, water-stable substance in the absence of oxygen. The use of the more sterically demanding C5Me5 ligand results in a crystalline state that is comprised of

5 58 hexameric clusters, [(h -C5Me5)In]6. However, this cluster is weakly bonded and

5 monomeric [(h -C5Me5)In] has been shown to exist in dilute solution and the vapor phase.

Molecular orbital calculations reveal that, like the aluminum and gallium

5 analogues, monomeric [(h -C5Me5)In] exists as a ground state singlet. As such,

5 [(h -C5Me5)In] possesses a lone pair of electrons that should, in principle, be available for donor-acceptor bond formation. However, recognizing the periodic 197 group trend of decreasing Lewis basicity with increasing atomic number for e.g.

5 trialkyl group 15 compounds, it was anticipated that [(h -C5Me5)In] would be a

5 5 somewhat weaker Lewis base than [(h -C5Me5)Al] or [(h -C5Me5)Ga].

5 Nevertheless, it was decided to investigate the reaction of [(h -C5Me5)In] with

B(C6F5)3 in the hope of preparing the first example of a compound with an indium®boron donor-acceptor bond. The result of this experiment, however, was even more interesting in the sense that a novel “inverse sandwich” di-indium cation was produced.

THF InCl3 + 3 NaCp In

-3 150 °C, 10 torr, -C10H10

InCl + LiCp Benzene 60 °C In

Scheme 3.19. Synthesis of (C5H5)In from Cp3In

Results and Discussion

5 The low-temperature reaction of equimolar quantaties of [(h -C5Me5)In] monomer and B(C6F5)3 in toluene solution resulted, after workup, in a 13% yield of

5 + - colorless crystals with the empirical composition [(h -C5Me5)In2] [B(C6F5)4] (23). 198 11B NMR spectroscopic data were particularly useful in that the 11B chemical shift

(d -13.5) was inconsistent with the formation of the donor-acceptor complex, (h5-

11 C5Me5)In®B(C6F5)3 because the B chemical shifts for the analogous gallium

5 complexes (Dipp2nacnac)Ga®B(C6F5)3 and (h -C5Me5)Ga®B(C6F5)3, occur at d -

20.3 and –17.9, respectively. In fact, the 11B chemical shift observed for 23

59 - corresponds well with the value reported for the anion [B(C6F5)4] . The presence of this anion in the product was confirmed by 19F NMR spectroscopy. The 19F chemical shifts measured for 23 (d -134.0, -165.5 and –168.1) are in excellent agreement with the literature values60 for the ortho-, para-, and meta- fluorine

- atoms, respectively of [B(C6F5)4] . The presence of the latter anion having been established, it was clear that cation(s) must also be present. Unfortunately, the 1H and 13C NMR data for 23 were uninformative because they showed complete ring equivalence. Accordingly, it was necessary to appeal to X-ray crystallography for an unequivocal structure assignment.

Compound 23 crystallizes in the C2/c space group with Z = 4. Details of the data collection, structure solution and refinement are compiled in Table 3.23 and selected metrical parameters are listed in Tables 3.24 and 3.25. Unfortunately, the data set was of mediocre quality (R1 = 0.1752); nevertheless, it was more than adequate to establish the overall molecular structure. Attempts to obtain better crystals are underway currently. As shown in Figure 3.11 the central core of [23]+

5 features an h -bonded In atom on each face of the bridging-C5Me5 group. The In-

199 ring centroid (Ct01) distances of 2.45(3) Å are considerably are longer than those

61 5 reported for monomeric (2.288(4) Å) and hexameric (2.302(4) Å) [(h -C5Me5)In].

5 + As mentioned previously in Chapter 2.7, multidecker cations, [(h -C5Me5)3Sn2]

5 + + and [(toluene)2(h -C5Me5)In2] , the metal-Ct01-metal angle in [23] is close to linear (av 178.0º). However, in contrast to the previous example of an indium inverse sandwich complex, [23]+ does not exhibit h6-capping to arene molecules.

Instead, the triple-decker structure of [23]+ is completed by an unprecedented h6-

- capping of indium atoms to the C6F5 groups of the [B(C6F5)4] anion. The average

In-C6F5 ring centroid distance of 3.79(3) Å is considerably longer than the In-arene

5 centroid distance in [(toluene)2(h -C5Me5)In2] (3.490(4) Å) and those reported previously for [In(I)·2mesitylene]+ (2.83 and 2.89 Å).62 Nevertheless, it is

5 + interesting to note that, as in the case of [(toluene)2(h -C5Me5)In2] , the C6F5-(m-

C5Me5)-C6F5 moieties are distinctly bent (av 125.7º for Ct03-In(1)-Ct01) and that the overall cationic geometry is cisoid.

200 B1_3 In1_2 In1 Ct01

B1_4

Ct03 Ct03_2

5 + 5 Figure 3.11. The central core of [In2(h -C5Me5)] featuring an h -bonded In atom 6 on each face of the (m-C5Me5) group as well as h -capping by - adjacent C6F5 groups from [B(C6F5)4] .

A plausible mechanism for the formation of [23]+ (Scheme 3.20) involves the initial pentamethylcyclopentadienide removal and subsequent C6F5-exchange

- reactions to give (C5Me5)B(C6F5)2 and [B(C6F5)4] . The initial abstraction of C5Me5 by B(C6F5)3 is facilitated by the inert pair effect and the resistance of a pair of s electrons to be lost or participate in covalent bond formation. The rearrangement

60 reactions of C6F5 substituents on group 13 atoms is well documented and a similar reaction pathway has been suggested to explain the formation of the tin multidecker

5 + -63 + cation, [(h -C5Me5)3Sn2] [Ga(C6F5)4] . Prior to solvent removal, [23] was most

5 + likely capped with toluene molecules, much like the [(toluene)2(h -C5Me5)In2] cation. In the p-coordinated in phosphate64 and gallate65 salts of [Mes*NP(arene)]+, the loss of the capping arenes from the solid material can occur under dynamic vacuum; a similar process is proposed for 23. Compound [23]+ represents the first

201 - example of a hexahapto interaction with the C6F5 groups of the [B(C6F5)4] anion, a species that is widely regarded as a non-coordination anion.32

In In

B(C F ) 2 + 6 5 3 Cp*B(C F ) Toluene 6 5 3

In

B(C6F5)3 In - 2C7H8 B(C F ) 6 5 4 - Cp*B(C6F5)2

In

5 Scheme 3.20. Abstraction of C5Me5 moiety from [(h -(C5Me5)In] with B(C6F5)3 to + - give [23] [B(C6F5)4]

Conclusions

The synthesis of the first inverse sandwich main group cation featuring an

6 - unprecedented h capping of a metal to the C6F5 groups of the [B(C6F5)4] anion has

5 + - been accomplished. The salt [In(m-h -C5Me5)In] [B(C6F5)4] which was prepared

5 by treatment of [In(h -C5Me5)]6 with B(C6F5)3, has been characterized by X-ray crystallography. In the absence of an arene solvent for p-stacking, the [In(h5-

5 C5Me5)In] cation still adopts a cisoid geometry, featuring C6F5-(m-h -C5Me5)-C6F5 moieties that are distinctly bent. 202

Chapter 3

Experimental

General procedures

All solvents (diethylether, THF, benzene, toluene, hexane, pentane) were distilled over sodium benzophenone ketyl, or CaH2 (CH2Cl2) and degassed prior to use. Solid reactants were handled in a VAC Vacuum Atmospheres or M-Braun argon-filled drybox. All reactions were performed under a dry, oxygen-free argon atmosphere or under vacuum using standard Schlenk or drybox techniques; all glassware was oven-dried before use.

5 The group 13 trihalides and [(h -C5Me5)In]6 were purchased from a commercial source and used without further purification. Bromopentafluoroborane was also procured commercially and distilled at 40 °C/0.01 torr prior to use.

Tris(pentafluorophenyl)borane and C5Me5H were prepared according to literature procedures66 or purchased from a commercial source and used without further

67 68 5 8 5 purification. The compounds t-BuDAB, Mes2DAB, [(h -C5Me5)Al]4, [(h -

9 43 69 70 C5Me5)Ga]6 Al(C6F5)3 toluene, Ga(C6F5)3, and In(C6F5)3 were prepared according to literature methods.

203 Physical Measurements

Low-resolution EI mass spectra were obtained on a Bell and Howell 21-491 instrument; low-resolution CI mass spectra were run on a Finnigan MAT TSQ-700; and high-resolution mass spectra were measured on a VG Analytical ZAB-VE sector instrument. Solution-phase NMR spectra were recorded at 295 K, unless otherwise noted, on a GE QE-300 instrument (1H, 300 MHz; 11B, 96 MHz; 13C, 75

MHz; 19F, 282 MHz; 27Al, 78.21 MHz) or a Varian Inova-500 spectrometer (1H, 500

MHz; 11B, 160 MHz; 13C, 125 MHz; 19F, 470 MHz; 27Al, 130 MHz). All NMR samples were flame-sealed or run immediately following removal from the drybox.

Benzene-d6 was dried over sodium-potassium alloy and distilled prior to use.

Toluene-d8 and CD2Cl2 were obtained in sealed vials from a commercial source and used without further purification. 1H and 13C NMR spectra are reported relative to tetramethylsilane (d 0.00) and are referenced to solvent. 11B chemical shifts are

19 reported relative to BF3·Et2O (d 0.00), F chemical shifts are reported relative to

27 3+ C6F6 (d -162.9), and Al chemical shifts are reported relative to [Al(D2O)6] (d

0.00). All 13C spectra were obtained under conditions of broadband proton decoupling unless otherwise noted. Variable-temperature (VT) NMR studies utilized equilibration times of ten minutes at each temperature. Melting points were obtained in sealed capillaries under argon (1 atm) on a Fisher-Johns apparatus and are uncorrected. Elemental analyses were performed by Atlantic Microlab, Inc.,

Northcross, GA. 204 X-ray Crystallography

Suitable single crystals were covered with perfluorinated polyether oil and the X-ray data were collected on either a Nonius Kappa CCD diffractometer, or a

Siemens P4 diffractometer. Structure determinations and refinements were performed by Dr. Charles Macdonald, Dr. Andreas Voigt, or Dr. Brian McBurnett at

The University of Texas at Austin. All structures were solved by direct methods and refined by full-matrix least squares on F2 using the Siemens SHELX PLUS 5.0

(PC) software package.71 All non-hydrogen atoms were allowed anisotropic thermal motion and hydrogen atoms, which were included at calculated positions

(C-H 0.96 Å), were refined using a riding model and a general isotropic thermal parameter. The total number of reflections, collection ranges, and final R-values are listed in the appropriate tables for each molecule.

Data from the Siemens P4 diffractometer were collected at 213 K using graphite-monochromated Mo Ka radiation (l = 0.71073 Å). Accurate unit cell parameters were determined by recentering 25 optimal high angle reflections. A correction was applied for Lorentz-polarization. Three standard reflections were measured every 1800 seconds during each data collection, and no decreases in intensities were observed.

Data from the Nonius-Kappa CCD diffractometer were collected at 153 K using an Oxford Cryostream low-temperature device and graphite monochromated

Mo Ka radiation (l = 0.71073 Å). A correction was applied for Lorentz-

205 polarization. A total of 105 frames of data were collected using w-scans with a scan range of 1.9 and a counting time of 482 seconds per frame.

Preparation of Al[N(t-Bu)CH=CHN(t-Bu)]2 (10)

A solution of (t-Bu)N=CH-CH=N(t-Bu) (0.18 g, 1.06 mmol) in 15 mL of toluene was added dropwise to a stirred suspension of [(C5Me5)Al]4 (0.18 g, 1.08 mmol of [(C5Me5)Al] units) in 10 mL of toluene at 25 °C. The resulting reaction mixture was allowed to stir overnight, during which time the solids dissolved. The reaction mixture was heated to 50 °C for approximately 3 h, cooled to room temperature and filtered. The resulting green/brown solution was then concentrated in vacuo until the volume was ca. 10 mL; slow cooling to –20 °C afforded a crop of green crystals of 10, 0.12 g, 0.33 mmol, 62% yield based on t-BuDAB; mp 186-187

· °C. The paramagnetic compound [Al(t-BuDAB)2] has been synthesized previously

25 + + and characterized by Raston et al. MS (CI , CH4): m/z 363 (M , 100%); HRMS

+ + (CI , CH4) calcd for C20H40AlN4 (M ), 363.5471; found 363.5477.

5 Preparation of (h -C5Me5)AlN(Mes)CH=CHN(Mes) (12)

A solution of MesN=CH-CH=NMes (0.53 g, 1.81 mmol) in 30 mL of toluene was added dropwise to a stirred suspension of [(C5Me5)Al]4 (0.30 g, 0.46 mmol) in 20 mL of toluene at 25 °C. The resulting reaction mixture was warmed to

60 °C for 2 h, during which time all of the solids dissolved. The reaction mixture

206 was cooled to 25 °C and stirred for an additional 12 h. The resulting amber solution was filtered, then concentrated in vacuo until the volume was ca. 20 mL; slow cooling to –20 °C afforded a crop of yellow crystals of 12, 0.32g, 0.70 mmol, 39%

1 yield; mp 213-226 °C (dec). H NMR (C6D6): d 6.91 (s, 4 H, CHMes), 5.15 (s, 2 H,

NCH), 2.42 (s, 12 H, o-Me), 2.25 (s, 6 H, p-Me), 1.65 (s, 15 H, Cp* ring); 13C-{1H}

NMR (C6D6): d 146.6 (s, ipso-CMes), 136.5 (s, o-CMes), 133.2 (s, p-CMes), 128.8 (s, m-CMes), 116.1 (s, NCC), 115.1 [s, Cp* ring], 21.1 (s, p-Me), 18.8 (s, o-Me), 9.9 (s,

27 1 + Cp* Me); Al-{ H} NMR (C6D6): d 45 (w½ = 6200 Hz); MS (CI , CH4): m/z 507

+ + + (M , 100%); HRMS (CI , CH4) calcd for C30H29AlN2 (M ), 454.2929; found

454.2928.

5 Preparation of (h -C5Me5)GaN(Mes)CH=CHN(Mes) (13)

A solution of MesN=CH-CH=NMes (0.53 g, 1.81 mmol) in 30 mL of toluene was added dropwise to a stirred suspension of [Ga(C5Me5)]6 (0.37 g, 0.30 mmol) in 20 mL of toluene at - 78 °C. The resulting reaction mixture was warmed to room temperature overnight, during which time the solution turned dark red.

Upon removal of the solvent in vacuo, compound 13 was obtained as a sticky red oil. Further drying of the product at 50 °C, resulted in a waxy solid that resisted all

1 attempts at crystallization. H NMR (C6D6): d 7.11 (m, 4 H, CHMes), 5.60 (s, 2 H,

NCH), 2.42 (s, 12 H, o-Me), 2.25 (s, 6 H, p-Me), 1.50 [s, 15 H, Cp*]; 13C-{1H}

NMR (C6D6): d 147.0 (s, ipso-CMes), 136.5 (s, o-CMes), 133.2 (s, p-CMes), 128.8 (s, 207 m-CMes), 120.1 (s, Cp* ring), 116.1 (s, NCC), 20.2 (s, p-Me), 19.3 (s, o-Me), 12.9 [s,

+ + + Cp* Me]; MS (CI , CH4): m/z 497 (M , 100%); HRMS (CI , CH4) calcd for

+ C30H29GaN2 (M ), 497.0159; found 497.0164.

5 Preparation of (h -C5Me5)AlB(C6F5)3 (14)

The addition of 30 mL of toluene to a mixture of [Al(C5Me5)]4 (0.15 g, 0.93 mmol of Al(C5Me5) units) and B(C6F5)3 (0.47 g, 0.92 mmol) resulted in a yellow colored solution. The reaction mixture was allowed to stir for 16 h at room temperature, following which the volatiles were removed in vacuo. The resulting purple oil was maintained at room temperature, to afford a crop of colorless crystals of 14 over a period of days, 0.25 g, 0.37 mmol, 40% yield; mp 126-129 °C (dec).

1 19 1 H NMR (C6D6): d 1.39 (s, Cp*, 15 H); F-{ H} NMR (C6D6): d -127.2 (s, m-

27 1 C6F5), -154.9 (s, p-C6F5), -159.8 (s, o-C6F5); Al-{ H} NMR (C6D6): d -59.4 (w½

+ + + = 1564 Hz); MS (CI , CH4): m/z 675 [(M+H , 0.93%); 512 [B(C6F5)3 , 66.98%];

+ + + 164 [Cp*AlH2 , 2.02%]; HRMS (CI , CH4) calcd for C28H16AlBF14 (M ), 655.0859; found 655.0884.

5 Preparation of (h -C5Me5)AlAl(C6F5)3 (16)

A solution of [Al(C5Me5)]4 (0.065 g, 0.40 mmol of Al(C5Me5) units) was

4 treated with Al(C6F5)3×toluene (250 mg, 0.4 mmol) in 30 mL of toluene at 25 °C.

The reaction mixture was allowed to stir for 4 h at 25 °C, then the yellow-colored

208 reaction mixture was heated to 50 °C for 30 min. Following slow cooling to 25 °C, the reaction mixture was filtered through Celite®. The filtrate was concentrated in vacuo to afford a dark amber oil from which yellow crystals of (h5-

C5H5)Al®Al(C6F5)3 were formed over a period of day, 220 mg, 80% yield; mp 131-

1 13 1 3 °C. H NMR (C6D6): d 1.49 (s, Cp*, 15 H); C{ H} NMR (C6D6): d 149.9 (d, o-

1 1 1 C6F5, JCF = 224 Hz), d 141.8 (d, p-C6F5, JCF = 239 Hz), 137.3 (d, m-C6F5, JCF =

19 1 226 Hz), 129.2 (s, ipso- C6F5), 115.9 [s, Cp* ring], 8.4 [s, Cp* Me]; F-{ H} NMR

27 1 (C6D6): d -122.0 (s, m-C6F5), -153.1 (s, p-C6F5), -161.7 (s, o-C6F5); Al-{ H} NMR

(C6D6): d 106 [br, (C6F5)3AlAlCp*, w1/2 = 6122 Hz], -115 (s, (C6F5)3AlAlCp*). MS

+ + (CI , CH4): m/z 691 [(M+H , 1.84%); 528 [Al(C6F5)3, 19.83%]; 164 [Cp*AlH2,

+ + 2.71%]; HRMS (CI , CH4) calcd for C28H15Al2F15 (M ), 690.0565 found 690.0572.

3 Preparation of (h -C5Me5)Al (C6F5)2 (17)

A solution of In(C6F5)3 (0.76 g, 1.24 mmol) in 30 mL of toluene was added dropwise to a stirred suspension of [(C5Me5)Al]4 (0.20 g, 1.24 mmol of [(C5Me5)Al] units) in 20 mL of toluene at -76 °C. The resulting reaction mixture was warmed slowly to room temperature and stirred for 12 h, during which time the solids dissolved. The resulting amber/red solution was filtered, then concentrated under reduced pressure until the volume was ca. 20 mL; slow cooling to –20 °C afforded a crop of colorless crystals of 17, 0.30 g, 0.62 mmol, 50% yield; 158 °C. 1H NMR

19 1 (C6D6): d 1.63 (s, Cp*, 15 H); F-{ H} NMR (C6D6): d -119.0 (s, m-C6F5), -149.0 209 27 1 (s, p-C6F5), -155.8 (s, o-C6F5); Al-{ H} NMR (C6D6): d 57 (w1/2 = 4505 Hz); MS

+ + + + (CI , CH4): m/z 496 [(M , 17.95%); 477 [(M -F) , 36.71%]; 329 [(M-C6F5) , 100%];

+ + HRMS (CI , CH4) calcd for C22H15AlF10 (M ), 496.0829; found 496.0817.

Preparation of (Dipp2nacnac)GaB(C6F5)3 (20)

With rapid stirring, a pale yellow toluene solution (20 mL) of

(Dipp2nacnac)Ga (0.768 g, 1.5 mmol) was added dropwise to B(C6F5)3 (0.730 g, 1.5 mmol) in toluene (10 mL). After several minutes the solution became colorless.

The toluene was removed under reduced pressure and the residue was dissolved in hexane (30 mL). The hexane solution was concentrated to a volume of approximately 10 mL, and allowed to cool to ca. –20°C overnight. After 20 h, large colorless crystals of 20 were obtained, 1.21 g, 81% yield; mp 160-162°C. 1H NMR

3 3 (C6D6) d 7.02 (t, p-H, JHH = 7.5 Hz, 2H), 6.79 (d, m-H on phenyl, JHH = 7.8 Hz),

3 4.99 (s, 1H, methine CH), 2.81 (sept, JHH = 6.6 Hz, 4H, CHMe), 1.39 (s, 6H, CMe),

3 3 11 1.02 (d, JHH = 6.6 Hz, 12H, CHMe2), 0.88 (d, JHH = 6.6 Hz, 12H, CHMe2): B

13 1 NMR (C6D6) d –20.3: C { H} NMR (C6D6) d 170.7 (CN), 149.9 (br, o-C6F5),

146.8 (br, p-C6H5), 142.3 (CMe), 141.3 (o-C on phenyl; CCHCMe2), 138.5 (br, m-

C6H5), 135.4 (br, i-C6H5), 128.4 (p-C on phenyl), 124.6 (m-C on phenyl), 101.2 (g-

19 1 C), 29.8 (CHMe2), 24.7 (CHMe2), 24.4 (CMe), 23.0 (CHMe2). F { H} (C6D6) d –

129.4 (o-C6F5), –156.1 (p-C6F5), –160.2 (m-C6F5).

210 5 Preparation of (h -C5Me5)GaB(C6F5)3 (21)

A solution of B(C6F5)3 (0.62 g, 1.22 mmol) in 30 mL of toluene was added to a pale yellow solution of [(C5Me5)Ga]6 (0.25 g, 1.22 mmol of [(C5Me5)Ga] units) in 20 mL of toluene at -78 °C. The stirred yellow-colored reaction mixture was maintained at -78 °C for 1 h, following which it was allowed to warm slowly to room temperature and stirred for an additional 4 h. The resulting tan colored solution was filtered through Celite®. The filtrate was concentrated in vacuo until the volume was ca. 10 mL; slow cooling to –20 °C afforded a crop of colorless

1 crystals, 0.65 g, 0.91 mmol, 75% yield; mp 125 °C (dec). H NMR (C6D6): d 1.66

11 1 13 (s, Cp*, 15 H); B-{ H} NMR (C6D6): d -17.9 (br, w1/2 = 2887 Hz); C NMR

1 1 (C6D6): d 147.6 (d, o-C6F5, JCF = 239 Hz), 141.3 (d, p-C6F5, JCF = 254 Hz), 137.6

1 (d, m-C6F5, JCF = 252 Hz), 129.2 (s, ipso-C6F5), 114.6 (s, Cp* ring), 8.5 (s, Cp*

19 1 Me); F-{ H} NMR (C6D6): d -131.2 (s, m-C6F5), -153.8 (s, p-C6F5), -163.0 (s, o-

C6F5).

5 Preparation of (h -C5Me5)GaAl(C6F5)3·1/2 Toluene (22)

A solution of [(C5Me5)Ga]6 (0.25 g, 1.22 mmol of [(C5Me5)Ga] units) in 20 mL of toluene was treated with Al(C6F5)3·toluene (0.756 g, 1.22 mmol) in 30 mL of toluene at -76 °C. After being stirred for 1 h at -76 °C, the yellow-colored reaction mixture was allowed to warm slowly to room temperature. After stirring for 4 h, the solution was filtered through Celite®, then concentrated under reduced pressure until 211 the volume was ca. 5 mL; slow cooling to –20 °C afforded a crop of colorless crystals of 22, 0.55 g, 0.76 mmol, 62% yield; mp 110-130 °C (dec). 1H NMR

13 1 1 (C6D6): d 1.65 (s, Cp*, 15 H); C{ H} NMR (C6D6): d 149.8 (d, o-C6F5, JCF = 254

1 1 Hz), d 142.2 (d, p-C6F5, JCF = 253 Hz), 137.3 (d, m-C6F5, JCF = 240 Hz), 128.3 (s,

19 1 ipso-C6F5), 115.4 (s, Cp* ring), 8.6 (s, Cp* Me); F-{ H} NMR (C6D6): d -122.3

27 (m, m-C6F5), -151.9 (m, p- C6F5), -161.4 (m, o-C6F5); Al NMR (C6D6): d 70 (br,

+ Cp*GaAl(C6F5)3, w1/2 = 4098 Hz); MS (CI , CH4): m/z 205 [(Cp*)Ga, 100%]; 329

+ + [Cp*AlC6F5 , 36.62%]; 403 [Ga(C6F5)2 ,13.25%]; 539 [(Cp*)Ga(C6F5)2, 11.71%];

570 [Ga(C6F5)3, 5.59%].

5 + - Preparation of [(h -C5Me5)In2] [B(C6F5)4] (23)

5 A solution of [(h -C5Me5)In] (0.25 g, 1.0 mmol) in toluene (40 mL) was treated with an equimolar quantity of B(C6F5)3 (0.51 g, 1.0 mmol) at -78 °C. The reaction mixture was allowed to warm slowly to 0 ºC over several hours. The resulting tan colored reaction mixture was filtered through Celite® and all volatiles were removed from the filtrate in vacuo. The resulting tan colored oil was placed under dynamic vacuum (3 h, 10-3 torr) slight warming, after which time small colorless crystals of 23 were formed. (0.10 g, 13% yield of crystalline material) 1H

19 2 NMR (C6D6) d 1.45 (s, 15H, Cp*); F NMR (C6D6): d -134.0 (d, JF-F 21.0 Hz, p-

2 2 11 C6F5), -165.5 (“t”, JF-F 20.5 Hz, p-C6F5), 168.1 (“t”, JF-F 20.5 Hz, m-C6F5). B

NMR (C6F5): d -13.5. 212

Chapter 3

Tables of Crystallographic and

Theoretical Data

213 5 Table 3.1. Crystal Data and Structure Refinement for (Mes2DAB)Al(h -C5Me5) (12)

Identification code test

Empirical formula C30 H39 Al N2 Formula weight 454.61 Temperature 179(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/n Unit cell dimensions a = 9.8413(9) Å a= 90°. b = 12.3276(13) Å b= 102.182(10)°. c = 22.244(3) Å g = 90°. Volume 2637.9(5) Å3 Z 4 Density (calculated) 1.145 Mg/m3 Absorption coefficient 0.097 mm-1 F(000) 984 Crystal size 0.53 x 0.44 x 0.41 mm3 Theta range for data collection 1.87 to 27.51°. Index ranges -1<=h<=12, -1<=k<=16, -28<=l<=28 Reflections collected 8013 Independent reflections 6054 [R(int) = 0.0363] Absorption correction None Max. and min. transmission N/A and N/A Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6054 / 0 / 348 Goodness-of-fit on F2 0.962 Final R indices [I>2sigma(I)] R1 = 0.0460, wR2 = 0.1172 R indices (all data) R1 = 0.0731, wR2 = 0.1281 Largest diff. peak and hole 0.247 and -0.327 e.Å-3

214 5 Figure 3.3. Molecular structure of (Mes2DAB)Al(h -C5Me5) showing the numbering scheme.

5 Table 3.2. Selected Bond Lengths [Å] for (Mes2DAB)Al(h -C5Me5) (12)

Al(1)-N(2) 1.8260(14) N(2)-C(2) 1.412(2) Al(1)-N(1) 1.8274(13) N(2)-C(12) 1.430(2) Al(1)-C(21) 2.212(2) C(2)-C(1) 1.331(2) Al(1)-C(22) 2.228(2) C(22)-C(21) 1.417(2) Al(1)-C(25) 2.233(2) C(21)-C(25) 1.430(2) Al(1)-C(23) 2.238(2) C(22)-C(23) 1.432(2) Al(1)-C(24) 2.257(2) C(24)-C(25) 1.413(2) N(1)-C(1) 1.401(2) C(24)-C(23) 1.422(2) N(1)-C(3) 1.429(2)

Table 3.3. Selected Bond Angles [°] for (Mes2DAB)Al(C5Me5) (12) N(2)-Al(1)-N(1) 89.79(6) X(1)-Al(1)-N(1) 135.9(11) X(1)-Al(1)-N(2) 134.2(11) C(1)-N(1)-C(3) 116.81(13) C(1)-N(1)-Al(1) 108.89(10) C(3)-N(1)-Al(1) 133.82(11) C(2)-N(2)-C(12) 115.83(13) C(2)-N(2)-Al(1) 108.67(10) C(12)-N(2)-Al(1) 133.38(11) C(1)-C(2)-N(2) 116.2(2) C(2)-C(1)-N(1) 116.5(2) 215 Table 3.4. Crystal Data and Structure Refinement for Mes2DAB (11)

Identification code dab

Empirical formula C20 H24 N2 Formula weight 292.41 Temperature 173(2) K Wavelength 0.71073 Å Crystal system monoclinic

Space group P21/c Unit cell dimensions a = 13.324(3) Å a= 90°. b = 4.4009(9) Å b= 108.24(3)°. c = 15.357(3) Å g = 90°. Volume 855.2(3) Å3 Z 2 Density (calculated) 1.136 Mg/m3 Absorption coefficient 0.066 mm-1 F(000) 316 Crystal size 0.2 x 0.2 x 0.3 mm3 Theta range for data collection 3.22 to 27.42°. Index ranges -15<=h<=17, -5<=k<=5, -19<=l<=17 Reflections collected 11039 Independent reflections 1863 [R(int) = 0.0638] Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1863 / 0 / 148 Goodness-of-fit on F2 1.155 Final R indices [I>2sigma(I)] R1 = 0.0908, wR2 = 0.2806 R indices (all data) R1 = 0.1135, wR2 = 0.2999 Largest diff. peak and hole 0.404 and -0.330 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x+2,-y,-z+1

216

Figure 3.4. Molecular structure of 1,4-bis(2,4,6-trimethylphenyl)-1,4-diazabuta- 1,3-diene (11) showing the atom numbering scheme.

Table 3.5. Selected Bond Lengths [Å] for Mes2DAB (11)

C(1)-N(1) 1.274(5) C(12)-C(17) 1.513(5) C(1)-C(1)#1 1.467(7) C(13)-C(14) 1.386(5) N(1)-C(11) 1.432(4) C(14)-C(15) 1.398(5) C(11)-C(16) 1.406(5) C(14)-C(18) 1.509(5) C(11)-C(12) 1.407(5) C(15)-C(16) 1.387(5) C(12)-C(13) 1.390(5) C(16)-C(19) 1.500(5)

Table 3.6. Selected Bond Angles [°] for Mes2DAB (11)

N(1)-C(1)-C(1)#1 119.3(4) C(14)-C(13)-C(12) 122.1(4) C(1)-N(1)-C(11) 117.6(3) C(13)-C(14)-C(15) 118.4(3) C(16)-C(11)-C(12) 120.7(3) C(13)-C(14)-C(18) 121.0(4) C(16)-C(11)-N(1) 117.9(3) C(15)-C(14)-C(18) 120.6(3) C(12)-C(11)-N(1) 121.3(3) C(16)-C(15)-C(14) 121.8(3) C(13)-C(12)-C(11) 118.4(3) C(15)-C(16)-C(11) 118.6(3) C(13)-C(12)-C(17) 119.7(4) C(15)-C(16)-C(19) 121.1(3) C(11)-C(12)-C(17) 121.8(3) C(11)-C(16)-C(19) 120.3(3)

217 5 Table 3.7. Crystal data and Structure Refinement for (h -C5Me5)AlB(C6F5)3 (14)

Identification code d

Empirical formula C28 H15 Al B F15 Formula weight 674.19 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 9.534(2) Å a= 91.04(3)°. b = 9.902(2) Å b= 104.10(3)°. c = 15.658(3) Å g = 105.93(3)°. Volume 1372.9(5) Å3 Z 2 Density (calculated) 1.631 Mg/m3 Absorption coefficient 0.195 mm-1 F(000) 672 Crystal size 0.5 x 0.4 x 0.4 mm3 Theta range for data collection 2.95 to 27.48°. Index ranges -12<=h<=12, -12<=k<=12, -19<=l<=20 Reflections collected 11088 Independent reflections 6252 [R(int) = 0.0264] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6252 / 0 / 406 Goodness-of-fit on F2 1.282 Final R indices [I>2sigma(I)] R1 = 0.0630, wR2 = 0.1593 R indices (all data) R1 = 0.1036, wR2 = 0.1757 Largest diff. peak and hole 0.620 and -0.263 e.Å-3

218

5 Figure 3.5. Molecular structure of (h -C5Me5)Al®B(C6F5)3 (14) showing the atom numbering scheme.

5 Table 3.8. Selected Bond Lengths [Å] for (h -C5Me5)AlB(C6F5)3 (14)

Al-C(4) 2.161(3) C(4)-C(3) 1.418(4) Al-B 2.171(3) C(4)-C(9) 1.518(4) Al-C(1) 2.161(3) C(5)-C(10) 1.507(5) Al-C(5) 2.165(3) C(5)-C(1) 1.449(5) Al-C(3) 2.178(3) C(2)-C(3) 1.416(5) Al-C(2) 2.186(3) C(2)-C(1) 1.428(5) C(11)-B 1.629(4) C(2)-C(7) 1.519(5) C(17)-B 1.637(4) C(3)-C(8) 1.534(5) B-C(23) 1.636(4) C(1)-C(6) 1.520(5) C(4)-C(5) 1.408(5) Al-X(1) (centroid) 1.802(3)

219 5 Table 3.9. Selected Bond Angles [°] for (h -C5Me5)AlB(C6F5)3 (14)

B-Al-X(1) (centroid) 172.9(1) C(11)-B-C(17) 114.7(2) C(11)-B-C(23) 111.3(2) C(17)-B-C(23) 113.8(2) B-Al-C(1) 151.44(13) B-Al-C(3) 139.20(13) B-Al-C(5) 150.94(13)

Table 3.10. Summary of Theoretical Calculations for 15

Compound Symmetry Energy Rel. Energy Al-Al (Å) 27Al 27Al (au) (kcal/mol) Shielding NMR Shift

H2AlAlH2 D2h (plan.) -487.2655687 0 2.620 D2d (perp.) -487.2682911 -1.71 2.594 H3AlAlH C3v -487.2509491 9.17 2.705

2 CpHAlAlH2 Cs h –Cp (plan.) -680.253883 0 2.575 2 Cs h –Cp (perp.) -680.2626141 -5.48 2.541 3 Cs h –Cp (plan.) -680.2510644 1.77 2.568 5 CpAlAlH3 Cs h –Cp -680.2710853 -10.79 2.741 CpAlAlH3 705.1658 -107.88 CpAlAlH3 488.3250 108.96 † - Cp = pentamethylcyclopentadienyl, [C5H5] .

All calculations carried out with the Gaussian 9472 package of programs.

Each molecule/ion was fully optimized in the indicated symmetry at the

B3LYP73/A74 level of theory. The GIAO75 NMR calculations were performed at the BP8676/A level of theory in the B3LYP/A optimized geometries; we have found that BP86 gives more accurate predictions of chemical shifts than B3LYP. The 27Al

+3 chemical shifts are referenced to [Al(H2O)6] optimized in Th symmetry and calculated at the same level (absolute shielding: d 597.2865) and the values for shielding and chemical shift are reported in parts per million (ppm).

220 5 Table 3.11. Crystal Data and Structure Refinement for (h -C5Me5)AlAl(C6F5)3 (16)

Identification code c2c

Empirical formula C28 H15 Al2 F15 Formula weight 690.36 Temperature 133(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 30.635(6) Å a= 90°. b = 9.814(2) Å b= 111.10(3)°. c = 20.236(4) Å g = 90°. Volume 5676.4(20) Å3 Z 8 Density (calculated) 1.616 Mg/m3 Absorption coefficient 0.220 mm-1 F(000) 2752 Crystal size 0.2 x 0.1 x 0.1 mm3 Theta range for data collection 2.98 to 25.10°. Index ranges -28<=h<=33, -11<=k<=11, -22<=l<=21 Reflections collected 8481 Independent reflections 3815 [R(int) = 0.0868] Absorption correction None Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3815 / 0 / 411 Goodness-of-fit on F2 1.456 Final R indices [I>2sigma(I)] R1 = 0.0767, wR2 = 0.1944 R indices (all data) R1 = 0.1248, wR2 = 0.2316 Largest diff. peak and hole 0.435 and -0.406 e.Å-3

221

5 Figure 3.6. Molecular structure of (h -C5Me5)®Al(C6F5)3 (16) showing the atom numbering scheme.

5 Table 3.12. Selected Bond Lengths [Å] for (h -C5Me5)AlAl(C6F5)3 (16)

Al(2)-C(21) 1.982(7) Al(1)-C(15) 2.189(6) Al(2)-C(41) 1.997(7) Al(1)-C(14) 2.200(7) Al(2)-C(31) 1.999(7) C(15)-C(14) 1.416(10) Al(2)-Al(1) 2.591(2) C(15)-C(11) 1.432(10) Al(1)-C(12) 2.162(6) C(14)-C(13) 1.448(10) Al(1)-C(13) 2.165(7) C(11)-C(12) 1.415(11) Al(1)-C(11) 2.172(7) C(13)-C(12) 1.406(12) Al(1)-X(1A) 2.591(8)

5 Table 3.13. Selected Bond Angles [°] for (h -C5Me5)AlAl(C6F5)3 (16)

Al(2)-Al(1)-X(1A) 170.1(3) C(21)-Al(2)-C(41) 111.0(3) C(21)-Al(2)-C(31) 108.5(3) C(41)-Al(2)-C(31) 113.5(3) C(21)-Al(2)-Al(1) 104.1(2) C(41)-Al(2)-Al(1) 111.2(2) C(31)-Al(2)-Al(1) 108.0(2) 222 5 Table 3.14. Crystal Data and Structure Refinement for (h -C5Me5)Al(C6F5)2 (17)

Identification code t

Empirical formula C22 H15 Al F10 Formula weight 496.32 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Orthorhombic Space group Pnma Unit cell dimensions a = 9.049(2) Å a= 90°. b = 19.160(4) Å b= 90°. c = 11.902(2) Å g = 90°. Volume 2063.6(7) Å3 Z 4 Density (calculated) 1.598 Mg/m3 Absorption coefficient 0.195 mm-1 F(000) 1000 Crystal size 0.4 x 0.3 x 0.3 mm3 Theta range for data collection 3.02 to 36.66°. Index ranges -15<=h<=15, -24<=k<=24, -11<=l<=11 Reflections collected 4469 Independent reflections 2435 [R(int) = 0.0269] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2435 / 0 / 154 Goodness-of-fit on F2 1.168 Final R indices [I>2sigma(I)] R1 = 0.0719, wR2 = 0.2183 R indices (all data) R1 = 0.0939, wR2 = 0.2418 Largest diff. peak and hole 0.660 and -0.580 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: x,-y+3/2,z

223

3 Figure 3.7. Molecular structure of (h -C5Me5)Al(C6F5)2 (17) showing the atom numbering scheme.

3 Table 3.15. Selected Bond Lengths [Å] for (h -C5Me5)Al(C6F5)2 (17)

Al-C(11) 1.672(3) C(4)-C(3) 1.672(6) Al-C(1) 2.018(3) C(1)-C(2) 1.296(4) Al-C(12) 2.067(3) C(1)-C(6) 1.658(5) C(13)-C(13)#1 1.440(5) C(3)-C(2) 1.386(5) C(13)-C(12) 1.577(5) C(5)-C(6) 1.416(4) C(4)-C(5) 1.294(5) C(11)-C(12) 1.508(4)

3 Table 3.16. Selected Bond Angles [°] for (h -C5Me5)Al(C6F5)2 (17)

C(11)-Al-C(1) 114.60(11) C(1)-Al-C(12) 93.40(11) C(11)-Al-C(1)#1 114.60(11) C(1)#1-Al-C(12) 159.34(10) C(1)-Al-C(1)#1 103.5(2) Al-C(11)-C(21) 106.6(3) C(1)-Al-C(12)#1 159.34(10) C(11)-C(12)-C(13) 114.1(2) C(1)#1-Al-C(12)#1 93.40(11) 224 5 Table 3.17. Crystal Data and Structure Refinement for (h C5Me5)GaB(C6F5)3 (21)

Identification code p21c

Empirical formula C28 H15 B F15 Ga Formula weight 716.93 Temperature 133(2) K Wavelength 0.71073 Å Crystal system Monoclinic

Space group P21/c Unit cell dimensions a = 9.2222(18) Å a= 90°. b = 24.000(5) Å b= 93.67(3)°. c = 12.063(2) Å g = 90°. Volume 2664.5(9) Å3 Z 4 Density (calculated) 1.787 Mg/m3 Absorption coefficient 1.158 mm-1 F(000) 1416 Crystal size 0.3 x 0.3 x 0.2 mm3 Theta range for data collection 2.99 to 27.47°. Index ranges -11<=h<=11, -31<=k<=30, -15<=l<=14 Reflections collected 34738 Independent reflections 6009 [R(int) = 0.0413] Completeness to theta = 27.47° 98.7 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6009 / 0 / 466 Goodness-of-fit on F2 1.089 Final R indices [I>2sigma(I)] R1 = 0.0318, wR2 = 0.0786 R indices (all data) R1 = 0.0393, wR2 = 0.0821 Largest diff. peak and hole 0.436 and -0.483 e.Å-3

225

5 Figure 3.9. Molecular structure of (h -C5Me5)Ga®B(C6F5)3 (21) showing the atom numbering scheme. Fluorine atoms have been removed for clarity.

5 Table 3.18. Bond Lengths [Å] for (h -C5Me5)GaB(C6F5)3 (21)

Ga-CT01 1.8646(4) C(31)-B 1.632(3) Ga-B 2.161(2) C(21)-B 1.624(3) Ga-C(11) 2.2157(19) C(13)-C(14) 1.433(3) Ga-C(12) 2.2247(19) C(13)-C(12) 1.430(3) Ga-C(13) 2.226(2) C(15)-C(14) 1.432(3) Ga-C(15) 2.2301(19) C(15)-C(11) 1.436(3) Ga-C(14) 2.237(2) C(12)-C(11) 1.437(3) C(41)-B 1.627(3)

5 Table 3.19. Selected Bond Angles [°] for (h -C5Me5)GaB(C6F5)3 (21)

CT01-Ga-B 160.96(15) C(21)-B-Ga 102.96(12) C(21)-B-C(31) 115.87(16) C(31)-B-Ga 105.07(12) C(21)-B-C(41) 113.33(15) C(41)-B-Ga 105.09(12) C(31)-B-C(41)

226 5 Table 3.20. Crystal Data and Structure Refinement for (h -C5Me5)GaAl(C6F5)3 (22)

Identification code sqz1

Empirical formula C28 H15 Al F15 Ga Formula weight 733.10 Temperature 123(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 10.055(2) Å a= 99.95(3)°. b = 16.544(3) Å b= 90.12(3)°. c = 18.868(4) Å g = 93.96(3)°. Volume 3083.6(11) Å3 Z 4 Density (calculated) 1.579 Mg/m3 Absorption coefficient 1.029 mm-1 F(000) 1448 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data collection 2.97 to 27.47°. Index ranges -13<=h<=13, -21<=k<=20, -24<=l<=24 Reflections collected 57049 Independent reflections 13940 [R(int) = 0.0663] Absorption correction None Max. and min. transmission n/a and n/a Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 13940 / 0 / 821 Goodness-of-fit on F2 1.090 Final R indices [I>2sigma(I)] R1 = 0.0542, wR2 = 0.1268 R indices (all data) R1 = 0.0940, wR2 = 0.1414 Largest diff. peak and hole 0.720 and -0.534 e.Å-3

227

5 Figure 3.10. Molecular structure of (h -C5Me5)Ga®Al(C6F5)3 (22) Featuring both crystallographically independent molecules. Hydrogen and fluorine atoms have been eliminated for clarity.

5 Table 3.21. Selected Bond Lengths [Å] for (h -C5Me5)GaAl(C6F5)3 (22)

Ga(2)-Al(2) 2.5226(10) Al(1)-C(21) 1.998(3) Ga(1)-C(15) 2.173(3) Al(1)-C(31) 2.006(3) Ga(1)-C(11) 2.205(3) C(45)-C(43) 1.379(5) Ga(1)-C(14) 2.216(3) C(15)-C(14) 1.437(5) Ga(1)-C(13) 2.253(3) C(15)-C(11) 1.439(4) Ga(1)-C(12) 2.268(3) C(14)-C(13) 1.429(5) Ga(1)-Al(1) 2.5083(11) C(11)-C(12) 1.412(5) Al(1)-C(41) 1.994(3) C(13)-C(12) 1.436(5)

5 Table 3.22. Selected Bond Angles [°] for (h -C5Me5)GaAl(C6F5)3 (22)

CT01-Ga(1)-B 160.68(6) C(41)-Al(1)-Ga(1) 109.93(10) C(41)-Al(1)-C(21) 114.45(13) C(21)-Al(1)-Ga(1) 103.24(10) C(41)-Al(1)-C(31) 113.65(13) C(31)-Al(1)-Ga(1) 96.86(9) C(21)-Al(1)-C(31) 116.39(13) 228

5 + - Figure 3.12. Molecular structure of [In2(h -C5Me5)] [B(C6F5)4] showing the atom numbering scheme. Fluorine and hydrogen atoms have been eliminated for clarity.

B1_3 In1_2 In1 Ct01

B1_4

Ct03 Ct03_2

5 + 5 Figure 3.11. The central core of [In2(h -C5Me5)] featuring an h -bonded In atom 6 on each face of the (m-C5Me5) group as well as h -capping by - adjacent C6F5 groups of [B(C6F5)4] . 229 5 + Table 3.23. Crystal Data and Structure Refinement for [(h -C5Me5)In2] - [B(C6F5)4]

Identification code c2c

Empirical formula C68 H30 B2 F40 In4 Formula weight 2087.82 Temperature 133(2) K Wavelength 0.71069 Å Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 28.915(5) a= 90.000(5)°. b = 17.323(5) Å b= 134.947(5)°. c = 20.465(5) Å g = 90.000(5)°. Volume 7255(3) Å3 Z 4 Density (calculated) 1.911 Mg/m3 Absorption coefficient 1.400 mm-1 F(000) 4016 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data collection 3.08 to 30.47°. Index ranges -35<=h<=36, -17<=k<=23, -27<=l<=22 Reflections collected 25773 Independent reflections 8558 [R(int) = 0.0605] Completeness to theta = 30.47° 77.6 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 8558 / 1 / 517 Goodness-of-fit on F2 0.916 Final R indices [I>2sigma(I)] R1 = 0.1752, wR2 = 0.4979 R indices (all data) R1 = 0.2224, wR2 = 0.5261 Largest diff. peak and hole 3.308 and -3.390 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x+1,y,-z+3/2; -x,y,-z+1/2

230 5 + - Table 3.24. Selected Bond Lengths [Å] for [(h -C5Me5)In2] [B(C6F5)4]

C(11)-C(12)#1 1.39(2) C(41)-B(1) 1.99(2) C(11)-C(12) 1.39(2) C(51)-B(1) 2.00(2) C(11)-In(1)#1 2.693(10) C(61)-B(1) 2.009(18) C(11)-In(1) 2.693(10) C(21)-C(22) 1.38(2) C(12)-C(13) 1.41(3) C(21)-In(2) 2.705(10) C(13)-C(13)#1 1.44(4) C(21)-In(2)#2 2.705(10) C(21)-C(22)#2 1.38(2) C(22)-In(2) 2.702(19) C(31)-B(1) 2.029(18) In(1)-Ct(01) 2.45

In(1)-Ct(02) (C6F5) 3.79

5 + - Table 3.25. Selected Bond :Angles [°] for [(h -C5Me5)In2] [B(C6F5)4]

Ct03-In(1)-Ct01 125.7 C(21)-C(22)-C(23) 108.6(16) C(12)#1-C(11)-C(12) 111(2) C(221)-C(22)-C(23) 116.2(17) C(12)#1-C(11)-C(111) 124.7(11) C(21)-C(22)-C(23) 108.6(16) C(12)-C(11)-C(111) 124.7(11) C(221)-C(22)-C(23) 116.2(17) C(12)#1-C(11)-In(1)#1 76.4(9) C(21)-C(22)-In(2) 75.3(8) C(12)-C(11)-In(1)#1 76.0(9) C(221)-C(22)-C(23) 116.2(17) C(111)-C(11)-In(1)#1 114.8(5) C(21)-C(22)-In(2) 75.3(8) C(12)#1-C(11)-In(1) 76.0(9) C(121)-C(12)-C(11) 144(3) C(12)-C(11)-In(1) 76.4(9) C(121)-C(12)-C(13) 108(3) C(111)-C(11)-In(1) 114.8(5) C(11)-C(12)-C(13) 107.0(16)

231 References and Notes

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235

(37) Bailey, N. A.; Bird, P. H.; Wallbridge, M. G. H. Inorg. Chem. 1968, 7, 1575.

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(40) All BP8615 calculations were performed using the Gaussian 94 (Revision B

2) suite of programs. All-electron basis sets were used for C, H, F. (6-31G

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See also, (b) Wehmschulte, R. J.; Ruhlandt-Senge, K.; Olmstead, M. M.;

Hope, H.; Sturgeon B. E.; Power, P. P. Inorg. Chem. 1993, 32, 2983; (c)

Wiberg, N.; Amelunxen, K.; Blank, T.; Nöth H.; Knizek, J. Organometallics

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Phys. Rev. A 1988, 38, 3098; (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B

1988, 37, 785; (d) Vosko, S. H.; Wilk L.; Nusair, M. Can. J. Phys. 1980, 58,

1200. All DFT calculations were performed using the Gaussian 94 (revision

B2) suite of programs. All-electron basis sets were used for C, H (6-31G(d))

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236

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The X-ray crystal structure of Ga(C6F5)3×THF has been determined in our

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(70) In(C6F5)3 was prepared by a similar procedure to that described in the Ph.D.

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J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrewski, V. G.; Ortiz, J. V.;

Foresman, J. B.; Cioslowski, J.; Stefanow, B. B.; Nanayakkara, A.;

Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;

Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;

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785. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.

(74) Basis sets: 6-31G* for C and H, 6-31+G* for Al.

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240

CHAPTER 4

Reactions of Group 13 Cyclopentadienides with a Nucleophilic Carbene

Introduction

There has been considerable recent interest in the reactions of nucleophilic carbenes with main group Lewis acids.1 Borane adducts with (formally) neutral carbon donors such as carbon monoxide, isonitriles, or phosphine ylides are well established. Since conventional carbene complexes show pronounced metal-to- ligand p backdonation, electron-poor (coordination) fragments are not well suited for stabilizing carbene ligands. However, N-heterocyclic carbenes do not depend on backdonation due to delocalization of the nitrogen lone pair; 1:1 adducts with BH3 or BF3 are thermally stable and can even be sublimed without decomposition. In the context of aluminum and gallium chemistry, it has been demonstrated that imidazol-

2 2-ylidenes will form 1:1 complexes with MMe3 (M = Al, Ga) and MH3 (M = Al,

3 Ga). The metal-Ccarbene bonds in the monomeric, tetrahedrally coordinated GaMe3 and AlMe3 adducts are significantly longer than the metal-Cmethyl bonds (Al-Ccarbene

2.124(6) Å; Al-Cmethyl 1.940(5) and 2.062(7) Å). In related chemistry, it has been shown that the outcome of the reaction of homoleptic cyclopentadienylaluminum compounds with isonitriles is dependent upon the cyclopentadienyl ring

241 1 4 substituents. Thus, while Al(h -C5Me5)3 forms a 1:1 complex with t-BuNC, the more sterically hindered alane (1,2,4-Me3C5H2)3Al undergoes an insertion reaction with this isocyanide to form a heterometallacycle.5 Attempts to prepare the fully

6 methylated cyclopentadienyl alane, Al(C5Me5)3, have not been successful thus far ;

7 however, the gallium analogue, Ga(C5Me5)3, is known and does not form complexes with Et2O or THF. Herein it is reported that the latter gallane undergoes an unprecedented reaction with tetramethylimidazol-2-ylidene.

Results and Discussion

1 (h -C5Me5)2GaH·carbene Complex

Treatment of Ga(C5Me5)3 with an equimolar quantity of tetramethylimidazol-2-ylidene8 in toluene solution results, after isolation and recrystallization, in a 54% yield of Ga(C5Me5)2H·carbene (1). A preliminary structure assignment for 1 was based on 1H and 13C NMR spectroscopic data which evidenced the presence of two C5Me5 rings, a carbene, and a hydride. However, the hapticities of the C5Me5 rings were not clear from the NMR data hence an X-ray crystallographic study was undertaken.

Compound 1 crystallizes in the triclinic space group P-1 with Z = 2 with no unusually short intermolecular contacts and one disordered molecule of toluene per formula unit. Details of the data collection, structure solution and refinement are compiled in Table 4.1 and selected metrical parameters are listed in Tables 4.2 and

242 4.3. The crystalline state features a four-coordinate gallium atom bonded to two h1- attached C5Me5 rings along with the carbene and hydride ligands, as shown in

Figure 4.1. The geometry at gallium is distorted tetrahedral. Thus the bond angle between the two C5Me5 ring carbons, C(11) and C(21), is 121.9(2)°, while that between C(11) and the carbenic carbon, C(31), is 105.2(2)°. The hydride ligand was located and refined isotropically and the Ga-H bond distance of 1.62(5) Å is

3b comparable to those reported for the GaH3 complex of 1,3-diisopropyl-4,5- dimethylimidazol-2-ylidene (1.58(5) and 1.62(3) Å). The Ga-C (carbene) bond

3b distance of 2.057(5) Å in 1 is also similar to that reported for the latter GaH3 complex (2.071(5) Å). The Ga-C(C5Me5) bond distances in 1, which average

7 2.110(5) Å, are slightly longer than those reported for Ga(C5Me5)3 [Av 2.038(4)

Å], presumably due to the increase in the gallium coordination number from 3 to 4.

1 Figure 4.1. Molecular structure of (h -C5Me5)2GaH carbene complex (1) showing the atom numbering scheme. 243 N N Ga + :C Ga :C N N

2

H H H H N H H Ga :C

N

1 1 Scheme 4.1. Plausible mechanism for the formation of the (h -C5Me5)2GaH carbene complex (1)

A plausible mechanism for the formation of 1 (Scheme 4.1) involves the

- initial displacement of a [C5Me5] anion and formation of a carbene adduct of the decamethylgallocenium cation 2.9 Support for this view is provided by the fact that

- a similar [C5H5] displacement/carbene coordination reaction has been observed previously with d-block metallocenes (Scheme 4.2).10 However, in the case of the gallocenium cation the carbene adduct is evidently unstable and undergoes reaction

- with the [C5Me5] counterion via hydride transfer to form 1 and tetramethylfulvene.11 An alternative mechanism that leads to the same products

· involves the elimination of the [C5Me5] radical upon treatment of Ga(C5Me5)3 with tetramethylimidazol-2-ylidene to form a carbene adduct of the (unknown) gallyl

radical [Ga(C5Me5)2] . In main group pentamethylcyclopentadienyl compounds, it

· has been shown in a single electron oxidation process the [C5Me5] radical is

244 + · eliminated, and a cationic E(R) species is formed; the [C5Me5] radical dimerizes to

11 (C5Me5)2 or reacts under hydrogen transfer to give tetramethylfulvene. Therefore, the observed product 1 would then have been formed by transfer of a hydrogen atom

· 12 from [C5Me5] to the carbene adduct. As pointed out by Jutzi and Reumann, the

- [C5Me5] anion and the [C5Me5] radical are rather stable entities and hence either or both of them can serve as leaving groups.

N

C:

N M M N N [C5H5] C C

N N

M = Ni, Cr

Scheme 4.2. Reaction of tetramethylimidazol-2-ylidene with transition metal metallocenes

1 (h -C5Me5)2AlH·Carbene Complex

2 It is particularly interesting to note that when MeAl(h -C5Me5)2 was treated with tetramethylimidazol-2-ylidene using the same procedure as that described

1 above for the Ga(h -C5Me5)3 reaction, the product was the colorless, crystalline (h-

C5Me5)2AlH carbene complex (3). The proposed formulation for 3 was consistent with mass spectral data and the presence of Al-H and C5Me5 groups was evident from 1H NMR spectroscopic data. Furthermore, the 27Al NMR chemical shift fell in the region expected for a tetra-coordinate aluminum atom; however, to establish e.g.

245 the hapticity of the cyclopentadienyl ring it was necessary to perform an X-ray crystal structure analysis. Individual molecules of 3 crystallize in the triclinic space group P-1 with Z = 2 with one disordered molecule of toluene present per formula unit; there are no unusually short intermolecular contacts (Figure 4.2). Details of the data collection, structure solution and refinement are compiled in Table 4.4 and selected metrical parameters are listed in Tables 4.5 and 4.6. The C5Me5 groups are attached to aluminum in an h1 fashion and the geometry about the aluminum atom is distorted tetrahedral. Thus the bond angle between the two C5Me5 ring carbons,

C(8) and C(22), is 119.8(12)°, while that between C(8) and the carbenic carbon,

C(11), is 107.6(11)°. The hydride ligand was located and refined isotropically and

3b the Al-H bond distance of 1.50(5) Å is comparable to those reported for the AlH3 complex of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1.53(4) and 1.51(3)

Å). The Al-C (carbene) bond distance of 2.052(3) Å in 2 is also similar to that

3b reported for the latter AlH3 complex (2.046(5) Å). The Al-C(C5Me5) bond distances in 2, which average 2.094(3) Å, are slightly longer than those reported2 for the AlMe3 complex of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (av 2.001(6)

Å), presumably due to the increased size of the pentamethylcyclopentadienyl ligands.

246

1 Figure 4.2. Molecular structure of (h -C5Me5)2AlH·carbene complex (3) showing the atom numbering scheme.

A reasonable mechanism for the formation of 3 has yet to be established; however, adventitious water does not appear to be the cause of the reaction.

Interestingly, hydride transfer products have also been also been formed in the reaction of nucleophilic carbenes with PF5 a case where simple adduct formation is difficult to control due to the extreme reactivity of the two components (Scheme

4.3).13

Mes Mes Mes F F N N F N F C6H5CH3 C: + P F C P F + CH F N F N HPF6 F N F Mes Mes Mes Major Product Scheme 4.3. Reaction of a nucleophilic carbene with PF5 247 Conclusions

In summary, the reaction of Ga(C5Me5)3 with tetramethylimidazol-2-ylidene

1 unexpectedly affords the carbene complex Ga(h -C5Me5)2H·carbene (1). Similarly

2 1 the reaction of MeAl(h -C5Me5) with tetramethylimidazol-2-ylidene affords Ga(h -

C5Me5)2H·carbene (3), the aluminum analogue of 1. Both complexes have been fully characterized, and possible reaction mechanisms for the formation of 1 have been presented.

248

Chapter 4

Experimental

General procedures

All solvents (diethylether, THF, benzene, toluene, hexane, pentane) were distilled over sodium benzophenone ketyl, or CaH2 (CH2Cl2) and degassed prior to use. Solid reactants were handled in a VAC Vacuum Atmospheres or M-Braun argon-filled drybox. All reactions were performed under a dry oxygen-free argon atmosphere or under vacuum using standard Schlenk or drybox techniques; all glassware was oven-dried before use.

The group 13 trihalides were purchased from a commercial source and used without further purification. Pentamethylcyclopentadiene was prepared according to the literature procedure14 or purchased from a commercial source and used without further purification. The compounds 1,3,4,5-tetramethylimidazolo-2-

8 7 15 ylidene, Ga(C5Me5)3, and MeAl(C5Me5)2 were prepared according to literature methods.

Physical Measurements

Low-resolution EI mass spectra were obtained on a Bell and Howell 21-491 instrument; low-resolution CI mass spectra were run on a Finnigan MAT TSQ-700; and high-resolution mass spectra were measured on a VG Analytical ZAB-VE 249 sector instrument. Solution-phase NMR spectra were recorded at 295 K, unless otherwise noted, on a GE QE-300 instrument (1H, 300 MHz; 13C, 75 MHz; 27Al,

78.21 MHz) or a Varian Inova-500 spectrometer (1H, 500 MHz; 13C, 125 MHz;

27Al, 130 MHz). All NMR samples were flame-sealed or run immediately following removal from the drybox. Benzene-d6 was dried over sodium-potassium alloy and distilled prior to use. Toluene-d8 and CD2Cl2 were obtained in sealed vials from a commercial source and used without further purification. 1H and 13C NMR spectra are reported relative to tetramethylsilane (0.00 ppm) and are referenced to

11 19 solvent. B chemical shifts are reported relative to BF3(Et2O) (0.00 ppm), F

27 chemical shifts are reported relative to C6F6 (-162.9 ppm), and Al chemical shifts

3+ 13 are reported relative to [Al(D2O)6] (0.00 ppm). All C spectra were obtained under conditions of broadband proton decoupling unless otherwise noted. Variable- temperature (VT) NMR studies utilized equilibration times of ten minutes at each temperature. Melting points were obtained in sealed capillaries under argon (1 atm) on a Fisher-Johns apparatus and are uncorrected.

X-ray Crystallography

Suitable single crystals were covered with perfluorinated polyether oil and the X-ray data were collected on Nonius Kappa CCD diffractometer. Structure determinations and refinements were performed by Dr. Charles Macdonald at The

University of Texas at Austin. All structures were solved by direct methods and

250 refined by full-matrix least squares on F2 using the Siemens SHELX PLUS 5.0

(PC) software package.16 All non-hydrogen atoms were allowed anisotropic thermal motion and hydrogen atoms, which were included at calculated positions

(C-H 0.96 Å), were refined using a riding model and a general isotropic thermal parameter. The total number of reflections, collection ranges, and final R-values are listed in the appropriate tables for each molecule.

Data from the Nonius-Kappa CCD diffractometer were collected at 153 K using an Oxford Cryostream low-temperature device and graphite monochromated

Mo Ka radiation (l = 0.71073 Å). A correction was applied for Lorentz- polarization. A total of 105 frames of data were collected using w-scans with a scan range of 1.9 and a counting time of 482 seconds per frame.

1 Preparation of (h -C5Me5)2GaH·Carbene complex (1)

A solution of 1,3,4,5-tetramethylimidazol-2-ylidene8 (0.074 g. 0.60 mmol) in

7 toluene (20 mL) was added dropwise to a stirred solution of Ga(C5Me5)3 (0.280,

0.59 mmol) in 20 mL of toluene at –78 °C. While warming to room temperature over an 8 h period, the color of the reaction mixture darkened slowly from pale yellow to amber. After being stirred at room temperature for a further 24 h, the dark amber solution was filtered through Celite®, and the filtrate was concentrated to a volume of 2 mL. The resulting red oil was cooled to –20 °C to afford a crop of

+ amber crystals, 0.15 g, 54% yield; mp 112-113 °C (dec). HRMS (CI , CH4), calcd

251 + 1 for C27H42GaN2, (M-H) : 463.2604; found 463.2615. H NMR (C6D6): d 7.13 (m,

3H, o & m-Ar), 7.02 (m, 2H, p-Ar), 3.17 (s, 6H, N-Me), 2.10 (s, 3H, Ar-Me), 1.96

13 1 (s, 30H, C5Me5), 1.28 (s, 6H, NCMe), 0.20 (s, 1H, Ga-H). C{ H} NMR (C6D6): d

140.40 (s, NCN), 137.48 (s, ipso-Ar), 129.27 (s, o-Ar), 128.51 (s, p-Ar), 128.29

(NCCN), 127.50 (s, m-Ar), 119.18 (s, C5Me5), 34.96 (s, N-Me) 21.50 (Ar-CH3),

13.30 (s, C5Me5), 7.83 (s, NCMe). Compound 1 crystallizes with one disordered toluene molecule per formula unit.

1 Preparation of (h -C5Me5)2AlH Carbene complex (2)

A solution of 1,3,4,5-tetramethylimidazol-2-ylidene (0.20 g, 1.60 mmol) in toluene (20 mL) was added dropwise to a stirred pale yellow solution of (h2-

C5Me5)2AlMe (0.50, 1.60 mmol) in toluene (20 mL) at – 78 °C. The reaction mixture was allowed to warm to room temperature and stir for 48 h. The resulting amber solution was filtered through Celite®, and concentrated to a volume of 5 mL.

A crop of amber rod-shaped crystals was deposited over several weeks of storage at

+ room temperature, 0.5 g, 73% yield; mp 129-130 °C. MS (CI , CH4): m/z 421 [(M-

+ + + H) , 29.94%]; 411 [Cp*AlH(C7H12N2)2) , 68.02%]; 297 [(C5Me5)2Al , 57.89%];

+ + 287 [Cp*AlH(C7H12N2) , 100%] ; 259 [Cp*(C7H12N2), 19.76%]; 163 [Cp*Al+H ,

+ + 73.50%); HRMS (CI , CH4): calcd for C27H44AlN2 (M + H) 423.3320; found,

+ 423.3331; calcd for C24H40AlN4 [Cp*AlH(C7H12N2)2] 411.3068; found, 411.3087;

+ calcd for C17H28AlN2 [Cp*AlH(C7H12N2)] 287.2068; found, 287.2052; calcd for

252 + 1 C17H27N2 [Cp*(C7H12N2)] , 259.2174; found, 259.2178; H NMR (C6D6): d 3.059

(s, 6H, N-Me), 1.992 (s, 30H, Cp*-Me), 1.761 (s, 6H, NCMe), -0.086 (s, 1H, AlH);

13 1 C{ H} NMR (C6D6): d 124.334 (s, NCCN), 116.14 (s, Cp* ring), 33.66 (s, N-

27 Me), 12.03 (s, Cp*-Me), 7.70 (s, NCMe); Al NMR (C6D6): d 146.1 (br, w1/2 =

4300 Hz). Compound 2 crystallizes with one disordered toluene molecule per formula unit.

253

Chapter 4

Tables of Crystallographic

Data

254

1 Figure 4.1. Molecular structure of the (h -C5Me5)2GaH·carbene complex (1) showing the atom numbering scheme.

255 1 Table 4.1. Crystal Data and Structure Refinement for (h -C5Me5)2GaH·Carbene (1)

Identification code shelxm

Empirical formula C27 H43 Ga N2 Formula weight 465.35 Temperature 153(2) K Wavelength 0.71069 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 8.6290(3) Å a= 91.4770(10)°. b = 9.9040(3) Å b= 78.9840(10)°. c = 17.8440(3) Å g = 75.1050(10)°. Volume 1442.07(7) Å3 Z 2 Density (calculated) 1.072 Mg/m3 Absorption coefficient 0.968 mm-1 F(000) 500 Crystal size 0.5 x 0.5 x 0.3 mm3 Theta range for data collection 2.92 to 27.54°. Index ranges -11<=h<=11, -12<=k<=12, -17<=l<=23 Reflections collected 24166 Independent reflections 6616 [R(int) = 0.0748] Completeness to theta = 27.54° 99.3 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 6616 / 0 / 289 Goodness-of-fit on F2 1.031 Final R indices [I>2sigma(I)] R1 = 0.0944, wR2 = 0.2704 R indices (all data) R1 = 0.1195, wR2 = 0.2877 Largest diff. peak and hole 4.039 and -0.893 e.Å-3

256 1 Table 4.2. Selected Bond Lengths [Å] for (h -C5Me5)2GaH·Carbene (1)

C(11)-C(15) 1.475(8) C(22)-C(221) 1.503(8) C(11)-C(12) 1.480(8) C(23)-C(24) 1.448(9) C(11)-C(111) 1.590(8) C(23)-C(231) 1.513(9) C(11)-Ga 2.102(5) C(24)-C(25) 1.360(9) C(12)-C(13) 1.362(8) C(24)-C(241) 1.509(9) C(12)-C(121) 1.489(8) C(25)-C(251) 1.497(9) C(13)-C(14) 1.453(9) C(31)-N(32) 1.344(7) C(13)-C(131) 1.506(8) C(31)-N(35) 1.357(7) C(14)-C(15) 1.372(8) C(31)-Ga 2.057(5) C(14)-C(141) 1.505(8) C(33)-C(34) 1.343(9) C(15)-C(151) 1.502(9) C(33)-N(32) 1.392(7) C(21)-C(22) 1.473(8) C(33)-C(331) 1.503(9) C(21)-C(25) 1.492(8) C(34)-N(35) 1.405(7) C(21)-C(211) 1.542(8) C(34)-C(341) 1.483(8) C(21)-Ga 2.119(5) C(321)-N(32) 1.454(8) C(22)-C(23) 1.347(9) C(351)-N(35) 1.450(7)

1 Table 4.3. Selected Bond Angles [°] for (h -C5Me5)2GaH·Carbene (1)

C(15)-C(11)-C(12) 104.9(4) C(22)-C(23)-C(24) 108.3(6) C(15)-C(11)-C(111) 119.2(5) C(25)-C(24)-C(23) 109.9(5) C(12)-C(11)-C(111) 117.2(5) C(24)-C(25)-C(21) 107.8(5) C(22)-C(21)-C(25) 103.8(5) N(32)-C(31)-N(35) 104.5(4) C(22)-C(21)-C(211) 116.8(5) C(34)-C(33)-N(32) 107.1(5) C(25)-C(21)-C(211) 117.7(5) C(33)-C(34)-N(35) 105.8(5) C(23)-C(22)-C(21) 110.0(5) C(33)-C(34)-C(341) 131.8(6) C(31)-N(35)-C(34) 111.2(5) N(35)-C(34)-C(341) 122.4(6) C(31)-Ga-C(11) 105.2(2) C(31)-N(32)-C(33) 111.4(5) C(31)-Ga-C(21) 114.8(2) C(11)-Ga-C(21) 121.9(2)

257

1 Figure 4.2. Molecular structure of the (h -C5Me5)2AlH·carbene complex (3) showing the atom numbering scheme.

258 1 Table 4.4. Crystal Data and Structure Refinement for (h -C5Me5)2AlH·Carbene (3)

Identification code shelx

Empirical formula C28 H45 Al N2 Formula weight 436.64 Temperature 153(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = 8.6798(2) Å a= 91.8030(10)°. b = 9.8298(2) Å b= 100.7170(10)°. c = 17.8638(4) Å g = 105.6370(10)°. Volume 1436.77(5) Å3 Z 2 Density (calculated) 1.009 Mg/m3 Absorption coefficient 0.086 mm-1 F(000) 480 Crystal size 0.4 x 0.5 x 0.3 mm3 Theta range for data collection 3.04 to 30.39°. Index ranges -11<=h<=12, -13<=k<=13, -21<=l<=24 Reflections collected 22446 Independent reflections 7468 [R(int) = 0.0509] Completeness to theta = 30.39° 86.2 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7468 / 0 / 301 Goodness-of-fit on F2 1.089 Final R indices [I>2sigma(I)] R1 = 0.0934, wR2 = 0.2604 R indices (all data) R1 = 0.1179, wR2 = 0.2798 Largest diff. peak and hole 2.117 and -0.841 e.Å-3 ______Symmetry transformations used to generate equivalent atoms: -x,-y+1,-z+1

259 1 Table 4.5. Bond Lengths [Å] for (h -C5Me5)2AlH·Carbene (3)

Al(01)-C(011) 2.052(3) C(007)-C(015) 1.440(4) Al(01)-C(008) 2.088(3) C(007)-C(024) 1.503(4) Al(01)-C(022) 2.100(3) C(008)-C(019) 1.472(4) N(002)-C(011) 1.356(4) C(008)-C(017) 1.531(4) N(002)-C(010) 1.394(4) C(009)-C(028) 1.366(4) N(003)-C(011) 1.354(4) C(009)-C(022) 1.471(4) N(003)-C(021) 1.389(4) C(009)-C(025) 1.503(4) C(004)-C(013) 1.356(5) C(010)-C(021) 1.339(5) C(004)-C(022) 1.490(4) C(013)-C(028) 1.449(5) C(004)-C(020) 1.504(4) C(013)-C(032) 1.508(5) C(005)-C(033) 1.403(9) C(015)-C(023) 1.504(4) C(005)-C(031) 1.463(9) C(018)-C(022) 1.536(4) C(006)-C(015) 1.377(4) C(019)-C(027) 1.500(4) C(006)-C(008) 1.476(4) C(028)-C(030) 1.499(5)

1 Table 4.6. Bond Angles [°] for (h -C5Me5)2AlH·Carbene (3)

C(011)-Al(01)-C(008) 107.56(11) C(006)-C(015)-C(007) 108.7(3) C(011)-Al(01)-C(022) 115.59(11) C(006)-C(015)-C(023) 127.4(3) C(008)-Al(01)-C(022) 119.76(12) C(007)-C(015)-C(023) 123.9(3) C(033)-C(005)-C(031) 122.4(6) C(007)-C(019)-C(008) 108.6(3) C(015)-C(006)-C(008) 108.5(3) C(007)-C(019)-C(027) 127.4(3) C(015)-C(006)-C(026) 127.4(3) C(008)-C(019)-C(027) 124.0(3) C(008)-C(006)-C(026) 123.9(3) C(010)-C(021)-N(003) 106.8(3) C(019)-C(007)-C(015) 109.2(3) C(019)-C(008)-C(017) 120.5(3) C(019)-C(007)-C(024) 127.5(3) C(006)-C(008)-C(017) 119.0(3) C(015)-C(007)-C(024) 123.4(3) C(021)-C(010)-N(002) 106.4(3) C(019)-C(008)-C(006) 104.6(2)

260 References and Notes

(1) For recent reviews, see: (a) Carmalt, C. J.; Cowley, A. H. Adv. Inorg. Chem.

2000, 50, 1; (b) Bourissou, D.; Guerret, O.; Gabbaï, F. P.; Bertrand, G.

Chem. Rev. 2000, 100, 39; (c) Arduengo III, A. J. Acc. Chem. Res. 1999, 32,

913.

(2) Li, X. W.; Su, J. R.; Robinson, G. H. Chem. Commun. 1996, 2683.

(3) (a) Arduengo III, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F. J. Am.

Chem. Soc. 1992, 114, 9724; (b) Francis, M. D.; Hibbs, D. E.; Hursthouse,

M. B.; Jones, C.; Smithies, N. A. J. Chem. Soc., Dalton Trans. 1998, 3249.

(4) Fisher, J. D.; Wei, M.-Y.; Willett, R.; Shapiro, P. J. Organometallics 1994,

13 3324.

(5) Shapiro, P. J.; Vij, A.; Yap, G. P. A.; Rheingold, A. L. Polyhedron, 1995,

14, 203.

(6) Shapiro, P. J. Coord. Chem. Rev. 1991, 189, 1.

(7) Schumann, H.; Nickel, S.; Weimann, R. J. Organomet. Chem. 1994, 468, 43.

(8) Kuhn, N.; Kratz, T. Synthesis 1993, 561.

(9) For the synthesis of the decamethylgallocenium cation, see: Macdonald, C.

L. B.; Gorden, J. D.; Voigt, A.; Cowley, A. H. J. Am. Chem. Soc. 2000, 122,

11725.

(10) Abernethy, C. D., Clyburne, J. A. C.; Cowley, A. H.; Jones, R. A. J. Am.

Chem. Soc. 1999, 121, 2329. 261

(11) Davies, A. G., J. Chem. Soc., Perkin Trans. 2 1981, 692.

(12) Jutzi, P.; Reumann, G. J. Chem. Soc., Dalton Trans. 2000, 2237.

(13) Arduengo III, A. J.; Davidson, F.; Krafczyk, R.; Marshall, W. J.;

Schmutzler, R. Monatshefte fûr Chemie 2000, 131, 251.

(14) Quindt, V.; Saurenz, D.; Schmitt, O.; Schlär, M.; Dezember, T.;

Wolmershäuser, G.; Sitzmann, H. J. Organomet. Chem. 1999, 579, 376.

(15) Burns, C. T.; Shapiro, P. J.; Budzelaar, P. H. M.; Vij, A. Organometallics

2000, 19, 3361.

(16) Sheldrick, G. M., SHELXTL PC Version 5.0, Siemens Analytical X-ray

Instruments, Inc., 1994.

262 Appendix. Listing of Compound Numbers by Chapters

Chapter 2

1 3 (1) (h (s)-C5Me5)2BCl (14) [(h -C5Me5)(C6F5)GaCl]2 1 1 1 (2) (h (s)-C5Me5)2BBr (15) (h -C5Me5)2GaCl2Ga(C6F5)(h -C5Me5) 1 1 2 (3) (h (s)-C5Me5)2BMe (16) (h (p)-C5Me5)(h -C5Me5)GaC6F5 1 5 + - (4) “(h-C5Me5)2AlCl” (17) [(h (p)-C5Me5)(h -C5Me5)Ga] [AlCl4] 2 2- (5) (h -C5Me5)2AlMe (18) [Me2Si(h-C5Me4)(N-t-Bu)] , CGC 1 1 (6) [(h (s)-C5Me5)2GaCl]2 (19) [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×THF 1 (7) (h-C5Me5)2GaBr (20) [Me2Si(h -C5Me4)(N-t-Bu)]GaMe×THF 1 2 1 (8) (h (p)-C5Me5)(h -C5Me5)GaMe (21) [Me2Si(h -C5Me4)(N-t-Bu)]AlMe×carbene 1 5 5 + (9) (h (p)-C5H5)(h -C5H5) 2Be (22) [Me2Si(h -C5Me4)(N-t-Bu)]M + 1 5 + 5 + [10] [(h -C5Me5)(h -C5Me5)B] (23) [H2Si(h -C5H4)(N-CH4)]M + 5 + 1 [11] [(h -C5Me5)2Al] (24) [Me2Si(h -C5Me4)(N-t-Bu)]AlCl×Et2O 5 + 5 5 5 + (12) [(h -C5Me5)(C6F5)AlCl]2 [25] [(h -Cp*)Sn(m-h -Cp*)Sn(h -Cp*)] + 1 3 + + 6 5 6 + [13] [(h -C5Me5)(h -C5Me5)Ga] [26] [(h -C7H8)In(m-h -Cp*)In(h -C7H8)]

Chapter 3

5 5 (1) [(h -C5Me5)Al]4 (16) (h -C5Me5)AlAl(C6F5)3 3 (2) (h-C5Me5)6Al6P4 (17) (C6F5)2Al(h -C5Me5) (3) [(h-C5Me5)AlE]4 (E = S, Se, Te) (18) HC{MeC(2,6-i-Pr2C6H3)N}2Ga 5 5 (4) (h -C5Me5)3Al3E2 (E = As, Sb) (19) [(h -C5Me5)Ga]6 (5) 1,4-diazabuta-1,3-diene (20) HC{MeC(2,6-i-Pr2C6H3)N}2GaB(C6F5)3 5 (21) (h -C5Me5)Ga®B(C6F5)3 5 (10) Al[N(t-But)CH=CHN(t-But)]2 (22) (h -C5Me5)Ga®Al(C6F5)3 5 + - (23) [In(m-h -C5Me5)In] [B(C6F5)4] 5 (12) (h -C5Me5)AlN(Mes)CH=CHN(Mes)

(13) (h-C5Me5)GaN(Mes)CH=CHN(Mes) 5 (14) (h -C5Me5)AlB(C6F5)3 (15) HAlAlH3

R R R Mes N N N N Cp*Al Cp*Al M R' M: N N N N Mes R R R (6) (7) (8) (9) (11)

263 Chapter 4

1 (1) (h -C5Me5)2GaH (tetramethylimidazol-2-ylidene) 1 (3) (h -C5Me5)2AlH (tetramethylimidazol-2-ylidene)

N

Ga :C N

(2)

264

Vita

John David Gorden was born in Fort Worth, Texas, on April 26, 1972, the son of Robert Gorden and Patricia Gorden. After graduating from Kaiserslautern

American High School, Kaiserslautern, Germany, he entered The University of

Texas at Arlington in Arlington, Texas. He received the degree of Bachelor of

Science Centennial Scholar in Chemistry from The University of Texas at Arlington in December 1996. After spending the summer as a research scientist with Alcon

Research Laboratories, he entered the Graduate School of The University of Texas at Austin in 1997. He married Anne Elizabeth Vivian of Richardson, Texas, on

November 4, 2000.

Permanent address: 1829 Hillcrest Fort Worth, TX 76107

This dissertation was typed by the author.

265