Donor Stabilized Germylenes and Their Transition Metal Complexes: Structure, Bonding, and Thermochemistry

Donor stabilized germylenes and their transition metal complexes: structure, bonding, and thermochemistry

Marc T. F. Baumeister

A Thesis presented to The University of Guelph

In partial fulfilment of requirements for the degree of Master of Science in Chemistry

Guelph, Ontario, Canada

ABSTRACT

DONOR STABILIZED GERMYLENES AND THEIR TRANSITION METAL COMPLEXES: STRUCTURE, BONDING, AND THERMOCHEMISTRY

Marc T.F. Baumeister Advisor: University of Guelph, 2011 Professor Michael Denk

This thesis investigates the stabilization of divalent germanium using substituted diethanol amine ligands. Germylenes of type RN(CH2CH2OH)2Ge were obtained from N-heterocyclic germylenes and N-alkyl diethanol amines in yields of up to 94%. Single crystal X-ray diffraction confims the presence of a transannular Ge-N dative bond in all cases. In addition, intermolecular dimers containing Ge2O2 rings are formed for R = Me and Et. Reaction of the four germylenes L with nickel carbonyl yielded the respective germylene complexes

L2Ni(CO)2 and LNi(CO)3. The germylenes and their complexes were investigated with DFT methods. Only four methods, SVWN, BB1K, MPWB1K and M062x gave acceptable Ge-N distances. Dimerization energies of the germylenes were examined with the thermochemically accurate M062x method. At the

M062x/Def2-TZVP level, the dimerization energies of the germylenes are very small (ΔG° ≈ 0 kcal/mol). The experimentally observed dimerization or lack thereof may accordingly be determined by packing effects in the solid state or solvation energies in solution.

Acknowledgements

There are numerous people that I would like to thank but foremost of them is my advisor Dr. Michael Denk, a man who always had new ideas to pursue, anecdotes to tell and calculations to do. Thank you for giving me the opportunity to work in your laboratory and encouraging me throughout my Masterʼs work.

Additionally, I would like to thank the members of my committee: Dr.

Adrian Schwan, Dr. Marcel Schlaf and Dr. Dmitriy Soldatov for their time and feedback. My thesis is stronger thanks to their constructive criticism and input.

Besides Michael I am indebted to the past members of the Denk group.

Jeff, and Mike who introduced me to the Denk laboratory and got me started, which I hope I was able to pass along to Adam. Although the Denk group was small I could always count on the comradery of the Schwan group. Stefan,

Natasha, Irena, Selim and Suneel, it was a pleasure to share an office with you and getting to experience the ups and downs of a larger group.

Additionally, I cannot express my appreciation and gratitude towards

Becky, Chad, Dom, Eric, Francis and Renee. Always ready to grab a coffee, talk about chemistry or blow off steam. I don't know if I could have finished this without you guys.

Finally, my parents for their endless support.

iii Table of Contents

Acknowledgements iii Table of Contents iv List of Abbreviations viii List of Tables x List of Schemes xii List of Figures xv List of Numbered Compounds xviii

iv Chapter 1. Introduction 1 1.1 Carbenes and their heavier analogues 2 1.2 Alkyl, amido and alkoxy complexes: Transition metals vs. main group 4 1.2.1 Transition metal complexes 4 1.2.2 Stable group 14 sextet species 6 1.2.3 Ground state of carbenes and heavier analogues: Singlet vs. Triplet 11 1.2.4 Stabilizing the singlet ground state 14 1.2.4.1 Kinetic stabilization 14 1.2.4.2 Thermodynamic stabilization 16 Inductive effects 16 Mesomeric effects 16 Aromaticity 17 1.2.4.3 Stability through high coordination numbers 18 Intermolecular dative bonds 20 Intramolecular dative bonds 20 1.2.5 Computational evidence of stabilizing effects 21 1.2.6 Polyamine ligand system 23 1.2.7 Ligand design 25 1.2.8 Synthetic targets 27 1.3 Main group – transition metal complexes 28 1.4 Computational investigation to determine relative stability 30 Chapter 2. Results and Discussion 32 2.1.1 Synthesis of N-alkyl diethanol amines 10a-d 33 2.1.2 Reaction of diethanol amine with 2-bromopropane: Synthesis of N-isopropyl diethanol amine 10c 33 2.1.3 Purification and drying of diethanol amines 10a-d 34 2.1.4 Synthesis of germanium–diethanol amine complexes 11 35 2.1.5 Attempted synthesis of germylene 11 through elimination of trimethylsilylchloride 35

v 2.1.5.1 Reaction of N-alkyl diethanolamine 10a and d with bis(trimethylsilyl)amine: Synthesis of 4-alkyl-1,7- bis(trimethylsilyl)-1,7-di-oxo-4-aza-heptane 36 2.1.5.2 Attempted synthesis of germylene 11 through reduction of dichloro germocane 40 37 2.1.5.3 Reaction of ligands 39a and d with germanium tetrachloride: Synthesis of 1,1-dichloro-5-alkyl-2,8-di- oxa-5-aza-1-germa-bicyclo[3.3.0]octane 40 37 2.1.5.4 Attempted reduction of germocane 40a with alkali metals 39

2.1.6 Synthesis of germylene 11a using GeCl2•dioxane as a starting material 40 2.1.7 Alcoholysis of amido germylenes 43 2.1.7.1 Reaction of germylene 16 with N-alkyl diethanol amine: Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane 11 43 2.1.7.2 Experimental structure of crystalline germylenes 11 45 2.1.7.3 NMR spectroscopy and the solution structure of germylene 11 49 2.1.7.4 Mass spectra of germylenes 11 51

2.2 Reaction of 11 with Ni(CO)4 53 2.2.1 Synthesis of (5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane) nickel carbonyls 43 54 2.2.2 Experimental structure of crystalline nickel germylenes 43 54 2.2.3 Spectroscopic analysis of the solution structure of nickel- germylenes 43 57 3.1 Synthesis of silicon–diethanol amine complexes 58 3.1.1 Synthesis of 1-chloro-2,8-di-oxa-5-aza-1-sila-bicyclo[3.3.0] octane 42 59 4.1 Computational investigations 61

vi 4.1.1 General comments on the calculations 61 4.1.2 Structural optimization of germylenes 62 4.1.2.1 Considering structural conformations 64 4.1.2.2 Wiberg bond orders and charge densities 64 4.1.3 Thermochemistry 69 4.1.3.1 Calculated dimerization energies 69 4.1.3.2 HOMO-LUMO gaps 72 Chapter 3. General Comments and Future Work 74 Chapter 4. Experimental 79 Chapter 5. References 100 Chapter 6. Appendix 107

vii List of Abbreviations

Ad Adamantyl BB1K Becke88-Becke95 1-parameter model for kinetics BSSE Basis set superposition error Cp* Cyclopentadienyl DFT Density functional theory EI Electron ionization Et Ethyl HOMO Highest occupied molecular orbital Hz Hertz IR Infrared INEPT Insensitive nuclei enhanced by polarization transfer iPr iso-propyl LTA Lead tetracetate LUMO Lowest unoccupied molecular orbital MALDI Matrix assisted laser desorption/ionization Me Methyl Mes Mesityl mm Millimole MPWB1K Modified Perdew and Wang Becke95 1-parameter model for kinetics MS Mass spectroscopy NaHMDS Sodium bis(trimethylsilyl)amide NMR Nuclear magnetic resonance np neo-pentyl nPr n-propyl ORTEP Oak Ridge thermal ellipsoid plot program PBE Perdue Burke Ernzerhof functional

viii PCy3 Tricyclohexylphosphine Ph Phenyl pm picometers pp Parts per million SMD Solvation model density tBu Tert-butyl TFA Trifluoroacetic acid TOF Time of flight °C Degrees Celsius

ix List of Tables

Table 1. Experimental and calculated singlet - triplet energy u

Table 2. Heats of hydrogenation [kcal/mol] of selected

germylenes calculated at the CBS-Q level to quantify

the stability gained from different ligand systems. 22

Table 3. Selected experimental bond distances [pm] associated

with the germanium center of 11 for both the

monomers and dimers 45

Table 4. Selected experimental bond angles associated with

the germanium center of 11 for both the monomers

and dimers 48

Table 5. Experimental 1H and 13C shifts of the ethylene

backbone of germylenes 11 in C6D6 50

Table 6. Selected bond distances [pm] for germanium-nickel

complexes 43a-d 56

Table 7. CO valence bands [cm-1] for the carbonyl complexes of

LNi(CO)3 and L2Ni(CO)2 in CH2Cl2 57

Table 8. Experimental 1H and 13C shifts of the ethylene

backbone of nickel-germylenes complexes 40 in C6D6 58

Table 9. 1H, 13C and 29Si NMR shifts for the silanes 44 and 45 60

Table 10. RMS error [pm] and linear correlation coefficients for

computational and experimental (single crystal X-ray)

x of selected structural parameters ([pm] [°]) for

germylene 11c (DFT/Def2-TZVP, CBS-4m). Solvation

at the SMD level. See Appendix for 11a-d 63

Table 11. Wiberg bond orders and atomic valencies for selected

monomeric germylenes 11 (MPWB1K/Def2-TZVP) 66

Table 12. Selected structural bond lengths [pm] and Wiberg

charge densities for monomeric germylenes 11

(MPWB1K/Def2-TZVP ultrafine level). Experimental

structural data from single crystal X-ray structures

where available 67

Table 13. Wiberg-NBO analysis for selected germylenes

(MPWB1K/Def2-TZVP ultrafine level) 68

Table 14. Dimerization energies DG° [kcal/mol] for selected

germylenes (11d-c) and dimeric germylenes (11a-b)

(M062x/Def2-TZVP, CBS-4m, ultrafine grid size) 70

Table 15. Orbital energies (HOMO, LUMO, HOMO-LUMO gaps,

[kcal/mol]) for selected germylenes. M062x/Def2-TZVP

level, THF (SMD) solvent model, ultrafine integration

grid. Ge-N dative bond distances [pm] for comparison 73

xi List of Schemes

Scheme 1. Synthesis of group 4 metal amido and alkoxy complexes 5

Scheme 2. Synthesis of 1,3-di-phenyl-imidazolidin-2-ylidene 6

Scheme 3. Dimerization of alkyl substituted germylene and stannylene 7

Scheme 4. Synthesis of bis(di-tert-butyl-4-methylphenoxy) germylene 8 7

Scheme 5. Zeldin procedure to germylene 11a 8

Scheme 6. Initial synthesis of saturated N-heterocyclic germylene 10

Scheme 7. Synthesis of the saturated and unsaturated N–heterocyclic

germylenes 10

Scheme 8. Pyridine containing diethanolamine germylene and stannylene11

Scheme 9. Lewis acid activated insertion into C-H bond 15

Scheme 10. Resonance stabilization of divalent elements 17

Scheme 11. Visual representation of isogyric and isodesmic reactions 22

Scheme 12. One-pot polyamine synthesis and percent yield from 1,2-

dibromoethane 23

Scheme 13. Synthesis and crystal structure of a donor stabilized

phosphenium cation 34 24

Scheme 14. Reaction of triamine ligands with silicon tetrahalides or trihalides

Scheme 15. Convergent synthesis of stannylene 35 27

Scheme 16. Target molecules of this thesis 28

Scheme 17. Germylene coupling to nickel carbonyl 29

xii Scheme 18. Synthesis of N-isopropyl diethanol amine 10c 33

Scheme 19. Synthesis of alkoxy–borane complex 36

Scheme 20. Synthesis of 4-alkyl-1,7-bis(trimethylsilyl)-1,7-di-oxo-4-aza-

heptane 39 37

Scheme 21. Synthesis of 1,1-dichloro-5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane (R = Me, tBu) 38

Scheme 22. Attempted reduction of of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-

1-germa-bicyclo[3.3.0]octane 40a through alkali metals 39

Scheme 23. Attempted synthesis route to germylene 11a from GeCl2•dioxane

i.) R1=H X=Li 1.nBuLi/hexanes -78°C→r.t. 2.GeCl2•dioxane/THF

3.D ii.) R1= Si(Me)3 X=Si(Me)3 1.GeCl2•dioxane/dioxane 2.D 41

Scheme 24. Proposed formation of germanium dichloride complex 41 42

Scheme 25. Germylene 26 synthesized by Zemlyansky et al. 43

Scheme 26. Synthesis of germylene 16 43

Scheme 27. Alcoholysis of 16: Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane 11 44

Scheme 28. Synthesis of germanium-nickel carbonyl complexes 54

Scheme 29. Synthesis of 1-chloro-2,8-di-oxa-5-aza-1-sila-bicyclo[3.3.0]

octane 42 59

Scheme 30. Attempted deprotonation of chloro-silane 44 with sodium

bis(trimethylsilyl)amide 59

Scheme 31. Proposed formation of silane 45 through silylene 46 60

xiii Scheme 32. Attempted deprotonation of silane 44 with DBU 61

Scheme 33. Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane 11 76

Scheme 34. Synthesis of dialkoxycarbenes 78

xiv List of Figures

Figure 1. Representative N-heterocyclic carbenes and their

analogues 2

Figure 2. Characteristic reactions of germylenes 3

Figure 3. First and second-generation Grubbsʼ ruthenium

catalysts 3

Figure 4. Common ligands used to stabilize electron deficient

metals 4

Figure 5. The [W(NPh)(m-OMe)(OMe)3]2 dimer 6

Figure 6. Mellerʼs N-heterocyclic germylene 9

Figure 7. Stable N–heterocyclic carbenes, germylenes, and

silylenes 9

Figure 8. MO diagram comparing singlet vs. triplet states for

divalent species 12

Figure 9. Lappertʼs germylenes 14

Figure 10. Effect on increasing electronegativity on the ground

state multiplicity 16

Figure 11. Structural differences between the saturated 23 and

unsaturated 24 phosphenium chlorides. ORTEP view

thermal ellipsoids are at the 50% probability level 18

Figure 12. bis(pentamethylcyclopentadienyl) silylene, germylene,

and stannylene 19

xv Figure 13. Structure of germanium dichloride dioxane 20

Figure 14. Relative energies of germylenes 26-28 PBE/TZ2p 21

Figure 15. Possible ligand candidates 26

Figure 16. Second generation Grubbsʼ catalyst. 29

Figure 17. Where do germylenes 11 lie with respect to other

germylenes? 31

Figure 18. Simplified structure of germocane 31 showing the

coordinated nitrogen partially blocking the Ge-Cl s*

orbitals 40

Figure 19. Ge2-O2 ring structure adopted by germylenes 11a and

11b (not shown) 46

Figure 20. Dimeric germylenes 11a (left) and 11b (right). ORTEP

plots with thermal ellipsoids at 50%. 47

Figure 21. Monomeric germylenes 11c (left) and 11d (right).

ORTEP plots with thermal ellipsoids at 50%. 47

Figure 22. Mirror plane in the crystal structure of germylene 11d 49

1 Figure 23. H spectra of germylenes 11 showing the CH2CH2 spin

system 51

Figure 24. EI+ TOF MS spectra showing the [M]+ peaks of the

germylene 11 series 52

Figure 25. Structurally characterized nickel germylene complexes

38 and 42 53

xvi Figure 26. Possible conformations of the monomeric germylenes 64

Figure 27. HOMO and LUMO di-grams of 5-tert-butyl-2,8-di-oxa-

5-aza-1-germa-bicyclo[3.3.0]octane, protons removed

for clarity. 72

Figure 28. Germanium-nickel carbonyls isolated 77

xvii List of Numbered Compounds

R R Ph Me Si 3 Me Si PCy 3 N N 3 Mes N N Mes N Me3Si Me3Si N E E Cl Cl C E ArO Ru Ge N N Ru N Me Si Ge Cl Ph Cl Ph 3 Me3Si N PCy PCy ArO R R 3 3 Ph Me3Si Me3Si

1 2 3 4 5 6 7 8

np Ad tBu tBu tBu tBu ArO OH O N N N N N N Cl Ge R N R N Ge Ge C Ge Si Ge Ge Cl OH O N N N N N N Cl np Ad tBu tBu tBu tBu

9 10 11 12 13 14 15 16 17

tBu tBu Ph Ph Me3Si tBu tBu OH O SiMe3 Me3Si N N E Ge tBu tBu N Ge Ge P Cl OH O tBu H Me3Si tBu N Me3Si tBu tBu Ph Ph tBu tBu 18 19 20 tBu 21 22 23

R tBu N NH N N N Ge N N O Ge O O O P Cl E NH O Ge O N N R tBu

24 25 26 27 28 29

xviii

R R NH R NH R N R NH tBu N N R N O O N R N R tBu N P P(O)2Cl2 tBu N Sn R N Si N N R N O O R NH N R tBu R NH R NH R

30 31 32 33 34 35 36

tBu tBu tBu OSiMe3 O OSiMe3 O Cl N N C N R N R N Ge Cl Ge Ni(CO) Ge Ni Ge OSiMe O Cl 3 3 Me N Ge N N N C Cl tBu tBu O tBu OSiMe3

37 38 39 40 41

tBu O tBu O O O O O Ni(CO)3 H H Me N Si Me N Si Me N Si Ge Ge R N Ge Ni(CO)3 Cl N(SiMe ) O O O 3 2 O (OC)3Ni O O tBu tBu 46 42 43 44 45

xix

Chapter 1. Introduction

1 1.1 Carbenes and their heavier analogues

Carbenes and their heavier analogues (bearing organic substituents) have been known for the last five decades as reactive intermediates.1, 2 However, the difficulty in isolating such species can be attributed to their increased reactivity rather than inherent instability. Research in this area has led to the use of specialized ligands, such as 1 and 2 that can stabilize divalent species electronically and sterically through the presence of substituents R.3

R R >E- >E >E+ N N B C N E E N N Al Si P R R Ga Ge As 1 2

Figure 1. Representative N-heterocyclic carbenes and their analogues

Compounds of type 1 and 2 are not limited to elements of group 14

(Figure 1). The isoelectronic group 13 and 15 compounds are anionic and cationic respectively compared to the neutral group 14 compounds.4, 5 In all cases the central atom is formally surrounded by six electrons resulting in a sextet species. To resolve this electron deficiency carbenes and their analogs react in characteristic manners. They can insert into σ bonds,6 add to unsaturated bonds,2 form adducts with Lewis acids and Lewis bases,7 and react with transition metals to give stable complexes with TM=E bonds (Figure 2).8 In the absence of reactive partners dimerization8 and polymerization can occur.

2 R Ge Y X R R Ge R Ge R Y R X

R O O R X - Y R X Ge Ge Ge R R R Y O O

O Z R C C Ge R Z Ge R O R R Ge R

Figure 2. Characteristic reactions of germylenes

The most notable use of carbenes in recent history is in the formation of catalytic active transition metal complexes. First demonstrated by Hermann et al. in a Heck coupling reaction,9 further research carried out on cross metathesis reactions using carbene ligands led to the 2005 Nobel Prize in Chemistry for

Grubbsʼ 2nd generation catalyst seen in Figure 3.10, 11 The increased thermal and chemical stability afforded to the catalyst by switching from a phosphine in complex 3 to a carbene ligand in complex 4 is a main topic in current research.

PCy3 Mes N N Mes Cl Cl Ru Ru Cl Ph Cl Ph PCy3 PCy3 3 4

Figure 3. First and second-generation Grubbsʼ ruthenium catalysts

3 The next section will outline the stepwise progression in stabilizing low valent transition metal and group 14 elements focusing on divalent germanium, while also providing the synthetic background for this thesis.

1.2 Alkyl, amido and alkoxy complexes: Transition metals vs. main

group

1.2.1 Transition metal complexes

Research on the stabilization of low valent species has been a slow gradual progression since the 1950ʼs starting with the work done by D.C.

Bradleyʼs and M.F. Lappertʼs groups in amido transition metal complexes.12 In particular the research presented by Bradley et al. on the stabilization of metal complexes highlighted the suitability of using alkyl, amido and alkoxy ligands

(Figure 4). Alkoxy ligands are at a steric disadvantage when compared to both alkyl and amido ligands since chain branching and functionalization cannot occur at the oxygen itself. The increased steric bulk afforded by alkyl or amido ligands regulates the accessibility of the metal center and therefore its reactivity.

R R R N O M M M

R = alkyl substituent

Figure 4. Common ligands used to stabilize electron deficient metals

4 Most early transition metal complexes with alkoxides and amides were prepared by Bradleyʼs group by the two methods shown in Scheme 1.13, 14 While the amides of Ti(IV) and Zr(IV) are thermally stable and can be sublimed or distilled at reduced pressure, the alkoxides showed markedly different volatility depending on the amount of branching present.15

NR2

MCl4 + 4 LiNR2 M + 4 LiCl NR2 R2N NR2

NR2 OR

M + 4 ROH M + 4 HNR2 NR2 OR R2N RO NR2 OR

M = Ti, Zr R = Me, Et, nPr, tBu

Scheme 1. Synthesis of group 4 metal amido and alkoxy complexes

Metal alkoxides preferentially “auto complex” to form dimeric or polymeric structures. The charge separation between the Oδ-–Mδ+ increases the donor strength of MOR compared to that of the corresponding ether, ROR, making the formation of the four membered ring favourable (Figure 5).16 The degree to which metal alkoxides form associated polymers depends on a number of factors, such as size and shape of the alkoxide group and the valency, atomic radius and coordination number of the metal. Subsequent research on the stabilization of both transition metals and main group elements focused on the use of amido ligands rather than alkoxides, as the following sections will highlight.

5 Me Me Me O O Me O O NPh W W PhN O O Me O O Me Me Me

17 Figure 5. The [W(NPh)(µ-OMe)(OMe)3]2 dimer

1.2.2 Stable group 14 sextet species

One of the first stable carbene species reported was 1,3-diphenyl- imidazolidin-2-ylidene (5) by Wanzlick et al. in 1961. Wanzlick proposed the isolation of carbene 5 based on the carbene–like reactivity exhibited.18, 19 The actual product from the thermal 1,1–elimination is an electron rich enetetramine dimer, a class of compounds that was unprecedented in 1961 (Scheme 2).

Ph Ph Ph Ph N H ! N N N C -CHCl3 N CCl3 N N N Ph Ph Ph Ph 5

Scheme 2. Synthesis of 1,3-di-phenyl-imidazolidin-2-ylidene

The groundbreaking work done by Lappert in the 1970ʼs introduced the first stable carbene analogs of the heavier group 14 elements. Stabilized using bulky alkyl ligands attached to the central atom, compounds 6a and 6b were monomeric in solution but dimerized in the solid state (Scheme 3).20-22

6 Me3Si Me3Si SiMe3 Me3Si solid state Me3Si SiMe3 E E E solution Me3Si Me3Si SiMe3 Me3Si Me3Si SiMe3 6 E = Sn (a) 1974 Ge (b) 1976

Scheme 3. Dimerization of alkyl substituted germylene and stannylene

To prevent dimerization in the solid state Lappert switched to the isoelectric amido–complex 7 (Scheme 4). The amido ligand which has been shown previously to stabilize electron deficient transition metal compounds,23 also stabilized the first dicoordinate compounds of germanium and tin.12

Me3Si Me3Si N 2 ArOH ArO Ge Ge Ar = 2,6-tBu-4-Me-C6H2 Me3Si N ArO Me3Si 7 8

2 LiOAr · OEt2 ArO ArO GeCl2 · Dioxane Ge + Ge ArO Cl 8 9

Scheme 4. Synthesis of bis(di-tert-butyl-4-methylphenoxy) germylene 8

After the successful synthesis of a divalent amido germylene and stannylene, Lappert reported the first stable divalent alkoxy germanium compound 8 in 1980 (Scheme 4).24 Both reactions of Scheme 4 give the desired product; however starting with the amido germylene 7 gave only one germanium

7 containing product, while starting from GeCl2•dioxane also produced the mixed chloro–alkoxide 9.

Also in 1980, Zeldin and Silverman claimed the synthesis of the alkoxy complex 11a (Scheme 5). The compound was obtained by first treating GeI2 with a sodium ethoxide solution to give Ge(EtOH)2• xEtOH which was characterized by 1H NMR.25 After removal of the sodium iodide formed by filtration, N-methyl- diethanolamine 10a was added. Germylene 11a was purified by sublimation at

70°C at 10-4 torr, at 55% yield (Scheme 5).26 The compound is insoluble in pentane and cyclohexane, but soluble in benzene, toluene and chlorobenzene.

The observed solubility lead Zeldin to assume the formation of a transannular N-

Ge bond, however, this could also have resulted from the formation of Ge-O dimers.

OH O GeI2 + EtOH Ge(OEt)2 · nEtOH + Me N Me N Ge OH O 10a 11a

Scheme 5. Zeldin procedure to germylene 11a

Forgoing the use of intramolecular donors, Meller reported the N- heterocyclic germylene 12 that is structurally similar to those of Wanzlick carbenes.27-29 Dimerization of 12 is prevented not only by the bulky neo-pentyl substituents, but, also presumably by the extended π -electron system (Figure 6).

8 np N Ge N np 12

Figure 6. Mellerʼs N-heterocyclic germylene

The first stable N-heterocyclic carbene 13 was reported by the Arduengo group in 1991,30 which occurred concurrently with the synthesis of the N- heterocyclic germylene 14 (Figure 7).5 Using the same ligand system Denk subsequently synthesized the first stable silylene 15 in 1994.31 The remarkable stability of such compounds has been attributed to the delocalization of the π– electron of the nitrogen lone pairs and the ethylene backbone, resulting in an aromatic system.32, 33

Ad tBu tBu N N N C Ge Si N N N Ad tBu tBu 13 14 15

Figure 7. Stable N–heterocyclic carbenes, germylenes, and silylenes

In 1992, Denk in the Herrmann group observed the formation of both the saturated N–heterocyclic germylene as the expected product, and the unsaturated germylene as an unexpected side product (Scheme 6).5 Due to their similar physical properties, germylenes 14 and 16 could not be separated by

9 sublimation or crystallization. However treating the mixture with HgCl2 selectively removes the more reactive germylene 16. Both germylenes are stable indefinitely under inert atmosphere but are very sensitive to moisture, 16 more so then 14. The synthesis of pure samples of 14 and 16 can be achieved through different approaches as shown in Scheme 7.

tBu tBu tBu NLi N N GeCl2 · Dioxane + Ge + Ge NLi N N tBu tBu tBu 14 16

Scheme 6. Initial synthesis of saturated N-heterocyclic germylene

tBu tBu tBu tBu

NLi N N Cl 2 Li N GeCl2 · Dioxane + Ge Ge Ge NLi N N Cl THF N tBu tBu tBu tBu 14 17 16 Scheme 7. Synthesis of the saturated and unsaturated N–heterocyclic germylenes

Recent work by Huang et al. using substituted pyridine diethanol amine ligand 18 showed coordination between the pyridine nitrogen and either the germanium or tin center (19, Scheme 8).34 The presence of the transannular dative bond placed the germanium in a near trigonal pyramidal environment where one vertex is occupied by the lone pair. While the germylene is monomeric

10 upon crystallization, the stannylene dimerizes (O1–Sn–O1ʼ four membered rings) in both the solid state and benzene solutions. The authors further suggested that the presence of substituents at the β carbon was necessary to prevent further polymerization of both the germylene and stannylene.34

Ph Ph E = Ge OH O ((Me3Si)2N)2E: Sn N N E OH -2 (Me3Si)2NH O

Ph Ph 18 19

Scheme 8. Pyridine containing diethanolamine germylene and stannylene

1.2.3 Ground state of carbenes and heavier analogues: Singlet vs.

Triplet

The ground state electron configuration of carbenes, silylenes, germylenes and stannylenes is determined by both the heteroatom and the substituents that surround it. Understanding the relationship between the two has been a highly researched topic. Using a carbene as an example, the two non–bonded electrons can exist in either a singlet or triplet ground state, dictating the observed reactivity. Triplet carbenes behave as 1,1–diradicals and react in stepwise fashion, while singlet carbenes react in concerted manner.

11 py p!

E px E

Energy Triplet Singlet Near Linear Bent ~sp 2 " ~sp

Figure 8. MO diagram comparing singlet vs. triplet states for divalent species

As seen in Figure 8, a near linear species would follow Hundʼs first rule and have one electron in each of the degenerate px and py orbitals resulting in a triplet ground state. Moving towards a singlet ground state requires the mixing of pure s and p(x) orbitals resulting in the sp hybridized orbital σ while the py orbital

(πP) remains unchanged. However, pairing the electrons in the σ orbital has to overcome increased electron–electron Coulombic repulsion, thus the singlet– triplet gap (ΔEST) is roughly equal to the electron–electron repulsion minus the energy required to promote an electron into a non–bonding p orbital.35

Despite being highly reactive, the experimental ground state of carbenes have been studied extensively thanks in part to the pioneering work done by

Herzberg in Germany, and after 1935, Canada.36-39 The spectroscopic work carried out by Herzberg determined that methylene has a triplet ground state

3 1 ( B1), which is 11 kcal/mol more stable than the corresponding singlet ( A1). For his seminal work on the electronic configuration of free radicals, Herzberg was awarded a Nobel Prize in 1971.

12 The silicon and germanium analogues, silylene and germylene respectively, could in principle exist as either triplet or singlet ground states.

However, in all cases examined so far, the ground state is a singlet.

Spectroscopic work carried out by Berkowitz et al. on H2Si: determined that the singlet ground state is 21 kcal/mol lower in energy then the triplet ground state.40

Unfortunately, ΔEST for H2Ge: has not been determined experimentally; however using high precision computational methods it has been calculated (Table 1).

Table 1. Experimental and calculated singlet - triplet energy gaps [kcal/mol]

H2C: H2Si: H2Ge: Exp. -9.0536 2140 - CBS-4m -10.8 19.1 24.5 CBS-Q -8.1 21.8 23.6 CBS-QB3 -7.9 22.0 24.6 G3 -9.5 21.8 25.6 G4 -8.6 22.6 25.0 CBS-APNO -9.0 - - B3LYP -11.4 20.8 26.8

As seen in Table 1, the triplet ground state becomes increasingly unfavourable as the atomic number increases. In singlet methylene the two electrons are confined to the small HOMO where coulombic repulsion is substantial. Separating the electrons relieves this repulsion and leads to an overall decrease in energy despite the p orbitals being higher in energy, thus a triplet ground state is preferred. For the heavier analogues, the size of the orbitals increase, resulting in both a decrease in the coulombic repulsion and an increase in the energy gap between the orbitals leads to a singlet ground state.

13 1.2.4 Stabilizing the singlet ground state

The stabilization of monomeric divalent group 14 compounds have can be achieved through kinetic or thermodynamic stabilization, which can be broken down into kinetic and thermodynamic factors.41-43 However, in reality, these cannot be cleanly separated and the stabilization of the divalent state is achieved through a combination of both factors.

1.2.4.1 Kinetic stabilization

Germylenes that are predominately stabilized through steric hindrance are rare but there are a few cases reported in the literature. In 1976, Lappertʼs group

21 reported Ge(CH(SiMe3)2)2 (6a). Compound 6a is monomeric in both the gas phase and solution, but forms dimers in the solid state. Jutzi et al. demonstrated that substitution of just one of the CH(SiMe3)2 groups with C(SiMe3)3 (20) introduced enough steric bulk to prevent dimerization (Figure 9).44

Me3Si Me3Si SiMe3 Me3Si Me3Si Ge Ge Me3Si Me3Si Me3Si Me3Si 6a 20

Figure 9. Lappertʼs germylenes

14 In 1987, du Montʼs group reported the isolation of bis(2,4,6-tri-tert- butylphenyl)germylene, (Mes*2Ge: 21), which was found to decompose at room temperature through C-H activation to give 22 (Scheme 9).6, 41, 45

tBu

tBu tBu tBu GeCl2 · Dioxane + 2 tBu Li Ge tBu tBu tBu

21 tBu tBu tBu

tBu + LA

tBu tBu Ge LA Ge tBu tBu H tBu tBu

tBu tBu 22

Scheme 9. Lewis acid activated insertion into C-H bond

It was not until 1996 when Jutzi et al. showed that pure 21 is in fact persistent at -30˚C for months and although decomposition occurs at higher temperatures, C-H activation does not.46 The C-H insertion is triggered by Lewis acids such as GeCl2•dioxane, GeCl4, or Lewis acids, such as BBr3, AlCl3, and

TiCl4. The proposed mechanism involves the formation of a donor-acceptor complex (Scheme 9). The removal of electron density from the Mes2*Ge: in conjunction with the close proximity of an ortho tert-butyl group results in an electrophilic attack by the Ge resulting in the formation of a Ge–C and Ge–H

15 bond. Compound 21 also exhibits a lack of reactivity towards conjugated dienes, which was attributed to the strong steric shielding around the germanium.

1.2.4.2 Thermodynamic stabilization

Inductive effects

As discussed previously (Table 1) methylene has a triplet ground state due to the small difference between the s orbital and the corresponding p orbital, but different substituents can lead to a singlet ground state (Figure 10).47

Electronegative α substituents lower the s orbital energy level without changing the relative energy of the πP orbital.

t t s s Li H H2N F C C C C Li H H2N F

Electronegativity

Figure 10. Effect on increasing electronegativity on the ground state multiplicity

Mesomeric effects

Resonance or mesomeric effects require a positive overlap between the central atomʼs p orbitals, and n and π orbitals of adjacent atoms. Groups with lone pairs α to the central atom (-NR2, -OR, -SR, -X) are +R groups and donate electron density into the empty p orbitals (Scheme 10). In contrast, alkyl groups

32, 41 (-R, -RHn(SiMe3)3-n) have only minimal effects on the stability of carbenes.

16 R Y R Y R Y E E E R Y R Y R Y

Scheme 10. Resonance stabilization of divalent elements

Amido carbenes benefit greatly from a strong π N→C back donation leading to near full p orbitals on the carbene carbon, but the effect is thought to diminish for Si and Ge due to a mismatch in orbital size.32, 33 The energetically accessible HOMO and LUMO orbitals therefore ensure that germylenes can act as both Lewis bases (through the Ge lone pair) and a Lewis acid (through their empty p orbitals). Details are discussed below.

Aromaticity

Compared to the saturated silylenes, germylenes, and phosphenium cations of type 2, the corresponding unsaturated analogues 1 show remarkably enhanced stability (Figure 11). The unsaturated compounds have six delocalized

π-electrons between the nitrogen and ethylene group resulting in a 4n+2 aromatic system that was determined experimentally,4 and theoretically48-50 to be the source of the increased stability.

The saturated phosphenium cation 23 is soluble in hexane and benzene and can be sublimed at 80°C at 0.1 torr. Conversely the unsaturated phosphenium chloride 24 is only sparingly soluble in benzene, insoluble in

17 hexane and non-volatile suggesting that compound 24 is an ionic compound.

Analysis confirms the covalent and ionic character of 23 and 24.

23 24

Figure 11. Structural differences between the saturated 23 and unsaturated 24 phosphenium chlorides. ORTEP view thermal ellipsoids are at the 50% probability level4

The single crystal X-ray structure of phosphenium salts reported by Denk et al. in 1996 highlights the difference between the unsaturated 23 and saturated system 24 (Figure 11).4 It shows that the saturated 23 has a bent backbone and a covalent P-Cl bond, while the planar 24 has an ionic P-Cl bond.

1.2.4.3 Stability through high coordination numbers

A highly successful method for stabilizing the singlet ground state in carbene analogues has been to increase the coordination number of the central atom. In the strictest sense the central atom is no longer dicoordinated however the oxidation state and the observed reactivity are very similar.51-53

18 E = Si E Ge Sn

Figure 12. bis(pentamethylcyclopentadienyl) silylene, germylene, and stannylene

29 The most notable member of this series is Si(Cp*)2, 25 has a Si NMR shift of -577 ppm; a shift that represents the most shielded silicon nucleus reported to date.53, 54 Besides the axially symmetric silylene, the unit cell also contains a bent structural isomer highlighting the increased steric demands of the singlet lone pair (Figure 12).

Divalent singlet species by definition have empty p orbitals. Atoms with a lone pair can coordinate to these empty p orbitals of the divalent center resulting in a dative bond. Dative bonds result from the positive overlap of atomic orbitals between a donor and acceptor, however the electrons are still formally associated with the donor atom and there is no charge separation.55 The overall strength of a dative bond is typically much weaker (<30 kcal/mol) then that of a covalent bond. The strength of the dative bond will increase with increasing electron density on the donor atom and decreasing electron density on the acceptor atom.55 In the following sections examples of dative bonds to sextet species will be explored.

19 Intermolecular dative bonds

In 1998, the crystal structure of GeCl2•dioxane was re-determined by Denk et al., which resulted in a revision of its point group to C2/c from Cc.7 The revised structure shows infinite chains of GeCl2 units with perpendicular coordinated dioxanes, placing the germanium in a six coordinate environment (Figure 13).

Unlike most air and moisture sensitive dicoordinate germanium compounds,

GeCl2•dioxane can be handled in air for brief periods of time and therefore is a frequently used starting material for synthesis of other divalent germanium compounds.

O Cl Cl Ge Ge Ge Cl Cl O

Figure 13. Structure of germanium dichloride dioxane7

Intramolecular dative bonds

Combining the donor and acceptor atoms into one molecule can lessen the entropic barrier of formation associated with intermolecular dative bonds. An example of this is the bis(ethanolamine) germylene reported in 2003 by

Zemlyansky et al. which contains two intramolecular dative bonds.56 The

20 germanium atom adopts a distorted pseudo trigonal bipyramidal geometry with the lone pair occupying the equatorial position (Figure 14). DFT calculations

(PBE functional, ECP TZ2p basis set) showed that the transition from 26 to 27 to

28 requires 7.6 and 11.6 kcal/mol, respectively.56

O Ge O N N N Ge N N O Ge O O O

26 27 28 E = 0 E = 7.6 E = 19.2

56 Figure 14. Relative energies of germylenes 26-28 PBE/TZ2p

1.2.5 Computational evidence of stabilizing effects

A convenient way to compare the stability of a series of related compounds is the computational comparison through isodesmic reactions.

Isodesmic reactions are defined as “transformations in which the number of bonds of each formal type are conserved, and only the relationships among the bonds are altered.”57 The relative stability of germylenes can be compared through their hydrogenations calculated at the CBS-Q level of theory. CBS-Q calculations involve a number of steps that quantify electron–electron correlation, basis set truncation effects, as well as configuration interactions and have been known to give very accurate energies. While the hydrogenations are isogyric

21 (reaction A and B) by comparing two reactions (reaction ΔAB), the overall process is isodesmic (Scheme 11).

A A + H2 AH2 Isogyric

B B + H2 BH2 Isogyric

!AB A2 + BH2 AH2 + B2 Isodesmic

Scheme 11. Visual representation of isogyric and isodesmic reactions

Table 2. Heats of hydrogenation [kcal/mol] of selected germylenes calculated at the CBS-Q level to quantify the stability gained from different ligand systems.

Reaction ∆E (298.15 K)

a H H2 H H Ge Ge -41.0

H H H H H

N N H2 H b Ge Ge -1.2 N N H H H O O c H2 H Ge Ge 2.2

O O H O O H2 H d Ge Ge 4.4 O O H H H N N H2 H e Ge Ge 11.1 N N H H H

The data in Table 2 highlights the stability afforded by electronegative

π donor atoms adjacent to the germanium centre resulting in a positive heat of

22 hydrogenation in all cases except reaction b. A quantitative estimate for the stability afforded by the aromatic ring system can be obtained by comparing the saturated ring (b and c) to their respective unsaturated counterpart (d and e).

1.2.6 Polyamine ligand system

Previous work done by the Denk group showed how the synthetic usefulness of sterically demanding N,Nʼ-dialkyl ethylenediamines in stabilizing carbenes, silylenes, germylenes and stannylenes. In particular using N,Nʼ-di-tert- butyl ethylenediamine (29d) as a stabilizing ligand of germylene 16 which can then used as a starting material for other divalent germanium species. However until recently N,Nʼ-di-tert-butyl ethylenediamine was not commercially available.

With this in mind higher yielding synthetic procedures for 29 were sought.

R R R R R Br NH N NH NH NH RNH2 H O r.t. Br 2 NH N N R N R N R R R 29 30 NH N R N R R Yield (%) 31 NH N R R 29 30 31 32 33 R - Me a 10 9 2 1 32 NH Et b 28 3 6 2 - R iPr c 49 7 14 1 0.1 33 tBu d 70 9 2 - - Ph e 70 10 10 - - Scheme 12. One-pot polyamine synthesis and percent yield from 1,2- dibromoethane

Denk and Krause provided a one pot synthetis that works well for R = tBu, but the yield for R = Me, Et, iPr is signifigantly lower (Scheme 12).58 In addition to the N,Nʼ-substituted ethylenediamines 29, the piperazines 30, triamines 31, and higher polyamines are also formed and were isolated. The triamine, 1,4,7-tri-tert- butyl-1,4,7-tri-aza-heptane 31d, offered the interesting opportunity to extend the stabilization of germylenes to larger ring systems.

tBu NH

PCl3 + Et3N + tBu N NH tBu

31d 34

Scheme 13. Synthesis and crystal structure of a donor stabilized phosphenium cation 34

Mike Krause, working in the Denk group, obtained the phosphenium salt by simply reacting 1,4,7-tri-tert-butyl-1,4,7-tri-aza-heptane 31d with PCl3 in the presence of an auxiliary base (Scheme 13).59 Similar to the unsaturated N- heterocyclic phosphenium cation 24 all three P-Cl bonds have dissociated, presumably due to the formation of a transannular N(3)→P dative bond. The counterion of compound 34 is thought to be a result of oxidation by atmospheric oxygen.

24 Based on these findings Jeff Hastie investigated more efficient synthetic routes to the 1,4,7-tri-tert-butyl-1,4,7-tri-aza-heptane ligand and its reaction with other element halides. The long-term goal was the stabilization of divalent and tetravalent Si, Ge, Sn, and P compounds although only tetravalent compounds were obtained in this context (Scheme 14).60

tBu tBu NH N X 2 Et3N X + Si R N R N Si X X X2 -2 Et NHX N 2 X NH 3 tBu tBu

Scheme 14. Reaction of triamine ligands with silicon tetrahalides or trihalides

R X X2 Cyclization

tBu Cl Cl No tBu Br Br No tBu I I No tBu Cl H Yes Me Br Br Yes Me Cl Cl Yes Me Cl H Yes

Scheme 14 illustrates the important role of steric bulk. The steric demand of three tert-butyl groups prevented the cyclization of all but the hydridosilane despite the increased reactivity of the dihalosilanes. Modifying the structure of the ligand by replacing the tert-butyl on the donor nitrogen with a methyl allowed for cyclization to occur for the larger tetrahalosilanes.

1.2.7 Ligand design

25 Before further research investigating the stabilization of divalent elements with transannular dative bonds a few problems with the structure of the ligand had to be addressed. Ideally, the overall structure of the ligand would not be changed from 31d, but a structurally analogous ligand that is either commercially available or easily synthesized would be used eliminating synthetic difficulties that slowed previous work (Figure 15).

X E = C Y,X = N E Y E Y E Si O Ge S X Sn P

Figure 15. Possible ligand candidates

Retaining the internal nitrogen Y provides the desired strong donor that can be sterically fine tuned with alkyl groups of different size. This should allow for a gradual change in the strength of the dative bond and as a result the electron density on the heteroatom E. Choosing oxygen as heteroatom X has the advantage that the respective ligands, namely diethanol amines 10 are commercially available and rather inexpensive.

Stannylenes are comparatively easier to synthesize than germylenes and silylenes due to the stability of divalent tin due to the inert pair effect (Scheme

14).61 The presence of a trans-annular dative bond in the tin complex 35 was inferred through spectroscopic changes in the methylene protons compared to the corresponding free ligand. Tzschach et al. expanded this initial work carried out by Zeldin et al. in 1976 by measuring the 2J(119Sn–N–13C) coupling constants

26 in non–polar solvents and identifying the dimerization through osmometric measurement of the molecular weight.62

-NaCl SnCl + 2 tBuN(CH2CH2ONa)2 O tBu N Sn t -tBuOH O Sn(O Bu) + tBuN(CH2CH2OH)2 35

Scheme 15. Convergent synthesis of stannylene 35

Compared to germylene 11a, stannylene 35 and its corresponding methyl analogue have been investigated with temperature dependent 1H and 13C NMR

1 by Zschunke et al. in 1983. At reduced temperature (180 K) in CH2Cl2, the H spectrum is reported to show two superimposed ABXY splitting patterns that coalesce at higher temperatures into one ABXY spectrum. At 378 K both protons

62 of one CH2 group are chemically equivalent resulting in an AAʼXXʼ system. The complexity of the stannylene is in marked contrast to the simple triplet that was reported by Zeldin for 11a despite both being measured on NMR spectrometer of comparable field (35 200 MHz, 11a 220 MHz).

1.2.8 Synthetic targets

In principle, ligand 10 is promising for main group and transition metals

(Scheme 16). The goal of this thesis is to obtain stable germylenes and silylenes of this ligand as an entry into the field. Once isolated their complexes with transition metals will be investigated.

27 O R N C O

O 1.Cl2CS O 2. K R N TM R N Si TM(NR ) O 2 2 O OH Si2Cl6 36 R N OH PCl3 10 15 Et3N R = Me (a) Et (b) O O iPr (c) R N P Cl R N Ge tBu (d) O O 10

Scheme 16. Target molecules of this thesis

Unfortunately a number of barriers prevent an effortless transition into silylene chemistry. The foremost problem is the alcoholysis of the analogous N- heterocyclic silylene likely giving the insertion product rather than the corresponding dialkoxy silylene. Additionally unlike tin and germanium, silicon does not have a stable divalent halide that can be used as a precursor for further reactions. Instead trichlorosilane/triethylamine or hexachlorodisilane are used as easily accessible Cl2Si: substitutes.

1.3 Main group – transition metal complexes

Since the discovery of singlet transition metal carbenes by Fischer in 1964 and triplet transition metal carbenes by Schrock in 1975, there are a number of catalytic reactions that have benefited from transition metal carbene complexes.

N-heterocyclic carbenes as ligands for the palladium based, Negishi, and Suzuki-

28 Miyaura cross coupling reactions and most famously, alkene metathesis reactions mediated by the second generation Grubbsʼ catalyst 4 have resulted in increased stability and reactivity of the catalytically active species (Figure 16).

With similar or stronger σ–donating ability than electron-rich alkyl phosphines,

N-Heterocyclic carbene metal complexes have higher stability at elevated temperatures and often result in stronger ligand to metal bonds.

Mes N N Mes Cl Ru Cl Ph PCy3 4

Figure 16. Second generation Grubbsʼ catalyst.

N-Heterocyclic germylenes have been shown to also form complexes with transition metals as shown in the reaction of 16 with nickel carbonyl by Denk in

Herrmannʼs group in 1992 (Scheme 17).5 Subsequent substitution of a second carbonyl occurs very rapidly at r.t. without the need for forcing conditions.

tBu tBu tBu tBu tBu OO tBu N CC N Ni(CO)4 NN N Ge Ge Ni(CO)3 GGeeNNii Ge -CO -CO N N NN CC N O tBu tBu tBtBuu O tBu 1165 37 3388

Scheme 17. Germylene coupling to nickel carbonyl

29 The ever-increasing need for catalyst specificity for both substrate and conditions by fine tuning the electronics of the transition metal centre provide demand for new ligand designs, thus providing strong motivation for the present study.

1.4 Computational investigation to determine relative stability

Computational and synthetic work done previously in the Denk group63 has become a driving force each providing new avenues for one another. The synthetic targets of this project pose a number of challenges both synthetically

(discussed previously) and computationally. In computational studies it is usually difficult to accurately reproduce the structures of compounds that involve weak interactions such as partial bonds, transition states, hydrogen bonds, dative bonds, and weak interactions as in dispersion-dominating van der Waals bonding of molecules.64 However, methods capable of dealing successfully with these challenges have recently become available and thus a combination of computational methods and experimental findings can now be used to compare the properties and stability of 11 with respect to germylenes 14 and 16 (Figure

17).

30 tBu tBu N O N Ge R N Ge Ge N O N tBu tBu 16 11 14

Stability?

Figure 17. Where do germylenes 11 lie with respect to other germylenes?

Chapter 2. Results and Discussion

32 2.1.1 Synthesis of N-alkyl diethanol amines 10a-d

N-Alkyl diethanol amines 10a-d are commercially available with the exception of N-isopropyl diethanol amine (10c) which is not available as a pure product. The synthesis of 10c is described in the following section.

2.1.2 Reaction of diethanol amine with 2-bromopropane: Synthesis of

N-isopropyl diethanol amine 10c

Diethanol amine 10c was obtained through a literature procedure (Scheme

18).65 An excess of 2-bromopropane was dissolved in a neat weighed amount of diethanol amine in a one piece condenser flask. The product was neutralized with

NaOH and extracted giving a crude product (86% yield). Vacuum distillation at

102-107°C gave a pure product (35% yield). The low yield is partially due to the high purity needed for further reactions. Another factor is the similar boiling points of the product (122-123 °C, 3.5 torr66 [Calculated 295-296 °C, 760 torr]) and starting material (268 °C, 760 torr67) at reduced temperature.

H ! + Br + HBr N N HO OH HO OH 10c

Scheme 18. Synthesis of N-isopropyl diethanol amine 10c

33 2.1.3 Purification and drying of diethanol amines 10a-d

The air and moisture sensitive nature of germylenes required to pre-dry the diethanol amines. In the literature procedure outlined by Silverman, ligand

10a was dried over sodium26 or magnesium68 prior to distillation. While initially dry ligands dried with reactive metals are not protected from “spoiling” of the ligand if it is accidentally exposed to moisture. More recent papers on the synthesis of dialkoxy germylenes either do not specify a drying procedure or state that the ligands were used without further purification.

Several methods for drying ligands 10a-d were attempted. Small portions of powdered calcium hydride (CaH2) were added to a Schlenk tube containing

10a over the course of 2 days. The mixture was stirred and excess gases (H2) were vented at regular intervals. Stirring was stopped after the cessation of gas formation (bubbling). Despite sitting undisturbed over a week the CaH2 remained suspended throughout the mixture with no indication of sedimentation. The mixture was placed in a micro-distillery and distilled under vacuum. Surprisingly the distillate was still slightly cloudy assumedly containing a small amount of

CaH2. In a separate attempt an equal volume of dry THF was added to the

CaH2/10a mixture but again the CaH2 remained suspended after a week.

An alterative literature method is the addition of powdered barium oxide

(BaO) to an alcohol and stirring with or without heat.69, 70 Barium oxide dries through a combination of absorption and adsorption and settles quickly due to its high density(5.72 g/cm3).71 Ligands 10a,b and d were stored in a Schlenk tube

34 after they were first distilled under vacuum. Small portions of powdered BaO were then added and the tube was shaken suspending the BaO throughout the ligand. Initial BaO portions clumped together and settled quickly whereas later portions remained powdered indicating the ligand was now dry.

2.1.4 Synthesis of germanium–diethanol amine complexes 11

The principle routes to alkoxy germylenes reported in the literature have focused on relatively few similar methods; nucleophilic substitution from dichlorogermylenes, reduction of dichlorogermylenes, “transesterification” of simple alkoxy germylenes or metathesis (ligand exchange) of amino germylenes with alcohols. Several methods for the synthesis of germylenes 11 that were carried out during this Masterʼs work are outlined below.

2.1.5 Attempted synthesis of germylene 11 through elimination of

trimethylsilylchloride

A convenient cyclization of trivalent boron complexes was described in

2002 by Aldridge et al. using a protected N-methyl diethanol amine 39a (Scheme

19).72 The reaction proceeded through initial formation of a nitrogen–boron dative bond at room temperature followed by sequential elimination of trimethylsilyl fluoride and formation of the cyclized product. The formation of the intermediates was followed through monitoring of the reaction mixture by 11B and 19F NMR

35 spectra over the course of the reaction. The synthesis of germylene 11a and d was attempted using this method as a template.

OSiMe3

OSiMe3 RT F Me N + BF3 · OEt2 Me N B F OSiMe3 F 39a OSiMe3 55°C 48 - 72 hrs -FSiMe3

O O 55°C Me N B F Me N B F O -FSiMe3 F

OSiMe3

72 Scheme 19. Synthesis of alkoxy–borane complex

2.1.5.1 Reaction of N-alkyl diethanolamine 10a and d with

bis(trimethylsilyl)amine: Synthesis of 4-alkyl-1,7-

bis(trimethylsilyl)-1,7-di-oxo-4-aza-heptane

Silylation of the diethanol amine 10a and d was carried out with bis(trimethylsilyl)amine or trimethylsilylchloride and triethylamine. The literature procedure outlined in Scheme 20 was the preferred method for a number of reasons. The formation of two equivalents of [Et3N]HCl makes stirring the mixture difficult during the end of the addition. Additionally the [Et3N]HCl salt needs to be filtered using a dry non–polar solvent that still dissolves the ligand 39.

OH SiMe OSiMe 3 ! 3 R N + HN R N SiMe OH 3 OSiMe3 R Yield (%) OH SiMe3 OSiMe3 10 39 ! a Me 75 R N + HN R N d tBu 76 OH SiMe3 OSiMe3 10 39

Scheme 20. Synthesis of 4-alkyl-1,7-bis(trimethylsilyl)-1,7-di-oxo-4-aza-heptane

2.1.5.2 Attempted synthesis of germylene 11 through reduction of

dichloro germocane 40

Synthetic work investigated the suitability of reduction of the corresponding pentavalent spirocyclic germanium, (described in literature as a germocane), compound 40 with alkali metals (Scheme 21). Reductive elimination has been shown to be an efficient method in the synthesis of amido–germylenes 165 and

1227 however no mention of reduction leading to alkoxy–germylenes have been reported in the literature.

2.1.5.3 Reaction of ligands 39a and d with germanium tetrachloride:

Synthesis of 1,1-dichloro-5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane 40

Ligand 39a was chosen because it is also used in as a starting material for the literature described procedure of germocane 40 (Scheme 21). While it is known that the sterically less demanding methyl substituted analog will cyclize, it

37 was of interest to determine if increased steric demand (40d) would lead to the same outcome.

Germocane 40a was obtained through literature methods; an equimolar amount of GeCl4 was added to ligand 39a in CHCl3. The reaction was stirred overnight at reflux, which upon cooling yielded a white precipitate. Removal of the solvent and volatile material followed by washing with CHCl3 gave spectroscopically pure material (exp. m.p. 212-213°C, lit. m.p. not known).

OSiMe 3 CHCl O 3 Cl R Yield (%) R N + GeCl4 R N Ge + 2 Me3SiCl ! Cl a Me 83 OSiMe3 O d tBu 27 39 40

Scheme 21. Synthesis of 1,1-dichloro-5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane (R = Me, tBu)

Germocane 40d was synthesized in similar fashion however the soluble reaction mixture contained multiple tert-butyl containing products as determined

1 by H NMR. Removal of the solvent gave white crystals above a brown oil. The mixture was dissolved in boiling CH3CN and place in a freezer after cooling to r.t. to promote crystallization. The supernatant liquid was removed and the above procedure was repeated until the removed solvent was clear and colourless yielding the product as a white powder.

38 2.1.5.4 Attempted reduction of germocane 40a with alkali metals

O O THF M Me N Ge Cl + 2.2 M Me N Ge + 2 MCl Cl Anthracene O O Li K 40a 11a

Scheme 22. Attempted reduction of of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1- germa-bicyclo[3.3.0]octane 40a through alkali metals

To a suspension of germocane 40a in THF, 2.2 equiv. of an alkali metal was added and stirred until all alkali metal was dissolved (Scheme 22). The resulting brown suspension settled from the solvent when stirring was stopped.

1 13 H and C NMR in C6D6 and CDCl3 of the crude reaction mixture showed no soluble material that corresponded to the starting material or expected product.

Although it appeared that the alkali metal completely dissolved and therefore reacted, the lack of spectroscopic evidence for any product proved confusing. Anthracene was added to determine if the alkali metal had irreversibly reacted with the germocane 40a or if it was still available. Addition of anthracene did not result in a change in the 1H and 13C NMRs of the crude product or the appearance of the solution.

The difficulties encountered in the reduction of germocane 40a could be due to the proposed mechanism of the reduction. An electron from the alkali metal add to one of the Ge-Cl σ* orbitals forming an anionic radical. A chlorine atom is eliminated as Cl- leaving a germanium radical. The second electron pairs

39 with the germanium radical reforming an anionic radical followed by elimination of a second chloride results in a germylene. However in the case of germocane 40 the coordinating nitrogen partially blocks the σ* orbitals preventing the reaction from proceeding (Figure 18).

Cl R N Cl O O

Figure 18. Simplified structure of germocane 31 showing the coordinated nitrogen partially blocking the Ge-Cl σ* orbitals

The difficulties encountered in reducing a tetravalent germanium atom to the corresponding divalent state demanded different synthetic approaches to be investigated. Ligand metathesis of a divalent germanium atom would circumvent this problem.

2.1.6 Synthesis of germylene 11a using GeCl2•dioxane as a starting

material

Subsequent attempts to synthesis germylene 11a focused on using

GeCl2•dioxane as a starting material due to its stability, modest solubility in polar solvents and facile synthesis. The formation of the HCl side-product poses a problem due to the germylene subsequently inserting into the H–Cl bond. To

40 circumvent this problem, deprotonation and silylation of ligand 10 were investigated (Scheme 23).

OR O 1 i. Me N Me N Ge + 2 XCl ii. OR1 O

10 11a

Scheme 23. Attempted synthesis route to germylene 11a from GeCl2•dioxane i.)

R1=H X=Li 1.nBuLi/hexanes -78°C→r.t. 2.GeCl2•dioxane/THF 3.Δ ii.) R1= Si(Me)3

X=Si(Me)3 1.GeCl2•dioxane/dioxane 2.Δ

i) Addition of GeCl2•dioxane to the suspension of deprotonated ligand in

1 13 THF gave a slightly grey suspension. Analysis of the H and C spectra in C6D6 of the crude reaction mixture showed only residual THF and dioxane peaks. The lack of starting material is presumably due to the insolubility of the lithium salt in

C6D6. The crude reaction was then refluxed for 72 hours to attempt to force a reaction. Analysis of the crude 1H NMR show multiple peaks none of which correspond to the starting ligand 10 or suggest the formation of a cyclized product.

ii) Compared to the previous reaction two modifications to the reaction conditions were made. The solvent was changed from THF to dioxane allowing for higher reaction temperatures to be reached before the solvent boils and ligand 10 was silylated (for synthesis see Scheme 20). Silylation of the ligand has two benefits: the ligand is soluble in the reaction and NMR solvents and the expected byproduct, trimethylsilylchloride, is easily removed under vacuum.

41 1H and 13C NMR spectra of the crude reaction mixture after stirring at r.t. for one day showed broad multiplets shifte slightly downfield (0.4 ppm) from the free ligand. Stirring was continued for two additional days with no change in the

NMR of the crude solution.

Based on the 1H and 13C NMR and the previous work carried out by

Aldridge et al. itʼs possible that the nitrogen lone pair of ligand 39 has coordinated to the germanium dichloride forming compound 41 (Scheme 24). The reaction mixture was heated to 140°C (aluminum block) for one day and NMR of the crude reaction (yellow solution over grey powder) mixture was taken. The spectra still showed the shifted ligands peak in addition to numerous small non-diagnostic peaks from 4.2 to 0.6 ppm. The remaining solvent was then removed under vacuum and the reaction was melted together at 140°C (aluminum block). Again

NMR was taken but no diagnostic peaks were observed.

OSiMe3

OSiMe 3 r.t. Cl Me N + GeCl2 · Dioxane Me N Ge Dioxane Cl OSiMe3

39 OSiMe3 41

Scheme 24. Proposed formation of germanium dichloride complex 41

42 2.1.7 Alcoholysis of amido germylenes

High yielding synthetic procedures for alkoxy–germylenes through the alcoholysis of the much more reactive amido–germylenes has been shown in previous sections to give the desired product cleanly (ex. Scheme 25).56

Me N Me Me (Me3Si)2N Me Ge + 2 N O Ge O + HN(SiMe3)2 (Me3Si)2N OH Me N Me 7 26

Scheme 25. Germylene 26 synthesized by Zemlyansky et al.

2.1.7.1 Reaction of germylene 16 with N-alkyl diethanol amine:

Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane 11

The highly reactive and volatile germylene 16 was synthesized following the literature procedure,5 as outlined in Scheme 26. Colourless, dendritic crystals were isolated through sublimation at 50°C (0.1 Torr).

tBu tBu tBu 2.2 Et3N NH GeCl4 N Cl 2.2 Li N Ge Ge - Et NHCl - 2 LiCl NH 3 N Cl N tBu tBu tBu 29d 17 16

Scheme 26. Synthesis of germylene 16

Once isolated, a weighed amount of crystalline germylene 16 was dissolved in THF, to which a nearly equimolar amount of dried diethanol amine was added as a solution in THF (Scheme 27). The resulting white turbid solution was allowed to stir for 20 minutes at which time the solvent was removed under vacuum. The germylene series is insoluble in hexanes allowing the removal of the N,N'-di-tert-butylethylenediamine byproduct through washing of the crude oil.

The spectroscopically (1H, 13C NMR) pure white powder can be further purified to give crystals of X-ray quality through sublimation at 120°C (0.1 Torr). Germylene

11 is stable indefinitely under argon, but upon exposure to air decomposes to a number of products including the free ligand and possible insertion products of water.

tBu tBu Yield (%) OH N O NH 11a 94 R N + Ge R N Ge + 11b 92 OH N O NH 11c 91 tBu tBu 11d 92 10 16 11 29d

Scheme 27. Alcoholysis of 16: Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane 11

The procedure outlined in Scheme 27 gives germylenes 11b-d, in nearly quantitative yield with respect to diethanol amine before sublimation. Repeating the procedure at room temperature for ligand 11a gave a byproduct that appeared to have the 1H NMR splitting pattern of an ethylene backbone

44 consistent with a cyclized product. Germylene 11a can be separated from this byproduct through sublimation, but carrying out the reaction at 0°C prevented the formation of the byproduct. Multiple attempts to isolate the byproduct and identify were carried out but were unsuccessful.

By single crystal X-ray diffraction of the sublimed crystals both methyl and ethyl germylenes were found to form dimers in the solid state. Conversely, the iso-propyl and tert-butyl germylenes remained monomers. It is interesting to note, that the sublimation temperatures required did not vary greatly between the monomeric and dimeric germylenes regardless of the alkyl group present. This suggests that the dimers decompose into monomers during sublimation; furthermore this highlights the extremely weak nature of the Ge-O dative bond

(Figure 19).

2.1.7.2 Experimental structure of crystalline germylenes 11

The synthesis and X-ray diffraction analysis of the complete germylene series 11 allows for the analysis of the structural differences that occur with changing alkyl group.

Table 3. Selected experimental bond distances [pm] associated with the germanium center of 11 for both the monomers and dimers

Ge-O(1) Ge-O(2) Ge-N Ge-O(1)b 11aa 193.62(14) 184.84(14) 236.73(17) 211.43(14) 11ba 190.72(9) 185.13(9) 227.61(11) 228.55(9) 11c 184.02(13) 184.14(14) 216.05(15) 11d 183.0(9) 182.8(8) 219.7(11) a Ge2O2 motif in dimeric germylenes

45 Table 3 shows selected bond distances for both the dimeric and monomeric germylene series. Both dimeric germylenes consist of a four membered ring with two Ge(1)–O(1b) dative bonds forming a four membered

Ge2O2 ring. The length of the Ge–O dative bond increases, shortening of the transannular Ge–N dative bond by nearly 9 pm (Me 236.73(17) and Et

227.81(11)). If steric demand would be the limiting factor in determining the Ge–

N bond length the distance on the methyl germylene would be expected and increase as the alkyl group expands. The shortening of the Ge–N therefore has to be due to the increased electron density introduced by the ethyl group.

O O Ge NMe Me N Ge O O

Figure 19. Ge2-O2 ring structure adopted by germylenes 11a and 11b (not shown)

Structural differences occur not only across the range of alkyl groups but also between the two dimeric germylenes. As seen in Figure 19 and Figure 20 the methyl germylene dimer pair arranges in such a way that the torsion angle measured through space between CH3(1)–N(1)–N(2)–CH3(2) moieties are exactly 180° to one another while the analogous angle in the ethyl germylene is

88.11°.

Figure 20. Dimeric germylenes 11a (left) and 11b (right). ORTEP plots with thermal ellipsoids at 50%.

Comparing the crystal structure of one germanium containing unit of the dimeric germylenes to the monomeric germylenes shows structural similarities between the compounds with the smallest and largest alkyl groups. As seen in the ORTEP plots in Figure 20 and 21 germylene 11a and 11c adopt a boat conformation with both OCH2CH2 moieties folding away from the alkyl group

(syn). For the tert-Butyl and methyl germylene this is not the case as one “wing” is folded up resulting in a modified boat structure (anti).

Figure 21. Monomeric germylenes 11c (left) and 11d (right). ORTEP plots with thermal ellipsoids at 50%.

The increased branching in the alkyl group appears to rotate in such a way that minimizes the steric interactions between it and the ring. The ethyl group can

47 point away from the germanium and the ring adopts an anti conformation.

Germylene 11c requires one methyl group to be pointing towards the now syn ring, placing two hydrogens of the ethylene bridges close to one another. Finally in 11d, the ring adopts the more stable anti conformation since the tert-Butyl has no choice but to place two methyl groups towards the ring.

Table 4. Selected experimental bond angles associated with the germanium center of 11 for both the monomers and dimers

O(1)-Ge-O(2) N-Ge-O(1) N-Ge-O(2) O(1)-Ge-O(1b) O(2)-Ge-O(1b) Ge-O(1)-Ge(b) 11aa 100.43(6) 77.40(6) 79.56(6) 73.45(6) 85.93(6) 106.55(7) 11ba 102.93(4) 81.93(4) 79.80(4) 72.35(4) 86.15(4) 106.92(4) 11c 101.72(7) 84.87(5) 84.45(5) 11d 97.7(4) 91.5(3) 81.4(3) a Ge2O2 motif in dimeric germylenes

With the addition of a dative bond coordinating to the germanium a distorted trigonal pyramidal structure is observed for the monomeric germylenes with the lone pair in the fourth position (Table 4). Even accounting for the increased electronic repulsion introduced by the lone pair the angles surrounding the germanium in 11 and 11d are smaller then expected due, in part, to the semi rigid structure of the bicyclic ring.

Figure 22. Mirror plane in the crystal structure of germylene 11d

Unfortunately a direct comparison of bond lengths cannot be carried out due to a mirror plane that exists in the crystal structure of germylene 11d (Figure

22). In an attempt to crystallize a different modification of the crystal, hexanes were layered over a concentrated THF solution, however, the crystals did not differ from those obtained from the sublimation.

2.1.7.3 NMR spectroscopy and the solution structure of germylene 11

Listed in Table 5 are the 1H and 13C NMR shifts of the ethylene fragments in 11. The lack of dramatic change between 11c and 110d, which are monomeric in the solid state, suggests all four germylenes are monomeric in solution. It is interesting to note the increased complexity of the ethylene backbone-splitting pattern as the size of R group changes (Figure 23).

49 Table 5. Experimental 1H and 13C shifts of the ethylene backbone of germylenes

11 in C6D6

1H 13C

NCH2 OCH2 NCH2 OCH2 11a 1.80 - 1.83 1.84 - 1.94 3.91 - 3.97 4.01 - 4.07 61.0 66.6 11b 1.77 - 1.82 1.98 - 2.05 4.04 - 4.08 57.9 67.8 11c 1.68 - 1.70 2.13 - 2.17 4.09 - 4.15 55.4 68.9 11d 1.42 - 1.59 2.44 - 2.51 4.05 - 4.10 4.19 - 4.22 54.0 68.1

Germylene 11a and 11d exhibit similar splitting of the OCH2 moiety while in 11b and 11c these signals have merged. It could be argued that this is a result of the syn/anti conformation and that each compound is locked in that geometry in the solution state, however one would expect a more complicated splitting pattern in the anti configuration due to a lack of mirror plane along the dative bond. Deconvolution of the coupling constants of 11a and 11d showed three unique coupling associated with each proton. Carrying out the same analysis of

11b and 11c also shows three coupling constants however the geminal and axial coupling appears to have nearly identical J coupling which manifest as a doublet of triplets. This splitting pattern is tentatively assigned as an AAʼXXʼ system for based on observed splitting patterns and simulation of the spectra using Brukerʼs

TopSpin program taking second order effects into account.73

50 11a

11b

11c

11d

1 Figure 23. H spectra of germylenes 11 showing the CH2CH2 spin system

Germylene 11a was analyzed by variable temperature NMR to confirm the identity of the species in solution. Over the range of 15 – 50 °C there was no spectrum that contained more then one methyl group. The only notable change over the series is the coalescence of the NCH2 moiety and downfield shift of it and the methyl as temperature increases.

2.1.7.4 Mass spectra of germylenes 11

Germylenes 11a-d were analyzed by time of flight mass spectroscopy using electron ionization which showed the parent molecule in all cases (Figure

24). The primary fragmentation pattern of the larger alkyl groups shows initial

+ elimination of CH2O followed by loss of alkyl group leading to a common

11a + monoisotopicMBR182 peak of [CH2NCH2CH2OGe] (145.97 m/z). This24-Mar-2011 further breaks MD14153 (0.016) Is (0.10,0.01) C5H11NO2Ge TOF MS EI+ 191.0002 100 3.48e12

+ 189.0011+ down to GeOH and [CH2NCH2CH2] finally ISOTOPEleading MODEL to elemental germanium and 187.0032 %

193.0005 smaller amineMBR183 fragments. 194.0035 24-Mar-2011 MD141520 (0.017) Is (0.10,0.01) C6H13NO2Ge TOF MS EI+ 205.0159 3.45e12 100MD14153 20 (0.333) Cm (20:46-220:242) TOF MS EI+ 191.0016 100 ISOTOPE 3.82e4 203.0167 189.0029 MODEL Me 201.0189187.0081 %

% 204.0184 207.0162 193.0025 206.0190 172.9869 202.0220 208.0192 209.0210 0 174.9918 179.0853 185.9940 193.0850 196.9650 208.9628 175.9908 203.0270 204.1158 207.0312 213.9843 0 m/z HBR162MD14152170 51 (0.850)172 174Cm (50:65-325:340)176 178 180 182 184 186 188 190 192 194 196 198 200 202 204 206 208 210 21228-Mar-2011TOF214 MS EI+ 205.0154 1.14e4 MD14158A100 (0.017) Is (0.10,0.01) C7H15GeNO2 TOF MS EI+ 219.0316 100 203.0189 Et3.42e12 201.0228 217.0324 THEORETICAL MODEL

% 215.0345 207.0251 % 204.0238 201.1009 205.1086 218.0342 195.0979 197.9407 209.0274 212.0990 194.1069 199.0156 221.0318 208.0323 210.9629 0 220.0347 m/z 194 195 196 197 198 199 200 201216.0377202 203 204 205222.0349206223.0369207 208 209 210 211 212 0

MD14158A 39 (0.650) Cm (28:39-3:14x1.200) TOF MS EI+ 219.0315 100 3.19e3 217.0412 iPr

215.0422 % 218.0449 221.0442

215.1383 220.0427 227.0844 229.0816 208.9467 222.8610 205.0922 208.0623 213.0106 225.0727 229.1654231.0887 0 m/z MBR030 22-Feb-2011 MD14011 68206 (1.133) 208Cm (48:68-5:25x1.500)210 212 214 216 218 220 222 224 226 228 230 TOF232 MS EI+ 203.0399 100 2.85e4

201.0408 tBu

199.0425 %

233.0487 205.0392 231.0468

229.0507

188.0189 235.0538 260.9633 214.0978 288.9967 0 m/z 190 200 210 220 230 240 250 260 270 280 290 300

Figure 24. EI+ TOF MS spectra showing the [M]+ peaks of the germylene 11 series

In an attempt to observe the dimer, the germylene series were analyzed by laser desorption ionization (LDI) and matrix-assisted laser desorption ionization (MALDI). Despite observing the monomeric parent molecules in all cases no m/z consistent with either dimeric germylene were detected. The largest hurdle was the fine balance of laser intensity required to ionize the molecule without completely fragmentation. Dihydrobenzoic acid (DHB) was used as the matrix in the MALDI experiments however a high intensity laser beam was

52 still required which also ionized residual compounds and salts from the “clean” plate. Overall neither LDI nor MALDI provided a consistent fragmentation pattern across the series of germylenes that was seen in the EI–MS.

2.2 Reaction of 11 with Ni(CO)4

Transition metal-germylene complexes were synthesized to compare the reactivity versus other germylenes and gain empirical evidence for the donor strength of germylenes of type 11 with varying alkyl substituents. Metal carbonyls were used due to the relationship between observed carbonyl stretching in the IR spectrum and the molecular and electronic environment of the metal atom.74 Nickel tetracarbonyl was chosen because it is the most reactive commercially available homoleptic transition metal carbonyl, on the basis of previous experience working with Ni(CO)4 in the Denk group, and its established availability in the lab. Unfortunately, there are relatively few nickel-germylene compounds reported in literature making extensive comparison difficult (Figure

25).

tBu tBu O tBu C tBu N N O O Ni(CO)3 Ge Ni Ge Ge Ge N C N (OC)3Ni O O tBu tBu O tBu tBu 38 42

Figure 25. Structurally characterized nickel germylene complexes 385 and 4275

53 2.2.1.1 Synthesis of (5-alkyl-2,8-di-oxa-5-aza-1-germa-

bicyclo[3.3.0]octane) nickel carbonyls 43

Two fold molar excess of Ni(CO)4/THF solution was added to a solution of

11a-d. Excess gas (CO) was released as the reaction stirred for one day

(Scheme 28).

Yield (%) n O O Ni(CO)4 43a 81 2 R N Ge R N Ge Ni(CO)4-n 43b 73 1 O THF O -n CO 43d 96 1 11 43

Scheme 28. Synthesis of germanium-nickel carbonyl complexes

Removal of the solvent gave spectroscopically pure compounds for 43a,d and d. Unfortunately despite multiple attempts of the isolation of the 43c once the

THF was removed completely the compound decomposed to a black oil not observed in any of the other reactions. The 1H and 13C NMR of the black oil showed a mixture of 43c and starting germylene that could not be separated. The tentative assignment is partial decomposition of 43c to the free germylene, nickel(0) and carbon monoxide.

2.2.2 Experimental structure of crystalline nickel germylenes 43

Single crystal X-ray structures analysis of compounds 43a, b and d were carried out on crystals grown from layering hexanes over concentrated THF

54 solutions. The ORTEP plots of the nickel-germanium complexes 43 (Figure 26 and 27) and key structural bonds (Table 6) are given below.

Figure 26. (5-alkyl-2,8-di-oxa-5-aza-1 germa-bicyclo[3.3.0]octane)nickel carbonyls 40b and 40d. ORTEP plots with thermal ellipsoids at 50%

The N-Ge dative bond lengths in the nickel complexes (Table 6) are decreased by a statistically significant amount (>3σ) compared to those in the free germylenes. The greatest difference is observed for the nickel-germylene

43b (20.0 pm) and is attributed to breaking of the dimer and the ethyl chain pointing away from the carbonyl groups. In contrast, two of the methyl groups of

43d point towards the nickel lengthening both the Ge-Ni and Ge-N bond length and twisting the Ni(CO)3 fragment placing one carbonyl in-line with the tBu group.

Comparing at the crystal structure of all three nickel-germylenes, there is uniform adoption of the syn conformation that was not seen in the free germylenes.

Figure 27. Bis(5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel dicarbonyl. ORTEP plots with thermal ellipsoids at 50%

Table 6. Selected bond distances [pm] for germanium-nickel complexes 43a-d.

43a 43b 43d Ni-Ge(1) 226.28(5) Ni-Ge(1) 228.60(4) Ni-Ge(1) 230.16(3) Ni-Ge(2) 227.36(5)

Ge(1)-N(1) 207.3(2) Ge(1)-N(1) 207.62(13) Ge(1)-N(1) 213.08(14) Ge(2)-N(2) 209.4(2)

Ge(1)-O(3) 182.35(17) Ge-O(1) 181.58(12) Ge-O(1) 181.74(13) Ge(1)-O(4) 182.6(2) Ge-O(2) 180.90(12) Ge-O(2) 180.89(13) Ge(2)-O(6) 181.89(17) Ge(2)-O(5) 182.95(19)

In fact the other dialkoxy germylene nickel tricarbonyl 42 (228.3(2) pm in literature75 and the di-N-heterocyclic germylene 38 Ge(1)-Ni 229.69(4), Ge(2)-Ni

229.13(3))5, are not markedly different suggesting that there is no appreciable difference between the donor strength of the germylene ligands (Figure 25).

56 2.2.3 Spectroscopic analysis of the solution structure of nickel-

germylenes 43

-1 Table 7. CO valence bands [cm ] for the carbonyl complexes of LNi(CO)3 and

L2Ni(CO)2 in CH2Cl2

-1 VCO (cm )

L A1 B1 E 76 PPhCl2 2092 2016 2018, 165a 2074 2005, 1966 43d 2071 1997 43b 2071 1989 75 [(CO3)NiGe(OtBu)2]2 2070 2000 76 PPh3 2069 1990 CO 2057

- +77 GeH3 PPh4 2043 2025, 1940

43a 2008 1949

5a (16)2(NHGe)2 2003 1945 a Nujol CsI plates

The number, intensity and modes of the carbonyl stretching frequencies in solution agree with the local point group symmetry (C3v 43b,d C2v 43a) of the complexes in the solid state. The similarities between the germylene ligands are highlighted in Table 7 which summarizes the carbonyl stretching frequencies of nickel carbonyl complexes 43 and others found in literature. The A1 stretching frequencies of germylenes 43 show that they act as relatively good σ donors but poor π acceptors, and are comparable to triphenylphosphine.

The 1H and 13C NMR of the nickel germylenes reflect the change in

1 electronic environment from the free germylenes. The H NMR shifts of the NCH2

57 moiety are shifted slightly upfield but not to a significant degree. On the other

1 hand the OCH2 H NMR peaks are all shifted on average of 0.3 pm upfield compared to the free germylenes and the pair of multiplets have collapsed into one in 35a and 35d.

Table 8. Experimental 1H and 13C shifts of the ethylene backbone of nickel- germylenes complexes 40 in C6D6

1 H 13C

NCH2 OCH2 NCH2 OCH2 CO 40a 1.82- 1.88 3.63 – 3.81 58.6 62.8 197.8 40b 1.65 – 1.69 1.80 – 1.87 3.75 – 3.77 57.1 66.1 197.4 a 40c 1.52 - 1.55 2.03 - 2.10 3.79 - 3.89 54.9 67.3 197.2 40d 1.48 - 1.51 2.47 - 2.50 3.88 - 3.91 54.2 66.8 197.0 aCrude product

3.1 Synthesis of silicon–diethanol amine complexes

The success seen in stabilizing germylenes 11 with the alkoxy ligand 10 provided an opportunity to expand into silylene chemistry. With the limited success seen in the reduction of dichloro germocanes 40, reactions using trichlorosilane as Cl2Si: precursors were prioritized.

58 3.1.1 Synthesis of 1-chloro-2,8-di-oxa-5-aza-1-sila-bicyclo[3.3.0]

octane 42

OSiMe3 O THF Cl Me N + HSiCl3 Me N Si + 2 Me3SiCl H OSiMe3 O

39 42

Scheme 29. Synthesis of 1-chloro-2,8-di-oxa-5-aza-1-sila-bicyclo[3.3.0] octane

Building on work done on germylene precurors carried out in this thesis and by Jeff Hastie in the area of silanes, compound 42 was obtained from the addition of trichlorosilane to a solution of 39a in THF (Scheme 29). Over time a white precipitate formed around the solvent edge highlighting the insoluble nature of the product. 1H and 13C NMR spectra of the crude reaction product showed a spectroscopically pure product with stereotypical splitting of the ethylene backbone. Crystals grown under vacuum in a sealed glass tube over a temperature gradient of 182 – 25°C were of X-ray quality. X-ray analysis showed a nearly linear Cl–Si–N axis but the complete structure could not be determined due to a disorder in the crystal.

O Me3Si O Cl THF N(SiMe3)2 Me N Si + NNa Me N Si + NaCl H H O Me3Si O 44 45

Scheme 30. Attempted deprotonation of chloro-silane 44 with sodium bis(trimethylsilyl)amide

59 Initial trials at deprotonating silane 44 with sodium bis(trimethylsilyl)amide

(NaHDMS). Due to the poor solubility, an equimolar mass of NaHMDS was added to a suspension of 44 in THF and allowed to stir overnight (Scheme 30).

1H and 13C NMR analysis showed a product that was consistent (shift and integration) with nucleophilic substitution of the chlorine atom by bis(trimethylsilyl)amide rather than deprotonation (Table 9). The proposed mechanism for the substitution proceeds through the formation of an intermediate silylene (Scheme 31).

O Me Si O Me Si O Cl 3 3 N(SiMe ) Me N Si + NH Me N Si + NH Me N Si 3 2 Na H O Me3Si O Me3Si O

45 46 Scheme 31. Proposed formation of silane 45 through silylene 46

Table 9. 1H, 13C and 29Si NMR shifts for the silanes 44 and 45

1H 29Si 2 NCH2 OCH2 CH3 SiH [J (SiH)] Si 44 1.55 - 1.60 1.77 - 1.81 3.27 - 3.30 3.33 - 3.37 1.41 5.43 [333 Hz] -76.93

45 1.96 - 2.01 3.42 - 3.52 1.92 5.03 [282 Hz] -52.73

Due to the substitution that occurred with NaHDMS a less nucleophilic base was investigated, and as an alternative, DBU was chosen (Scheme 32).

Initial spectroscopic evidence in C6D6 does not show a soluble product. The lack

60 of evidence for the formation of a stable silylene suggests that other synthetic procedures need to be investigated in future projects.

Cl O O Cl THF N Me N Si Me N Si + H DBU O N O H 44

Scheme 32. Attempted deprotonation of silane 44 with DBU

2.3 Computational investigations

The series of structurally characterized germylenes are a valuable set to evaluate different computational methods. Nearly all commonly used DFT methods struggle to accurately reproduce weak interactions such as the experimental Ge-N distance resulting in inaccurate structures and calculated thermochemical values. By comparing the calculated to experimental structures the most accurate methods can be determined and used in future cases where the experimental structure is not known.

2.3.1 General comments on the calculations

All calculations were carried out with the Gaussian 09M suite of programs,

Rev. A.02.73 Energies were converted using the factor 1 Hartree = 627.51 kcal/mol. All optimized structures are verified as local minima through frequency calculations. The use of the standard integration grid gave false minima that were

61 only detected after the use of the ultrafine integration grid revealed virtual frequencies.74, 75

2.3.2 Structural optimization of germylenes

After an extensive screening process involving different DFT methods available in G09, only four DFT methods, namely SVWN76, BB1K64, MPWB1K77,

78 and M062x79, 80 gave acceptable Ge-N distances (Table 10). All methods were tested with the 6-311+G(3df,p)81 and Def2-TZVP82 basis sets which gave near identical results allowing for the use of the computationally less demanding Def2-

TZVP basis set to be used.83-87 Basis set truncation effects were measured by comparing Def2-TZVP with Def2-QZVP83-87 data. The maximum deviation between the two was only 0.37 pm (11c). The structures were accordingly well converged at the DFT/Def2-TZVP level.

Table 10 outlines the root mean squared error (RMS) and linear correlation coefficient of selected bond lengths (Ge-O and Ge-N) between the experimental and calculated structures. The RMS is used to determine the average difference between calculated and observed bond lengths and the linear correlation coefficient determines the relationship between the two sets of values.

The linear correlation coefficient values range from -1 to 1, where a larger positive correl. means the stronger the linear relationship between the two sets of values.

62 Table 10. RMS error [pm] and linear correlation coefficients for computational and experimental (single crystal X-ray) of selected structural parameters ([pm] [°]) for germylene 11c (DFT/Def2-TZVP, CBS-4m). Solvation at the SMD level. See

Appendix for 11a-d.

Solvent Ge-O(1) Ge-O(2) Ge-N O(1)-Ge-O(2) RMS Correl EXP-syn 184.02 184.14 216.05 101.72 - - CBS-4m 189.97 182.18 219.99 100.02 7.40 0.9801 SVWN — 184.73 183.24 221.49 100.84 5.56 0.9993 SVWN Benzene 184.84 183.47 218.84 100.91 2.98 0.9993 SVWN THF 184.84 183.64 216.14 101.00 0.96 0.9994 M062x — 183.19 184.64 225.08 100.56 9.08 0.9996 M062x Benzene 183.47 184.85 221.31 100.55 5.34 0.9996 M062x THF 183.68 184.92 218.11 100.66 2.23 0.9996 MPWB1K — 183.09 181.54 220.82 100.09 5.51 0.9993

MPWB1K Benzene 183.35 181.84 218.04 99.96 3.11 0.9992

MPWB1K THF 183.28 181.94 214.52 100.23 2.78 0.9992

The structures all predict Ge-N distances that are significantly longer then those observed in the single crystal X-ray structure. Addition of solvation models

(Benzene [SMD]88, THF SMD]88) reduces this deviation and improves both the error and correlation. The residual errors are most likely the result of packing effects in the experimental structures. The approximation of anisotropic solid state packing effects through isotropic solvent models cannot be expected to produce a perfect match even if the computational method and basis sets employed are highly accurate. The improvements gained by the inclusion of a solvation model are nevertheless significant as they document the strong influence of the local environment on the Ge-N distances. Key structural parameters of germylene 11c are outlined in Table 11 highlighting the sensitive nature of the calculated structure.

63 2.3.2.1 Considering structural conformations

A comparison of accurate computational structures of the germylenes is further complicated by the presence of three different conformations the ring structure can adopt. In isomer A one ethylene bridge points towards the N-alkyl group while the other CH2CH2 points away forming a boat-chair conformation.

This conformation is seen in the single crystal X-ray structure of germylene 11a and 11d. The experimental structure of germylene 11b and 11c are represented by isomer B with each bridge pointing down (boat), conversely isomer C both

1 CH2CH2 group point up forming a crown conformation (Figure 26). In solution H

NMR suggest neither conformation is dominant but rather a rapid equilibrium existing between conformations.

R R R H H H H H H N H N H H N C C C C C C C Ge H C Ge C H Ge H H H H O HO H O O O HO C C C H H H H H H A B C

Figure 26. Possible conformations of the monomeric germylenes

2.3.2.2 Wiberg bond orders and charge densities

To gain a more detailed insight into the structure and bonding of the germylenes 11, Wiberg charges and bond orders were obtained at

MPWB1K/Def2-TZVP level. The MPWB1K method was chosen because of its

64 slightly better structural accuracy for both the germylenes and nickel germyelenes (see Appendix). Wiberg bond indices are an optional component to a natural bond order calculation achieved through the addition of the command bndidx to the end of the input file.73 The natural bond order analysis gives the electron population of the natural atomic orbitals, their type (core, valence or

Rydberg [excited]) and the corresponding energies.89-91 The Wiberg bond orders calculation gives two indexes, first a matrix containing the number of covalent bonds that form between an atom and every other atom in a molecule and second, the sum of the covalent bonds each atom forms. A Wiberg bond order of one represents a single covalent bond, two a double bond and so on. The Wiberg bond orders of germylenes 11 in conformation A are given in Table 11.92, 93

A comparison of the Wiberg bond indices of the Ge-N bond of 11a-d without a solvation model show a fairly consistent bond order of ~0.25 despite the variable length of the corresponding bond. The addition of a solvation model results in an increase in the Ge-N bond order. Using benzene as an example the bond order increases to ~0.31 in 11H but gradually decreases to ~0.26 as the size of the N-alkyl grows. The formally trivalent nitrogen atom now has a sum of bond orders of ~3.25 which is readily attributed to the formation of the Ge-N dative bond. It is interesting to note the relatively low bond order (~0.50) of the

Ge-O bond. This coupled with the Wiberg charge densities (Table 12) of both oxygen and germanium atoms reveals a high degree ionicity for the Ge-O bond.

65 Table 11. Wiberg bond orders and atomic valencies for selected monomeric germylenes 11 (MPWB1K/Def2-TZVP).

Solvent Ge-O Ge-O Ge-N Ge O O N a 11H — 0.487 0.513 0.275 1.390 1.625 1.645 3.126 Benzene 0.489 0.509 0.309 1.423 1.616 1.632 3.135 THF 0.489 0.507 0.323 1.436 1.606 1.621 3.141

a 11a — 0.481 0.513 0.248 1.370 1.621 1.643 3.255 Benzene 0.482 0.509 0.267 1.388 1.611 1.631 3.260 THF 0.483 0.507 0.287 1.407 1.601 1.620 3.266

a 11b — 0.482 0.511 0.245 1.371 1.622 1.643 3.259 Benzene 0.483 0.508 0.264 1.389 1.612 1.631 3.264 THF 0.484 0.506 0.283 1.407 1.603 1.620 3.270

a 22c — 0.484 0.507 0.248 1.385 1.641 1.623 3.264 Benzene 0.484 0.504 0.266 1.402 1.613 1.630 3.269 THF 0.484 0.501 0.283 1.419 1.619 1.603 3.274

a 11d — 0.481 0.506 0.246 1.398 1.640 1.620 3.259 Benzene 0.481 0.503 0.263 1.413 1.629 1.610 3.264 THF 0.481 0.500 0.281 1.430 1.618 1.600 3.268

b 11d — 0.468 0.518 0.240 1.388 1.620 1.638 3.252 Benzene 0.466 0.512 0.258 1.402 1.626 1.609 3.258 THF 0.466 0.508 0.277 1.417 1.615 1.599 3.263 a) syn b) anti

As an interesting additional piece of information gained, the Wiberg bond calculations supply the valence electron configuration for each atom along with the number of electrons attributed to each bond or lone pair. For example the lone pair on the germanium of 11a contains 1.97 electrons and shows predominantly s character (Table 13). It is also interesting to note the % character of the germylene lone pair. Although is does not vary greatly

66 throughout the series there is a huge deviation from the idealized sp2 hybridization.

Table 12. Selected structural bond lengths [pm] and Wiberg charge densities for monomeric germylenes 11 (MPWB1K/Def2-TZVP ultrafine level). Experimental structural data from single crystal X-ray structures where available

Ge-N Ge-O Ge-O Ge O O N 11Ha — 220.38 181.58 183.34 1.257 -0.912 -0.896 -0.663 Benzene 213.94 183.69 183.33 1.235 -0.903 -0.916 -0.668 THF 213.94 182.33 183.69 1.225 -0.925 -0.913 -0.667

11aa — 220.16 181.48 183.48 1.272 -0.913 -0.897 -0.493 Benzene 217.24 181.82 183.69 1.259 -0.920 -0.905 -0.496 THF 214.55 182.13 183.86 1.246 -0.928 -0.913 -0.498

11ba — 219.99 181.50 183.37 1.274 -0.913 -0.897 -0.497 Benzene 217.18 181.84 183.54 1.261 -0.920 -0.905 -0.499 THF 214.60 182.13 183.67 1.248 -0.927 -0.914 -0.501

11ca — 220.64 179.77 181.05 1.270 -0.899 -0.913 -0.497 Benzene 218.00 181.84 183.35 1.258 -0.920 -0.907 -0.499 THF 215.52 182.13 183.54 1.245 -0.915 -0.927 -0.502 Exp 216.05(15) 184.02(13) 184.14(14)

11da — 222.26 181.37 183.14 1.268 -0.900 -0.915 -0.510 Benzene 219.46 181.70 183.45 1.257 -0.908 -0.923 -0.513 THF 215.52 182.13 183.54 1.244 -0.915 -0.930 -0.516

11db — 227.50 180.53 183.02 1.266 -0.903 -0.908 -0.505 Benzene 224.09 181.04 183.32 1.257 -0.911 -0.916 -0.509 THF 220.97 181.47 183.55 1.246 -0.919 -0.924 -0.512 Exp 219.7(11) 182.8(8) 183.0(9) a) syn b) anti

67 Table 13. Wiberg-NBO analysis for selected germylenes (MPWB1K/Def2-TZVP ultrafine level)

% Character Electron “count” s p d 11H 1.97 80.62 19.34 0.04 11a 1.96 81.07 18.90 0.04 11b 1.97 79.14 20.83 0.04 11c 1.97 79.08 20.88 0.04 11d 1.97 79.90 20.06 0.04

The presence of dative bonds in 11a-d naturally leads to the question if these compounds should still be considered to be germylenes. In the strict sense, germylenes are germanium compounds with formal oxidation state +II and coordination number two. The term coordination number is topological (number of next neighbours) and groups together neighbours with strong, weak and occasionally non existent interaction. Coordination numbers have therefore to be used with a degree of caution to predict or classify reactivity patterns. The second point refers to the reactivity of germylenes. The overwhelming majority of germylene reactions reported are carried out with reactants that have at least one lone pair; in donor solvents or both. The observed reactivity will accordingly be that of germylene Lewis base complex rather than that of the free sextet species.

In this sense, compounds 11 are better reactivity models than the respective uncoordinated germylenes.

68 2.3.3 Thermochemistry

2.3.3.1 Calculated dimerization energies

The monomeric nature of all four germylenes in solution is contrasted by the dimerization of two in the solid state. The origin of this dualistic nature is not immediately apparent and could be attributed to increased donor stabilization or simple packing effects. Investigating this phenomenon is not without its pitfalls.

The size of the dimers preclude the use of highly accurate multi-step methods.

While the significantly faster CBS-4m method94-96 is applicable, compounds with heavier elements that require basis sets with d or f functions can also give rather large errors. Most DFT methods do not model weak interactions, i.e. dative bonds, requiring dispersion corrections that become increasingly important as the system size increases.97, 98

Fortunately, the M062x method, a hybrid DFT method very high thermochemical accuracy developed by Zhao and Truhlar,79 has become widely available while this study was in progress. Unlike previous DFT methods, the

M062x method includes dispersion corrections. Dimerization energies obtained at the M062x/Def2-TZVP level are given in Table 15. The thermochemical impact of solvation was studied at the SMD level. CBS-4m data are included for comparison only. To study the effect of the Ge-N dative bond, a germanium alkoxides without dative stabilization, (MeO)2Ge:, is included as reference compound. The role of basis set superposition errors (BSSE) were evaluated through counterpoise calculations. BSSE are introduced due to the use of finite

69 basis sets being used in the calculation. The dimers naturally contain twice the orbitals compared to the corresponding monomers and due to overlap of the virtual orbitals artificially lower the total energy of the dimer compared to the monomer. Counterpoise calculations add the orbitals of the entire complex but only the atoms of one monomer resulting in a more complete basis set, lowering the energy of the monomer.99

Table 14. Dimerization energies ΔG° [kcal/mol] for selected germylenes (11d-c) and dimeric germylenes (11a-b) (M062x/Def2-TZVP, CBS-4m, ultrafine grid size)

Correction Dimer CBS-4m CBS-4m M062x M062x M062x/Def2- Benzene Benzene TZVP BSSEb 11a — anti -8.22 -4.39 -6.40 -2.28 1.53 BSSE anti — — -4.87 -0.75

11b — anti -7.31 -2.78 -5.06 -1.30 1.50 BSSE anti -3.56 +0.20

11c — anti -7.55 -4.75 -4.02 -0.40 1.46 BSSE anti -2.56 +1.06

11d — anti -8.88 -5.66 -5.56 -2.36 1.48 BSSE anti -4.08 -0.89

(MeO)2Ge: — -14.12 -11.89 -21.10 -18.77 a 1.67 a) Dimerization energy at the G4 SMD level (benzene): -17.04 kcal/mol

Superficially, the M062x calculations suggest that all four germylenes 11a- d should dimerize. However the inclusion of solvation effects lowers the dimerization energies by ~4 kcal/mol. Removal of basis set superposition artifacts leads to a further reduction of ~1.5 kcal/mol. The inclusion of both effects gives values that are very close to zero. The dimerization energies given in

70 Table 13 are in direct contrast to a previous DFT study investigating dimerization of 11a at the PBE/TZ2P level which game dimerization values -11 to -12 kcal/mol.

100 This can be attributed in part to the differences in their calculated structure.

The M062x/Def2-TZVP data show that the significant variations in the Ge-

N distances do not translate into large energy changes. This can be illustrated by a comparison of the syn- and anti-conformers of 11d which differ in energy by only 0.3 kcal/mol, but show Ge-N distances of 232.8 pm (anti-11d) and 227.4 pm

(syn-11d). To achieve the typical accuracy of ± 1.5 pm usually expected from accurate DFT structures, an energy accuracy of about 0.1 kcal/mol would be required – well outside the reach of even the most accurate computational approaches available today.

The fact that the dimerization energies are all very similar regardless of the substituent R rules out simplistic interpretations based on the steric demand of the nitrogen substitent. The importance of the Ge-N dative bond can be quantified by comparing the dimerization energies of 11a-d (Ge-N dative bond) with those of dimethoxygermylene (no dative bond). Based on the ΔG° values, the dative bond stabilizes the monomeric germylenes 11 by 16-17 kcal/mol. To assess the overall quality of the M062x/Def2-TZVP approach, the dimerization energy of (MeO)2Ge: was calculated at the G4 level. For benzene as solvent

(SMD model), the M062x/Def2-TZVP dimerization energy ΔG° of –18.77 kcal/mol is in excellent agreement with the G4 value of –17.04 kcal/mol and a similar accuracy can be assumed for the other germylenes 11a-d.

71 2.3.3.2 HOMO-LUMO gaps

A closer view at the HOMO and LUMO energies is of interest to understand how the dative bond changes the energy levels of the frontier orbitals

(Figure 27).

Figure 27. HOMO and LUMO di-grams of 5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane, protons removed for clarity.

Compared with dimethoxygermylene, the germylenes 11a show increased basicity (increase in HOMO energies by ~ 20 kcal/mol), and reduced Lewis acidity (increase in LUMO energies by ~ 35 kcal/mol)(Table 15). While the nature of the HOMO is unchanged (Ge lone pair) the nature of the LUMO changes from a germanium 3p empty orbital to an antibonding Ge-N σ* orbital.

72 Table 15. Orbital energies (HOMO, LUMO, HOMO-LUMO gaps, [kcal/mol]) for selected germylenes. M062x/Def2-TZVP level, THF (SMD) solvent model, ultrafine integration grid. Ge-N dative bond distances (in pm) for comparison

HOMO LUMO ΔE Ge-N 11a -168.46 +23.90 192.36 216.17 11b -167.93 +23.87 191.80 216.65 11c -166.94 +23.59 190.53 218.10 11d -166.00 +26.27 192.27 220.10

(MeO)2Ge -188.85 -9.75 179.10 —

Chapter 3. General Comments and Future Work

74 This thesis has detailed the investigation of the stabilization of divalent dialkoxy germanium using an intermolecular Ge-N dative bond and the reactions of these compounds. Various synthetic procedures were explored for 5-alkyl-2,8- di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane 11.

Reductions of germocane 40a were attempted using lithium and potassium metal however in both cases neither a product nor starting materials could be isolated. The precise reason is not understood due to the lack of information regarding the mechanism of the reduction. For future work, the use of cyclic voltammetry could be used to determine if stronger reducing conditions are required for 40a or if it will not proceed.

Two synthetic routes starting from germanium dichloride dioxane and either the N-alkyl dilithium diethanoxide or 1,7-bis(trimethylsilyl)-4-methyl-1,7-di- oxa-4-aza-heptane 39a were attempted. The dilithium diethanoxide route did not give a soluble product in benzene-d6 nor was the starting material recovered due to their poor solubility in non-polar solvents. The reaction starting from the silylated ligand showed shifted backbone peaks in the 1H NMR suggesting the formation of a intermolecular Ge-N dative bond. However even increasing temperatures in THF and 1,4-dioxane or melting the starting materials together did not form the cyclized product.

A more convenient synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane 11 was achieved through the addition of N-alkyl diethanol amine to a solution of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane

75 (Scheme 33). A spectroscopically (1H and 13C NMR) pure material was obtained simply by washing the product with hexanes and crystals were grown through slow sublimation in a sealed glass tube under vacuum.

tBu tBu OH N O NH R N + Ge R N Ge + OH N O NH tBu tBu 10 16 11 29d

Scheme 33. Synthesis of 5-alkyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane 11

After sublimation, the series was analyzed by single crystal X-ray diffraction allowing for the analysis of structural parameters. All germylenes adopted a bicyclic donor stabilized ring structure featuring a transannular dative bond between the nitrogen and the germanium. Moving from the germylene 15a to 15d the solid dative bond length decreases from 236.73 pm to 219.7 pm, which may be in part due to the formation of dimers in 11a and 11b.

The bicyclic ring adopts one of two structures in the solid state differing in the orientation of the ethylene backbones. Germylenes 11a and 11d were found to be anti with one pointing towards the N-alkyl group and the other pointing away. Conversely germylenes 11b and 11c adopted a syn conformation with both ethylene bridges pointing away form the N-alkyl group. Computational evidence shows only a small energy difference between the two observed

76 conformations suggesting the variation in conformation may be a result of crystal packing effects.

An experimental comparative study the length of the Ge-N dative bond and its strength is difficult due to the formation of dimers in 11a and 11d necessitating the use of computational models for this thesis. However the use of gas phase electron diffraction could be used to study the presumably monomeric structure for all four germylenes.

A series of nickel-germanium complexes (Figure 29) were synthesized through the addition of a solution of 11 to nickel carbonyl giving 43. The IR spectra of these compounds show CO stretching frequencies comparable to analogous triphenyl phosphine ligands.

O O C O O O Me N Ge Ni Ge N Me Et N Ge Ni(CO)3 tBu N Ge Ni(CO)3 O C O O O O 43a 43b 43d

Figure 28. Germanium-nickel carbonyls isolated

Preliminary work was done in the synthesis of stable dialkoxy silylenes 36. We were able to isolate the pentavalent bicyclic silane 44 through the addition of

Cl3SiH to the silylated ligand 39. Crystals were grown through slow sublimation and analyzed by single crystal X-ray diffraction, however a disorder in the unit cell prevented determination of the complete structure.

77 Future work using N-alkyl diethanol amine ligands to stabilize carbenes could be carried out following the synthetic procedure reported by Warkentin et al. in 2003 (Scheme 34).101 The formation of the carbene was determined through trapping experiments with tert-butanol. In the absence of a trapping agent the carbene fragmented to a diradical and could not be isolated as a persistent carbene. It would be interesting to determine if the addition of a C-N dative bond would stabilize the carbene and result in a persistent carbene species.

Ph Ph Ph (Im)2CO 1. H2NNH2 NH2 OH OH O O HN O OH 2. Me2CO O O

LTA CH2Cl2 Ph Ph O O AcO Ph 100 °C TFA N O O N O N O OH tBuOH CH2Cl2 tBuO H N O

Scheme 34. Synthesis of dialkoxycarbenes

Chapter 4. Experimental

79 General Procedure

Melting points were recorded in sealed capillaries and are uncorrected. NMR spectra were recorded using Bruker-300 (1H, and 13C NMR) and Bruker-400 spectrometers (1H, 13C, 17O, and 29Si NMR) and Bruker-600 spectrometer (1H,

13C, and 15N). All chemical shifts are given in parts per million (ppm) with tetramethylsilane as an internal standard. IR data were recorded as Nujol mulls,

NaBr pellets or solution cell using a Nicolet 380 FTIR spectrophotometer. Nujol was dried over molten sodium prior to use. Commercial reagents were used without purification unless otherwise indicated. All solvents were pre-dried over

Na/K alloy or CaH2 and stored under argon atmospheres, unless otherwise stated. All procedures were performed under inert atmospheres (argon,

99.994%) using standard Schlenk line techniques, or performed inside of an argon glove box (Mbraun).

80 Reaction of N-alkyl diethanolamine with hexamethyldisilazane: 1,7- bis(trimethylsilyl)-4-alkyl-1,7-di-oxa-4-aza-heptane (General procedure)

OH SiMe OSiMe 3 ! 3 R N + HN R N OH SiMe3 OSiMe3 10 39

A mixture N-alkyl diethanolamine (neat, 20 mmol), hexamethyldisilazane

(40 mmol) was boiled at 150°C for one week monitoring the reaction by 1H NMR.

Excess hexamethyldisilazane was removed under vacuum and the product was distilled under vacuum to give the product as a colourless oil.

1,7-bis(trimethylsilyl)-4-methyl-1,7-di-oxa-4-aza-heptane. (39a) [CAS 76710-

52-6].

Colourless oil (3.94 g, 83%).

1 H NMR (C6D6, 400 MHz) 0.11 (s, 18 H, Si(CH3)3), 2.22 (s, 3 H, NCH3), 2.56 –

3 3 2.60 (t, J = 6.7 Hz,4 H, CH2N), 3.65 – 3.69 (t, J = 6.7 Hz, 4 H, CH2O).

13 C NMR (C6D6, 100 MHz) 0.4(Si(CH3)3), 43.6 (NCH3), 60.8 (CH2N), 61.5

(OCH2).

1,7-bis(trimethylsilyl)-4-tert-butyl-1,7-di-oxa-4-aza-heptane. (39d) [CAS

113849-58-4]. Colourless oil (4.36 g, 76%).

81 1 H NMR (CDCl3, 300 MHz) 0.12 (s, 18 H, Si(CH3)3), 1.05 (s, 9 H, NC(CH3)3),

3 3 2.61 – 2.66 (t, J = 7.9 Hz, 4 H, CH2N), 3.47 – 3.53 (t, J = 7.9 Hz, 4 H,

CH2O).

13 C NMR (CDCl3, 75 MHz) 0.4 (Si(CH3)3), 27.1 (NC(CH3)3), 53.8 (CH2N), 54.6

(NC(CH3)3), 63.9 (OCH2).

82 Reaction of 1,7-bis(trimethylsilyl)-4-alkyl-1,7-di-oxa-4-aza-heptane with germanium tetrachloride: 1,1-dichloro-5-alkyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane.

OSiMe 3 CHCl O 3 Cl R N + GeCl4 R N Ge + 2 Me3SiCl ! Cl OSiMe3 O

39 40

Synthesis of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (40a) [CAS 722458-50-6].

To a solution of 1,7-bis(trimethylsilyl)-4-tert-butyl-1,7-di-oxa-4-aza-heptane (1.04 g, 3.97 mmol) in dry CHCl3 (4 mL) was added germanium tetrachloride (0.85 g,

3.98 mmol). Stirring of the resulting pink solution at 80°C overnight, resulted in a orange solution. Cooling the reaction mixture to room temperature led to the formation of a precipitate which was washed with dried boiling CHCl3 (3 x 10 mL)

The residue consists of spectroscopically pure 40a (.852 g, 83 %) as a white powder m.p. 212-213 °C Lit. m.p. not known.

1 H NMR (CDCl3, 400 MHz) 2.70 (s, 3 H, NCH3), 2.86 – 2.92 (m, 2 H, CH2N),

2.98 – 3.06 (m, 2 H, CH2N), 3.98 – 4.10 (m, 4 H, CH2O).

13 C NMR (CDCl3, 100 MHz) 44.4 (NCH3), 55.0 (NCH2), 58.8 (OCH2).

83 Synthesis of 1,1-dichloro-5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (40d) No CAS.

To a solution of 1,7-bis(trimethylsilyl)-4-tert-butyl-1,7-di-oxa-4-aza-heptane

(2.26 g, 7.39 mmol) in dry CHCl3 (10 mL) was added germanium tetrachloride

(2.46 g, 11.47 mmol). Stirring of the resulting pink solution at 70°C overnight, resulted in an orange solution. Cooling the reaction mixture to in refrigerator did not lead to precipitation. Removal of the solvent under vacuum and washing of the remaining brown oil with dried CHCN (3 x 5 mL) gave spectroscopically pure

40d (0.601 g, 27%) as a white powder.

1 H NMR (CDCl3, 400 MHz) 1.28 (s, 9 H, NC(CH3)3), 2.36 – 3.22 (bm, 4 H,

CH2N), 4.00 (m, 4 H, CH2O).

13 C NMR CDCl3, 100 MHz) 26.6 (NC(CH3)3), 51.8 (CH2N), 58.7 (NC(CH3)3), 64.6

(OCH2).

84 Reaction of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane with alkali metals.

O O THF Me N Ge Cl + 2.2 M Me N Ge + 2 MCl Cl O O

40a 11a

Reaction of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane with lithium metal.

To a suspension of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane (0.270 g, 1.04 mmol) in dry THF (10 mL) , lithium metal

(0.017 g, 2.42 mmol) was added. A majority of the lithium metal (~ 75 %) remained after two days stirring. The reaction turned brown after being sonicated for two hours but some lithium still remained. 1H and 13C NMR of the crude reaction mixture only showed residual THF peaks. A small amount of sublimed anthracene (0.019 g, 0.17 mmol) was added to the reaction and set to stir for 8 hours. The remaining lithium metal dissolved but the 1H and 13C NMR of the crude reaction mixture only showed peaks that can be attributed to anthracene and THF.

85 Reaction of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane with potassium metal.

To a suspension of 1,1-dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane (0.252 g, 0.967 mmol) in dry THF (5 mL) , potassium metal

(0.083 g, 2.12 mmol) was added. Small bubbles formed around the potassium but the potassium did not dissolve. The reaction turned brown after stirring for 12 hours but most potassium still remained but was no longer shiny. 1H and 13C

NMR of the crude reaction mixture only showed residual THF peaks. A small amount of sublimed anthracene (0.037 g, 0.33 mmol) was added to the reaction and set to stir for 8 hours. The remaining lithium metal dissolved but the 1H NMR of the crude reaction mixture only showed peaks that can be attributed to anthracene and THF.

86 Reaction of diethanol amine with bromo propane: synthesis of 1,1- dichloro-5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane. (10c) [CAS

121-93-7].

H ! + Br + HBr N N HO OH HO OH 10c

2-bromopropane (40.4g, .325 mol) was dissolved neat weighed amount of diethanol amine (33.7g, .320 mol) was boiled to 80°C. The resulting biphasic system (colourless liquid on top of a slightly yellow solution. Over a period of two days over the bottom layer increased. After cooling and removing volatile materials under vacuum, an equimolar amount of NaOH in 20 mL H2O was added to the remaining white solid. The solution was extracted with chloroform (3 x 20mL), the organic layer was separated, the solvent was removed. The remaining crude product (38.3 g, 80% yield) was distilled under reduced pressure

(0.1 torr) to give a pure product. (102-107°C, 35% yield).

1 3 H NMR (C6D6, 400 MHz) 0.74 – 0.76 (d, 6 H, CH(CH3)2), 2.22 – 2.26 (t, J =

5.5 Hz, 4 H, CH2N), 2.58 – 2.67 (sept, 1 H, CH(CH3)), 3.34 – 3.40 (t,

3 J = 5.5 Hz, 4 H, OCH2).

13 C NMR (C6D6, 100 MHz) 18.1 (CH(CH3)2), 51.3 (CH(CH3)2), 52.2 (CH2N),

60.69 (OCH2).

87 Reaction of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane with N- methyl diethanolamine: synthesis of 5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (11a) [CAS 71872-15-6].

tBu tBu

OH N THF O NH Me N + Ge Me N Ge + OH N O NH tBu tBu 10a 15 11a 29d

To a solution of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane (0.31 g,

1.27 mmol, 1.1 eq) in dry THF (4 mL) was added N-methyl diethanolamine (0.13 g, 1.13 mmol, 1 eq.) in dry THF (4 mL). Stirring of the resulting turbid solution overnight, removal of the solvent under vacuum and washing of the remaining colourless oil with dried hexanes (3 x 5 mL) gave spectroscopically pure 1 (0.20 g,

92 %) as colourless, air sensitive powder. X-ray quality crystals were grown by slow vacuum sublimation 100 °C/0.1Torr in a sealed glass tube. Melting point of the sublimed material 73-74°C Lit. m.p. 71°C.26

1 H NMR (C6D6, 400 MHz) 1.89 (s, 3 H, CH3), 1.94 (m, 4 H, CH2N), 3.95 – 4.04

(m, 4 H, CH2OC).

13 C NMR (C6D6, 100 MHz) 45.3 (CH3), 61.0 (CH2N), 66.6 (OCH2).

GC MS (EI+) 191 [M+ 38%], 161 [45%], 146 [18%], 117 [16%], 116 [11%], 91

[27%], 74 [21%], 71 [30%], 42 [100%].

MS (LDI, DHB) 192 (M+H 12%) 118 (27%).

FT-IR (Nujol) 1315 w, 1296 w, 1075 s, 1050 s, 1001 m, 893 s.

88 Reaction of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane with N-ethyl diethanolamine: synthesis of 5-ethyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (11b) No CAS.

tBu tBu

OH N THF O NH Et N + Ge Et N Ge + OH N O NH tBu tBu 10b 15 11b 29d

To a solution of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane (0.30 g,

1.24 mmol, 1.2 eq) in dry THF (4 mL) was added N-ethyl diethanolamine (0.13 g,

1.01 mmol, 1 eq.) in dry THF (4 mL). Stirring of the resulting turbid solution overnight, removal of the solvent under vacuum and washing of the remaining colourless oil with dried hexanes (3 x 5 mL) gave spectroscopically pure 1 (0.189 g, 92 %) as colourless, air sensitive powder. X-ray quality crystals were grown by vacuum sublimation 100 °C/0.1Torr in a sealed glass tube. Melting point of the sublimed material 76-77°C Lit. m.p. 65°C.68

1 3 H NMR (C6D6, 400 MHz) 0.51 – 0.54 (t, J = 7.2 Hz, 3 H, CH3), 1.78 – 1.80 (m,

3 2 H, CH2N), 1.99 – 2.03 (m, 2 H, CH2N), 2.25 – 2.28 (q, J = 7.2 Hz, 2

H, CH2CH3), 4.04 – 4.08 (m, 4 H, OCH2).

13 C NMR (C6D6, 100 MHz) 10.7 (CH3), 53.0 (CH2CH3), 57.9 (CH2N), 67.8

(OCH2).

GC MS (EI+) 205 [M+ 37%], 161 [66%], 146 [61%], 91 [32%], 74 [26%], 56

[76%], 42 [100%].

89 + + MS (LDI, DHB) 337 [(CH3CH2N(CH2CH2O)2)2Ge) H 6%], 206 [M H 13%],

154 [27%], 155 [30], 134 [100%].

FT-IR (Nujol) 1666 m, 1291 w, 1261 m, 1078 S, 1035 m, 988 m.

90 Reaction of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane with N-isopropyl diethanolamine: synthesis of 5-iso-propyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (11c) No CAS.

tBu tBu

OH N THF O NH iPr N + Ge iPr N Ge + OH N O NH tBu tBu 10c 15 11c 29d

To a solution of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane (0.32 g,

1.30 mmol, 1.1 eq) in dry THF (4 mL) was added N-iso-propyl diethanolamine

(0.16 g, 1.12mmol, 1 eq.) in dry THF (4 mL). Stirring of the resulting turbid solution overnight, removal of the solvent under vacuum and washing of the remaining colourless oil with dried hexanes (3 x 5 mL) gave spectroscopically pure 1 (0.19 g, 92 %) as colourless, air sensitive powder, X-ray quality crystals were grown by vacuum sublimation 100 °C/0.1Torr in a sealed glass tube.

Melting point of the sublimed material 79-81 °C.

1 2 H NMR (C6D6, 400 MHz) 0.65 – 0.67 (d, 6 H, CH(CH3)2, J = 6.6), 1.68 – 1.70

(m, 2 H, CH2N), 2.13 – 2.17 (m, 2 H, CH2NC), 2.55 – 2.61 (sept, 1 H,

2 CH(CH3)2, J = 6.6), 4.09 – 4.15 (m, 4 H, OCH2).

13 C NMR (C6D6, 100 MHz) 19.5 (CH(CH3)2), 55.4 (CH2N), 57.8 (CH(CH3)2), 68.9

(OCH2).

GC MS (EI+) 219 [M+ 11%], 189 [49%], 165 [100%], 146 [65%], 105 [23%],

91 [16%], 74 [5%], 56 [48%], 42 [3%].

MS (LDI) 226 [M+Li 73%], 220 [M+H 88%], 58 [100%].

91 FT-IR (NaCl) 1365 m, 1191 w, 1140 m, 1053 m, 1035 m, 921 w, 901 m.

92 Reaction of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane with N-tert-

Butyl diethanolamine: synthesis of 5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. (11d) No CAS.

tBu tBu

OH N THF O NH tBu N + Ge tBu N Ge + OH N O NH tBu tBu 10d 15 11d 29d

To a solution of 2,5-bis(tert-butyl)-2,5-di-za-1-germa-cyclopentane (0.41 g,

1.69 mmol, 1 eq) in dry THF (4 mL) was added N-tert-butyl diethanolamine (0.27 g, 1.67 mmol, 1 eq.) in dry THF (4 mL). Stirring of the resulting turbid solution overnight, removal of the solvent under vacuum and washing of the remaining colourless oil with dried hexanes (3 x 5 mL) gave spectroscopically pure 1 (0.36 g,

92 %) as colourless, air sensitive powder. X-ray quality crystals were grown by vacuum sublimation 100 °C/0.1Torr in a sealed glass tube. Sublimation point of the material 119 - 120 °C..

1 2 3 H NMR (C6D6, 400 MHz) 0.82 (s, 9 H, CH3), 1.42 – 1.59 (dt, J = 12.1 Hz, J =

2 3 3 3.8 Hz, 2 H, CH2N), 2.44 – 2.51 (ddd, J = 12.1 Hz, J = 9.2 Hz, J =

2 3 3 5.9 Hz, 2 H, CH2NC), 4.05 – 4.10 (ddd, J = 10.7 Hz, J = 5.9 Hz, J =

2 3 3 3.4 Hz, 2 H, OCH2), 4.19 – 4.22 (ddd, J = 10.7 Hz, J = 9.3 Hz, J =

4.5 Hz, 1.92 H, OCH2).

13 C NMR (C6D6, 100 MHz) 27.7 (CH3) 54.0 (CH2N), 59.6 (C(CH3)3), 68.1 (OCH2).

GC MS (EI+) 233 [M+ 7%], 203 [39%], 146 [100%], 91 [27%], 74 [8%], 56

[55%].

93 MS (LDI, DHB) 234 [M+H 9%] 162 [100%]

FT-IR (Nujol) 1365 m, 1191 w, 1140 m, 1053 m, 1035 m, 921 w, 901 m.

94 Reaction of 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane with nickel tetracarbonyl: synthesis of bis(5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel dicarbonyl. (43a) No CAS.

O C O -2 CO O O Me N Ge + Ni(CO)4 Me N Ge Ni Ge N Me O O C O O 11a 43a

To a solution of 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane

(0.152 g, .801 mmol, 1 eq) in dry THF (4 mL) was added Ni(CO)4 (0.30 g, 1.74 mmol, 2 eq.) in dry THF (2.3 mL). Stirring of the solution lead to the formation of gas and resulted in a slightly pink solution. Removal of the solvent under vacuum gave spectroscopically pure 1 (0.16 g, 81 %) as off yellow, air sensitive powder.

X-ray quality crystals were grown by layering a solution of 34a in THF with hexanes. Decomposition temperature 85 - 88 °C black oil.

1 H NMR (C6D6, 400 MHz) 0.82 (s, 9 H, CH3), 1.42 – 1.59 (m, 2 H, CH2N), 2.44

– 2.51 (m, 2 H, CH2N), 4.05 – 4.10 (m, 2 H, OCH2), 4.19 – 4.22 (m,

1.92 H, OCH2).

13 C NMR (C6D6, 100 MHz) 27.7 (CH3) 54.0 (CH2N), 59.6 (C(CH3)3), 68.1 (OCH2).

MS (LDI, DHB) 190 (M+H 12%) 118 (CH3N(CH2CH2O)2 27%)

FT-IR (CH2Cl2) 2008 s, 1949 s.

Reaction of 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane with nickel tetracarbonyl: synthesis of (5-ethyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel tricarbonyl. (43b) No CAS.

95 O - CO O CO Et N Ge + Ni(CO) 4 Et N Ge Ni CO O O CO 11b 43b

To a solution of 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane

(0.174 g, .854 mmol, 1 eq) in dry THF (4 mL) was added Ni(CO)4 (0..375 g, 2.20 mmol, 2.6 eq.) in dry THF (4 mL). Stirring resulted in formation of gas and the solution turned slightly green. Removal of the solvent under vacuum gave spectroscopically pure 1 (0.215 g, 73 %) as off slightly orange, air sensitive powder. X-ray quality crystals were grown by layering a solution of 34b in THF with hexanes. Decomposition temperature 93 - 95 °C black oil.

1 H NMR (C6D6, 400 MHz) 0.82 (s, 9 H, CH3), 1.42 – 1.59 (m, 2 H, NCH2), 2.44

– 2.51 (m, 2 H, NCH2), 4.05 – 4.10 (m, 2 H, OCH2), 4.19 – 4.22 (m,

1.92 H, OCH2).

13 C NMR (C6D6, 100 MHz) 27.7 (CH3) 54.0 (CH2N), 59.6 (C(CH3)3), 68.1 (OCH2).

MS (LDI) 397 [M2+H 17%], 206 [M+H 90%], 116 [100%].

FT-IR (CH2Cl2) 2071 m, 1989 s.

Reaction of 5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane with nickel tetracarbonyl: synthesis of (5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel tricarbonyl. (43d) No CAS.

96 O - CO O CO tBu N Ge + Ni(CO) 4 tBu N Ge Ni CO O O CO 11d 43d

To a solution of 5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane

(0.351 g, 1.51 mmol, 1 eq) in dry THF (4 mL) was added Ni(CO)4 (0.548 g, 3.21 mmol, 2 eq.) in dry THF (4 mL). Stirring resulted in formation of gas and the solution turned slightly pink. Removal of the solvent under vacuum gave spectroscopically pure 1 (0.54 g, 96 %) as off slightly yellow, air sensitive powder. X-ray quality crystals were grown by layering a solution of 34d in THF with hexanes. Decomposition temperature 95 - 97 °C black oil.

1 H NMR (C6D6, 400 MHz) 0.82 (s, 9 H, CH3), 1.42 – 1.59 (m, 2 H, CH2N), 2.44

– 2.51 (m, 2 H, NCH2), 4.05 – 4.10 (m, 2 H, OCH2), 4.19 – 4.22 (m,

1.92 H, OCH2).

13 C NMR (C6D6, 400 MHz) 27.7 (CH3) 54.0 (CH2N), 59.6 (C(CH3)3), 68.1 (OCH2).

MS (LDI, DHB) 234 [M+H 9%], 162 [100%]

FT-IR (CH2Cl2) 2071 m, 1997 s.

FT-IR (Nujol) 2008 s, 1949 s.

Reaction of 1,7-bis(trimethylsilyl)-4-alkyl-1,7-di-oxa-4-aza-heptane with trichloro silane: synthesis of 1-chloro-5-methyl-2,8-di-oxa-5-aza-1-sila- bicyclo[3.3.0]octane. (44)

OSiMe3 O THF Cl Me N + HSiCl3 Me N Si + 2 Me3SiCl H OSiMe3 O

39 44

97 To a solution of 1,7-bis(trimethylsilyl)-4-methyl-1,7-di-oxa-4-aza-heptane

(0.34 g, 1.31 mmol) in dry THF (2 mL) was added trichlorosilane (0.26 g, 1.89 mmol) neat. Stirring of the resulting turbid solution overnight, removal of the solvent under vacuum gave spectroscopically pure 1 (0.17 g, 73%) as white, powder. Crystals were grown by vacuum sublimation 120 °C/0.1Torr in a sealed glass tube but were not suitable for X-ray analysis. Decomposition temperature

242 °C.

1 H NMR (C6D6, 400 MHz) 1.04 (s, 3 H, CH3), 1.55 – 1.60 (m, 2 H, CH2N), 1.76

– 1.81 (m, 2 H, CH2NC), 3.27 – 3.30 (m, 2 H, OCH2), 3.33 – 3.97 (m, 2

H, OCH2), 5.43 (s, 1 H SiH).

13 C NMR (C6D6, 100 MHz) 27.7 (CH3) 53.1 (CH2N), 58.7 (OCH2).

29 1 Si NMR (C6D6, 79.5 MHz) - 77.2 ( J = 334 Hz SiH).

MS (LDI, DHB) 234 [M+H 9%], 162 [100%]

FT-IR (NaCl) 1365 m, 1191 w, 1140 m, 1053 m, 1035 m, 921 w, 901 m.

Reaction of 1-chloro-5-methyl-2,8-di-oxa-5-aza-1-sila-bicyclo[3.3.0]octane with sodium trimethylsilyl amide: 1-bis(trimethylsilyl)-5-methyl-2,8-di-oxa-

1,5-aza-1-sila-bicyclo[3.3.0]octane (45)

98 O Me3Si O Cl THF N(SiMe3)2 Me N Si + NNa Me N Si + NaCl H H O Me3Si O 44 45

To a suspension of 1-chloro-5-methyl-2,8-di-oxa-5-aza-1-sila- bicyclo[3.3.0]octane (0.142 g, 0.78 mmol, 1 eq) in dry THF (5 mL) was added sodium bis(trimethylsilyl)amide (.147 g, .803 mmol) as powder. Stirring resulted no visible change, and removal of the solvent under vacuum gave a white powder. The product was not further purified.

1 H NMR (C6D6, 400 MHz) .43 (s, 17 H, (Si(CH3)3), 1.92 (s, 3 H, CH3), 1.96 –

2.01 (m, 4 H, CH2N), 3.42 – 3.69 (m, 4 H, OCH2), 5.03 (s, 1 H SiH).

13 C NMR (C6D6, 100 MHz) 4.6 (Si(CH3)3), 42.0 (CH3) 55.8 (CH2N), 61.2 (OCH2).

29 1 Si NMR (C6D6, 79.5 MHz) - 77.2 ( J = 281 Hz SiH).

Chapter 5. References

100 (1) Skell, P. S.; Goldstein, E. J. J. Am. Chem. Soc. 1964, 86, 1442-1442. (2) Gusel'Nikov, L. E.; Flowers, M. C. Chem. Commun. (London) 1967, 864-865. (3) West, R. Science 1984, 225, 1109-1114. (4) Denk, M. K.; Gupta, S.; Ramachandran, R. Tetrahedron Lett. 1996, 37, 9025- 9028. (5) Herrmann, W. A.; Denk, M.; Behm, J.; Scherer, W.; Klingan, F.; Bock, H.; Solouki, B.; Wagner, M. Angew. Chem. Int. Ed Engl. 1992, 31, 1485-1488. (6) Lange, L.; Meyer, B.; Du Mont, W. W. J. Organomet. Chem. 1987, 329, C17- C20. (7) Denk, M. K.; Khan, M.; Lough, A. J.; Shuchi, K. Acta. Crystallogr. C 1998, 54, 1830-1832. (8) Denk, M. K.; Hezarkhani, A.; Zheng, F. Eur. J. Inorg. Chem. 2007, 2007, 3527-3534. (9) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R. J. Angew. Chem. Int. Ed Engl. 1995, 34, 2371-2374. (10) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956. (11) Bielawski, C. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 2000, 39, 2903-2906. (12) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. In Metals and metalloid amides : Syntheses, structures, and physical and chemical properties; E. Horwood ; Halsted Press: Chichester, 1980; . (13) Bradley, D. C.; Mehrotra, R. C.; Wardlaw, W. J. Chem. Soc. 1952, , 4204- 4209. (14) Bradley, D. C.; Thomas, I. M. J. Chem. Soc. 1960, 3857-3861. (15) Bradley, D. C.; Mehrotra, R. C.; Wardlaw, W. J. Chem. Soc. 1952, 2027- 2032. (16) Bradley, D. C. In Metal Alkoxides; Cotton, F. A., Ed.; Progress in Inorganic Chemistry; John Wiley & Sons, Inc: Hoboken, 1960; Vol. Vol. 2, pp 303-361. (17) Nielson, A. J.; Waters, J. M.; Bradley, D. C. Polyhedron 1985, 4, 285-297. (18) Wanzlick, H. W. Angew. Chem. Int. Ed Engl. 1962, 1, 75-80. (19) Wanzlick, H. W.; Schikora, E. Chem. Ber. 1961, 94, 2389-2393.

101 (20) Harris, D. H.; Lappert, M. F. J. Chem. Soc. Chem. Commun., 1974, 895-896. (21) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc., Dalton Trans. 1976, , 2268-2274. (22) Goldberg, D. E.; Hitchcock, P. B.; Lappert, M. F.; Thomas, K. M.; Thorne, A. J.; Fjeldberg, T.; Haaland, A.; Schilling, B. E. R. J. Chem. Soc., Dalton Trans. 1986, 2387-2394. (23) Bradley, D. C. In Metal alkoxides and dialkylamides; Emeléus, H. J., Sharpe, A. G., Eds.; Advances in inorganic chemistry; Academic Press: 1972; Vol. 15, 259-322. (24) Cetinkaya, B.; Gumrukcu, I.; Lappert, M. F.; Atwood, J. L.; Rogers, R. D.; Zaworotko, M. J. J. Am. Chem. Soc. 1980, 102, 2088-2089. (25) Silverman, L. D.; Zeldin, M. Inorg. Chem. 1980, 19, 270-272. (26) Silverman, L. D.; Zeldin, M. Inorg. Chem. 1980, 19, 272-273. (27) Meller, A.; Graebe, C. P. Chem. Ber. 1985, 118, 2020-2029. (28) Pfeiffer, J.; Noltemeyer, M.; Meller, A. Z. Anorg. Allg. Chem. 1989, 572, 145- 150. (29) Kuhl, O. Coord. Chem. Rev. 2004, 248, 411-427. (30) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361- 363. (31) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.; Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J. Am. Chem. Soc. 1994, 116, 2691- 2692. (32) Boehme, C.; Frenking, G. J. Am. Chem. Soc. 1996, 118, 2039-2046. (33) Heinemann, C.; Meller, T.; Apeloig, Y.; Schwarz, H. J. Am. Chem. Soc. 1996, 118, 2023-2038. (34) Huang, M.; Lermontova, E. K.; Zaitsev, K. V.; Churakov, A. V.; Oprunenko, Y. F.; Howard, J. A. K.; Karlov, S. S.; Zaitseva, G. S. J. Organomet. Chem. 2009, 694, 3828-3832. (35) Tomioka, H. Acc. Chem. Res. 1997, 30, 315-321. (36) Herzberg, G. Science 1972, 177, pp. 123-138.

102 (37) Herzberg, G.; Shoosmith, J. Nature 1959, 183, 1801-2. (38) Herzberg, G. Rev. Mod. Phys. 1942, 14, 195-7. (39) Herzberg, G. Can. J. Phys. 1961, 39, 1511-13. (40) Berkowitz, J.; Greene, J. P.; Cho, H.; Ruscic, B. J. Chem. Phys. 1987, 86, 1235-48. (41) Barrau, J.; Rima, G. Coord. Chem. Rev. 1998, 178-180, 593-622. (42) Zemlyanskii, N. N.; Borisova, I. V.; Nechaev, M. S.; Khrustalev, V. N.; Lunin, V. V.; Antipin, M. Y.; Ustynyuk, Y. A. Russ. Chem. Bull. 2004, 53, 980-1006. (43) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000, 210, 251-277. (44) Jutzi, P.; Becker, A.; Stammler, H. G.; Neumann, B. Organometallics 1991, 10, 1647-1648. (45) Mochida, K.; Fujii, A.; Tsuchiya, N.; Tohji, K.; Udagawa, Y. Organometallics 1987, 6, 1811-1812. (46) Jutzi, P.; Schmidt, H.; Neumann, B.; Stammler, H. Organometallics 1996, 15, 741-746. (47) Gaspar, P. P.; Xiao, M.; Pae, D. H.; Berger, D. J.; Haile, T.; Chen, T.; Lei, D.; Winchester, W. R.; Jiang, P. J. Organomet. Chem. 2002, 646, 68-79. (48) Denk, M. K.; Gupta, S.; Lough, A. J. Eur. J. Inorg. Chem. 1999, 1999, 41-49. (49) Lehmann, J. F.; Urquhart, S. G.; Ennis, L. E.; Hitchcock, A. P.; Hatano, K.; Gupta, S.; Denk, M. K. Organometallics 1999, 18, 1862-1872. (50) Urquhart, S. G.; Hitchcock, A. P.; Lehmann, J. F.; Denk, M. Organometallics 1998, 17, 2352-2360. (51) Abel, E. W.; Stone, F.; Gordon, A.; Wilkinson, G. In Comprehensive organometallic chemistry II: a review of the literature 1982-1994; Pergamon: Oxford; New York, 1995. (52) Jutzi, P. Pure Appl. Chem. 1989, 61, 1731-1736. (53) Jutzi, P.; Holtmann, U.; Kanne, D.; Krueger, C.; Blom, R.; Gleiter, R.; Hyla- Kryspin, I. Chem. Ber. 1989, 122, 1629-1639. (54) Jutzi, P.; Kanne, D.; Kriiger, C. Angew. Chem. Int. Ed Engl. 1986, 25, 164- 164.

103 (55) Haaland, A. Angew. Chem. Int. Ed Engl. 1989, 28, 992-1007. (56) Zemlyansky, N. N.; Borisova, I. V.; Kuznetsova, M. G.; Khrustalev, V. N.; Ustynyuk, Y. A.; Nechaev, M. S.; Lunin, V. V.; Barrau, J.; Rima, G. Organometallics 2003, 22, 1675-1681. (57) Hehre, W. J.; Radom, L.; Schleyer, P.; Pople, J. A. In Ab initio molecular orbital theory; John Wiley and Sons: New York, 1986; Vol. 548. (58) Denk, M. K.; Krause, M. J.; Niyogi, D. F.; Gill, N. K. Tetrahedron 2003, 59, 7565-7570. (59) Krause, M. J.; Denk, M. Unpublished results, 2003. (60) Hastie, J.; Masterʼs thesis; Donor Stabilized Amido Complexes, University of Guelph, Guelph, 2009. (61) Zeldin, M.; Gsell, R. J. Inorg. Nucl. Chem. 1978, 40, 597-601. (62) Zschunke, A.; Muegge, C.; Scheer, M.; Jurkschat, K.; Tzschach, A. J. Crystallogr. Spectrosc. Res. 1983, 13, 201-210. (63) Denk, M.; Unpublished results, 2009-2011. (64) Zhao, Y.; Truhlar, D. G. J. Phys. Chem. A 2004, 108, 6908-6918. (65) Yang, Q.; Lin, J.; Li, F. Synth. Commun. 2001, 31, 2817. (66) Hanby, W. E.; Rydon, H. N. J. Chem. Soc. 1947, 513-519. (67) Zenkevich, I. G. J. of Anal. Chem., 2010, 65, 267-275. (68) Silverman, L.; Doctor of Philosophy thesis, Synthesis and characterization of germanium(II) dialkoxides and heterocyclic derivatives, Polytechnic Institute of New York, New York, 1980. (69) Meredith, B. L.; Christiansen, W. G. J. Pharm. Sci. 1931, 20, 653-655. (70) Smith, G. F. Industrial & Engineering Chemistry Analytical Edition 1929, 1, 72-74. (71) Weast, R. C., Ed.; In CRC handbook of chemistry and physics: 1st student edition; Headington Hill Hall: Boca Raton, 1989; Vol. 17. (72) Aldridge, S.; Calder, R. J.; Coombs, D. L.; Jones, C.; Steed, J. W.; Coles, S.; Hursthouse, M. B. New J. Chem. 2002, 26, 677-686.

104 (73) Frisch, M. J., et al Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford CT 2009. (74) Wheeler, S. E.; Houk, K. N. J. Chem. Theory Comput. 2010, 6, 395-404. (75) Martin, J. M. L.; Bauschlicher, C. W.; Ricca, A. Comput. Phys. Commun. 2001, 133, 189-201. (76) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211. (77) Zhao, Y.; Truhlar, D. G. Phys. Chem. Chem. Phys. 2005, 7, 2701-2705. (78) Zhao, Y.; Lynch, B. J.; Truhlar, D. G. Phys. Chem. Chem. Phys. 2005, 7, 43- 52. (79) Zhao, Y.; Truhlar, D. G. J. Phys. Chem. A 2006, 110, 5121-5129. (80) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650-654. (81) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639-5648. (82) Schuchardt, K. L.; Didier, B. T.; Elsethagen, T.; Sun, L.; Gurumoorthi, V.; Chase, J.; Li, J.; Windus, T. L. J. Chem. Inf. Model. 2007, 47, 1045-1052. (83) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297-3305. (84) Peterson, K. A.; Figgen, D.; Goll, E.; Stoll, H.; Dolg, M. J. Chem. Phys. 2003, 119, 11113-11123. (85) Karttunen, A. J.; Linnolahti, M.; Pakkanen, T. A. J. Phys. Chem. C 2008, 112, 16324-16330. (86) Leininger, T.; Nicklass, A.; Küchle, W.; Stoll, H.; Dolg, M.; Bergner, A. Chem. Phys. Lett. 1996, 255, 274-280. (87) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theoretica Chimica Acta 1991, 78, 247-266. (88) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378-6396. (89) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899-926. (90) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211-7218. (91) Weinhold, F.; Landis, C. R. Chem. Educ. Res. Pract. 2001, 2, 91-104. (92) Breneman, C. M.; Wiberg, K. B. J. Comput. Chem. 1990, 11, 361-373.

105 (93) Wiberg, K. B. Tetrahedron 1968, 24, 1083-1096. (94) Montgomery, J.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A. J. Chem. Phys. 2000, 112, 6532-6542. (95) Ochterski, J. W.; Petersson, G. A.; Montgomery, J. J. Chem. Phys. 1996, 104, 2598-2619. (96) Montgomery, J.; Ochterski, J. W.; Petersson, G. A. J. Chem. Phys. 1994, 101, 5900-5909. (97) Grimme, S. J. Comput. Chem. 2004, 25, 1463-1473. (98) Swart, M.; Sola, M.; Bickelhaupt, F. M. J. Comput. Chem. 2011, 32, 1117- 1127. (99) Koch, W.; Holthausen, M. C. In A chemist's guide to density functional theory; Wiley-VCH: New York, 2001, 299. (100) Mengmeng, H.; Karlov, S. S.; Zabalov, M. V.; Zaitsev, K. V.; Lemenovskii, D. A.; Zaitseva, G. S. Russ. Chem. Bull. 2009, 58, 1576-1580. (101) Merkley, N.; Warkentin, J. Can. J. Chem., 2002, 80, 1187-1195.

106

Chapter 6. Appendix

107 Crystal data and structure refinement for 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane

Empirical formula C10 H22 Ge2 N2 O4 Formula weight 379.57 Temperature 120(2) K Wavelength 1.54178 Å Crystal system, Space group Monoclinic, P2(1)/n Unit cell dimensions a = 6.8890(4) Å α = 90°. b = 10.9418(5) Å β = 101.140(2)°. c = 9.6454(5) Å γ = 90°. Volume 713.35(6) Å3 Z, Density (calculated) 4, 1.767 Mg/m3 Absorption coefficient 5.286 mm-1 F(000) 384 Crystal size 0.20 x 0.20 x 0.15 mm3 Theta range for data collection 6.18 to 65.14°. Index ranges -7<=h<=8, -12<=k<=12, -11<=l<=11 Reflections collected 6501 Independent reflections 1175 [R(int) = 0.0251] Completeness to theta = 65.14°, 96.5 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1175 / 0 / 84 Goodness-of-fit on F2 1.052 Final R indices [I>2sigma(I)] R1 = 0.0214, wR2 = 0.0551 R indices (all data) R1 = 0.0218, wR2 = 0.0555 Extinction coefficient 0.0091(4) Largest diff. peak and hole 0.341 and -0.224 e.Å-3

Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5- methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) C(1) 3173(3) 8802(2) 5865(2) 16(1) C(2) 3851(3) 8812(2) 7452(2) 16(1) C(3) 1157(3) 7559(2) 8053(2) 16(1) C(4) -1062(3) 7770(2) 7697(2) 16(1) C(5) 2549(3) 9235(2) 9576(2) 19(1) Ge(1) -277(1) 9981(1) 6634(1) 12(1) N(1) 2109(2) 8773(2) 8126(2) 13(1) O(1) 1697(2) 9714(1) 5484(2) 14(1) O(2) -1535(2) 8482(1) 6456(2) 16(1)

108

Bond lengths [Å] for 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Length [A] Bond Length [A] Bond Length [A] C(1)-O(1) 1.421(2) C(3)-C(4) 1.518(3) C(5)-H(5B) 0.9800 C(1)-C(2) 1.512(3) C(3)-H(3A) 0.9900 C(5)-H(5C) 0.9800 C(1)-H(1A) 0.9900 C(3)-H(3B) 0.9900 Ge(1)-O(2) 1.8484(14) C(1)-H(1B) 0.9900 C(4)-O(2) 1.412(2) Ge(1)-O(1) 1.9362(14) C(2)-N(1) 1.472(3) C(4)-H(4A) 0.9900 Ge(1)-O(1)#1 2.1143(14) C(2)-H(2A) 0.9900 C(4)-H(4B) 0.9900 Ge(1)-N(1) 2.3673(17) C(2)-H(2B) 0.9900 C(5)-N(1) 1.463(3) O(1)-Ge(1)#1 2.1143(14) C(3)-N(1) 1.478(3) C(5)-H(5A) 0.9800

Bond angles [deg] for 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Angle [°] Bond Angle [°] O(1)-C(1)-C(2) 108.81(16) H(4A)-C(4)-H(4B) 108.2 O(1)-C(1)-H(1A) 109.9 N(1)-C(5)-H(5A) 109.5 C(2)-C(1)-H(1A) 109.9 N(1)-C(5)-H(5B) 109.5 O(1)-C(1)-H(1B) 109.9 H(5A)-C(5)-H(5B) 109.5 C(2)-C(1)-H(1B) 109.9 N(1)-C(5)-H(5C) 109.5 H(1A)-C(1)-H(1B) 108.3 H(5A)-C(5)-H(5C) 109.5 N(1)-C(2)-C(1) 109.17(16) H(5B)-C(5)-H(5C) 109.5 N(1)-C(2)-H(2A) 109.8 O(2)-Ge(1)-O(1) 100.43(6) C(1)-C(2)-H(2A) 109.8 O(2)-Ge(1)-O(1)#1 85.93(6) N(1)-C(2)-H(2B) 109.8 O(1)-Ge(1)-O(1)#1 73.45(6) C(1)-C(2)-H(2B) 109.8 O(2)-Ge(1)-N(1) 79.56(6) H(2A)-C(2)-H(2B) 108.3 O(1)-Ge(1)-N(1) 77.40(6) N(1)-C(3)-C(4) 106.98(16) O(1)#1-Ge(1)-N(1) 144.35(6) N(1)-C(3)-H(3A) 110.3 C(5)-N(1)-C(2) 112.11(17) C(4)-C(3)-H(3A) 110.3 C(5)-N(1)-C(3) 111.32(16) N(1)-C(3)-H(3B) 110.3 C(2)-N(1)-C(3) 113.42(16) C(4)-C(3)-H(3B) 110.3 C(5)-N(1)-Ge(1) 112.31(13) H(3A)-C(3)-H(3B) 108.6 C(2)-N(1)-Ge(1) 104.19(12) O(2)-C(4)-C(3) 109.48(16) C(3)-N(1)-Ge(1) 102.94(12) O(2)-C(4)-H(4A) 109.8 C(1)-O(1)-Ge(1) 120.31(12) C(3)-C(4)-H(4A) 109.8 C(1)-O(1)-Ge(1)#1 122.34(12) O(2)-C(4)-H(4B) 109.8 Ge(1)-O(1)-Ge(1)#1 106.55(6) C(3)-C(4)-H(4B) 109.8 C(4)-O(2)-Ge(1) 112.53(12)

109

Anisotropic displacement parameters (Å2x 103) for 5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 C(1) 14(1) 18(1) 16(1) 3(1) 3(1) 6(1) C(2) 10(1) 20(1) 18(1) 3(1) 1(1) 2(1) C(3) 18(1) 13(1) 16(1) 4(1) 2(1) 0(1) C(4) 17(1) 18(1) 14(1) 6(1) 1(1) -4(1) C(5) 19(1) 24(1) 12(1) -1(1) -3(1) 1(1) Ge(1) 12(1) 12(1) 11(1) 0(1) 2(1) 2(1) N(1) 12(1) 14(1) 11(1) 1(1) 0(1) 0(1) O(1) 13(1) 16(1) 12(1) 3(1) 2(1) 4(1) O(2) 14(1) 20(1) 13(1) 5(1) -2(1) -4(1)

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

x y z U(eq) H(1A) 4307 8970 5400 19 H(1B) 2627 7989 5551 19 H(2A) 4707 8095 7751 19 H(2B) 4628 9561 7745 19 H(3A) 1525 7132 8971 19 H(3B) 1582 7052 7316 19 H(4A) -1760 6976 7553 20 H(4B) -1496 8198 8489 20 H(5A) 3641 8763 10128 29 H(5B) 1374 9152 10002 29 H(5C) 2928 10098 9570 29

110 Crystal data and structure refinement for 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane

Empirical formula C12 H26 Ge2 N2 O4 Formula weight 407.53 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Monoclinic, C2/c Unit cell dimensions a = 17.680(2) Å α = 90°. b = 9.3325(10) Å β = 109.196(2)°. c = 10.083(2) Å γ = 90°. Volume 1571.2(4) Å3 Z, Density (calculated) 4, 1.723 Mg/m3 Absorption coefficient 3.840 mm-1 F(000) 832 Crystal size 0.40 x 0.30 x 0.20 mm3 Theta range for data collection 2.44 to 27.85°. Index ranges -23<=h<=22, -12<=k<=11, -13<=l<=13 Reflections collected 12293 Independent reflections 1840 [R(int) = 0.0244] Completeness to theta = 25.00°, 100.0 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1840 / 0 / 92 Goodness-of-fit on F2 1.047 Final R indices [I>2sigma(I)] R1 = 0.0152, wR2 = 0.0411 R indices (all data) R1 = 0.0156, wR2 = 0.0413 Largest diff. peak and hole 0.364 and -0.284 e.Å-3

Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5- ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) Ge(1) 5977(1) 1592(1) 3497(1) 13(1) O(1) 6031(1) 3521(1) 3106(1) 15(1) O(2) 4946(1) 1418(1) 3702(1) 14(1) N(1) 6248(1) 2448(1) 5719(1) 12(1) C(1) 5892(1) 4489(1) 4077(1) 15(1) C(2) 6359(1) 4012(1) 5573(1) 14(1) C(3) 5542(1) 2071(1) 6130(1) 15(1) C(4) 4785(1) 2074(1) 4851(1) 14(1) C(5) 6990(1) 1754(1) 6655(1) 16(1)

111

Bond lengths [Å] for 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Length [A] Bond Length [A] Bond Length [A] Ge(1)-O(1) 1.8513(9) N(1)-C(5) 1.4883(15) C(4)-H(4A) 0.9900 Ge(1)-O(2) 1.9072(9) C(1)-C(2) 1.5283(16) C(4)-H(4B) 0.9900 Ge(1)-N(1) 2.2761(11) C(1)-H(1A) 0.9900 C(5)-C(6) 1.5204(18) Ge(1)-O(2)#1 2.2855(9) C(1)-H(1B) 0.9900 C(5)-H(5A) 0.9900 O(1)-C(1) 1.4123(14) C(2)-H(2A) 0.9900 C(5)-H(5B) 0.9900 O(2)-C(4) 1.4194(14) C(2)-H(2B) 0.9900 C(6)-H(6A) 0.9800 O(2)-Ge(1)#1 2.2855(9) C(3)-C(4) 1.5226(16) C(6)-H(6B) 0.9800 N(1)-C(3) 1.4809(15) C(3)-H(3A) 0.9900 C(6)-H(6C) 0.9800 N(1)-C(2) 1.4863(15) C(3)-H(3B) 0.9900

Bond angles [deg] for 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Angle [°] Bond Angle [°] O(1)-Ge(1)-O(2) 102.93(4) O(1)-Ge(1)-O(2) 102.93(4) O(1)-Ge(1)-N(1) 81.93(4) O(1)-Ge(1)-N(1) 81.93(4) O(2)-Ge(1)-N(1) 79.80(4) O(2)-Ge(1)-N(1) 79.80(4) O(1)-Ge(1)-O(2)#1 86.15(4) O(1)-Ge(1)-O(2)#1 86.15(4)

O(2)-Ge(1)-O(2)#1 72.35(4) O(2)-Ge(1)-O(2)#1 72.35(4) N(1)-Ge(1)-O(2)#1 146.31(3) N(1)-Ge(1)-O(2)#1 146.31(3) C(1)-O(1)-Ge(1) 116.21(7) C(1)-O(1)-Ge(1) 116.21(7) C(4)-O(2)-Ge(1) 120.46(7) C(4)-O(2)-Ge(1) 120.46(7) C(4)-O(2)-Ge(1)#1 119.39(7) C(4)-O(2)-Ge(1)#1 119.39(7) Ge(1)-O(2)-Ge(1)#1 106.93(4) Ge(1)-O(2)-Ge(1)#1 106.93(4) C(3)-N(1)-C(2) 114.33(9) C(3)-N(1)-C(2) 114.33(9) C(3)-N(1)-C(5) 111.50(10) C(3)-N(1)-C(5) 111.50(10) C(2)-N(1)-C(5) 111.89(9) C(2)-N(1)-C(5) 111.89(9) C(3)-N(1)-Ge(1) 105.51(7) C(3)-N(1)-Ge(1) 105.51(7) C(2)-N(1)-Ge(1) 103.82(7) C(2)-N(1)-Ge(1) 103.82(7) C(5)-N(1)-Ge(1) 109.19(7) C(5)-N(1)-Ge(1) 109.19(7) O(1)-C(1)-C(2) 109.68(10) O(1)-C(1)-C(2) 109.68(10)

O(1)-C(1)-H(1A) 109.7 O(1)-C(1)-H(1A) 109.7 C(2)-C(1)-H(1A) 109.7 C(2)-C(1)-H(1A) 109.7 O(1)-C(1)-H(1B) 109.7 O(1)-C(1)-H(1B) 109.7 C(2)-C(1)-H(1B) 109.7 C(2)-C(1)-H(1B) 109.7 H(1A)-C(1)-H(1B) 108.2 H(1A)-C(1)-H(1B) 108.2 N(1)-C(2)-C(1) 109.74(9) N(1)-C(2)-C(1) 109.74(9)

112

Anisotropic displacement parameters (Å2x 103) for 5-ethyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 Ge(1) 12(1) 12(1) 14(1) -2(1) 5(1) 1(1) O(1) 19(1) 14(1) 14(1) -1(1) 8(1) -2(1) O(2) 13(1) 16(1) 12(1) -1(1) 4(1) -2(1) N(1) 12(1) 11(1) 13(1) 0(1) 4(1) 0(1) C(1) 18(1) 11(1) 15(1) 0(1) 7(1) 0(1) C(2) 17(1) 11(1) 15(1) -1(1) 5(1) -2(1) C(3) 15(1) 17(1) 13(1) 1(1) 5(1) -1(1) C(4) 13(1) 17(1) 13(1) 0(1) 5(1) -1(1) C(5) 15(1) 16(1) 15(1) 0(1) 1(1) 4(1)

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

x y z U(eq) H(1A) 5312 4521 3950 17 H(1B) 6064 5463 3912 17 H(2A) 6935 4227 5784 17 H(2B) 6167 4543 6250 17 H(3A) 5485 2770 6829 17 H(3B) 5620 1109 6569 17 H(4A) 4355 1543 5067 17 H(4B) 4602 3071 4606 17 H(5A) 7428 1930 6268 20 H(5B) 6900 706 6643 20 H(6A) 7315 3310 8196 31

113 Crystal data and structure refinement for 5-isopropyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane

Empirical formula C7 H15 Ge N O2 Formula weight 217.79 Temperature 123(2) K Wavelength 0.71073 Å Crystal system, Space group Monoclinic, P2(1)/c Unit cell dimensions a = 7.9503(7) Å α = 90° b = 8.2404(7) Å β = 14.1876(13) ° c = 14.1876(13) Å γ = 90° Volume 915.37(14) Å3 Z, Density (calculated) 4, 1.580 g/cm3 Absorption coefficient 3.301 mm-1 F(000) 448 Crystal size 0.28 x 0.24 x 0.10 mm3 Theta range for data collection 2.60 to 25.58° Index ranges -9<=h<=9, -7<=k<=9, -17<=l<=17 Reflections collected 6329 Independent reflections 1707 [R(int) = 0.0265] Completeness to theta = 25.00°, 99.8 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1707 / 0 / 102 Goodness-of-fit on F2 1.048 Final R indices [I>2sigma(I)] R1 = 0.0194, wR2 = 0.0505 R indices (all data) R1 = 0.0215, wR2 = 0.0520 Largest diff. peak and hole 0.331 and -0.275 e Å-3

114 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5- isopropyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) Ge(1) 2057(1) 10805(1) 1279(1) 20(1) O(1) -232(2) 10739(2) 1349(1) 30(1) O(2) 3044(2) 10748(2) 2553(1) 32(1) N(1) 1948(2) 8197(2) 1416(1) 16(1) C(1) -850(2) 9273(2) 1678(2) 26(1) C(2) 81(2) 7839(2) 1331(1) 21(1) C(3) 2815(2) 9298(2) 3047(1) 25(1) C(4) 2918(2) 7849(2) 2398(1) 20(1) C(5) 2665(2) 7311(2) 639(1) 19(1)

Bond lengths [Å] for 5-isopropyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Length [A] Bond Length [A] Bond Length [A] Ge(1)-O(1) 1.8402(13) O(2)-C(3) 1.413(2) C(1)-C(2) 1.521(2) Ge(1)-O(2) 1.8414(14) N(1)-C(4) 1.499(2) C(3)-C(4) 1.518(2) Ge(1)-N(1) 2.1605(15) N(1)-C(2) 1.498(2) C(5)-C(6) 1.528(2) O(1)-C(1) 1.414(2) N(1)-C(5) 1.513(2) C(5)-C(7) 1.527(2)

Bond angles [deg] for 5-isopropyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Angle [°] Bond Angle [°] O(1)-Ge(1)-O(2) 101.72(7) C(2)-N(1)-Ge(1) 104.10(10) O(1)-Ge(1)-N(1) 84.87(5) C(5)-N(1)-Ge(1) 112.87(10) O(2)-Ge(1)-N(1) 84.45(5) O(1)-C(1)-C(2) 109.90(15) C(1)-O(1)-Ge(1) 116.54(10) N(1)-C(2)-C(1) 110.61(14) C(3)-O(2)-Ge(1) 116.07(11) O(2)-C(3)-C(4) 109.77(15) C(4)-N(1)-C(2) 112.29(13) N(1)-C(4)-C(3) 109.91(14) C(4)-N(1)-C(5) 112.77(12) N(1)-C(5)-C(6) 111.82(14) C(2)-N(1)-C(5) 109.85(13) N(1)-C(5)-C(7) 111.52(13) C(4)-N(1)-Ge(1) 104.58(10) C(6)-C(5)-C(7) 111.02(14)

115

Anisotropic displacement parameters (Å2x 103) for 5-isopropyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 Ge(1) 23(1) 15(1) 23(1) 2(1) 5(1) -1(1) O(1) 21(1) 20(1) 47(1) 0(1) 3(1) 3(1) O(2) 40(1) 21(1) 28(1) -3(1) -9(1) -5(1) N(1) 15(1) 17(1) 17(1) 1(1) 2(1) 0(1) C(1) 17(1) 25(1) 35(1) -5(1) 4(1) 0(1) C(2) 16(1) 19(1) 26(1) -1(1) 2(1) -3(1) C(3) 24(1) 29(1) 20(1) -3(1) 0(1) -1(1) C(4) 20(1) 21(1) 18(1) 4(1) 2(1) 0(1) C(5) 20(1) 20(1) 17(1) 0(1) 3(1) 3(1) C(6) 27(1) 19(1) 27(1) -4(1) 7(1) 0(1) C(7) 24(1) 23(1) 25(1) 3(1) 9(1) 2(1)

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 5-isopropyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

x y z U(eq) H(1A) -2091 9176 1436 31 H(1B) -671 9275 2386 31 H(2A) -77 6867 1717 25 H(2B) -409 7603 655 25 H(3A) 1689 9314 3255 30 H(3B) 3710 9209 3625 30 H(4A) 4127 7618 2363 24 H(4B) 2431 6881 2664 24 H(5A) 1953 7617 13 23 H(6A) 1349 5163 734 36 H(6B) 3239 5129 1347 36 H(6C) 2959 4941 208 36 H(7A) 4576 9019 637 35 H(7B) 4827 7448 13 35 H(7C) 5266 7364 1156 35

116 Crystal data and structure refinement for 5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane

Empirical formula C8 H17 Ge N O2 Formula weight 231.82 Temperature 150(2) K Wavelength 0.71073 Å Crystal system, Space group Orthorhombic, Pnma Unit cell dimensions a = 15.9604(18) Å α = 90°. b = 8.3788(10) Å β = 90°. c = 7.4418(9) Å γ = 90°. Volume 995.2(2) Å3 Z, Density (calculated) 4, 1.547 Mg/m3 Absorption coefficient 3.042 mm-1 F(000) 480 Crystal size 0.48 x 0.27 x 0.23 mm3 Theta range for data collection 2.55 to 28.22°. Index ranges -20<=h<=20, -10<=k<=10, -9<=l<=7 Reflections collected 6895 Independent reflections 1231 [R(int) = 0.0339] Completeness to theta = 25.00°, 100.0 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1231 / 0 / 100 Goodness-of-fit on F2 1.021 Final R indices [I>2sigma(I)] R1 = 0.0652, wR2 = 0.1869 R indices (all data) R1 = 0.0674, wR2 = 0.1877 Largest diff. peak and hole 0.999 and -0.951 e.Å-3

117 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5- tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. Reiterate

x y z U(eq) Ge(1) 1114(1) 7500 2407(2) 18(1) O(1) -2(5) 7500 1841(13) 47(3) O(2) 1002(5) 7500 4852(11) 28(2) N(1) 1103(6) 10092(13) 2850(14) 14(2) C(1) -123(9) 9227(19) 1020(20) 26(3) C(2) 250(8) 10572(17) 2119(18) 18(3) C(3) 1110(8) 10230(17) 4843(17) 18(3) C(4) 660(9) 8775(18) 5604(19) 23(3) C(5) 1833(8) 10949(15) 1926(17) 14(2) C(6) 1759(8) 10744(17) -86(18) 19(3) C(7) 2660(8) 10210(20) 2550(20) 29(3) C(8) 1833(8) 12500 2426(19) 47(4)

Bond lengths [Å] for 5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Length [A] Bond Length [A] Bond Length [A] Ge(1)-O(1) 1.830(9) O(2)-C(4) 1.324(15) C(1)-C(2) 1.51(2) Ge(1)-O(2) 1.828(8) O(2)-C(4)#2 1.324(15) C(3)-C(4) 1.523(19) Ge(1)-N(1) 2.197(11) N(1)-C(3) 1.520(16) C(5)-C(6) 1.511(18) Ge(1)-N(1)#2 2.197(11) N(1)-C(2) 1.488(15) C(5)-C(7) 1.529(18) O(1)-C(1) 1.583(16) N(1)-C(5) 1.532(16) C(5)-C(8) 1.352(13) O(1)-C(1)#2 1.583(16) C(1)-C(1)#1 2.03(3)

Bond angles [deg] for 5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

Bond Angle [°] Bond Angle [°] C(2)-C(1)-O(1) 115.0(11) C(3)-N(1)-Ge(1) 103.1(8) C(2)-C(1)-C(1)#1 81.6(11) C(2)-N(1)-Ge(1) 102.4(8) O(1)-C(1)-C(1)#1 148.0(14) C(5)-N(1)-Ge(1) 112.9(7) C(1)-C(2)-N(1) 110.4(11) C(1)#2-O(1)-C(1) 132.2(12) N(1)-C(3)-C(4) 107.8(11) C(1)#2-O(1)-Ge(1) 102.0(6)

O(2)-C(4)-C(3) 107.1(10) C(1)-O(1)-Ge(1) 102.0(6) C(8)-C(5)-C(6) 112.5(12) C(4)#2-O(2)-C(4) 107.6(13) C(8)-C(5)-C(7) 107.6(12) C(4)#2-O(2)-Ge(1) 117.5(7) C(6)-C(5)-C(7) 109.0(11) C(4)-O(2)-Ge(1) 117.5(7) C(8)-C(5)-N(1) 109.1(11) O(2)-Ge(1)-O(1) 97.7(4) C(6)-C(5)-N(1) 109.4(10) O(2)-Ge(1)-N(1) 81.4(3) C(7)-C(5)-N(1) 109.3(10) O(1)-Ge(1)-N(1) 91.5(3) C(3)-N(1)-C(2) 110.0(10) O(2)-Ge(1)-N(1)#2 81.4(3) C(3)-N(1)-C(5) 113.9(10) O(1)-Ge(1)-N(1)#2 91.5(3) C(2)-N(1)-C(5) 113.4(10) N(1)-Ge(1)-N(1)#2 162.7(5)

118 Anisotropic displacement parameters (Å2x 103) for 5-tert-buty-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 C(1) 23(7) 25(8) 29(8) -1(6) -2(6) 0(6) C(2) 14(5) 23(7) 17(6) 7(5) 1(5) 3(5) C(3) 22(6) 19(6) 12(6) 0(5) -3(5) -2(5) C(4) 21(7) 25(7) 22(7) 0(6) 7(5) -2(6) C(5) 14(6) 10(5) 19(6) -1(5) 0(5) 1(5) C(6) 16(6) 18(7) 22(6) 3(5) 4(5) -1(5) C(7) 15(6) 45(9) 27(7) 22(8) 6(5) -3(6) C(8) 30(6) 81(11) 30(6) 0 -3(5) 0 N(1) 14(5) 17(5) 12(5) 0(4) 0(4) 0(4) O(1) 23(4) 81(8) 38(5) 0 -5(4) 0 O(2) 31(4) 25(4) 28(4) 0 2(3) 0 Ge(1) 19(1) 14(1) 22(1) 0 -1(1) 0

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane.

x y z U(eq) H(1A) 134 9247 -193 31 H(1B) -730 9427 872 31 H(2A) -130 10833 3129 22 H(2B) 308 11535 1360 22 H(3A) 820 11219 5221 21 H(3B) 1693 10269 5290 21 H(4A) 728 8733 6926 27 H(4B) 55 8825 5323 27 H(6A) 1253 11288 -513 28 H(6B) 1723 9605 -376 28 H(6C) 2252 11206 -673 28 H(7A) 3125 10688 1878 43 H(7B) 2649 9060 2349 43 H(7C) 2737 10427 3839 43 H(8A) 2325 13035 1916 70 H(8B) 1852 12571 3740 70 H(8C) 1323 13018 1985 70

119 Crystal data and structure refinement for bis(5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel dicarbonyl

Empirical formula C12 H22 Ge2 N2 Ni O6 Formula weight 494.21 Temperature 100(2) K Wavelength 1.54178 Å Crystal system, Space group Orthorhombic, P2(1)2(1)2(1) Unit cell dimensions a = 10.3976(3) Å α = 90° b = 12.2864(4) Å β = 90° c = 13.5486(4) Å γ = 90° Volume 1730.82(9) Å3 Z, Density (calculated) 4, 1.897 g/cm3 Absorption coefficient 5.640 mm-1 F(000) 992 Crystal size 0.44 x 0.38 x 0.30 mm3 Theta range for data collection 4.86 to 67.07° Index ranges -11<=h<=10, -14<=k<=14, -15<=l<=16 Reflections collected 10934 Independent reflections 2974 [R(int) = 0.0312] Completeness to theta = 65.00°, 98.6 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2974 / 0 / 211 Goodness-of-fit on F2 1.038 Final R indices [I>2sigma(I)] R1 = 0.0198, wR2 = 0.0518 R indices (all data) R1 = 0.0199, wR2 = 0.0518 Absolute structure parameter 0.00(2) Extinction coefficient 0.00284(12) Largest diff. peak and hole 0.495 and -0.354 e Å-3

120 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for di(5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel dicarbonyl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) Ni(1) 7100(1) 7432(1) 7604(1) 9(1) Ge(1) 5478(1) 7257(1) 6502(1) 9(1) Ge(2) 5912(1) 7587(1) 9006(1) 9(1) O(1) 8669(2) 5472(2) 7504(2) 28(1) O(2) 8424(2) 9495(2) 7296(2) 24(1) O(3) 5754(2) 7183(2) 5174(1) 16(1) O(4) 4083(2) 6377(1) 6679(1) 15(1) O(5) 4297(2) 8177(2) 8957(1) 16(1) O(6) 5756(2) 6566(1) 9970(1) 14(1) N(1) 4171(2) 8488(2) 6204(2) 11(1) N(2) 6283(2) 8707(2) 10135(2) 10(1) C(1) 8049(3) 6240(2) 7557(2) 14(1) C(2) 7889(3) 8685(2) 7411(2) 14(1) C(3) 4681(3) 7554(2) 4622(2) 17(1) C(4) 4154(3) 8596(2) 5095(2) 19(1) C(5) 2936(3) 8072(2) 6614(2) 14(1) C(6) 2873(3) 6847(2) 6429(2) 13(1) C(7) 4514(3) 9543(2) 6678(2) 16(1) C(8) 3982(3) 8886(2) 9747(2) 16(1) C(9) 5177(3) 9484(2) 10079(2) 14(1) C(10) 5522(3) 7002(2) 10925(2) 17(1) C(11) 6308(3) 8042(2) 11063(2) 14(1) C(12) 7513(3) 9309(2) 10017(2) 17(1)

Bond lengths [Å] for di(5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel dicarbonyl.

Bond Length [A] Bond Length [A] Bond Length [A] Ni(1)-C(2) 1.765(3) Ge(2)-N(2) 2.094(2) N(1)-C(4) 1.509(3) Ni(1)-C(1) 1.767(3) O(1)-C(1) 1.145(4) N(2)-C(12) 1.486(4) Ni(1)-Ge(1) 2.2628(5) O(2)-C(2) 1.150(4) N(2)-C(9) 1.496(3) Ni(1)-Ge(2) 2.2736(5) O(3)-C(3) 1.418(3) N(2)-C(11) 1.499(3) Ge(1)-O(3) 1.8235(17) O(4)-C(6) 1.425(4) C(3)-C(4) 1.533(4) Ge(1)-O(4) 1.826(2) O(5)-C(8) 1.418(3) C(5)-C(6) 1.527(3) Ge(1)-N(1) 2.073(2) O(6)-C(10) 1.421(3) C(8)-C(9) 1.513(4) Ge(2)-O(6) 1.8189(17) N(1)-C(5) 1.490(4) C(10)-C(11) 1.528(4) Ge(2)-O(5) 1.8295(19) N(1)-C(7) 1.490(3)

121

Bond angles [deg] for di(5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel dicarbonyl.

Bond Angle [°] Bond Angle [°] C(2)-Ni(1)-C(1) 117.28(13) C(5)-N(1)-C(7) 110.1(2) C(2)-Ni(1)-Ge(1) 109.37(9) C(5)-N(1)-C(4) 113.0(2) C(1)-Ni(1)-Ge(1) 108.27(9) C(7)-N(1)-C(4) 110.8(2) C(2)-Ni(1)-Ge(2) 107.65(9) C(5)-N(1)-Ge(1) 104.01(14) C(1)-Ni(1)-Ge(2) 113.80(9) C(7)-N(1)-Ge(1) 113.20(17) Ge(1)-Ni(1)-Ge(2) 98.870(19) C(4)-N(1)-Ge(1) 105.42(17) O(3)-Ge(1)-O(4) 102.99(9) C(12)-N(2)-C(9) 109.8(2) O(3)-Ge(1)-N(1) 86.98(8) C(12)-N(2)-C(11) 110.3(2) O(4)-Ge(1)-N(1) 86.38(8) C(9)-N(2)-C(11) 113.8(2) O(3)-Ge(1)-Ni(1) 122.60(7) C(12)-N(2)-Ge(2) 113.99(17) O(4)-Ge(1)-Ni(1) 124.18(6) C(9)-N(2)-Ge(2) 103.92(16) N(1)-Ge(1)-Ni(1) 123.22(6) C(11)-N(2)-Ge(2) 104.94(15) O(6)-Ge(2)-O(5) 102.57(9) O(1)-C(1)-Ni(1) 178.5(3) O(6)-Ge(2)-N(2) 86.83(8) O(2)-C(2)-Ni(1) 178.7(3) O(5)-Ge(2)-N(2) 86.27(9) O(3)-C(3)-C(4) 109.2(2) O(6)-Ge(2)-Ni(1) 126.17(6) N(1)-C(4)-C(3) 109.8(2) O(5)-Ge(2)-Ni(1) 120.14(6) N(1)-C(5)-C(6) 108.3(2) N(2)-Ge(2)-Ni(1) 124.44(7) O(4)-C(6)-C(5) 108.9(2) C(3)-O(3)-Ge(1) 112.39(15) O(5)-C(8)-C(9) 109.4(2) C(6)-O(4)-Ge(1) 115.48(14) N(2)-C(9)-C(8) 109.7(2) C(8)-O(5)-Ge(2) 115.40(16) O(6)-C(10)-C(11) 109.6(2) C(10)-O(6)-Ge(2) 114.13(14) N(2)-C(11)-C(10) 110.1(2)

122

Anisotropic displacement parameters (Å2x 103) for di(5-methyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel dicarbonyl. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 Ni(1) 9(1) 12(1) 8(1) 0(1) 0(1) 0(1) Ge(1) 9(1) 11(1) 7(1) -1(1) -1(1) 1(1) Ge(2) 9(1) 11(1) 7(1) -1(1) 0(1) -1(1) O(1) 23(1) 24(1) 36(1) -3(1) -2(1) 12(1) O(2) 29(1) 21(1) 22(1) 4(1) 3(1) -9(1) O(3) 14(1) 27(1) 8(1) -1(1) 2(1) 5(1) O(4) 13(1) 12(1) 19(1) 2(1) -1(1) 1(1) O(5) 10(1) 22(1) 16(1) -4(1) -3(1) 1(1) O(6) 19(1) 14(1) 10(1) 0(1) 3(1) -2(1) N(1) 12(1) 11(1) 10(1) 1(1) 0(1) -2(1) N(2) 8(1) 10(1) 10(1) -3(1) 1(1) 0(1) C(1) 11(1) 22(1) 11(1) -2(1) -1(1) 0(1) C(2) 15(1) 19(1) 8(1) -2(1) -2(1) 1(1) C(3) 18(1) 25(1) 9(1) 4(1) -3(1) 3(1) C(4) 24(2) 23(1) 9(1) 7(1) -2(1) 5(1) C(5) 13(1) 17(1) 11(1) -1(1) -1(1) 1(1) C(6) 10(1) 15(1) 14(1) 0(1) -1(1) -1(1) C(7) 20(2) 10(1) 20(1) 0(1) 1(1) -2(1) C(8) 9(1) 23(1) 15(1) -1(1) -2(1) 3(1) C(9) 14(2) 14(1) 16(1) -2(1) 1(1) 7(1) C(10) 24(2) 16(1) 10(1) 3(1) 3(1) 2(1) C(11) 19(2) 17(1) 8(1) 0(1) -4(1) 2(1) C(12) 14(2) 21(1) 18(1) -6(1) 2(1) -5(1)

123

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for di(5-methyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel dicarbonyl.

x y z U(eq) H(3A) 4005 6987 4612 21 H(3B) 4945 7702 3933 21 H(4A) 4687 9226 4893 22 H(4B) 3263 8725 4865 22 H(5A) 2202 8438 6288 17 H(5B) 2891 8222 7330 17 H(6A) 2185 6519 6837 16 H(6B) 2674 6704 5727 16 H(7A) 3898 10103 6474 25 H(7B) 5382 9758 6475 25 H(7C) 4487 9461 7398 25 H(8A) 3623 8462 10303 19 H(8B) 3323 9415 9528 19 H(9A) 5379 10075 9607 17 H(9B) 5027 9815 10735 17 H(10A) 5767 6462 11434 20 H(10B) 4595 7165 11001 20 H(11A) 5947 8472 11615 17 H(11B) 7208 7853 11229 17 H(12A) 7586 9861 10536 26 H(12B) 7529 9664 9369 26 H(12C) 8234 8799 10067 26

124 Crystal data and structure refinement for (5-ethyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel tricarbonyl

Empirical formula C9 H13 Ge N Ni O5 Formula weight 346.50 Temperature 100(2) K Wavelength 1.54178 Å Crystal system, Space group Orthorhombic, Pbca Unit cell dimensions a = 12.3132(5) Å α = 90° b = 12.5383(4) Å β = 90° c = 16.7565(6) Å γ = 90° Volume 2586.98(16) Å3 Z, Density (calculated) 8, 1.779 g/cm3 Absorption coefficient 4.781 mm-1 F(000) 1392 Crystal size 0.33 x 0.10 x 0.08 mm3 Theta range for data collection 5.28 to 67.35° Index ranges -13<=h<=14, -15<=k<=14, -19<=l<=18 Reflections collected 11631 Independent reflections 2286 [R(int) = 0.0256] Completeness to theta = 65.00°, 100.0 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2286 / 0 / 156 Goodness-of-fit on F2 1.125 Final R indices [I>2sigma(I)] R1 = 0.0216, wR2 = 0.0548 R indices (all data) R1 = 0.0225, wR2 = 0.0554 Extinction coefficient 0.00065(3) Largest diff. peak and hole 0.376 and -0.359 e Å-3

125 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for (5- ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) Ge(1) 2383(1) 2378(1) 2335(1) 14(1) Ni(1) 2370(1) 2536(1) 976(1) 17(1) O(1) 2935(1) 3438(1) 2951(1) 21(1) O(2) 1221(1) 1894(1) 2887(1) 19(1) O(3) 1492(1) 536(1) 334(1) 34(1) O(4) 1018(1) 4396(1) 602(1) 31(1) O(5) 4630(1) 2940(1) 507(1) 35(1) N(1) 3323(1) 1344(1) 3012(1) 14(1) C(1) 4132(1) 2059(1) 3404(1) 18(1) C(2) 3571(1) 3105(1) 3611(1) 18(1) C(3) 3869(2) 523(1) 2499(1) 20(1) C(4) 4609(2) -229(2) 2957(1) 27(1) C(5) 2541(1) 843(2) 3588(1) 18(1) C(6) 1517(1) 1521(1) 3659(1) 18(1) C(7) 1833(2) 1304(2) 586(1) 22(1) C(8) 1536(2) 3671(2) 754(1) 21(1) C(9) 3761(2) 2775(2) 701(1) 24(1)

Bond lengths [Å] for (5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

Bond Length [A] Bond Length Bond Length [A] [A] Ge(1)-O(2) 1.8090(12) Ni(1)-C(7) 1.803(2) N(1)-C(1) 1.491(2) Ge(1)-O(1) 1.8158(12) O(1)-C(2) 1.418(2) N(1)-C(3) 1.501(2) Ge(1)-N(1) 2.0762(13) O(2)-C(6) 1.423(2) N(1)-C(5) 1.501(2) Ge(1)- 2.2860(4) O(3)-C(7) 1.133(2) C(1)-C(2) 1.522(2) Ni(1) Ni(1)-C(8) 1.793(2) O(4)-C(8) 1.139(2) C(3)-C(4) 1.518(3) Ni(1)-C(9) 1.799(2) O(5)-C(9) 1.137(2) C(5)-C(6) 1.526(2)

126 Bond angles [deg] for (5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

Bond Angle [°] Bond Angle [°] O(2)-Ge(1)-O(1) 104.52(6) C(1)-N(1)-C(3) 111.45(13) O(2)-Ge(1)-N(1) 87.26(5) C(1)-N(1)-C(5) 113.44(13) O(1)-Ge(1)-N(1) 86.39(5) C(3)-N(1)-C(5) 111.57(13) O(2)-Ge(1)-Ni(1) 122.24(4) C(1)-N(1)-Ge(1) 103.73(10)

O(1)-Ge(1)-Ni(1) 120.37(4) C(3)-N(1)-Ge(1) 111.40(10) N(1)-Ge(1)-Ni(1) 127.08(4) C(5)-N(1)-Ge(1) 104.78(10) C(8)-Ni(1)-C(9) 111.12(9) N(1)-C(1)-C(2) 108.40(14) C(8)-Ni(1)-C(7) 113.24(9) O(1)-C(2)-C(1) 109.02(13) C(9)-Ni(1)-C(7) 113.49(9) N(1)-C(3)-C(4) 113.90(14) C(8)-Ni(1)-Ge(1) 106.24(6) N(1)-C(5)-C(6) 110.28(14) C(9)-Ni(1)-Ge(1) 105.25(6) O(2)-C(6)-C(5) 108.93(13) C(7)-Ni(1)-Ge(1) 106.81(6) O(3)-C(7)-Ni(1) 179.26(18) C(2)-O(1)-Ge(1) 115.77(10) O(4)-C(8)-Ni(1) 178.83(17) C(6)-O(2)-Ge(1) 111.87(10) O(5)-C(9)-Ni(1) 178.00(17)

Anisotropic displacement parameters (Å2x 103) for (5-ethyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel tricarbonyl. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]

U11 U22 U33 U23 U13 U12 Ge(1) 16(1) 16(1) 9(1) 1(1) -1(1) 0(1) Ni(1) 18(1) 22(1) 10(1) 2(1) 0(1) 0(1) O(1) 27(1) 14(1) 21(1) -1(1) -6(1) 1(1) O(2) 14(1) 29(1) 15(1) 4(1) -1(1) 0(1) O(3) 41(1) 28(1) 33(1) -8(1) 0(1) -2(1) O(4) 32(1) 31(1) 28(1) 4(1) -2(1) 8(1) O(5) 20(1) 55(1) 31(1) 9(1) 3(1) -1(1) N(1) 15(1) 14(1) 12(1) -1(1) 1(1) 1(1) C(1) 16(1) 19(1) 18(1) -3(1) -3(1) -1(1) C(2) 20(1) 18(1) 17(1) -3(1) -3(1) -1(1) C(3) 22(1) 19(1) 18(1) -5(1) 4(1) 3(1) C(4) 26(1) 22(1) 32(1) -5(1) 1(1) 8(1) C(5) 21(1) 19(1) 14(1) 3(1) 3(1) -1(1) C(6) 17(1) 24(1) 12(1) 3(1) 1(1) -2(1) C(7) 24(1) 28(1) 14(1) 1(1) 3(1) 4(1) C(8) 22(1) 27(1) 13(1) 1(1) 1(1) -2(1) C(9) 27(1) 31(1) 14(1) 4(1) -3(1) 4(1)

127 Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for (5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

x y z U(eq) H(1A) 4748 2194 3038 22 H(1B) 4417 1719 3894 22 H(2A) 3102 3006 4085 22 H(2B) 4121 3656 3738 22 H(3A) 4301 892 2085 24 H(3B) 3304 97 2225 24 H(4A) 5206 178 3195 40 H(4B) 4904 -766 2591 40 H(4C) 4193 -583 3379 40 H(5A) 2889 774 4118 22 H(5B) 2346 119 3400 22 H(6A) 919 1091 3888 21 H(6B) 1653 2134 4018 21

128 Crystal data and structure refinement for (5-tert-butyl-2,8-di-oxa-5-aza-1-germa- bicyclo[3.3.0]octane)nickel tricarbonyl

Empirical formula C11 H17 Ge N Ni O5 Formula weight 374.56 Temperature 150(2) K Wavelength 0.71073 Å Crystal system, Space group Monoclinic, P2(1)/n Unit cell dimensions a = 7.7097(4) Å α = 90°. b = 11.3411(6) Å β = 97.0900(10)°. c = 17.0882(9) Å γ = 90°. Volume 1482.71(13) Å3 Z, Density (calculated) 4, 1.678 Mg/m3 Absorption coefficient 3.310 mm-1 F(000) 760 Crystal size 0.15 x 0.13 x 0.08 mm3 Theta range for data collection 2.16 to 27.51°. Index ranges -7<=h<=9, -14<=k<=14, -22<=l<=21 Reflections collected 13415 Independent reflections 3326 [R(int) = 0.0227] Completeness to theta = 25.00°, 100.0 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3326 / 0 / 175 Goodness-of-fit on F2 1.083 Final R indices [I>2sigma(I)] R1 = 0.0223, wR2 = 0.0541 R indices (all data) R1 = 0.0255, wR2 = 0.0554 Largest diff. peak and hole 0.520 and -0.344 e.Å-3

129 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for (5- tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

x y z U(eq) Ge(1) 2741(1) 7960(1) 1985(1) 14(1) Ni(1) 2411(1) 7729(1) 637(1) 22(1) O(1) 5421(2) 6256(2) 406(1) 59(1) O(2) 2567(4) 10111(2) -16(1) 78(1) O(3) -807(3) 6441(3) 118(1) 77(1) O(4) 3912(2) 6807(1) 2571(1) 18(1) O(5) 3723(2) 9308(1) 2396(1) 19(1) N(1) 1062(2) 8040(1) 2885(1) 14(1) C(1) 4268(3) 6843(2) 493(1) 33(1) C(2) 2503(4) 9189(2) 238(1) 45(1) C(3) 436(3) 6956(3) 322(1) 41(1) C(4) 3523(2) 6698(2) 3356(1) 18(1) C(5) 1597(2) 6978(2) 3383(1) 18(1) C(6) 1635(2) 9156(2) 3326(1) 17(1) C(7) 3493(2) 9489(2) 3200(1) 18(1) C(8) -921(2) 8066(2) 2600(1) 17(1) C(9) -1493(2) 6904(2) 2189(1) 23(1) C(10) -1943(2) 8250(2) 3306(1) 25(1) C(11) -1327(2) 9059(2) 1999(1) 22(1)

Bond lengths [Å] for (5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

Bond Length [A] Bond Length [A] Bond Length [A] C(1)-O(1) 1.135(3) C(6)-N(1) 1.510(2) C(9)-H(9C) 0.9800 C(1)-Ni(1) 1.791(2) C(6)-C(7) 1.522(2) C(10)-H(10A) 0.9800 C(2)-O(2) 1.136(3) C(6)-H(6A) 0.9900 C(10)-H(10B) 0.9800 C(2)-Ni(1) 1.796(3) C(6)-H(6B) 0.9900 C(10)-H(10C) 0.9800 C(3)-O(3) 1.139(3) C(7)-O(5) 1.423(2) C(11)-H(11A) 0.9800 C(3)-Ni(1) 1.781(2) C(7)-H(7A) 0.9900 C(11)-H(11B) 0.9800 C(4)-O(4) 1.415(2) C(7)-H(7B) 0.9900 C(11)-H(11C) 0.9800 C(4)-C(5) 1.525(2) C(8)-C(11) 1.530(3) N(1)-Ge(1) 2.1308(14) C(4)-H(4A) 0.9900 C(8)-C(9) 1.532(3) O(4)-Ge(1) 1.8174(13) C(4)-H(4B) 0.9900 C(8)-C(10) 1.535(2) O(5)-Ge(1) 1.8089(13) C(5)-N(1) 1.503(2) C(8)-N(1) 1.547(2) Ni(1)-Ge(1) 2.3016(3) C(5)-H(5A) 0.9900 C(9)-H(9A) 0.9800 C(5)-H(5B) 0.9900 C(9)-H(9B) 0.9800

130 Bond angles [deg] for (5-tert-butyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

Bond Angle [°] Bond Angle [°] O(1)-C(1)-Ni(1) 178.2(2) C(8)-C(9)-H(9C) 109.5 O(2)-C(2)-Ni(1) 179.6(3) H(9A)-C(9)-H(9C) 109.5 O(3)-C(3)-Ni(1) 178.5(3) H(9B)-C(9)-H(9C) 109.5 O(4)-C(4)-C(5) 109.38(14) C(8)-C(10)-H(10A) 109.5 O(4)-C(4)-H(4A) 109.8 C(8)-C(10)-H(10B) 109.5 C(5)-C(4)-H(4A) 109.8 H(10A)-C(10)-H(10B) 109.5 O(4)-C(4)-H(4B) 109.8 C(8)-C(10)-H(10C) 109.5 C(5)-C(4)-H(4B) 109.8 H(10A)-C(10)-H(10C) 109.5 H(4A)-C(4)-H(4B) 108.2 H(10B)-C(10)-H(10C) 109.5 N(1)-C(5)-C(4) 110.45(14) C(8)-C(11)-H(11A) 109.5 N(1)-C(5)-H(5A) 109.6 C(8)-C(11)-H(11B) 109.5 C(4)-C(5)-H(5A) 109.6 H(11A)-C(11)-H(11B) 109.5 N(1)-C(5)-H(5B) 109.6 C(8)-C(11)-H(11C) 109.5 C(4)-C(5)-H(5B) 109.6 H(11A)-C(11)-H(11C) 109.5 H(5A)-C(5)-H(5B) 108.1 H(11B)-C(11)-H(11C) 109.5 N(1)-C(6)-C(7) 111.11(13) C(5)-N(1)-C(6) 110.29(13) N(1)-C(6)-H(6A) 109.4 C(5)-N(1)-C(8) 112.66(13) C(7)-C(6)-H(6A) 109.4 C(6)-N(1)-C(8) 110.98(13) N(1)-C(6)-H(6B) 109.4 C(5)-N(1)-Ge(1) 103.07(10) C(7)-C(6)-H(6B) 109.4 C(6)-N(1)-Ge(1) 103.25(10) H(6A)-C(6)-H(6B) 108.0 C(8)-N(1)-Ge(1) 115.96(10) O(5)-C(7)-C(6) 109.36(14) C(4)-O(4)-Ge(1) 115.86(10) O(5)-C(7)-H(7A) 109.8 C(7)-O(5)-Ge(1) 113.63(10) C(6)-C(7)-H(7A) 109.8 C(3)-Ni(1)-C(1) 110.56(12)

O(5)-C(7)-H(7B) 109.8 C(3)-Ni(1)-C(2) 114.30(13) C(6)-C(7)-H(7B) 109.8 C(1)-Ni(1)-C(2) 113.28(12) H(7A)-C(7)-H(7B) 108.3 C(3)-Ni(1)-Ge(1) 110.06(7) C(11)-C(8)-C(9) 107.59(15) C(1)-Ni(1)-Ge(1) 102.14(7) C(11)-C(8)-C(10) 110.20(15) C(2)-Ni(1)-Ge(1) 105.64(7) C(9)-C(8)-C(10) 109.36(15) O(5)-Ge(1)-O(4) 103.81(6) C(11)-C(8)-N(1) 109.72(14) O(5)-Ge(1)-N(1) 86.92(5) C(9)-C(8)-N(1) 110.21(14) O(4)-Ge(1)-N(1) 86.42(5) C(10)-C(8)-N(1) 109.72(14) O(5)-Ge(1)-Ni(1) 118.31(4) C(8)-C(9)-H(9A) 109.5 O(4)-Ge(1)-Ni(1) 117.07(4) C(8)-C(9)-H(9B) 109.5 N(1)-Ge(1)-Ni(1) 136.52(4)

131

U11 U22 U33 U23 U13 U12 Ge(1) 15(1) 16(1) 14(1) 0(1) 3(1) 0(1) Ni(1) 24(1) 29(1) 14(1) 0(1) 4(1) 1(1) O(1) 48(1) 89(2) 41(1) -13(1) 10(1) 29(1) O(2) 161(2) 38(1) 37(1) 12(1) 21(1) 5(1) O(3) 52(1) 153(2) 26(1) -6(1) -2(1) -54(1) O(4) 19(1) 18(1) 20(1) 2(1) 6(1) 4(1) O(5) 22(1) 16(1) 20(1) 0(1) 7(1) -4(1) N(1) 13(1) 14(1) 15(1) 0(1) 2(1) 1(1) C(1) 31(1) 47(1) 20(1) -6(1) 5(1) 4(1) C(2) 79(2) 39(1) 20(1) 2(1) 11(1) 6(1) C(3) 33(1) 77(2) 14(1) -1(1) 0(1) -9(1) C(4) 20(1) 16(1) 17(1) 2(1) 1(1) 2(1) C(5) 20(1) 18(1) 17(1) 5(1) 6(1) 3(1) C(6) 18(1) 16(1) 17(1) -4(1) 4(1) 0(1) C(7) 17(1) 16(1) 20(1) -2(1) 2(1) -1(1) C(8) 12(1) 21(1) 19(1) 0(1) 3(1) 1(1) C(9) 19(1) 25(1) 24(1) -1(1) 1(1) -4(1) C(10) 16(1) 38(1) 24(1) -4(1) 8(1) -1(1) C(11) 17(1) 24(1) 24(1) 1(1) 0(1) 5(1)

Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for (5-ethyl-2,8-di-oxa-5-aza-1-germa-bicyclo[3.3.0]octane)nickel tricarbonyl.

x y z U(eq) H(4A) 4259 7249 3702 21 H(4B) 3780 5885 3548 21 H(5A) 876 6292 3188 22 H(5B) 1394 7130 3935 22 H(6A) 1572 9040 3896 20 H(6B) 832 9806 3140 20 H(7A) 3713 10326 3344 21 H(7B) 4337 8998 3543 21 H(9A) -2702 6975 1939 34 H(9B) -1413 6266 2578 34 H(9C) -728 6728 1786 34 H(10A) -1640 9019 3548 38 H(10B) -1641 7625 3696 38 H(10C) -3200 8225 3127 38 H(11A) -692 8921 1545 33 H(11B) -961 9815 2244 33 H(11C) -2585 9077 1824 33

132

- 0.97 0.97 0.98 0.99 0.97 0.98 0.99 0.98 0.99 0.99 0.79 0.88 0.91 0.94 0.85 0.89 0.92 0.89 0.93 0.97 Correl.

- 13

3.6 7.1 9.6 6.8 9.6 5.8 13.1 10.8 11.7 28.6 19.5 17.2 14.9 23.2 19.7 16.1 19.4 15.7 11.7 RMS

O(1)

- Ge 71.3 - 73.45 72.92 73.31 73.14 72.95 74.01 73.73 73.43 74.05 73.55 73.27 72.35 72.69 71.78 71.39 71.65 71.52 71.37 71.21 71.05 70.85 O(2)

Ge(1') - O(1) 107.9 107.9 108.2 108.9 4m) and experimental (single crystal X - 106.55 107.08 106.69 106.83 105.99 106.27 106.56 105.95 106.46 106.73 106.92 107.25 107.58 108.28 108.36 108.77 109.07 - 107.046 d. Solvation at the SMD level. - Ge(1)

TZVP, CBS O(2)

- - Ge 97.5 99.4 - 98.93 99.91 96.92 98.14 99.25 96.49 97.89 98.97 98.58 99.51 100.1 100.43 100.92 102.93 101.07 101.63 102.22 100.19 100.94 100.82 O(1)

(DFT/Def2

O(1') - 199.7 203.8 211.43 203.02 204.67 204.55 205.48 206.57 203.99 204.83 206.14 228.55 204.07 211.38 212.64 214.16 212.12 213.43 215.23 212.69 214.71 217.45 Ge

N - 246 Ge 236.7 242.1 242.6 239.2 235.5 250.9 241.3 247.2 242.1 237.5 227.6 242.1 235.6 232.9 229.8 243.2 239.6 235.5 238.3 234.5 230.2

O(2) - 184.5 184.9 184.84 182.61 184.76 184.88 184.34 184.59 184.47 182.68 182.91 182.98 185.13 182.25 184.91 184.77 184.17 184.24 184.68 182.38 182.46 182.41 Ge

O(1) - 194.6 193.62 192.83 196.91 196.18 195.56 196.81 195.95 195.13 194.11 193.42 192.57 190.72 192.16 195.38 193.83 195.74 194.75 195.13 192.86 191.71 190.62 Ge

6 6 6 6 6 6

H H H H H H 6 6 6 6 6 6 — — — — — — THF THF THF THF THF THF C C C C C C Solv.

4m 4m - - ray) structural parameters of selected monomeric germylene 11a EXP EXP SVWN SVWN SVWN SVWN SVWN SVWN M062x M062x M062x M062x M062x M062x Method CBS CBS MPWB1K MPWB1K MPWB1K MPWB1K MPWB1K MPWB1K

RMS and linear correlation coefficients of computational (11a)2 (11b)2

133

1 1 1 1 1 1 1 1 1 1

0.98 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Correl.

3 1 7.4 5.6 9.1 5.3 2.2 5.5 3.1 2.8 2.9 7.6 4.2 2.2 8.7 4.7 8.6 1.5 13.2 13.2 RMS

O(1) -

------Ge - O(2)

Ge(1') -

------O(1) - Ge(1)

O(2)

- Ge 101 97.7 - 99.96 99.72 98.17 98.33 98.57 98.51 98.67 98.94 98.51 98.67 98.35 101.72 100.02 100.84 100.91 100.56 100.55 100.66 100.09 100.23 O(1)

O(1') — — — — — — — — — — — — — — — — — — — — - Ge

N - 220 218 Ge 216.1 221.5 218.8 216.1 225.1 221.3 218.1 220.8 214.5 219.7 221.6 227.1 223.4 220.2 232.8 228.1 223.9 232.8 228.1 219.7

O(2) - 182.8 184.8 184.14 182.18 183.24 183.47 183.64 184.64 184.85 184.92 181.54 181.84 181.94 180.76 182.14 182.64 182.99 184.52 183.06 182.15 182.67 181.37 Ge

O(1) - 183.0 185.1 184.8 184.02 189.97 184.73 184.84 184.84 183.19 183.47 183.68 183.09 183.35 183.28 182.22 184.78 185.01 182.15 182.67 184.94 184.52 183.35 Ge

6 6 6 6 6 6

H H H H H H 6 6 6 6 6 6 — — — — — — THF THF THF THF THF THF C C C C C C Solv.

4m 4m - - EXP EXP SVWN SVWN SVWN SVWN SVWN SVWN M062x M062x M062x M062x M062x M062x Method CBS CBS MPWB1K MPWB1K MPWB1K MPWB1K MPWB1K MPWB1K

11c 11d

134