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

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Donor Stabilized Germylenes and Their Transition Metal Complexes: Structure, Bonding, and Thermochemistry Donor stabilized germylenes and their transition metal complexes: structure, bonding, and thermochemistry by 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 © Marc Baumeister, December, 2011 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.
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