Studies Towards the Synthesis of a Heterobimetallic Zirconium Germanium Complex from Imidozirconocenes, Germanimines and Germylenes
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Studies towards the Synthesis of a Heterobimetallic Zirconium Germanium Complex from Imidozirconocenes, Germanimines and Germylenes By Peter Chapple A thesis Submitted to Victoria University of Wellington In partial fulfilment of the requirements for the degree of Masters of Science In Chemistry Victoria University of Wellington 2018 Abstract Early-late transition metal heterobimetallic complexes with direct metal to metal interactions are desirable synthetic targets due to the complementary reactivity of the two different metals present in these compounds. The electron-rich late transition metal (often Rh, Ir, Fe, or Mo), and electron-poor early transition metal create an ideal environment for heterolytic bond cleavage in what is often termed ‘cooperative reactivity’. This project aimed to synthesise a zirconium-germanium heterobimetallic complex based on a known heterobimetallic ligand scaffold; 1. The synthesis of the desired heterobimetallic 1 was attempted using two different synthetic approaches. The first involved the investigating the reactivity between an unsaturated zirconium nitrogen bond (an imidozirconocene) and a germanium(II) source with a lone pair of electrons (known as a germylene). The second approach investigated the reactivity between an unsaturated germanium nitrogen bond (a germanimine) and a zirconium(II) source. In order to have the highest chance of success, a wide range of germanium and zirconium complexes were synthesised. TMS TMS Mes) The novel germylenes include [Ge(NAPH )] (NAPH = [1,8-((CH3)3Si)N)2C10H6]) and [Ge(BIAN ] Mes (BIAN = [((2,4,6-Me(C6H2)N)2)C12H6)]). These proved to be unreactive towards the imidozirconium t species [Cp2Zr(NAr*)(THF)] and [Cp2Zr(NDipp)(THF)] (Ar* = (2,6-(C6H5)2CH)-4-( Bu)C6H2), Dipp = (2,6- ((CH3)2CH)C6H3)) as well as other amidozirconocenes. However, within these studies, the mixed TMS TMS - + coordination germanium species [[Ge(NAPH )Ge(Bu)(NAPH )] [Li(THF4)] ] and TMS TMS - + [[Ge(NAPH )Ge(Me)(NAPH )] [Li(THF4)] ]were synthesised. Density functional theory (DFT) molecular orbital calculations were used to help explain the observed reactivity. With regards to the second approach, routes to new germanimine complexes such as [(HMDS)2Ge(NMes)] ((HMDS) = ((CH3)3Si)2N), Mes = (2,4,6-CH3(C6H3))), were explored, and several methods for generating “Cp2Zr” were examined. Although these conditions proved unsuccessful for generating 1, the reaction between dialkyl zirconocene with azides to form novel zirconocene triazenido complexes was discovered and the sterics affecting the synthesis of new germanimine complexes was investigated. i Acknowledgements Primarily I would like to thank my research supervisor Dr. Robin Fulton, for her direction and support over the last two years. Without her guidance and patience, I would certainly not have been able to complete this thesis. Robin’s flexibility and openness towards suggestions always made me feel like I had real influence and ownership of my research and made the lab work much more enjoyable. Thank you to Assoc. Prof. Martyn Coles for his help with crystallography and for always making group meetings a pleasant experience, even when they were scheduled first thing in the morning. I would also like to thank the rest of the inorganic synthesis group, Mat, Cara, Putri, Loc, Dylan, Ryan, Struan and Amanda for making the lab an enjoyable place to work every day. Ryan deserves a special mention, as he taught me most of the practical synthetic chemistry I know and was always a useful sounding board for new ideas. To Dr. Matthias Lein, your assistance with the computational work was invaluable. I would also like to acknowledge VUW and the Curtis-Gordon scholarship for providing me with funding over the two years. Thanks to all my flatmates over the two years, who have had to put up with my constant facts about both chemistry and science in general, without your support writing this thesis would have been a lot more difficult. I must also thank my parents, both for their backing and for not forcing me into getting a real job when I finished my undergraduate studies. Finally, I must pay thanks to my wife Emily. Without your love (and constant reminders to keep working) this thesis would not have been possible. ii Contents 1 Introduction .......................................................................................................................................... 1 1.1 Project Aims .................................................................................................................................. 1 1.2 Group 14 Chemistry ...................................................................................................................... 2 1.3 Group 4 Chemistry ...................................................................................................................... 16 1.4 Imido-Bridged Bimetallic Compounds Synthesis and Reactivity ................................................ 24 2 Results and Discussion: Group 14 Chemistry ...................................................................................... 27 2.1 Germylene Synthesis ................................................................................................................... 27 2.2 DFT Analysis of Group 14 Structures .......................................................................................... 33 2.3 Mixed Coordination Germanium Species ................................................................................... 44 2.4 Bulky germanium amides. ........................................................................................................... 55 2.5 Synthesis of Germanimines ........................................................................................................ 61 2.6 Summary of Results .................................................................................................................... 78 3 Results and Discussion: Group 4 Chemistry ........................................................................................ 79 3.1 Synthesis of Amides and Imidozirconocene species ................................................................... 79 3.2 Insertion Reactions of Azides with alkylzirconocenes ................................................................ 94 3.3 Summary of Results .................................................................................................................. 103 4 Results and Discussion: Group 4 – Group 14 Heterobimetallics ...................................................... 104 4.1 Synthetic Strategy ..................................................................................................................... 104 4.2 Reactions between Group 4 and Group 14 Compounds .......................................................... 104 4.3 Summary of Results .................................................................................................................. 112 5 Appendices ........................................................................................................................................ 113 5.1 Experimental ............................................................................................................................. 113 5.2 1H And 13C NMR Spectra for Novel Compounds ....................................................................... 132 5.3 Crystal Structure and Refinement Data .................................................................................... 156 5.4 Partial Charges for 4 and 5 ........................................................................................................ 165 5.5 DFT Molecular Orbital Calculation Outputs for [Ge(HMDS)2]; I ................................................ 166 5.6 Crystal Structure Data for [Ar*N3] ............................................................................................ 168 5.7 Crystal Structure Data for [Ar*Cl] ............................................................................................. 169 5.8 Crystal Structure Diagram for [(Cp2Zr(NPh))2] .......................................................................... 170 5.9 References: ............................................................................................................................... 171 iii List of Figures Figure 1: Synthetic target heterobimetallic complex 1. ............................................................................... 1 Figure 2: Electron occupation of singlet and triplet metallene. ................................................................... 3 Figure 3: Orbital energy diagram showing relative stabilisation and destabilsation of HOMO through changes in the electronegativity of the α substituents. ............................................................................... 4 Figure 4: Common imido coordination modes. .......................................................................................... 11 Figure 5: Germanes XXIII and XXIV, products of azide insertion into germanimine bond. ........................ 14 Figure 6: Leung's complex (XXV) and Jones’s germanium dimer after hydrogen addition (XXVI). ............ 14 Figure 7: Resonance structures of XXVII and XXVIII. ................................................................................... 15 Figure 8: Imido bridged zirconocene dimer XXXI(d). .................................................................................. 17 Figure 9: Complexes shown in Table 1. ......................................................................................................