Reactivity of a Ruthenium Bis(Dinitrogen) Complex
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Reactivity of a Ruthenium Bis(Dinitrogen) Complex By Samantha Lau July 2018 Department of Chemistry Imperial College London A thesis submitted for Doctorate of Philosophy Declaration of Originality The work discussed in this thesis was conducted in the Department of Chemistry, Imperial College London, between October 2014 and April 2018. Unless stated otherwise, all the work is entirely my own and has not been submitted for a previous degree at this, or any other university. Copyright Declaration The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work. [1] Abstract This thesis investigated the reactivity of the ruthenium bis(dinitrogen) complex [Ru(H)2(N2)2(PCy3)2] 2 (1), an analogue of the ruthenium bis(dihydrogen) complex [Ru(H)2(η -H2)2(PCy3)2]. It was demonstrated that 1 was able to effect the sp2C–X (X= H, O) bond cleavage of acetophenone substrates to generate 5-membered organometallic intermediates. The by-products from the C–O cleavage reactions were identified as alcohols which also react with 1 at a faster or equal rate to the substrates. The mechanism of these C–X cleavage reactions were probed experimentally and computationally to show that the C–H bond cleavage pathway was operating through a σ-complex assisted metathesis pathway whereas the C–O cleavage pathway was operating through a Ru(II)/Ru(IV) redox mechanism. In addition, the reactivity of 1 with main group hydrides (aluminium, zinc and magnesium) was presented with the formation of a series of new ruthenium main group heterobimetallic hydride complexes, M•Ru (M = Al, Zn, Mg). These heterobimetallic hydride complexes contain either dinitrogen or dihydrogen ligated at the ruthenium centre depending on the partial pressure of N2 and H2 in the atmosphere. It was shown that the main group fragment can subtly tune the degree of dinitrogen activation in these M•Ru-N2 complexes, Mg > Zn > Al. This trend was rationalised by probing the bonding and frontier molecular orbitals of these complexes. Furthermore, 27Al solid state NMR spectroscopy was implemented to analyse the ruthenium aluminium heterobimetallic hydride complexes and it was determined that that there was no linear correlation between the isotropic chemical shift obtained in the 27Al solid state NMR spectra and the oxidation state of the complex. [2] For my family, my friends And Wing Lee [3] Acknowledgements You hear the horror stories of people doing PhDs and having a horrid time. Well, this was not one of them. In fact, I couldn’t have asked for a better group of people to share my journey with. At the helm of this group has been the most supportive and professional supervisor anyone could wish for. Mark, thank you for being a great mentor. I owe you a lifetime of gratitude and one scoop of mint choc-chip ice cream. Working and growing in your group has been an absolute privilege. To the rest of the members of Crimmin group, past and present: Adi, David, Olga, Michael, Alex, Wenyi, Andy, BWS Clare, Tom, B-Dawg BryBry, Greg C, Martí, Nick, Ryan, Richard, Baby Bird Greg B and of course Feriel, thanks for the beers, the many office games and of course just humouring my antics. Guys, I’ll see you at the 10th anniversary of Crimmyolympics ‒ though preferably sooner. In the meantime, please accept my thanks by being immortalised in my thesis through the medium of photoshop. Now the bonds you make during your PhD is something unique, stronger than any C–O bonds for sure, a shared experience that only your fellow PhD siblings can understand. With that in mind, to the Goblins, a special thanks for being such great dogs. I’m so grateful and lucky to have had you guys by my side from beginning to end. Furthermore, it is no understatement to say my thesis could not be complete without the help of Pete Haycock, Dick Sheppard and Andrew White, thank you for running my samples even if they were not always up to your standards. I hope your instruments never fail you and that you will have access to daylight in your new offices in White City. In addition, thank you Ian and Steve for your guidance, whiskeys and grams and grams of RuCl3. Also, a special shout out to The Model Answers for ensuring I still have a social life outside of academia. To my parents, I don’t know if you’ll ever read this but thank you for everything. Mum, Dad, I hope I’ve made you proud even if I am not the type doctor you anticipated me to be. To my sister Katie, you are my yolk. Thanks for reminding me that it is okay to just do nothing and take a breather in life. You have been the trailblazer in the family and probably allowed me and Ken to take paths we have. Finally, if there is one person who has truly experienced my PhD with me 24 hours a day, 7 days a week for 4 years, it is you Niall. Thank you. Sorry. And I love you. Now please give me my J.Young NMR tube drinking vessel, I’m parched. [4] CONTENT Declaration of Originality 1 Copyright Declaration 1 Thesis Abstract 2 Acknowledgements 4 List of Figures, Schemes and Tables 9 List of Abbreviations 15 Publications 16 1 CHAPTER ONE – RUTHENIUM BIS(DIHYDROGEN) 2 COMPLEX [Ru(H)2(η -H2)2(PCy3)2] AND ITS DERIVATIVES 1.1 INTRODUCTION 17 2 1.2 CHEMISTRY OF [Ru(H)2(η -H2)2(PCy3)2] 19 1.2.1 Hydrogenation 19 1.2.2 Small Molecules (CO, CO2, CS2, N2 and Halocarbons) 22 1.2.3 Alcohols 25 1.2.4 X–H activation (X = C, N, O) 26 1.2.5 σ-complexes with E–H bond (E = B, Si and Ge) 30 1.3 RESULTS AND DISCUSSIONS 50 1.3.1 Synthesis and reactivity of [Ru(H)2(N2)2(PCy3)2] (1) 50 1.4 CONCLUSION 54 1.5 REFERENCES 55 2 2 CHAPTER TWO – sp C–O BOND ACTIVATION BY AN ISOLABLE RUTHENIUM(II) BIS(DINITROGEN) COMPLEX: THEORY AND EXPERIMENT 2.1 INTRODUCTION 58 2.1.1 Biomass viability 58 [5] 2.2 C–O ACTIVATION 59 2.2.1 Nickel 59 2.2.2 Ruthenium 73 2.2.3 Iridium 81 2.3 RESULTS AND DISCUSSIONS 83 2.3.1 C–H activation 84 2.3.2 C–O activation 85 2.3.3 By-Product 86 2.3.4 Mechanistic and DFT Studies 89 2.3.5 Expansion of scope 100 2.3.6 Functionalisation 106 2.4 CONCLUSION 109 2.5 FUTURE WORK 109 2.6 REFERENCES 111 3 CHAPTER THREE – FORMATION OF A SERIES OF M•Ru (M = Al, Zn, Mg) HETEROBIMETALLIC HYDRIDE COMPLEXES 3.1 INTRODUCTION 115 3.1.1 Al•Ru heterobimetallic complexes 115 3.1.2 Zn•Ru heterobimetallic complexes 123 3.1.3 Mg•Ru heterobimetallic complexes 129 3.2 RESULTS AND DISCUSSIONS 130 3.2.1 Synthesis and characterisation 130 3.2.2 M•Ru-N2 135 3.2.3 Tuneable N2 activation 140 3.2.4 Reactivity with CO2 and HBpin 144 3.3 CONCLUSION 146 3.4 FUTURE WORK 147 3.5 REFERENCES 148 [6] 4 CHAPTER FOUR – REACTIONS OF β-DIKETIMINATE STABILISED ALUMINIUM DIHDYRIDE COMPLEXES WITH RUTHENIUM(II) BIS(DINITROGEN) COMPLEX 4.1 INTRODUCTION 150 4.1.1 Tetrameric Aluminium(I) Compounds 150 4.1.2 Molecular Aluminium(I) Compounds 154 4.2 RESULTS AND DISCUSSIONS 156 4.2.1 Synthesis and characterisation 156 4.2.2 27Al MAS NMR spectroscopy 169 4.3 CONCLUSION 174 4.4 FUTURE WORK 174 4.5 REFERENCES 176 5 CHAPTER FIVE – SUPPORTING INFORMATION 5.1 GENERAL 178 5.2 CHAPTER ONE: EXPERIMENTAL 179 5.2.1 Materials 179 5.2.2 Synthesis 179 5.2.3 Intermediate 1-H2/N2 180 5.3 CHAPTER TWO: EXPERIMENTAL 183 5.3.1 Materials 183 5.3.2 Synthesis 183 5.3.3 General Procedure for Reduction of Arylketone to Arylethanol 185 5.3.4 Ru-Mediated C–H Bond Activation 187 5.3.5 Ru-Mediated C–O Bond Activation 191 5.3.6 Identification of By-Products from C–O Bond Activation 198 5.3.7 Competition and Inhibition Reactions 204 5.3.8 Directing group 207 5.4 CHAPTER THREE: EXPERIMENTAL 216 5.4.1 Materials 216 [7] 5.4.2 Synthesis of Heterobimetallics 216 5.4.3 Substitution reaction 220 5.4.4 Variable Temperature NMR data 228 5.4.5 Kinetic Experiments 232 5.4.6 D2 Labelling Experiments 233 5.4.7 DFT and QTAIM 235 5.5 CHAPTER FOUR: EXPERIMENTAL 239 5.5.1 Materials 239 5.5.2 Synthesis of Al•Ru heterobimetallic hydride complexes 239 5.5.3 Variable Temperature NMR Data 244 5.5.4 T1 Data 249 6 APPENDIX 6.1 MULTINUCLEAR NMR SPECTRA 254 6.2 X-RAY DATA 279 [8] List of Figures, Schemes and Tables Figure 1.1. (Left) Kubas' dihydrogen complex. (Right) Ruthenium bis(dihydrogen) complex, 1-2H2 Figure 1.2. (Top) Orbitals involved in dihydrogen bonding to ruthenium centre. (Bottom) Two extreme modes of coordination of dihydrogen 2 2 Figure 1.3.