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Synthesis and Reactivity of Transition Metal and Main Group Hydrogenation Catalysts

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Synthesis and Reactivity of Transition Metal and Main Group Hydrogenation Catalysts Synthesis and Reactivity of Transition Metal and Main Group Hydrogenation Catalysts by Eliar Mosaferi A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Chemistry University of Toronto © Copyright by Eliar Mosaferi 2019 Synthesis and Reactivity of Transition Metal and Main Group Hydrogenation Catalysts Eliar Mosaferi Doctor of Philosophy Department of Chemistry University of Toronto 2019 Abstract Since its discovery by Paul Sabatier, catalytic hydrogenation of unsaturated substrates has become the single largest industrial process to date and encompasses the production of many products, such as foods, agrochemicals, pharmaceuticals, and materials. Over the last century research in the area has predominantly focused on the use of transition metals such as palladium, platinum, rhodium, and ruthenium to develop heterogeneous and homogeneous hydrogenation catalysts. The research presented herein focuses on the use of ruthenium complexes bearing electron-rich phosphorylated N-heterocyclic carbene ligands as well as the development of main- group compounds for frustrated Lewis pair catalysis. Complexes [Ru(0)LL’2(CO)] and [RuHL2(CO)][Cl], where L = N-phosphorylated N- heterocyclic carbene (NHCP), and L’ = triphenylphosphine, were prepared as a mixture by treatment of RuHCl(CO)(PPh3)3 with excess NHCP carbene and separated by crystallization. The zero-valent complex [Ru(0)LL’2(CO)] was shown to undergo rapid oxidative addition to the corresponding Ru(II) species when treated with small molecules to afford complexes of the general type [RuHXLL’(CO)], where L = N-phosphorylated N-heterocyclic carbene, L = triphenylphosphine, and X = H, SiPh3, or Si(H)Ph2. ii The reaction of NHCP carbene with [RuCl2(p-cymene)]2 resulted in the isolation of the piano- stool half-sandwich complex [RuCl2(p-cymene)(NHCP)] as well as an unusual arene-activated species. The half-sandwich complex was treated with a halide-abstracting agent to afford the cationic compound [RuCl(p-cymene)(NHCP)]+, which was shown to rapidly undergo dihydrogen activation via an outer-sphere mechanism involving the phosphine appended to the carbene ligand. To demonstrate the utility of main-group catalysts, trityl cations of the form [(4-MeO- C6H4)xCPh3-x][BR4] were synthesized, where x = 1 and 3, and R = F, or C6F5. Treatment of equimolar solutions of [(4-MeO-C6H4)CPh2][BF4] and sterically encumbered phosphines with dihydrogen resulted in activation of dihydrogen but no catalytic activity was observed. The air- and moisture-stable [(4-MeO-C6H4)CPh2][BF4] was shown to be a potent Lewis acid catalyst in the hydrothiolation of olefins. iii Acknowledgments First and foremost, I would like to thank Professor Douglas Stephan for giving me the opportunity to complete my degree in his group. His vast knowledge, unwavering support, and infectious enthusiasm have been invaluable in aiding my journey through grad school and as a result my experience has been immensely positive. I am thankful for the opportunities to learn and grow and will always look back on my years in his group with fondness. As well, I’d like to thank the members of my advisory committee, Prof. Morris and Prof. Song, for the invaluable advice throughout my degree. I would also like to thank all the members of the Stephan group, both past and present, for their support and help both in and outside the lab. The life of a graduate student is heavily influenced by the peers around them and I am truly grateful to have known these wonderful group of colleagues, friends, and mentors. In particular, I’d like to thank Dr. Adam McKinty, Dr. Michael Boone, Dr. Colin Douglas, Dr. Adelle Vandersteen, and all other past and present members of C.S.S.G. for keeping me humble and for always being ready with a helping hand. In particular, the meetings held over glasses of Red Leaf juice were particularly useful. I’d especially like to thank Dr. Tim Johnstone, Dr. Andrew Jupp, and Kevin Szkop for their technical and mental support and the pleasant chats over afternoon coffee. As well I’d like to thank Dr. Andrew Jupp, Dr. Tim Johnstone, Kevin Szkop, Karlee Bamford, James Lafortune, and Alex Waked for editing my thesis and providing valuable feedback. And to all of the friends I have made in Toronto, whether in the lab or outside, I am forever grateful for your kindness, hospitality, and support. As always, my family has been incredibly supportive and without their sacrifices I would not be where I am today. My parents, Hassan and Maryam, have always pushed me to be my best in all aspects of my life. They have supported me through the different chapters of my life. My brother, Yashar, has also been instrumental in my life. Much like my parents, he has been there for me time and time again. It has been their encouragement, support, and unconditional love that has allowed me to persevere through challenges. I owe an immense debt of gratitude to them for their unconditional love and look forward to the opportunity to support and encourage them in the future. iv Last but not least, I would like to thank my incredible partner, Setareh Nourani. More than anyone she has been patient and supportive throughout this journey. Despite not being a chemist, she has patiently and enthusiastically played the role of my sound board and provided guidance when I faced problems in the lab. Equally, outside the lab she has shown an incredible amount of love and care and for that I owe her a great debt. Her enthusiasm and willingness to bear through my chemistry problems have been an invaluable asset. This work could not be completed without her undying support. v Table of Contents Acknowledgments.......................................................................................................................... iv Table of Contents ........................................................................................................................... vi List of Tables ................................................................................................................................. ix List of Schemes ................................................................................................................................x List of Figures ................................................................................................................................xv List of Abbreviations ................................................................................................................. xviii Chapter 1 Introduction .....................................................................................................................1 1.1 Chemistry and Impact on Society ........................................................................................1 1.2 Catalysis ...............................................................................................................................2 1.3 Transition Metal Hydrogenation ..........................................................................................3 1.3.1 Heterogeneous Catalysts ..........................................................................................3 1.3.2 Well-Defined Homogeneous Catalysts ....................................................................3 1.4 Metal-Free Hydrogenation .................................................................................................10 1.4.1 Main-Group Catalysis ............................................................................................10 1.4.2 Frustrated Lewis Pairs (FLP) .................................................................................12 1.4.3 FLP Hydrogenations ..............................................................................................16 1.5 N-Heterocyclic Carbenes (NHC) .......................................................................................18 1.5.1 History of NHC Carbenes ......................................................................................18 1.5.2 NHC Complexes in Hydrogenation .......................................................................23 1.6 Nitrile Butadiene Rubber ...................................................................................................25 1.7 Lanxess Project ..................................................................................................................26 1.8 Scope of this Thesis ...........................................................................................................27 1.9 Contributions to Knowledge ..............................................................................................27 1.9.1 Relevant Publications.............................................................................................27 vi 1.9.2 Conference Presentations .......................................................................................28 1.9.3 Undergraduate Mentoring ......................................................................................28 Chapter 1 References .....................................................................................................................30 Chapter 2 Coordination Chemistry of N-Heterocyclic Phosphanyl Carbenes ...............................38 2.1 Introduction ........................................................................................................................38 2.1.1 Zero-Valent Ruthenium Complexes ......................................................................38 2.1.2 N-Heterocyclic
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