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Strong Electron Donor Ligands and Their Catalytic Applications

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Strong Electron Donor Ligands and Their Catalytic Applications Strong Electron Donor Ligands and their Catalytic Applications by Conor Anthony Pranckevicius A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Chemistry University of Toronto © Copyright by Conor Pranckevicius (2016) Strong Electron Donor Ligands and their Catalytic Applications Conor Anthony Pranckevicius Doctor of Philosophy Department of Chemistry University of Toronto 2016 Abstract The coordination chemistry of several strong electron donor ligands, including anionic imidazol-4-ylidenes, cyclic bent allenes, carbodiphosphoranes, and carbodicarbenes were explored with transition metals including Au, Ag, Ru, Rh, Ir, and Fe. Chapter 2 explores the transition metal coordination chemistry of an anionic imidazol-4-ylidene. Ru complexes of this ligand were accessed by transmetalation of an anionic imidazol-4-ylidene Ag complex - the first instance of Ag mediated transmetalation of an anionic imidazolylidene. A coordinatively unsaturated Ru complex of this ligand was shown to decompose through a unique metal assisted proton transfer reaction. Rh complexes of this ligand have revealed its overall moderately strong donor ability. Chapter 3 details the synthesis of a family of Ru-hydrido species bearing strongly donating ‘cyclic bent allenes’ and reveals their very high activity in olefin hydrogenation catalysis. Chemoselective and diastereoselective hydrogenations, as well as hydrogenations of sterically hindered olefins are achieved at [ii] exceptionally low catalyst loadings. Chiral modifications of the cyclic bent allene ligands have been explored in Ir based systems. Chapter 4 explores the Fe chemistry of cyclic bent allenes and carbodiphosphoranes. These strong electron donors are shown to stabilize Fe in a rare highly unsaturated three-coordinate geometry in several instances. Chapter 5 details the synthesis of a new type of carbodicarbene, a ‘carbodicyclopropenylidene’, which is the first example of a carbodicarbene without heteroatomic stabilization. The main group and transition metal coordination chemistry of this ligand is investigated. The carbodicyclopropenylidene is shown also to be a strong electron donor. [iii] Acknowledgements I would first like to thank my supervisor, Professor Doug Stephan, for allowing me the incredible opportunity to pursue a Ph.D. under his direction, and for his continued encouragement for the exploration of new ideas and research directions. Doug, I am further indebted to you for the countless opportunities you have given me; international conferences, a research exchange, and exposure to leading scientists in our community. I am truly grateful for these things. Thanks Doug, really. I would like to thank the collaborators on the work presented in this thesis. In particular I would like to thank Louie Fan for his considerable help in performing the hydrogenation runs in Chapter 3. I would also like to thank Professor Guy Bertrand and Liu Liu at UCSD for contributing all of the computational work for Chapter 5. Thanks to all the many friends and mentors I have gained in the department over the years, too many to name! You guys made this whole experience so incredible. Thanks to the climbing crew for some sick adventures! (and for all the belaying ). And lastly, thanks to my parents for their continued love and support. [iv] Table of Contents Abstract .....................................................................................................................ii Acknowledgements ..................................................................................................iv List of Schemes ...................................................................................................... viii List of Figures........................................................................................................... x List of Tables .......................................................................................................... xiii List of Abbreviations ............................................................................................... xiii Copyright Acknowledgement ......................................................................................... xvi Chapter 1. The Coordination Chemistry of Divalent Carbon ........................................... 1 1.1 Why Study Science? .......................................................................................... 1 1.2 Divalent Carbon Ligands and their Applications ................................................. 2 1.2.1 Introduction .................................................................................................. 2 1.2.2 Electron Donor and Acceptor Scales ........................................................... 3 1.2.3 Imidazol-2-ylidenes and Related Species .................................................... 6 1.2.4 Applications of N-Heterocyclic Carbenes..................................................... 8 1.2.5 Acyclic Diaminocarbenes........................................................................... 13 1.2.6 Alkylaminocarbenes .................................................................................. 14 1.2.7 Imidazol-4-ylidenes (abnormal carbenes) .................................................. 15 1.2.8 Triazolylidenes ........................................................................................... 18 1.2.9 Ditopic N-Heterocyclic Carbenes ............................................................... 19 1.2.10 Cyclopropenylidenes ................................................................................. 21 1.2.11 Carbones ................................................................................................... 23 1.2.12 Ylids ........................................................................................................... 33 1.2.13 Dative Bonding in Main Group Compounds – an Evolving Discussion ...... 34 1.3 Hydrogenation Catalysis .................................................................................. 36 1.3.1 Rh and Ir based Catalysts ......................................................................... 37 1.3.2 Ru Catalysts. ............................................................................................. 40 1.3.3 First Row Hydrogenation Catalysts ........................................................... 42 1.4 The LANXESS Project ..................................................................................... 43 1.5 References ....................................................................................................... 44 Chapter 2. Coordination Chemistry of Anionic C4 bound Imidazolylidenes ................... 59 2.1 Introduction ...................................................................................................... 59 2.1.1 Motivation .................................................................................................. 59 [v] 2.1.2 Abnormal, Anionic and Ditopic Imidazolylidenes ....................................... 59 2.2 Results and Discussion .................................................................................... 62 2.2.1 Synthesis of a C4 Lithiated Imidazol-2-ylidene-Borane ............................. 62 2.2.2 Group 11 Complexes of An Anionic Imidazolin-4-ylidene .......................... 63 2.2.3 Ru Complexes of an Anionic Imidazol-4-ylidene ....................................... 66 2.2.4 Rh Complexes of an Anionic Imidazol-4-ylidene ....................................... 77 2.3 Conclusions...................................................................................................... 82 2.4 Experimental Section ....................................................................................... 83 2.4.1 Crystallographic Details ............................................................................. 83 2.4.2 Experimental Details .................................................................................. 86 2.5 References ....................................................................................................... 96 Chapter 3. Cyclic Bent Allene Complexes as Catalysts for Homogeneous Hydrogenation ............................................................................................................. 101 3.1 Introduction .................................................................................................... 101 3.1.1 Motivation ................................................................................................ 101 3.1.2 Carbones ................................................................................................. 102 3.1.3 Ru based Olefin Hydrogenation ............................................................... 103 3.2 Results and Discussion .................................................................................. 104 3.2.1 Ligand Synthesis ..................................................................................... 104 3.2.2 Initial Metalation Attempts ........................................................................ 105 3.2.3 Synthesis of Ru CBA Complexes ............................................................ 108 3.2.4 Catalytic Hydrogenation of Olefins .......................................................... 119 3.2.5 Further Variations of the Catalytic System ............................................... 127 3.2.6 Chiral Variations of the CBA – Ligand Synthesis ..................................... 131 3.2.7 Electronic Structure of Metal
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