Synthesis and Reactivity of Main Group Complexes for Applications in Small Molecule Activation Minh Tho Nguyen Chemistry Submit
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Synthesis and Reactivity of Main Group Complexes for Applications in Small Molecule Activation Minh Tho Nguyen Chemistry Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Faculty of Mathematics and Science, Brock University St. Catharines, Ontario © 2019 i Abstract The work described in this thesis is focused on the preparation of a series of novel main group complexes, featuring unusual structural and bonding situations, and the study of their reactivity toward small molecules. The new zinc complexes dimphZnBu (V-2) and dimphZnCl2Li(THF)3 (V-3), supported by a diiminophenyl (dimph) ligand were prepared. The reaction of complex V- 3 with LiHBEt3 resulted in hydride transfer to the C=N imine group to give an unusual zinc dimer (V-7). The latter transformation occurs via formation of compound (ɳ1(C),ĸ1(N)- i 2,6-(2,6- Pr2C6H3N=CH)2C6H3)2Zn (V-5) which can be also accessed by reduction of V-7 with KC8. Diiminophenyl (dimph) proved to be an excellent ligand platform to stabilise a low- valent phosphorus centre. The resultant compound dimphP (VI-2), which can be rationalised as an imino-stabilised phosphinidene or benzoazaphopshole, shows remarkable chemical stability toward water and oxygen. VI-2 reacts with excess strong acid HCl to generate the P(III) chloride (dimHph)PCl (VI-6). Surprisingly, substitution of t the chloride under some nucleophilic (KOBu ) and electrophilic conditions (Me3SiOTf) regenerates the parent compound VI-2 by proton removal from the weakly acidic CH2N position. A related species (dimH2ph)P (VI-10) is produced upon thermal rearrangement of the hydride (dimHph)PH (VI-9). The molecular structure and reactivity of compounds VI-2 and other related compounds are also discussed. The reduction of the O,C,O-chelated phosphorus (III) chloride (VI-16) ( O,C,O = 2,6-bis[(2,6-diisopropyl)phenoxyl]phenyl) with KC8 or PMe3 resulted in the formation of ii a cyclic three-membered phosphorus compound (VI-18). The intermediacy of phosphinidene VI-17 was confirmed by trapping experiments and a VT 31P{1H} NMR study. The reaction of in-situ generated phosphinidene with either PhSiH3 or HBpin resulted in the formation of an unprecedented phosphine (VI-23). The treatment of VI-16 with two equivalents of DippNHC carbene led to ArP(Cl)NHC product (VI-24). The germylone dimNHCGe (dimNHC = diimino N-Heterocyclic Carbene, VII-8) was successfully prepared by the reduction of germanium cation (VII-7) with KC8. The molecular structure of VII-8 was unambiguously established, using NMR spectroscopy and single-crystal X-ray diffraction analysis. The reactivity of VII-8 was investigated. VII-8 is inactive towards butadiene but undergoes an oxidative cyclization with tetrachloro-o-benzoquinone to give a tetragermanium derivative. VII-8 undergoes oxidation addition of CH3I and PhI, followed by an unusual migration of the Me and Ph groups from germanium to the carbene ligand. Related chemistry takes place upon protonation with dry HCl, which results in the migration of the hydride to the carbene ligand. iii Acknowledgements I would like to express my deepest and sincerest gratitude to my advisor Prof. Georgii I. Nikonov for offering me a valuable opportunity to join and work in his research group. His patient guidance, sustained encouragement, immense support, and unconditional belief throughout my Ph.D. gave me huge confidence and abilities and led me a great success in my research projects. Under his expertise supervision, my knowledge has been enriched, which allowing me to grow as a scientist. I would also like to thank Prof. Jeffrey Atkinson and Prof. Feng Li for being as my committee members and for their valuable comments and constructive suggestions during my Ph.D. research process. I would like to send a big thank to internal and external technicians including Mr. Razvan Simionescu for his assistance in NMR spectroscopy, Ms. Liqun Qui for her support in Mass Spectroscopy, Mark, and Nico for helping me in IR spectroscopy and UV-vis spectroscopy, Dr. Bulat Gabidullinb in the University of Ottawa, Dr. James F. Britten in McMaster University, and Dr. Denis Spasyuk in Canadian Light Source Inc. for X-ray data collection and for their assistance in solving the molecular structures described in this thesis. I also wish to thank Prof. Dmitri G. Goussev (Gusev) from Wilfrid Laurier University for sharing his valuable insights into DFT methods and calculations. I want to thank labmates, past and present: Dr. Terry Chu, Dr. Van Hung Mai, Iryna Alshakova, John Lortie, Anton Dmitrienko, Aishabibi Kassymbek, Joshua Clarke, Aliona Bazadsenka, Billy Petrushko, Jan-Willem Lamberink, Brandon Corbett for their friendship, iv help and support all the time of my Ph.D. research, and for all the fun we had in the last four and half years at Brock. Last but not the least, I would like to express special thanks to my family: my parents Mr.&Mrs. Nguyen, my eldest brother Thanh, and my little sister Thom, who have provided me with moral and emotional support throughout my life. Finally, I thank my beloved fiancée Phuoc-Sang for his unlimited sharing, support and encouragement through all the happiness and difficulties over the past years. Thanks for all your encouragement! v Table of Contents Abstract ............................................................................................................................... i Acknowledgements .......................................................................................................... iv Table of Contents ............................................................................................................. vi Abbreviations ................................................................................................................. viii List of Scheme ................................................................................................................... x List of Figures ................................................................................................................. xvi List of Tables ................................................................................................................... xx I. Introduction ............................................................................................................... 1 Part A. Historical Background ........................................................................................ 3 II. Pincer complexes of main group elements .............................................................. 4 II.1. Main Group Complexes Supported by Bis(imino)ary NCN Pincer Ligand ........ 5 II.1.1. Group 13 ....................................................................................................... 6 II.1.2. Group 14 ....................................................................................................... 6 II.1.3. Group 15 ..................................................................................................... 12 II.2. Main Group Complexes Supported by Bis(imino)aryl Pyridine Ligand ........... 17 III.1.1. Group 1 ....................................................................................................... 19 III.1.2. Group 2 ....................................................................................................... 20 III.1.3. Group 13 ..................................................................................................... 23 III.1.4. Group 14 ..................................................................................................... 30 III.1.5. Group 15 ..................................................................................................... 32 III.1.6. Group 16 ..................................................................................................... 33 II.3. Main Group Complexes Supported by Bis(imino)aryl N-heterocyclic Carbene Platform ......................................................................................................................... 35 III. Phosphinidene .......................................................................................................... 36 IV. Zerovalent Heavier Group 14 Compound ............................................................. 58 IV.1 Heavier Group 14 Compound in Zero Oxidation State ...................................... 58 IV.2 The Reactivity of Zerovalent Heavy Group 14 Compounds .............................. 74 Part B. Results and Discussion ...................................................................................... 81 vi V. Synthesis and Characterization of Zinc Complexes Stabilised by 2,6-bis[(2,6- diisopropyl)imino]phenyl Pincer Ligand ...................................................................... 82 V.1 Introduction ........................................................................................................ 82 V.2 Synthesis, Characterization, and Reactivity of Zinc Complexes Stabilised by 2,6-bis[(2,6-Diisopropyl)imino]phenyl Pincer Ligand ................................................. 83 VI. Synthesis, Characterization, and Reactivity of Base-Stabilised-Phosphinidene 94 VI.1. Preparation, Characterization, and Reactivity of “Phosphinidene” Stabilised by 2,6-bis[(2,6-diisopropyl)imino]phenyl Pincer Ligand. ................................................. 94 VI.2. Preparation, Characterization, and Reactivity of “Phosphinidene” Stabilised by 2,6-bis[(2,6-diisopropyl)phenoxyl Pincer Ligand. ...................................................... 109