Synthesis, Catalysis and Stoichiometric Reactivity of Mo Imido Complexes Nicolas A. McLeod BSc. in Chemistry Chemistry Thesis submitted to the Faculty of Graduate Studies In the partial fulfillment of the requirements For the MSc. degree in chemistry Chemistry Department Faculty of Mathematics and Science Brock University St. Catharines, Ontario © Nicolas A. McLeod, 2014 Abstract The current thesis describes the syntheses, catalytic reactivity and mechanistic investigations of novel Mo(IV) and Mo(VI) imido systems. Attempts at preparing mixed bis(imido) Mo(IV) complexes of the type (RN)(R′N)Mo(PMe3)n (n = 2 or 3) derived from the t mono(imido) complexes (RN)Mo(PMe3)3(X)2 (R = Bu (1) or Ar (2); X = Cl2 or HCl, Ar=2,6- i Pr2C6H3) are also described. The addition of lithiated silylamides to 1 or 2 results in the 2 unexpected formation of the C-H activated cyclometallated complexes (RN)Mo(PMe3)2(η - t CH2PMe2)(X) (R = Ar, X = H (3); R = Bu, X = Cl (4)). Complexes 3 and 4 were used in the activation of R′E-H bonds (E = Si, B, C, O, P; R′ = alkyl or aryl), which typically give products of addition across the M-C bond of the type (RN)Mo(PMe3)3(ER′)(X) (4). In the case of 2,6- dimethylphenol, subsequent heating of 4 (R = Ar, R′ = 2,6-Me2C6H3, E = O) to 50 °C results in 2 C-H activation to give the cyclometallated complex (ArN)Mo(PMe3)3(κ -O,C-OPh(Me)CH2) (5). An alternative approach was developed in synthesizing the mixed imido complex t 2 t (ArN)( BuN)Mo(PMe3)(η -C2H4) (6) through EtMgBr reduction of (ArN)( BuN)MoCl2(DME) in the presence of PMe3. Complex 6 reacts with various hydro- and chlorosilanes to give β-agostic silylamido complexes and in one case, when Me2SiHCl is the silane, leads to the silanimine t 2 2 complex ( BuN)Mo(η -SiMe2-NAr)(Et)(η -C2H4) (7). Mechanistic studies on the formation of the Mo(VI) tris(silyl) complex t t ( BuN)Mo(SiHPh)(H){(μ-N Bu)(SiHPh)}(PMe3)2 (8) were done from the addition of three t 2 equivalents of PhSiH3 to ( BuN)Mo(PMe3)(η -C2H4), resulting in identification of β- and γ- agostic SiH…Mo intermediates. The reactivity of complex 8 towards ethylene and nitriles was studied. In both cases coupling of unsaturated substrates with the Mo-Si bond of the metalacycle i was observed. In the case of nitriles, insertion into the 4-membered disilaazamolybdacycle t 2 t results in complexes of the type ( BuN)Mo{(κ -Si,C-SiHPh-N Bu-SiHPh-N=C(R)}(PMe3)2. Catalytic hydrosilylation of carbonyls mediated by the β-agostic silylamido complex 3 t (ArN)2Mo(η -N Bu-SiMe2-H)(H) (9) was investigated. Stoichiometric reactions with organic substrates showed that catalysis with 9 does not proceed via the conventional insertion of substrate into the Mo-H bond. ii Acknowledgements I would like to first off acknowledge my supervisor, Dr. Georgii Nikonov for keeping me on-board and in-check for the last five years. I am grateful for the opportunity you gave me five years ago as an undergrad in allowing me to be a part of your group. I have gained an incredible amount of knowledge and life experience because of this and I thank you. To my committee members at Brock University, Dr. Melanie Pilkington and Dr. Art van der Est, I appreciate your honesty and ability to keep me on track during the course of my work. I am grateful to Dr. Stuart Rothstein and Dr. Tony Yan for their assistance in the administrative aspect of things. To John and Jordan Vandenhoff of the glassblowing shop and both young and old Steve at the Machine Shop, I appreciate all the work you guys did for us especially during the hectic times during the move. I have to thank and praise Razvan Simionescu (NMR technician) who has been instrumental in the culmination of this thesis. Thank you for the time and effort you devoted to instructing me how to better understand the world of NMR. I would also like to thank our crystallographer from the University of Ottawa; Dr. Ilya Korobkov. I am particularly grateful to all my colleagues and friends at Brock that I have been privileged to work with and meet including: Dr. Andrey Khalimon, Dr. Dmitry Gutsulyuk, Dr. Oleg Shirobokov, Phil Farha, Sun Hwa (Tori) Lee (Toreelee! Italian version), Dr. Ksenyia Revunova, Sergey Vischenko, Terry Chu, Van Hung Mai, Courtney Boone, Emma Gavey, Dr. Roger Gumbau-Brisa, Drew Marquadrt, Vimal and Joshni, Zemane Bekele, Iraj, Shufen Xu, Michelle Eisner and if I missed anyone I apologize. I have to thank all of my friends outside of school who have been patient with me all these years; you know who you are! I must thank Julie who has kept me sane and grounded all these years. I would also like to thank my family for their understanding and sacrifices throughout this time. iii Table of Contents Abstract ............................................................................................................................................ i Acknowledgements ........................................................................................................................ iii Table of Contents ........................................................................................................................... iv Abbreviations ................................................................................................................................. vi List of Figures ................................................................................................................................ ix List of Schemes ............................................................................................................................... x List of Tables ............................................................................................................................... xiii I. Introduction ................................................................................................................................. 1 II. Historical .................................................................................................................................... 3 II.1 Nonclassical Si-H···M Agostic Interactions in Transition Metal Complexes ..................... 3 II.1.1 β-Agostic NSi-H···M Transition Metal Complexes ................................................... 10 II.2 Hydrosilylation of Carbonyls Mediated by Transition Metal Complexes ......................... 17 II.2.1 Recent Mechanisms of Transition Metal Catalyzed Hydrosilylation of Carbonyls .... 19 II.2.2 Recent Advances in Hydrosilylation using Molybdenum Catalysts ........................... 28 II.3 Cyclometallation of Tertiary Phosphine Complexes ......................................................... 37 II.3.1 Phosphine Cyclometallation: M-C-P Rings of Group 3 to 5 Metals........................... 41 II.3.2 Phosphine Cyclometallation: M-C-P Ring of Group 6 Metals ................................... 47 II.3.3 Phosphine Cyclometallation: M-C-P Ring of Group 8 Metals ................................... 61 II.3.4 Phosphine Cyclometallation: M-C-P Ring of Group 9 Metals ................................... 66 II.3.5 Phosphine Cyclometallation: M-C-P Ring of Group 10 Metals ................................. 69 II.4 Preparation of Molybdenum Bis(imido) and Mono(imido) Complexes ............................ 75 III Results and Discussion ............................................................................................................ 82 III.1 Introduction ....................................................................................................................... 82 III.2 Synthesis of Symmetrical Mo(VI) Silylamido Complexes .............................................. 83 3 t III.2.1 Catalytic Hydrosilylation of Carbonyls using (ArN)2Mo(η -N Bu-SiMe2-H)H ........ 89 III.3 Base Induced Cyclometallation of PMe3 Ligand ............................................................ 104 2 III.3.1 E-H Bond Activation using (ArN)Mo(PMe3)2(η -CH2PMe2)H .............................. 108 t 2 III.3.2 E-H Bond Activation using ( BuN)Mo(PMe3)2(η -CH2PMe2)Cl ............................ 122 iv III.4 Synthesis and Reactivity of Unsymmetrical Mixed Imido Complexes .......................... 124 III.4.1 Reactivity of III-46 with chloro- and hydrosilanes .................................................. 127 t t III.5 Mechanistic and Reactivity Study of ( BuN)Mo(H)(SiH2Ph){(SiHPh)2(μ-N Bu)}(PMe3)2 ................................................................................................................................................. 134 III.5.1 VT NMR Study for complex III-51 ......................................................................... 139 III.5.2 Stoichiometric Reactivity with Carbonyls, Alkenes and Alkynes ........................... 144 III.5.3 Stoichiometric Reactivity with Nitriles ................................................................... 149 IV. Conclusions and Future Work .......................................................................................... 153 V. Experimental .......................................................................................................................... 155 General Methods and Instrumentation .................................................................................... 155 Preparation of starting materials and reagents ........................................................................ 156 Preparation of Mo(VI) Silylamido Complexes ....................................................................... 161 2 Reactions of (ArN)Mo(PMe3)2(η -CH2PMe2)H with E-H Bonds .........................................