Synthesis and characterisation of hydrido molybdenum and tungsten complexes having a hemilabile tridentate Si,Si,O-ligand: observation of stepwise hydrosilylation of a nitrile to form an N-silylimine on the metal centre

Abstract

Photoinduced decarbonylation of Cp*M(CO)₃Me (M = Mo and W, Cp* = η⁵-C₅Me₅) in the presence of xantsilH₂ [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)] in pentane gave bis(silyl)hydrido complexes Cp*M(κ²Si,Si-xantsil)(CO)₂(H) (1a: M = Mo and 1b: M = W) through two-fold Si–H oxidative addition and methane elimination. Further irradiation of 1a,b in toluene afforded tridentate xantsil complexes Cp*M(κ³Si,Si,O-xantsil)(CO)(H) (2a: M = Mo and 2b: M = W) viaCO dissociation. Reactions of complexes 2a,b with nitriles led to stoichiometric hydrosilylation at the CN triple bond. Thus, reaction of 2a,b with t-BuCN at room temperature afforded N-silyliminoacyl complexes 3a,b, through insertion of a nitrile into the M–Si bond, and the products slowly isomerised to the corresponding N-silylimine complexes 4a,bvia intramolecular hydrogen migration. On the other hand, reaction of 2a,b with PhCN afforded N-silylimine complexes 5a,b directly. The molecular structures of 1a, 3a and 5b were determined by X-ray crystallography, revealing that complex 3a has a 3-centre–2-electron (3c–2e) Mo–Si–H bond.