Metal−Silicon Triple Bonds: Reactivity of the Silylidyne Complexes [Cp*(CO)2M≡Si−Tbb] (M = Cr – W)

The different reactivity pattern of M≡Si and the M≡C bonds (M = transition metal) is illustrated by a series of reactions of the silylidyne complexes [Cp*(CO)₂M≡Si−Tbb] (1-M) (M = Cr – W; Cp* = η⁵ -pentamethylcyclopentadienyl; Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl)). Complexes 1-M were obtained selectively from Li[Cp*M(CO)₃] and the 1,2-dibromodisilene (E)-Tbb(Br)Si=Si(Br)Tbb. The reaction of 1-Mo and 1-W with two equivalents of mesityl isocyanate leads selectively to complex 2-Mo and 2-W, respectively, featuring a novel κ²O,O-imidocarbonatosilyl ligand. Ring opening of ethyloxirane occurs rapidly with 1-Mo and leads to the hydrido-enolatosilylidene complex 3-Mo illustrating the Si-centered electrophilicity of the silylidyne complex. Trimethylsilyldiazomethane induces a cleavage of the Mo≡Si bond of 1-Mo after a rapid double [2+1] cycloaddition of the terminal N-atom, resulting in the first silaamidinato complex 4-Mo. In comparison, the reaction of 1-Mo with mesityl azide gives after N₂ elimination the Mo-silaiminoacyl complex 5-Mo. All compounds were fully characterized and the isomerism and dynamics of 3-Mo in solution were analysed by a combination of spectroscopic and quantum-chemical studies.