Metal–silicon triple bonds: reactivity of the silylidyne complexes [Cp*(CO) ₂ M≡Si–Tbb] (M = Cr – W)

The different reactivity pattern of M[triple bond, length as m-dash]Si and M[triple bond, length as m-dash]C bonds (M = transition metal) is illustrated by a series of reactions of the silylidyne complexes [Cp*(CO)₂M[triple bond, length as m-dash]Si-Tbb] (1-M) (M = Cr - W; Cp* = <i>η</i> ⁵-pentamethylcyclopentadienyl; Tbb = 4-<i>tert</i>-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 (<i>E</i>)-Tbb(Br)Si[double bond, length as m-dash]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 <i>κ</i> ² <i>O</i>,<i>O</i>-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[triple bond, length as m-dash]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.