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

Abstract

The different reactivity pattern of MSi and MC bonds (M = transition metal) is illustrated by a series of reactions of the silylidyne complexes [Cp*(CO)₂MSi–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)SiSi(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 MoSi 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.