Reactions of Molybdenum Tetrahydrido Complex with Halohydrosilanes

The thermal reactions of [MoH4(dppe)(2)] (1, dppe = Ph2PCH2CH2PPh2) with RSiH2X afford [MoH2X(dppe){[Ph2PCH2CH2P(Ph)C6H4-o]RXSi-P,P,Si}] (R = Ph, X = Cl (5a); R = cyclo-C6H11, X = Cl (5b); and R = Ph, X = Br (6)) by activation of the Si-H bond of the silanes and the ortho C-H bond of the phenyl group in the dppe ligand. Reduction of the Si-Cl and Mo-Cl bonds in 5a with LiAlH4 leads to the formation of the original complex 1 as a result of unusual Si-C bond cleavage. Meanwhile, dehalogenative reduction of 5a using zinc metal gives the known compound [MoH3{[ph(2)PCH(2)CH(2)P(Ph)C6H4-o](2)(Ph)Si-P,P,P,P,Si}] (2). The experimental results reported herein provide certain evidence for the involvement of the silylene species in the unusual formation of the present polydentate phosphinoalkylsilyl ligands.