Some [tris(trimethylsilyl)methyl]phosphorus derivatives

Abstract

Treatment of Li[C(SiMe₃)₃] with PPh₂Cl gave the phosphine P[C(SiMe₃)₃]Ph₂, which, in spite of the steric crowding caused by the silicon ligand, was readily converted into the phosphonium salts [P{C(SiMe₃)₃}Ph₂H]I and [P{C(SiMe₃)₃}Ph₂Me]I; the latter on heating gave the ylid MePh₂PC(SiMe₃)₂. In methanol at room temperature the phosphine P[C(SiMe₃)₃]Ph₂ readily loses one Me₃Si group to give P[CH(SiMe₃)₂]Ph₂; the remaining Me₃Si groups are lost successively, with decreasing ease, giving finally PPh₂Me. These Si–C bond cleavages are catalysed by acid but inhibited by base, and it is suggested that the initial step is protonation of the phosphine. The quaternary salt [P{C(SiMe₃)₃}Ph₂Me]I successively loses its Me₃Si groups very readily in methanol, ultimately to give [PPh₂Me₂]I.