Bromo-di(silyl)methanes – Precursors to Disilylcarbanionic Ligands

The reaction of the series of methyl/phenylchlorosilanes Me₂PhSiCl, MePh₂SiCl and Ph₃SiCl with CHBr₃/n-BuLi to give the corresponding bromo-di(silyl)methanes has been investigated. The selectivity of the reaction proved to be strongly influenced by the number of phenyl groups bound to silicon. As already established for Me₃SiCl, Si–C coupling readily occurs with Me₂PhSiCl to give (Me₂PhSi)₂CHBr (1) in good yields, whereas MePh₂SiCl affords (MePh₂Si)₂CHBr (2) in lower yields. The molecular structures of 2 and the by-product (MePh₂Si)₂CBr₂have been determined by single crystal X-ray diffraction. In the case of the fully arylated species, Ph₃SiCl, only the monosilylated compound (Ph₃Si)CH₂Br (3) is generated. (HMe₂Si)₂CHBr (5) can be obtained starting from 1 by treatment with triflic acid to give (CF₃SO₃Me₂Si)₂CHBr (4), followed by reduction of 4 with LiAlH₄in diethyl ether. In situ metalation of 5 with n-BuLi affords (HMe₂)₂CHLi, which reacts instantaneously with a second equivalent of 5 to give the halogen-free dimer [(HMe₂Si)₂CH]SiMe₂CH₂SiMe₂H (6).