BROMO-DI(SILYL)METHANES - PRECURSORS TO DISILYLCARBANIONIC LIGANDS

The reaction of the series of methyl/phenylchlorosilanes Me(2)PhSiCl, MePh(2)SiCl and Ph(3)SiCl 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 grou ps bound to silicon. As already established for Me(3)SiCl, Si-C coupli ng readily occurs with Me(2)PhSiCl to give (Me(2)PhSi)(2)CHBr (1) in g ood yields, whereas MePh(2)SiCl affords (MePh(2)Si)(2)CHBr (2) in lowe r yields. The molecular structures of 2 and the by-product (MePh(2)Si) (2)CBr2 have been determined by single crystal X-ray diffraction. In t he case of the fully arylated species, Ph(3)SiCl, only the wmonosilfla ted compound (Ph(3)Si)CH2Br (3) is generated. (HMe(2)Si)(2)CHBr (5) ca n be obtained starting from 1 by treatment with triflic acid to give ( CF(3)SO(3)Me(2)Si)(2)CHBr (4), followed by reduction of 4 with LiAlH4 in diethyl ether. In situ metalation of 5 with n-BuLi affords (HMe(2)) (2)CHLi, which reacts instantaneously with a second equivalent of 5 to give the halogen-free dimer [(HMe(2)Si)(2)CH]SiMe(2)CH(2)SiMe(2)H (6) .