Concerning the Mechanism for Bifunctional Catalysis in the Methanolysis of Methoxymethylphenoxyphenylsilane

Article abstract of DOI:10.1021/jo00073a025

The formic acid-formate-catalyzed methanolysis of methoxy-d3-methylphenoxyphenylsilane (1D) was studied.The formation of phenol and the exchange of the deuterated methoxy group with solvent was studied as a function of total buffer concentration.Both processes show bifunctional catalysis involving a molecule of acid and a molecule of base in the transition state.The observation of bifunctional catalysis suggests a mechanism in which formation of the silicon-solvent bond is concerted with breaking of the silicon-leaving group bond (-OC6H5 or -OCD3).From analysis of the kinetic data it is concluded that the concerted bond-forming and bond-breaking processes do not occur on a pentavalent silicon species formed by a preequilibrium addition of solvent or formate anion to 1D.The results are interpreted in terms of a mechanism in which solvent attack occurs on a tetravalent silicon center with simultaneous breaking of the silicon leaving group bond.