The mechanism of solvolysis of beta-ketosilanes

Rates of hydrolysis of RC6H4COCH2SiR13 (R = 4-MeO, 4-, 3-Me, 4-, 3-Cl, H; R1 = Me3Et), with and without NaOH catalyst in THF-H2O (2:1) were measured spectrophotometrically at various temps. The effects of substituents R correlated with their Hammett ? consts. (? = 2.2 and 0.77 in neutral and the basic medium, resp.). The solvent isotope effect, the effect of substitution at Si and the activation parameters are reported and discussed. In THF-H2O, solvolysis occurred via a cyclic mechanism in which transfer of a proton from H2O to O of C:O was synchronous with the formation of the Si-O bond and probably with the breaking of the C-Si bond, whereas in basic medium the mechanism involved formation of a Si(V) intermediate in the rate detg. step of the reaction.