Direct substitution of benzylic alcohols with electron-deficient benzenethiols via π-benzylpalladium(ii) in water

Abstract

An efficient and environmentally benign method for the direct nucleophilic substitution of benzylic alcohols with electron-deficient benzenethiols in water is developed. π-Benzylpalladium(II) cation complexes show high catalytic activity for S-benzylation, which provides a mechanistic alternative to the borrowing hydrogen methodology. Hammett studies on the rate constants of S-benzylation by various substituted alcohols show good correlation between log(k_X/k_H) and the σ value of the respective substituents. From the slope, negative ρ values are obtained, suggesting that there is a build-up of positive charge in the transition state. Water plays an important role in the catalytic system for sp³ C–O bond activation and stabilization of the activated Pd(II) cation species.