Synthesis of benzylpalladium complexes through C–O bond cleavage of benzylic carboxylates: Development of a novel palladium-catalyzed benzylation of olefins

Benzylic carboxylates were found to react with Pd(0) complexes bearing tertiary phosphines to give benzylpalladium(II) carboxylate complexes with cleavage of the benzyl-oxygen bond. The benzylpalladium complexes having the trifluoroacetato ligand react with olefins such as ethyl acrylate to give olefin benzylation products. On the basis of these studies a novel palladium-catalyzed benzylation of olefins was developed without using organic halides as the starting materials. The method has another advantage of requiring no base as in the conventional Mizoroki–Heck process using organic halides. The catalytic cycle is proposed to be constituted of elementary processes of (a) oxidative addition of a benzyl carboxylate with C–O bond cleavage to a Pd(0) complex to give a benzylpalladium carboxylate, (b) olefin insertion into the benzylpalladium bond to give an alkylpalladium complex, and (c) β-H abstraction to liberate the benzylated olefin.