Role of halide ions in divalent palladium-mediated reactions: Competition between beta-heteroatom elimination and beta-hydride elimination of a carbon-palladium bond

The integral role of halide ions as a ligand in the reactions of stoichiome tric arylpalladium reagents and Pd(II)-catalyzed reaction of phenylmercuric acetate with various allylic compounds were studied. The halide ion was fo und to inhibit beta -H elimination and promote beta -heteroatom elimination in acidic media. In this reaction, a C-Pd intermediate with a beta -hetero atom (including halogen, acetoxy, alkoxy, and hydroxyl groups) gives only b eta -heteroatom elimination product in the presence of halide ions, while b eta -H elimination is effectively blocked.