The Mechanism of the Palladium Hydride β-Elimination Step in the Heck Reaction

The kinetics of competitive phenylation of alkenes with iodobenzene over palladium complexes (the Heck reaction) was studied. The effect of one alkene on the arylation rate of another alkene conflicts with the conventional mechanism of the Heck reaction in which the arylated alkene is formed through the unimolecular step of palladium hydride β-elimination. Based on experimental data obtained, another mechanism is proposed in which a reaction product is formed through the transfer of palladium hydride to the initial alkene molecule.