RATES AND MECHANISM OF THE FORMATION OF ZEROVALENT PALLADIUM COMPLEXES FROM MIXTURES OF PD(OAC)(2) AND TERTIARY PHOSPHINES AND THEIR REACTIVITY IN OXIDATIVE ADDITIONS

Mixtures of Pd(OAc)(2) and tertiary phosphines spontaneously afford palladium(0) complexes. Kinetic investigations demonstrate that this reaction proceeds from the complex Pd(OAc)(2)-(PR(3))(2) via an inner-sphere reduction which is the rate-determining step of the overall reaction. The phosphine is thus oxidized to the corresponding phosphine oxide. The formation of the palladium(0) complex is sensitive to electronic and steric factors. The more the triarylphosphine is substituted by electron-withdrawing groups, the faster the reaction. The palladium(0) complex thus formed reacts with phenyl iodide via an oxidation addition, and this reaction is faster when the phosphine is more electron-rich.