RATE AND MECHANISM OF OXIDATIVE ADDITION OF ARYL TRIFLATES TO ZEROVALENT PALLADIUM COMPLEXES - EVIDENCE FOR THE FORMATION OF CATIONIC (SIGMA-ARYL)PALLADIUM COMPLEXES

The rate of oxidative addition of Pd-0(PPh(3))(4) to aryl triflates is monitored by amperometry and conductivity measurements in DMF. The kinetics follow a Hammett correlation, the oxidative addition being faster when the aryl group is substituted with an electron-withdrawing group. This reaction proceeds in the absence of deliberately added halides, to afford a unique, well-defined, stable arylpalladium complex that has been characterized for the first time, by conductivity measurements and mass and IR spectroscopies, as a cationic complex Ar-Pd(PPh(3))(2)(+) with CF3SO3- as the counteranion. The oxidative addition is faster in the presence of added chloride and affords neutral complexes trans-Ar-PdX(PPh(3))(2). The aryl triflates are found to be less reactive with Pd-0(PPh(3))(4) than aryl iodides but slightly more reactive than aryl bromides.