Rate and Mechanism of Oxidative Addition of Aryl Triflates to Zerovalent Palladium Complexes. Evidence for the Formation of Cationic (σ-Aryl)palladium Complexes

Abstract

The rate of oxidative addition of Pd0(PPh3)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(PPh3)2+ with CF3SO3- as the counteranion. The oxidative addition is faster in the presence of added chloride and affords neutral complexes trans-Ar-PdX(PPh3)2. The aryl triflates are found to be less reactive with Pd0(PPh3)4 than aryl iodides but slightly more reactive than aryl bromides. © 1995, American Chemical Society. All rights reserved.