Mechanistic pathways for oxidative addition of aryl halides to palladium(0) complexes: A DFT study

Density functional calculations on the title reaction are reported using the gradient-corrected BP86 functional with a standard basis (LANL2DZ) and a larger basis of triple-zeta quality (EXT). Several reaction pathways for oxidative addition of aryl halides to Pd(0) species have been explored, particularly for the reaction of phenyl iodide with Pd(PMe3)(2)OAc-. We confirm that three-coordinate anionic Pd(0) species as proposed by Amatore and Jutand are stable intermediates and can serve as starting points for catalytic reactions. However, we did not find any evidence for the existence of the proposed five-coordinate Pd(II) complexes. Instead, stable four-coordinate intermediates were found, in which the aryl halides coordinate linearly to the palladium via the halide atom, with no significant energy barrier. With these adducts as a starting point, two energetically feasible pathways for the actual C-I cleavage reactions have been identified, which both lead to cis-configured Pd(II) complexes. The subsequent cis-trans isomerization requires significantly more activation than all preceding steps during the oxidative addition. The density functional calculations provide a plausible mechanism for the title reaction that is consistent with the available experimental facts.