Reductive Eliminations from Diarylpalladium(II) Complexes - A Combined Experimental and Computational Investigation

We have investigated the diverse mechanisms for the reductive elimination of biaryl compounds from diarylpalladium(II) complexes with a tetradentate ligand in a combined experimental and computational study. At least four distinct chemical triggers with specific regioselectivity exist for this elimination. Heating of the complexes in inert solvents (e.g., para-xylene) reveals their relatively high thermal stability as reflected by a very high barrier for a unimolecular reductive elimination. In contrast, electron-donor ligands like triphenylphosphine induce a facile reductive elimination via twofold associative ligand exchange as confirmed by kinetic experiments which are in excellent agreement with the computational results. Oxidants, such as H2O2, can trigger an oxidatively induced reductive elimination via palladium(IV) intermediates at room temperature. Rearrangement of the diarylpalladium(II) complexes can occur in organic acids, facilitating a reductive elimination with distinct regiochemical outcome.