The Effect of the cis-donor in pincer ligands on hydrogenolysis of Pd-OH: A DFT study

The hydrogenolysis of pincer palladium hydroxides was examined using DFT methods. Two possible mechanistic pathways - oxidative addition/reductive elimination and internal electrophilic substitution - were considered for each of five different PdOH complexes that varied in the identity of the donor atoms of the tridentate pincer ligand cis to the hydroxide. For each of the complexes examined, the internal electrophilic substitution pathway was found to be significantly lower in energy than an oxidative addition/reductive elimination pathway. For a PdOH complex bearing a hemilabile pincer ligand, addition of hydrogen resulted in dissociation of the labile arm of the ligand and hydrogenation of the Pd-OH bond to yield a hydride and bound water. This result is consistent with experimental observations for a similar system.