Detailed Study of C−O and C−C Bond-Forming Reductive Elimination from Stable C2N2O2−Ligated Palladium(IV) Complexes

This paper describes the synthesis of a series of PdIV complexes of general structure (N∼C)2PdIV(O2CR)2 (N∼C = a rigid cyclometalated ligand; O2CR = carboxylate) by reaction of (N∼C)2PdII with PhI(O2CR)2. The majority of these complexes undergo clean C−O bond-forming reductive elimination, and the mechanism of this process has been investigated. A variety of experiments, including Hammett plots, Eyring analysis, crossover studies, and investigations of the influence of solvent and additives, suggest that C−O bond-forming reductive elimination proceeds via initial carboxylate dissociation followed by C−O coupling from a 5-coordinate cationic PdIV intermediate. The mechanism of competing C−C bond-forming reductive elimination from these complexes has also been investigated and is proposed to involve direct reductive elimination from the octahedral PdIV centers.