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 Pd(IV) complexes of general structure (N~C)(2)Pd(IV)(O(2)CR)(2) (N~C = a rigid cyclometalated ligand; O(2)CR = carboxylate) by reaction of (N~C)(2)Pd(II) with PhI(O(2)CR)(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 Pd(IV) 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 Pd(IV) centers.