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 similar to C)(2)Pd-IV(O2CR)(2) (N similar to C = a rigid cyclometalated ligand; O2CR = carboxylate) by reaction of (N similar to C)(2)Pd-II with Phl(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 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.