Detailed Study of C−O and C−C Bond-Forming Reductive Elimination from Stable C<sub>2</sub>N<sub>2</sub>O<sub>2</sub>−Ligated Palladium(IV) Complexes
2009-08-12T00:00:00Z (GMT) by
This paper describes the synthesis of a series of Pd<sup>IV</sup> complexes of general structure (N∼C)<sub>2</sub>Pd<sup>IV</sup>(O<sub>2</sub>CR)<sub>2</sub> (N∼C = a rigid cyclometalated ligand; O<sub>2</sub>CR = carboxylate) by reaction of (N∼C)<sub>2</sub>Pd<sup>II</sup> with PhI(O<sub>2</sub>CR)<sub>2</sub>. 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<sup>IV</sup> 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<sup>IV</sup> centers.