Mechanism for Carbon−Oxygen Bond-Forming Reductive Elimination from Palladium(IV) Complexes

Abstract

Carbon−oxygen bond-forming reductive elimination from transient Pd(IV) aryl/acetate complexes was recently implicated as the product release step in Pd(II)-catalyzed arene oxygenation reactions. The mechanistic details of C−O bond formation from these Pd(IV) intermediates remain elusive and, therefore, are subjected to a systematic theoretical investigation in the present study. Three proposed mechanisms are examined including (A) pre-equilibrium dissociation of a benzoate ligand followed by reductive elimination from the resulting five-coordinate Pd(IV); (B) direct reductive elimination from the six-coordinate Pd(IV); and (C) dissociation of a pyridyl arm of one cyclometalated ligand followed by internal coupling. Through density functional theory calculations it is suggested that mechanism B is favored over the other two mechanisms. This conclusion is supported by the success of the theoretical model based on mechanism B to reproduce the experimental activation free energy barriers. The same theoretical...