Chemoselectivity in the Reductive Elimination from High Oxidation State Palladium Complexes – Scrambling Mechanism Uncovered

With the objective to increase understanding of the factors that control selectivities in high oxidation state palladium chemistry, we examined the chemoselectivity in the reductive elimination of a dinuclear Pd(III) complex bearing different apical ligands. Experimental, computational, and spectroscopic studies were applied to understand the product selectivity derived from the mixed Cl/OAc dinuclear Pd(III) complex. Analogous species were previously implicated in oxidative C-H functionalizations. The observed experimental chemoselectivity for ArCl was found to be inconsistent with the direct reductive elimination of the mixed Cl/OAc containing Pd(III) dimer. The latter complex is therefore not the key intermediate that ultimately determines the product selectivity. Our spectroscopic and computational studies of the stoichiometric reactivity suggest that the mixed dinuclear Pd(III) complex scrambles readily to give the two Pd(III) homodimers [AcO-Pd(III)-Pd(III)-OAc and Cl-Pd(III)-Pd(III)-Cl], of which the dichlorinated Pd(III) dimer ultimately gives ArCl upon reductive elimination.