Methane CH Activation by Palladium Complexes with Chelating Bis(NHC) Ligands: A DFT Study

Abstract

Palladium bis(NHC) complexes are able to catalytically activate and to promote the oxidation of methane. The conversion of methane to methyl trifluoroacetate catalyzed by the palladium bis(NHC) complex dibromido(1,1′-dimethyl-3,3′-methylenediimidazolin-2,2′-ylidene)palladium(II) was investigated by a DFT study on the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level of theory in combination with solvent and dispersion corrections. According to the DFT calculations the reaction proceeds by a palladium(II–II–IV) pathway without formation of palladium(0). A second redox cycle via a bromide–bromine shuttle, which mediates the oxidation of palladium(II) to palladium(IV), is proposed. Although CH activation by palladium(0) is predicted to be a very facile process, this pathway is very unlikely, due to the extraordinarily high reaction barrier for reductive elimination. CH activation by palladium(IV) has been investigated as well and might be a viable pathway comparable in energy to an activation by palladium(II) with o...