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

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 other ligand systems.