文摘
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鈥?dimethyl-3,3鈥?methylenediimidazolin-2,2鈥?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鈥揑I鈥揑V) pathway without formation of palladium(0). A second redox cycle via a bromide鈥揵romine 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.