Quantum chemical study of the catalytic activation of methane by copper oxide and copper hydroxide cations

The activation of methane and its subsequent conversion into more valuable feedstocks under ambient conditions are regarded as one of the major challenges in contemporary catalysis, due to its thermodynamically strong and kinetically inert C-H bond. Several enzymes and synthetic bioinorganic systems perform the activation of C-H bonds in methane and small hydrocarbons, mediated by transition metal mononuclear centers. Among them, monocopper cores and, in particular, CuO(+) and CuOH(+) have been suggested as efficient catalytic centers; this activity has not been experimentally proven until very recently, mainly due to the difficulty to produce sufficient amounts of active species to demonstrate the bond activation processes. The theoretical study presented here provides a thorough quantum chemical description of the activity of both species, together with molecular level insight into the elementary steps of the experimentally observed reactions. Post-HF (CCSD(T), CASPT2) and Density Functional Theory (DFT) methods have been used to unravel detailed electronic and mechanistic aspects of the reaction paths. Our study reveals the decisive role of the oxygen-centered radical in the reactivity of both species, and the improvement of the reactivity as a result of the protonation of the active species.