Catalytic Performance of a Dicopper-Oxo Complex for Methane Hydroxylation.

A dicopper(II) complex, [Cu2(μ-OH)(6-hpa)]3+, where 6-hpa is 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane, generates an oxyl radical of CuIIO• and catalyzes the selective hydroxylation of benzene to phenol. From the structural similarity to methane activation catalysts (e.g., bare CuO+ ion, Cu-ZSM-5, and particulate methane monooxygenase), it is expected to catalyze methane hydroxylation. The catalytic performance for the hydroxylation of methane to methanol by this dicopper complex is investigated by using density functional theory (DFT) calculations. The whole reaction of the methane conversion involves two steps without radical species: (1) C-H bond dissociation of methane by the CuIIO• moiety and (2) C-O bond formation with methyl migration. In the first step, the activation barrier is calculated to be 10.2 kcal/mol, which is low enough for reactions taking place under normal conditions. The activation barrier by the other CuIIO2• moiety is higher than that by the CuIIO• moiety, which should work to turn the next catalytic cycle. DFT calculations show that the dicopper complex has a precondition to hydroxylate methane to methanol. Experimental verification is required to look in detail at the reactivity of this dicopper complex.