Comparison of the Reactivity of Bis(μ-oxo)CuIICuIII and CuIIICuIII Species to Methane

Methane hydroxylation at the Binuclear copper site of particulate methane monooxygenase (AMMO) is studied by using density functional theory (DFT) calculations. The electronic and structural properties of the dinuclear copper species of bis(mu-oxo)(CuCuIII)-Cu-II and (CuCuIII)-Cu-III are discussed with respect to the C-H bond activation of methane. The bis(mu-oxo)(CuCuIII)-Cu-II species is highly reactive and considered to be an active species for the conversion of methane to methanol by pMMO, whereas the bis(mu-oxo)(CuCuIII)-Cu-III species is unable to react with methane as it is. If a Cu-O bond of the bis(mu-oxo)(CuCuIII)-Cu-III species is cleaved, the resultant (CuCuIII)-Cu-III species, in which only one oxo ligand bridges the two copper ions, can activate methane. However, its energetics for methane hydroxylation is less favorable than that by the bis(mu-oxo)(CuCuIII)-Cu-II species. The DFT calculations show that the bis(mu-oxo)(CuCuIII)-Cu-II species is more effective for the activation of methane than the bis(mu-oxo)(CuCuIII)-Cu-III species. The reactive bis(mu-oxo)(CuCuIII)-Cu-II species can be created either from the electron injection to the bis(mu-oxo)(CuCuIII)-Cu-III species or from the O-O bond cleavage in the mu-eta(1):eta(2)-peroxoCu(I)Cu(II) species.