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

Abstract

Methane hydroxylation at the dinuclear copper site of particulate methane monooxygenase (pMMO) is studied by using density functional theory (DFT) calculations. The electronic and structural properties of the dinuclear copper species of bis(μ-oxo)Cu^IICu^III and Cu^IIICu^III are discussed with respect to the C−H bond activation of methane. The bis(μ-oxo)Cu^IICu^III species is highly reactive and considered to be an active species for the conversion of methane to methanol by pMMO, whereas the bis(μ-oxo)Cu^IIICu^III species is unable to react with methane as it is. If a Cu−O bond of the bis(μ-oxo)Cu^IIICu^III species is cleaved, the resultant Cu^IIICu^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(μ-oxo)Cu^IICu^III species. The DFT calculations show that the bis(μ-oxo)Cu^IICu^III species is more effective for the activation of methane than the bis(μ-oxo)Cu^IIICu^III species. The reactive bis(μ-oxo)Cu^IICu^III species can be created either from the electron injection to the bis(μ-oxo)Cu^IIICu^III species or from the O−O bond cleavage in the μ-η¹:η²-peroxoCu^ICu^II species.