2020 Volume 75 Pages 57-65
Quantum chemical studies on methane C–H bond activation and hydroxylation by methane monooxygenase (iron and copper enzyme species), related metal-oxo species such as FeO+, metal-exchanged zeolites, and metal-oxide surfaces are reviewed. The tetrahedral Td structure of methane should be deformed into a C3v or D2d structure at coordinatively unsaturated metal-oxo species. Mechanistic aspects about methane hydroxylation by the bare transition-metal oxide ions such as FeO+, NiO+, and CuO+ are analyzed in detail by using density functional theory calculations. An important feature in the reaction is the spin crossover between the high-spin and low-spin potential energy surfaces in particular in the C–H activation process, the energy barrier of which is significantly decreased by the spin inversion. These mechanistic insights are reasonably extended to Fe, Co, Ni, and Cuexchanged zeolites and IrO2 and β-PtO2 (110) surfaces.
