DFT predictions for hydrogen atom transfer at the [FeO]²⁺ group: A distinct activity of the oxyl state Fe^III-O^•

Iron (hydr)oxo complexes are becoming major subject of investigations in the field of hydrocarbon partial oxidation for industrial applications. Most challenging goal is to design the oxidation of methane to methanol as effective as the natural one-step process realized by methane monooxygenase under mild conditions. Key intermediate of iron enzymes is commonly agreed to be the complex containing the [FeO]²⁺ group. One may suggest that the same group on iron hydroxides would perform the same or higher reactivity toward the H-abstraction as that in enzymes. This suggestion was proved to be true by the presented DFT predictions on the methane hydrogen abstraction process at terminal Fe-oxo group in model mono-, di- and tetramer iron hydroxide clusters. The most important result obtained is a distinct activity of the radicaloid oxyl state Fe^III-O^• as compared to ferryl state Fe^IV=O for the same [FeO]²⁺ group. If the oxyl state is ground for terminal Fe-oxo group in hydroxides, then it is more active than the same group in mono-iron enzymes complexes. Since the electron configuration of the [FeO]²⁺ group in various ligand environment is always a mixture of oxyl and ferryl contributions, the activity of the [FeO]²⁺ group is determined by the oxyl contribution.