Abstraction of the hydrogen atom of methane by iron-oxo species: The concerted reaction path is energetically more favorable

Two kinds of H-atom abstractions from methane by iron-oxo complexes with different charges are discussed from density functional theory calculations. A concerted H-atom abstraction via a four-centered transition state is shown to be energetically more favorable than a direct H-atom abstraction via a transition state with a linear C-H-O array. Iron-(IV)-oxo complexes appear to be the most effective for the cleavage of the C-H bond of alkanes in the concerted mechanism, which is rationalized from qualitative orbital interaction analyses. The results of this paper support the establishment of the two-step concerted mechanism that we have proposed for alkane hydroxylations by iron-oxo species. The proposed reaction mechanism may have relevance to our understanding of some catalytic and enzymatic processes concerning alkane hydroxylations if coordinatively unsaturated transition-metal oxides are responsible for such important chemical reactions.