Reaction pathway for the direct benzene hydroxylation by iron-ore species

The direct benzene hydroxylation by an iron-ore species is discussed from d ensity-functional-theory (DFT) calculations. The proposed reaction pathway is FeO+ + C6H6 --> OFe+(C6H6) --> [TS1] --> HO-Fe+-C6H5 --> [TS2] --> Fe+(C 6H5OH) --> Fe+ + C6H5OH, in which TS means transition state. This reaction is initiated by the formation of the reactant complex, OFe+(C6H6), exhibiti ng an eta(2)-C6H6 binding mode; benzene C-H bonds are activated on this com plex due to significant electron transfer from the benzene to the iron-oxo species. The reaction should proceed in a concerted manner, neither via the formation of radical species nor ionic intermediates. The reaction mechani sm is quite similar to the two-step concerted mechanism that we have propos ed originally for the direct methane hydroxylation by an iron-ore species. The quartet potential energy surface affords a low-cost reaction pathway fo r the benzene hydroxylation, spin inversion being unimportant in contrast t o the methane hydroxylation in which crossing between the sextet and quarte t potential energy surfaces plays an important role. We suggest that our tw o-step concerted mechanism should be widely applicable to hydrocarbon hydro xylations catalyzed by transition-metal oxides if coordinatively unsaturate d metal oxides are responsible for such important catalytic reactions.