Femtosecond Dynamics of the Methane - Methanol and Benzene - Phenol Conversions by an Iron - Oxo Species

Femtosecond dynamic behavior of the methane - methanol conversion by the bare iron - oxo complex (FeO⁺) is presented using the B3LYP density-functional-theory (DFT) method. We propose that the reaction pathway for the direct methane - methanol conversion is partitioned into the H atom abstraction via a four-centered transition state and the methyl migration via a three-centered transition state. It is demonstrated that both the H atom abstraction and the methyl migration occur in a concerted manner in a time scale of 100 fs. The concerted H atom abstraction and the direct H atom abstraction via a transition state with a linear C - H O(Fe) array are compared. The direct H atom abstraction of methane is predicted to occur in a time scale of 50 fs. Isotope effects on the concerted and the direct H(D) atom abstractions are also computed and analyzed in the FeO⁺/methane system. Predicted values of the kinetic isotope effect (k_H/k_D) for the H(D) atom abstraction of methane are 9 in the concerted mechanism and 16 in the direct abstraction mechanism at 300 K. Dynamics calculations are also carried out on the benzene - phenol conversion by the FeO⁺ complex. The general profile of the electronic process of the benzene - phenol conversion is identical to that of the methane - methanol conversion with respect to essential bonding characters. It is demonstrated that the concerted H atom abstraction and the phenyl migration require 200 and 100 fs to be completed, respectively, in the FeO⁺/benzene system.