Theoretical structural and electronic analyses with emphasis on the reactivity of iron oxide prototypes in methane c-h bond activation

Abstract

In the present work, a detailed theoretical investigation using B3LYP, CCSD(T) and ZORA-B3LYP calculations has been performed in order to investigate activation processes of methane C–H bond by iron oxide prototype series: FeOmn+ (m = 1, 2; n = 0, 1, 2). The main results indicate that, in accordance with previous experimental findings, only FeO+ monoxide is kinetically and thermodynamically feasible through the hydrogen abstraction mechanism, with an already known pathway described as “oxidative hydrogen migration”. The overall results indicate better thermodynamic and kinetic conditions for all iron monoxides, in relation to iron dioxides. Based on the energy values and the structural parameters, the 4-center abstraction mechanism should be thermodynamically more favorable in relation to the direct abstraction mechanism, due to the lack of Fe–C interaction for the direct abstraction mechanism. The AIM calculations indicate a larger ionic character for the Fe–O+ chemical bond, whereas a mixed participation, relative to ionic and covalent character, was found in chemical bonds of the remaining iron oxides.