THEORETICAL STUDY ON METHANE HYDROXYLATION BY MIMIC METHANE MONOOXYGENASE WITH bis(μ-OXO)DIMANGANESE CORE

The reaction mechanism for methane hydroxylation catalyzed by mimic methane monooxygenase (MMO) with bis(mu-oxo) dimanganese core has been investigated on the septet and nonet potential energy surfaces by hybrid density functional method B3LYP. The key reactive compound Q of MMO was modeled by trans-(H2CNH)(COOH) Mn(mu-O)(2)(mu-HCOO)(2)Mn(H2CNH)(COOH). The ground state of Q is located on the septet state, which has a diamond-core structure with two Mn(IV) atoms. It is shown that the reaction proceeds via a radical-rebound mechanism, in which the step of C-H cleavage is the rate-determining step both in the gas phase and solution. Furthermore, the reaction may proceed more easily as the polarity of solution is larger. On the other hand, the kinetic isotope effects (KIEs) for H atom abstraction from methane are taken into account on the basis of transition state theory with Wigner tunneling corrections. The mimic MMO with bis(mu-oxo) dimanganese core might be an effective mimic catalyst for methane hydroxylation.