DFT studies of thermal activation of methane by [Ru(H)(OH)]+

The dehydrogenation reaction mechanism of methane catalyzed by ligated transition-metal [Ru(H)(OH)]+ has been investigated theoretically. Activation of methane by [Ru(H)(OH)]+ complex is proposed to proceed in a one-step manner via one transition state: [Ru(H)(OH)]+ + CH4 → [Ru(H)(OH)(CH4)]+ → [TS] → [Ru(CH3)(OH)]+H2 → [Ru(CH3)(OH)]+ + H2. Both high-spin and low-spin potential energy surfaces are characterized in detail. The DFT calculations indicate the reactant and the product prefer to have a high-spin electron configuration for their metal center but a low-spin configuration for the metal center in its transition state. Consequently, a crossing between high-spin and low-spin potential energy surfaces takes place at both the entrance and the exit channels of the reaction. The [Ru(H)(OH)]+ complex is expected from the general energy profile of the reaction pathway to efficiently convert methane to methyl. Therefore, it is likely to be an excellent mediator for the activity of methane. The overall hydrogenation reaction catalyzed by the cationic [Ru(H)(OH)]+ is exothermic.