DFT studies for activation of C–H bond in methane by gas-phase (n = 1 − 3)

The mechanism of Rh n + (n = 1 − 3) catalyzed methane activation has been investigated theoretically. All structures on the potential energy surfaces are optimized at the density functional theory (DFT) level, using the empirically parametrized hybrid functional B3LYP. Relative energies are calculated both at the B3LYP level, using large basis sets RECP+6-311+G**. The B3LYP energies of important species on the potential energy surfaces were compared to CCSD(T) single-point energy calculations. All the three systems are two-state reactivity. For Rh+ and Rh 2 + with methane, the product are metal–carbene and hydrogen and the two reaction endothermic by 28.05 kcal/mol and 1.84 kcal/mol, respectively. While for Rh 3 + with methane, the product is a hydrogen-bridge bond molecule and the reaction exothermic by 55.30 kcal/mol so it can be performed spontaneously at room temperature. With the increase of the metal atom numbers n, the catalytic activity of Rh n + towards methane C–H bonds rise sharply, then the Rh 3 + is likely to be a better mediator than Rh+ and Rh 2 + for the activation of methane.