Carbon-Atom Exchange between [MC₂]⁺ (M = Os and Ir) and Methane: on the Thermodynamic and Dynamic Aspects

Gas-phase reactions of [OsC₂]⁺ and [IrC₂]⁺ with methane at ambient temperature have been studied using quadrupole-ion trap mass spectrometry combined with quantum chemical calculations. Both [OsC₂]⁺ and [IrC₂]⁺ undergo carbon-atom exchange reactions with methane. The associated mechanisms for the two systems are found to be similar. The differences in the rates of carbon isotope exchange reactions of methane with [MC₂]⁺ (M = Os and Ir) are explained by several factors like the energy barrier for the initial H₃C-H bond breaking processes, the molecular dynamics, orbital interactions, and the H-binding energies of the pivotal steps. Besides, the number of participating valence orbitals might be one of the keys to regulate the rate in the key step. The present findings may provide useful ideas and inspiration for designing similar processes.