Strong spin-orbit coupling facilitates C-H activation in the reactions of Os⁺ with CH₃F: Theoretical investigations

The relativistic effects are essential for a complete understanding of the reactions involving heavy transition metal cations with hydrocarbons. Despite this, spin-orbit coupling (SOC) along the reaction pathway is rarely considered. In this work, we demonstrate an unusual SOC on the chemical reactivity of a reaction of Os⁺ with methyl fluoride (CH₃F) using density functional theory (DFT), high-level ab initio, and spin-orbit multiconfigurational ab initio methods. With the inclusion of the SO effect in the relevant potential energy surfaces (PESs), C-H bond activation by an Os ⁺ cation occurs readily via almost barrierless (about 2 kcal/mol) PESs of the SO coupled ground state. In contrast, a substantial reaction barrier was observed for C-F bond activation. The calculated results are in line with recent systematic experimental findings for reactions of transition metal cations with CH₃F. These results show that the SO effect can facilitate specific bond activation in chemical reactions associated with catalytic transition metal cations.