Dioxygen insertion into the gold(I)-hydride bond: spin orbit coupling effects in the spotlight for oxidative addition

O-2 insertion into a Au(I)-H bond occurs through an oxidative addition/recombination mechanism, showing peculiar differences with respect to Pd(II)-H, for which O-2 insertion takes place through a hydrogen abstraction mechanism in the triplet potential energy surface with a pure spin transition state. We demonstrate that the spin-forbidden Au(I)- hydride O-2 insertion reaction can only be described accurately by inclusion of spin orbit coupling (SOC) effects. We further find that a new mechanism involving two O-2 molecules is also feasible, and this result, together with the unexpectedly high experimental entropic activation parameter, suggests the possibility that a third species could be involved in the rate determining step of the reaction. Finally, we show that the O-2 oxidative addition into a Au(I)- alkyl (CH3) bond also occurs but the following recombination process using O-2 is unfeasible and the metastable intermediate Au(III) species will revert to reactants, thus accounting for the experimental inertness of Au-alkyl complexes toward oxygen, as frequently observed in catalytic applications. We believe that this study can pave the way for further theoretical and experimental investigations in the field of Au(I)/Au(III) oxidation reactions, including ligand, additive and solvent effects.