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

Abstract

O₂ 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 O₂ 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 O₂ insertion reaction can only be described accurately by inclusion of spin orbit coupling (SOC) effects. We further find that a new mechanism involving two O₂ 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 O₂ oxidative addition into a Au(I)–alkyl (CH₃) bond also occurs but the following recombination process using O₂ 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.