Homolytic X-H Bond Cleavage at a Gold(III) Hydroxide: Insights into One-Electron Events at Gold.

C(sp 3 )-H and O-H bond breaking steps in the oxidation of 1,4-cyclohexadiene and phenol by a Au(III)-OH complex were studied computationally. The analysis reveals that for both types of bonds the initial X-H cleavage step proceeds via concerted proton coupled electron transfer (cPCET), reflecting electron transfer from the substrate directly to the Au(III) centre and proton transfer to the Au-bound oxygen. This mechanistic picture is distinct from the analogous formal Cu(III)-OH complexes studied by the Tolman group (J. Am. Chem. Soc. 2019, 141, 17236-17244), which proceed via hydrogen atom transfer (HAT) for C-H bonds and cPCET for O-H bonds. Hence, care should be taken when transferring concepts between Cu-OH and Au-OH species. Furthermore, the ability of Au-OH complexes to perform cPCET suggests further possibilities for one-electron chemistry at the Au centre, for which only limited examples exist.