Intimate relationship between C–I reductive elimination, aryl scrambling and isomerization processes in Au(iii) complexes

Abstract

¹⁹F NMR monitoring shows that heating trans-[Au^IIIRf₂I₂]⁻ solutions (Rf = C₆F₃Cl₂-3,5) leads to formation of cis-[AuRf₂I₂]⁻, [AuRf₃I]⁻ and [AuRfI₃]⁻via kinetic competition between isomerization and Rf/I scrambling. The system evolution is driven by the easy Rf–I reductive elimination from [AuRfI₃]⁻ (forming also [AuI₂]⁻), which is faster than any of the Rf–Rf couplings from the coexisting species, hindering the commonly desired and thermodynamically preferred C–C coupling. A kinetic model where I⁻ dissociation triggers both isomerization and transmetalation steps is proposed, which fits well the experimental data. DFT calculations support that the lower bond strength of Au^III–I compared to other halides produces a pathway switch that makes C–I coupling kinetically preferred. Consequently, it is better avoided in reactions looking for C–C coupling.