Intimate relationship between C-I reductive elimination, aryl scrambling and isomerization processes in Au(III) complexes.

Abstract

19F NMR monitoring shows that heating trans-[AuIIIRf2I2]- 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 AuIII-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.