Oxidative Addition of CH₃I to Au^– in the Gas Phase

Abstract

Reaction of the atomic gold anion (Au^–) with CH₃I under high-pressure helium gas affords the adduct AuCH₃I^–. Photoelectron spectroscopy and density functional theory calculations reveal that in the AuCH₃I^– structure the I and CH₃ fragments of CH₃I are bonded to Au in a linear configuration, which can be viewed as an oxidative addition product. Theoretical studies indicate that oxidative addition proceeds in two steps: nucleophilic attack of Au^– on CH₃I, followed by migration of the leaving I^– to Au. This mechanism is supported by the formation of an ion-neutral complex, [Au^–···<i>t</i>-C₄H₉I], in the reaction of Au^– with <i>t</i>-C₄H₉I because of the activation barrier along the S_N2 pathway resulting from steric effects. Theoretical studies are conducted for the formation mechanism of AuI₂^–, which is observed as a major product. From the thermodynamic and kinetic viewpoints, we propose that AuI₂^– is formed via sequential oxidative addition of two CH₃I molecules to Au^–, followed by reductive elimination of C₂H₆. The results suggest that Au^– acts as a nucleophile to activate C­(sp³)–I bond of CH₃I and induces the C–C coupling reaction of CH₃I