Mechanistic Investigation into the Gold-Catalyzed Decarboxylative Cross-Coupling of Iodoarenes

While
many gold-catalyzed reactions have been thoroughly developed,
most are not thought to involve redox events at gold. In contrast,
recent advances have demonstrated the feasibility of redox gold catalysis.
This report describes a detailed mechanistic investigation of the
gold-catalyzed decarboxylative cross-coupling, which likely proceeds
via a high-valent Au­(I/III) pathway. This investigation includes a
kinetic analysis, stoichiometric experiments with Au­(III) complexes,
and density functional theory calculations. These data support a turnover-limiting
oxidative addition to form a Au­(III) aryl complex, with an off-cycle
resting state. The dominant pathway appears to proceed through a silver-mediated
decarboxylation with a subsequent Ag­(I) to Au­(III) transmetalation.
These data provide some rationale for the significant counterion effects
between SbF6– and NTf2–.