Gold(I) Catalysis in cross-coupling reactions
Gold-catalysed cross coupling chemistry is an active field of research that has led to some controversy. Although several cross coupling reactions based on gold have been developed, reactions proceeding under homogeneous conditions via the oxidative addition of Csp2-X electrophiles to gold(I) are still unknown.
Neutral Au(I) complexes of type [AuXL] (X = weakly coordinating anionic ligand) or cationic complexes [AuLL’]X (L’ = weakly coordinating ligand) are active catalysts in a wide range of reactions that involve the selective electrophilic activation of alkynes, allenes, or alkenes, which are characterized by the invariance of the oxidation state of the metal throughout the catalytic processes (1). This is in contrast to that generally observed in well-known cross-coupling reactions catalysed by palladium, which occur through Pd(0)/Pd(II) catalytic cycles (2, 3), as well in processes that involve C-H functionalization of aromatic substrates (4, 5).
Under homogeneous conditions, it was proposed that the Sonogashira (6, 7) and Suzuki coupling reactions (8, 9) are catalysed by Au(I) complexes via the d (10) to d (8) redox pathway characteristic of palladium-catalysed processes (10, 11). It was argued that in this context Au(I) was acting like Pd(0), since both share the same d (10) configuration (7, 9). Thus, for example, the Sonogashira coupling of iodobenzene and ethyl p-iodobenzoate with simple terminal alkynes was reported to proceed with [AuCl(PPh3)] or comp ...