Synthesis of AuI- and AuIII-Bis(NHC) Complexes: Ligand Influence on Oxidative Addition to AuI Species

The oxidation chemistry of a range of Au-I-bis(NHC) (NHC = N-heterocyclic carbene) complexes with hypervalent iodine(III) oxidants has been explored. Au-I-bis(NHC) precursors have been synthesised by treatment of the corresponding [Au(NHC) Cl] derivatives with imidazol(idin) ium salts in the presence of K2CO3. The reactivity of the Au-I complexes towards PhICl2 has revealed an influence of the nature of the NHC ligands present in the complex on the outcome of the oxidation reaction: small and more strongly electron-donating NHC ligands favoured the formation of a Au-III species. On the basis of these results, a AuI complex bearing two 1-butyl-3-methylimidazol-2-ylidene (BMIM) ligands has been synthesised. This complex reacted with PhICl2 and also - for the first time in Au-NHC systems - with PhI(OAc)(2) and PhI(OAcF)(2) (OAcF = trifluoroacetate), affording stable Au-III-(NHC)(2) complexes bearing acetate ligands.