Synthesis of AuI- and AuIII-bis(NHC) complexes: ligand influence on oxidative addition to AuI species

Abstract

The oxidation chemistry of a range of AuI-bis(NHC) (NHC = N-heterocyclic carbene) complexes with hypervalent iodine(III) oxidants has been explored. AuI-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 AuI 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 AuIII 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 AuIII-(NHC)2 complexes bearing acetate ligands.