Reactivity of cationic gold(I) carbene complexes toward oxidative addition of bromine

We have synthesized and characterized several cationic complexes of gold(I) of the type [Au(L1)(L2)]+ (L1 = NHC, L2 = DIC; L1 = NHC, L2 = NAC; L1 = NAC, L2 = DIC; L1 = L2 = NAC; NHC = N-heterocyclic carbene; NAC = N-acyclic carbene, DIC = 2,6-dimethylphenylisocyanide). mplexes of type [Au(NHC)(DIC)]+ react with a slight excess of Br2 yielding the corresponding gold(III) species [Au(NHC)(DIC)Br2]+. The latter decompose with a rate that is modulated by the nature of the ancillary ligands. The oxidative addition of Br2 to complexes of the type [Au(NHC)(NAC)]+ and [Au(L)(NAC)]+ (L = DIC, NAC) has been also carried out and the ensuing gold(III) derivatives [Au(NHC)(NAC)Br2]+ and [Au(NAC)2Br2]+ are stable in solution whereas the complex [Au(NAC)(DIC)Br2]+ decomposes. Finally, on the basis of kinetic studies we have proposed propose a mechanism involving a fast pre-equilibrium forming an adduct containing the starting complex and Br2 followed by a slow rearrangement of the latter to yield the final gold(III) derivatives.