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(L-1)(L-2)](+) (L-1 = NHC, L-2 = DIC; L-1 = NHC, L-2 = NAC; L-1 = NAC, L-2 = DIC; L-1 = L-2 = NAC; NHC = N-heterocyclic carbene; NAC = N-acyclic carbene, DIC = 2,6-dimethylphenylisocyanide). The complexes of type [Au(NHC)(DIC)](+) react with a slight excess of Br-2 yielding the corresponding gold(III) species [Au(NHC)(DIC)Br-2](+). 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)Br-2](+) and [Au(NAC)(2)Br-2](+) are stable in solution whereas the complex [Au(NAC)(DIC)Br-2](+) 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 Br-2 followed by a slow rearrangement of the latter to yield the final gold(III) derivatives. (C) 2012 Elsevier B.V. All rights reserved.