Preparation and application of N-heterocyclic carbene complexes of Ag(I)

The current status (up to 31 July 2006) of Ag(I)–NHCs (NHC = N-heterocyclic carbene) is presented with various NHC systems ranging from five membered to seven membered rings, including imidazolium, benzimidazolium, imidazolinium, triazolium, pyrimidinium, pyrazolium, seven-membered amidinium, and naphthimidazolium moieties, etc. It is our intention to provide an updated, and comprehensive review on the subject of Ag(I)–NHCs, which may further accelerate work on this topic. The main features of this review are to focus on (a) the ease and limitations in the synthesis of Ag(I)–NHCs, (b) the parameters influencing the solid state structures of Ag(I)–NHCs, and (c) the efficacy of Ag(I)–NHCs in transmetallation reactions. In particular, we would like to evaluate the widely adopted Ag2O technique in the preparation of Ag(I)–NHCs and the subsequent NHC transfer reactions, to afford other metal–NHCs.