SILVER(I) N-HETEROCYCLIC CARBENES

Abstract

This review presents a detailed overview on the synthesis of Ag^I–NHCs and their role as carbene transferring agents as an easy access to various important transition metal-NHC complexes. The nature of NHC ligands, counter anions and solvents are recognized as key factors in the determination of Ag^I–NHCs and their derivatives. The lack of Ag–C_carbene bond coupling in various Ag^I–NHCs suggests the lability of Ag–C_carbene bond, which appears to be an appropriate reason in the transfer of carbene. It has been suggested by various authors that carbene transfer from Ag^I–NHCs is particularly useful when the carbene N-functionality contains base sensitive functional groups or acidic hydrogen. Importantly Ag^I–NHCs are less air sensitive than the free carbenes and are easy to synthesize. These properties allow them to be handled easily in further operations. Apart from the carbene transferring property, the nature of Ag–C_carbene bond, the influence of NHC on the Ag…Ag contacts and the molecular aggregation to generate novel structural motifs and supramolecular assemblies have also been emphasized.

We thank H.M.J. Wang, K.M. Lee, C.K. Lee and J.C.C. Chen for their excellent contribution in the exploration of Ag^I–NHCs during their PhD studies. We also acknowledge the support of National Science Council of Taiwan for providing the research grants.