Novel Coinage Metal-NHCs Complexes Derived from Triazoles, Imidazoles and Related Chelating Systems

Coinage metal-NHCs are widely studied for their intriguing structural properties and numerous applications [1]. Ag(I)-NHCs are the most studied among coinage metal-NHCs due to their easy preparation via the Ag2O route and because they are sources of other metal-NHCs through transmetallation. In addition, their diverse properties in bonding and structure and potential applications in medicine, nanomaterials, liquid crystals, and organic catalysis also contribute to the attraction of Ag(I)-NHCs. Recently we have explored the synthesis of pincer scorpionate type carbene ligands such as the bis(4-benzyl-1,2,4-triazol-4-ium-1-yl)dihydroborate, {[H2B(BnTzH)2]Br}, and related carbene-silver(I) and gold(I) complexes {Ag2[H2B(BnTz)2]2} and {Au2[H2B(BnTz)2]2}[2]. We have also reported trimetallic carbene complexes of general formula {Ag3[HB(RIm)3]2}Br (R = Bn, Mes and tBu), which were successfully employed in the synthesis of related gold(I) complexes by transmetallation; the silver complexes also proved to be active catalysts in the Sonogashira reaction [3]. Analogous trinuclear copper(I) complexes with triscarbene ligands have been synthesized and proved to be efficient catalysts of Ullmann-type reactions as well as of the Sonogashira reaction [4]. Moreover we have also reported the synthesis of hydrophilic bimetallic complexes of general formula {Na2[H2C(TzR)2]2Ag2} and {Na2[H2C(ImR)2]2Ag2}(R = PrSO3 or EtCOO) [5] by treatment, in degassed water solution, of the triazolium or imidazolium species with Ag2O. As an extension of this research field, we have developed the chemistry of some new water soluble zwitterionic mono-NHC ligands, where imidazolium rings have two alkylsulfonate or alkylcarboxylate side arms. Here we present the synthesis and characterization of these novel hydrophilic carbene ligand precursors {HIm4R,5R} (R = PrSO3 or CH2COOEt) and the related silver(I) carbene complexes of general formula {(Im4R,5R)AgCl}. Gold(I) and Copper(I) complexes have succesfully prepared by transmetallation reactions.