Synthesis of Silver Complexes with Chelating Bidentate N ‐Heterocyclic Ligands, their Application in Catalytic A ³ Coupling and as Antimicrobial Agents

We present a synthesis of novel silver complexes stabilized by bidentate ligands based on N-heterocyclic carbenes (NHC) linked with a bisamide linker. The ligand stabilizes the silver ion in a rare chelating mode. The synthesis of the complex depends on the equimolar ratio of the silver source and the ligand precursor. In case the excess of the silver source is used, the reaction leads to the formation of an unprecedented tetranuclear silver complex, stabilized by two equivalents of the ligand, where each of the silver atoms is coordinated by one NHC and one amide moiety. The silver complexes were applied as a catalyst in a multicomponent A(3) coupling and proved to be a very efficient catalyst. The reaction provided desired products in yields up to 96%, and the use of low catalytic loading, as low as 0.1 mol%, was possible without significantly compromising the effectivity of the reaction. Moreover, the complexes showed broad spectra of antimicrobial activity, with minimal inhibitory concentrations in the range of 1 to 31 mu g/ml against several Gram-positive and Gram-negative bacteria and fungi. Presented complexes represent synthetically challenging molecules, which show great applicability in catalysis and outstanding potential as antimicrobial agents.