Synthesis of a library of bifunctional N-heterocyclic carbene ligand precursors with hydrogen bond donor subunits

Bifunctional N-heterocyclic carbenes (NHCs) with additional hydrogen bond donor groups in the backbone are important organocatalysts and ligands for transition metal complexes. Herein, we report a straightforward synthetic approach to a library of bifunctional imidazolium salts, precursors for the respective NHCs with amidine, squaramide and (thio)urea moieties as hydrogen bond donors. The preparation of bifunctional palladium(II) and copper(I) NHC complexes and their application in catalysis is presented.