Novel N-Heterocyclic Carbene Ligands and their Metal Complexes

N-heterocyclic carbenes (NHCs) have found robust development and were widely used as ubiquitous ligands for organometallic complexes in the past two decades. Besides the most popular Arduengo carbenes, i.e. imidazol-2-ylidene and its analogues, novel carbenes derived from N-heterocycles other than imidazole have lately attracted increasing attention. In this work, metal complexes with novel N-heterocyclic carbene ligands, such as imidazol-4/5-ylidene, pyridazin-4-ylidene, and N-metallated N-heterocyclic carbene have been synthesized and characterized. In addition, inspired by a recent discovery that a carbon atom was chelated by NHC ligands to form carbodicarbene, efforts to synthesize a novel indene-derived carbene, in which NHC ligands coordinate to carbon atoms adjacent to the carbenic carbon atom, have been carried out.