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.