A New 2,1,3-Benzothiadiazole-Fused N-Heterocyclic Carbene and Its Metal Complexes

In the last few decades, N-heterocyclic carbenes (NHCs) have emerged as a powerful class of carbon-based ligands. Owing to their unique electronic and steric properties, they have been incorporated in a large variety of catalytically active metal complexes. One of the strategies that have been used to modify the ligand properties of NHCs is annulation with different carbo- and heterocyclic groups. It has been shown that annulation in the 4-5 position of the imidazole ring significantly influences the stability and the σ-donor/π- acceptor properties of the carbene species, and this may be used as a versatile tool for the fine-tuning of their electronic properties. Following a brief review of NHC history, the synthesis and structural characterization of a new class of fused N-heterocyclic carbene ligands with a rigid bidentate architecture will be reported. Complexes of type [(NHC)M(COD)Cl], [(NHC)M(CO)2Cl] (M = Rh and Ir) and [(NHC)MCl] (M = Au) were prepared and characterized using spectroscopic and crystallographic methods. The results of preliminary catalytic studies using these new complexes is also reported