Bipyridyl Functionalized NHC-Sulfenyl, Selenenyl Cations; Potential Species for Alkylation Reactions and Ligands in Copper(I) Catalysis.

Abstract

Reactions of bipyridyl-functionalized imidazole-thiones and selones with MeX (X = I, OTf) afforded sulfenyl and selenenyl cations [(NNC)EMe]X (2/3, E = S, Se). Further reactions of these main-group cations with [Cu(CH3CN)4]BF4, Cu(OTf) furnished dicationic [{Cu(µ-I)(NNC)EMe}2][Y]2 (5/6, Y = BF4, OTf) and tricationic copper(I) complexes [Cu{(NNC)EMe}2](OTf)2BF4 (7a/7b) when  employed [(NNC)EMe]I and [(NNC)EMe]OTf respectively. All these cationic complexes were characterized by various spectroscopic techniques, including X-ray diffraction analysis. The solid-state structures revealed novel bonding modes of the cations. The cationic nature of new complexes was analyzed by the 77Se NMR spectroscopy, which indicated different electronic environments around the selenium centers. The cations [(NNC)EMe]X (X= I, OTf), and (NNC)SMe bearing copper complex [{Cu(µ-I)(NNC)EMe}2][Y]2 proved as potential candidates for alkylation of various Lewis bases and as molecular catalyst in aldehyde-alkyne-amine coupling reactions, respectively. The latter catalytic reactions yielded a range of three-component products in good to excellent yields with low catalyst loading under solvent-free conditions, which demonstrate the potential utility of group-16 cations as ancillary ligands in homogeneous catalysis.