Nickel(II) Benzimidazolin-2-ylidene Complexes with Thioether-Functionalized Side Chains as Catalysts for Suzuki–Miyaura Cross-Coupling

Four
bis­(benzimidazolin-2-ylidene) nickel­(II) complexes featuring
thioether moieties in the side chain have been synthesized by reactions
of the respective benzimidazolium salts with nickel­(II) acetate in
molten tetrabutylammonium bromide as an ionic liquid. All complexes
were obtained as inseparable mixtures of trans-syn and trans-anti rotamers,
as evidenced by NMR spectroscopy. For one of the complexes, X-ray
diffraction confirmed the square-planar coordination geometry. The
catalytic activity of all complexes for Suzuki–Miyaura cross-coupling
was examined. Under the optimized conditions, both aryl bromides and
aryl chlorides were successfully coupled in the presence of triphenylphosphine
as additive. Yields ranged from good to moderate for electron-deficient
aryl halides, while electron-rich aryl halides were found to be unreactive.