N-heterocyclic carbenes (NHCs) are strong σ-donating ligands that coordinate to a range of metal ions, which can serve as powerful catalysts for modern organic transformations. NHCs offer some benefit over other common organometallic ligands like the phosphines, which typically show limited air and moisture stability. Nickel(II) complexes of both imidazole and benzimidazole based NHCs have been synthesized, characterized, and show moderate reactivity toward acetophenone to generate phenylethanol. Other first-row transition metal ions (including Mn2+, Fe2+, Co2+, Cu2+, and Zn2+) have also been explored, towards the efficient reduction of ketone in sustainable solvents. Copper(II) complexes with benzimidazole have shown the most reactivity in these reactions during the reduction of 2-acetylpyridine to 2-(1-hydroxyethyl)pyridine. This Lewis acid catalyzed conversion of ketones to alcohols provides opportunities for further method development that can be used in modern synthetic processes. Characterization of the NHC complexes were done by UV-vis spectroscopy, X-ray crystallography, and HR-MS techniques and the reaction products were analyzed by thin layer chromatography, GC-MS, and/or LC-MS methods.

Metal N-heterocyclic carbene complexes for catalytic ketone reduction

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