Pincer Complexes of Palladium- and Nickel-Containing 3-Butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene as Efficient Aqueous Sonogashira and Kumada Coupling Reactions

Abstract

Palladium and nickel complexes, [Pd(L)Cl](PF6) (1), [Ni(L)Cl](PF6) (2), and [Ni(L)2](PF6)2 (3), containing 3-butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene (L) have been synthesized and fully characterized by NMR and ESI-MS spectroscopy and X-ray diffraction analysis. The unsymmetrical NNC pincer complexes 1 and 2 are square planar with a chloride trans to the internal nitrogen atom of phenanthroline. Complex 3 is a paramagnetic octahedral complex with its central metal surrounded by two pincer ligands. A catalytic study shows that palladium compound 1 is highly active in copper-free Sonogashira cross-coupling reactions of aryl iodides at room temperature and aryl bromides at 80 °C in neat water. The nickel complex 2 exhibits good activity in the Kumada cross-coupling reaction of aryl chloride at room temperature.