Highly active Pd(II) catalysts with pyridylbenzoimidazole ligands for the Heck reaction

The air-, and thermo-stable palladium(II) complexes C1–C10 are prepared by the reaction of PdCl2(CH3CN)2 with pyridylbenzoimidazole. With various substituents on the pyridine ring, palladium atom was coordinated by two pyridylbenzoimidazole molecules via nitrogen atoms of benzoimidazole. The structure of complexes C3, C4, C6, and C7 has been confirmed by X-ray diffraction analysis. Without substituents on the pyridine ring, palladium atom was directly coordinated with two nitrogen atoms of pyridine and benzoimidazole nitrogen via intramolecular chelation (C10). These complexes performed the Heck olefination of aryl bromides in a good to high yield under phosphine-free conditions.

Graphical abstractTen different palladium(II) complexes containing pyridylbenzoimidazole ligands have been investigated as catalyst for the coupling between aryl bromide and olefin. The substituents on the benzoimidazole and pyridine ring had significant influences on the catalytic properties. The catalyst 4 shows the highest reactivity of coupling reaction with aryl bromide in NMP with K2CO3 at 140 °C.Figure optionsDownload full-size imageDownload as PowerPoint slide