Synthesis and Characterization of C,C-Type Palladacycles and Their Catalytic Application in Mizoroki–Heck Coupling Reaction

Abstract

Two series of ligand precursors, based on imidazo[1,2-a]pyridine and C2-phenyl substituted imidazole moieties, were developed and synthesized in high yields, featuring an N-CH2(C═O)Ar substituent on the imidazole ring. Upon reacting with palladium acetate, both series of ligands underwent double C–H bond activations at the methylene and o-aryl carbon sites on the N-CH2(C═O)Ar substituent, yielding C,C-type palladacycles bearing five-membered chelate rings. A dimeric palladium complex with bridging bromides was obtained from the ligand precursor with the bromide anion, whereas an ionic palladium complex with two “throw away” pyridine ligands was formed with the precursor of the tetrafluoroborate anion. All complexes are air-stable and were characterized by 1H and 13C NMR spectroscopy and elemental analysis. The structures of three of the new complexes were further established by single-crystal X-ray diffraction studies. These complexes have been screened for catalyzing Mizoroki–Heck coupling reaction using...