An efficient palladium catalyzed mizoroki-heck cross-coupling in water: synthesis, characterization and catalytic activities

Abstract

A series of new palladium complexes known as PEPPSI-type complexes 3 were successfully synthesized by reacting benzimidazolium salts 2a-e, potassium carbonate (K2CO3), and palladium chloride (PdCl2) in pyridine for 16 h at 80 °C. Both the benzimidazolium salts 2a-e and the resulting complexes 3 were characterized through spectroscopic data and elemental analysis. The Mizoroki-Heck coupling reaction, catalyzed by the homogeneous Pd, was effectively carried out in water without the need for any additional substances under aerobic conditions. The optimization of various key reaction parameters was performed to enhance the yield of the desired cross coupling product. The catalytic performance of these complexes in a catalytic system containing palladium complexes 3a, Et3N, and H2O was evaluated in the Mizoroki-Heck coupling reaction. The PEPPSI-type palladium complex 3a /Et3N/H2O/98 °C catalyst system exhibited high activity, with a turnover frequency (TOF) ranging from 12 to 14 /hour towards achieving the excellent yield of the Mizoroki-Heck coupling products for a wide range of electron withdrawing as well as electron donating aryl bromide and chlorides in shortest reaction time.