Phosphine-Free Bis(Pyrrolyl)pyridine Based NNN-Pincer Palladium(II) Complexes as Efficient Catalysts for Suzuki-Miyaura Cross-Coupling Reactions of Aryl Bromides in Aqueous Medium

Palladium complexes of phosphine free pincer based ligands are currently growing credence as efficient catalysts for C-C cross-coupling reaction under environmentally benign and mild reaction conditions. A series of new palladium complexes 2a-2c supported by 2,6-bis(pyrrolyl)pyridine based [NNN]-pincer ligands have been synthesized, and their catalytic activities for Suzuki-Miyaura cross-coupling reaction were examined. The palladium complexes (2a-2c) were synthesized by the reaction of 2,6-bis(pyrrolyl)pyridine ligands (LH2) with Pd(OAc)(2) in acetonitrile as a solvent. Electrochemical studies of complexes 2a-2c showed two prominent oxidation peaks, which were ascribed to the dianionic pyrrolide ligand and an oxidation peak that can be ascribed to palladium metal center. There is an exhibition of well-coordinated metal directed oxidation of the complexes which indicates a well-established electronic network. Computational studies on complexes 2a-2c further supported the experimental observations. These palladium complexes 2a-2c can efficiently catalyze Suzuki-Miyaura cross-coupling reaction of aryl bromides in an aqueous medium.