Synthesis, Crystal Structure, and DFT Studies of NHC Mediated Pd-Peppsi Complex: Application for Suzuki Reaction

Abstract

A novel air and moisture resistant Pd-PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) complex was synthesized via the reaction of benzimidazolium salt, PdCl2, KBr, K2CO3, and pyridine. The structure was characterized by spectroscopic methods such as 1H and 13C NMR, FT-IR, UV-vis. and single Xray diffraction techniques. In order to evaluate the synthesized Pd complex in a detailed manner in terms of structural, bonding, electronic, and thermodynamic characteristics, DFT-based calculations were carried out at the B3LYP/6-311++G (d, p)/LANL2TZ theory level. Natural bond orbital (NBO) analysis was implemented to provide more insights about the possible donor-acceptor interactions and types of hybridization. Also, TD-DFT calculations were performed to rationalize the nature of the observed electronic transitions. The complex showed high catalytic activity in the Suzuki-Miyaura cross coupling of aryl chlorides with phenylboronic acid. Aryl chlorides bearing either electron- donating or withdrawing substituents afforded a wide range of biaryl derivatives that were isolated in the range of 55-97 % yields (7 examples). The reactions were carried out at very low catalyst loading (0.25 mol%) in the presence of air using a green water-based solvent (ipr:H2O/ 1:3). The palladium complex was found to be efficient for the coupling of aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in high yields.