Phosphonate functionalized N-heterocyclic carbene Pd(II) complexes as efficient catalysts for Suzuki-Miyaura cross coupling reaction

Abstract

A N-heterocyclic carbene (NHC) ligand, L1 bearing a pendant phosphonate ester group is used to prepare two new NHC-Pd(II) complexes, [Pd(L1)2I2] (1) and [Pd(L1)(py)I2] (2) (py = pyridine). Hydrolysis of phosphonate ester group in 2 results another Pd(II)-NHC complex, [Pd(L2)(py)I2] (3) where a phosphonic acid group is attached to the NHC ligand L2. All the three complexes are characterized by analytical and spectroscopic studies while the molecular structures of 1-2 are also determined by single crystal X-ray diffraction measurement. The catalytic efficacies of 1-3 in Suzuki-Miyaura cross coupling reactions of aryl halides and aryl boronic acid are investigated. DFT calculations were performed to decipher the role phosphonate ester or phosphonic acid substituents on the catalytic efficacy.