Palladium(II) complexes bearing thioether-NHC ligand: Synthesis, characterization, and their application in Suzuki-Miyaura coupling

A series of palladium(II) complexes bearing thioether-functionalized N-heterocyclic carbene ligands, namely [Pd(N-(R-1,R-2,R-3)-N'-(2-(phenylthio)ethyl)-5,6-dimethylbenzimidazol-2-ylidene)Cl-2(py)] (R-1: 1-bromohexane, R-2: 1-bromododecane, R-3: 1-bromooctadecane, R': 2-chloroethyl phenyl sulfide, py: pyridine), have been synthesized and characterized. The synthesized ligands (2a-c) and complexes (3a-c) were characterized by NMR, FT-IR, and elemental analysis. The crystal structure of Pd(II) complex 3a was determined by single-crystal X-ray diffraction. X-ray diffraction analysis revealed that the palladium ion has a slightly distorted square-planar geometry. The catalytic activity of all complexes (3a-c) for the Suzuki-Miyaura cross-coupling reaction was examined. Under the optimized conditions, aryl bromides were successfully converted into corresponding coupled products. Yields ranged high for electron-rich aryl bromides, moderate for electron-neutral bromides, and low for electron-poor bromides.