Efficient N-heterocyclic carbene palladium(II) catalysts for carbonylative Suzuki-Miyaura coupling reactions leading to aryl ketones and diketones

New N, N′-substituted imidazolium salts (L1 and L2) and their corresponding diiodopyridinepalladium(II) complexes (C1 and C2) were successfully synthesized and characterized. Reactions of palladium iodide with the newly synthesized N, N′-substituted imidazolium iodides in pyridine afforded the corresponding new palladium-N-heterocyclic carbene pyridine complexes in high yields. The new palladium(II) complex C1 was characterized by single crystal X-ray diffraction analysis. The Pd(II) ion is bonded to the nitrogen atom of the pyridine, the carbon atom of the NHC carbene ligand and two trans iodides resulting in distorted square planar geometry. The two Pd-NHC-Py complexes C1 and C2 displayed higher catalytic activity in the carbonylative Suzuki-Miyaura coupling reactions with much lower catalyst loading as compared to the catalytic systems reported in the literature.