Novel (N-heterocyclic carbene)Pd(pyridine)Br₂ complexes for carbonylative Sonogashira coupling reactions: Catalytic efficiency and scope for arylalkynes, alkylalkynes and dialkynes

New N,N′-substituted imidazolium salts and their corresponding dibromidopyridine–palladium(II) complexes were successfully synthesized and characterized. Reactions of palladium bromide with the newly synthesized N,N′-substituted imidazolium bromides (2a and 2b) in pyridine afforded the corresponding new N-heterocyclic carbene pyridine palladium(II) complexes (3a and 3b) in high yields. Their single-crystal X-ray structures show a distorted square planar geometry with the carbene and pyridine ligands in trans position. Both complexes show a high catalytic activity in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with arylalkynes, alkylalkynes and dialkynes.