A pyridine bridged dicarbene ligand and its silver(I) and palladium(II) complexes: synthesis, structures, and catalytic applications

The potentially tridentate ligand 2,6-bis[(3-methylimidazolium-1-yl)methyl]pyridine dibromide reacts readily with silver(I) oxide in dichloromethane or dimethylsulfoxide to give a dinuclear silver(I)–carbene complex that was isolated as the tetrafluoroborate salt. Single crystal X-ray crystallography shows that each silver(I) ion is bridged by two ligands bonding through the carbene donors. Treatment of the silver(I) complex with suitable palladium(II) precursors gave the complexes PdCl[(CNC)]BF4 and [PdMe(CNC)]BF4 (CNC=2,6-bis[(3-methylimidazolin-2-yliden-1-yl)methyl]pyridine), in which the pyridyl and both carbene moieties are coordinated to a single palladium(II). The palladium(II) complexes have been fully characterised, including X-ray crystallography, and exhibit good activities in the Heck coupling reaction of 4-bromoacetophenone and n-butyl acrylate.