The Water-soluble N-heterocylic Carbenes Copper Complexes Catalytic Aerobic Oxidation Of Benzylic Alcohols In Water

N-Heterocylic carbenes (NHCs) complexes have been widely used as ligands in metal coordination chemistry and organometallic chemistry. Due to the strong electron donating properties and their versatile structures, the special structures can be designed and applied in different reactions. Hence, the design and synthesis of air-stable, and highly efficient transition metal complexes have high theoretical significance and practical values.We prepared a series of water-soluble precursors of N-heterocylic carbenes bearing hydrophilic groups in this paper. The water-soluble ligands were obtained through quaternarization of N-methylimidazole and2-pyridylimidazole with bromoalkyl ammonium bromide in acetonitrile, the water-soluble precursors of mesitylene imidazole ligand was prepared from the condensation of3-(3-bromopropyl)-1-phenyl-1H-imidazol-3-ium with an amino ammonium. The reaction of N-methylimidazole,2-pyridylimidazole and1,3-propane sultone in CH3CN gave the ligands with sulfonate ions.A series of water-soluble Cu NHC compounds were in-situ generated from commercially available copper powder and imidazolium salts, and they were used as catalyst in aerobic oxidation of benzyl alcohols to corresponding aldehyde. Duo to the high water solubility and good catalytic activity, the oxidation of benzyl alcohols could selectively proceed in water without using any bases at room temperature. The2-pyridylimidazole salts with quaternary ammonium salts showed high efficiency and environmentally friendly under mild conditions.