Copper(II) complexes of bidentate ligands containing nitrogen and sulfur donors: Synthesis, structures, electrochemistry and catalytic properties

Two nitrogen and sulfur containing ligands, 1-methyl-4-((4-methylimidazol-5-yl)methylthio)benzene (NS-mim) (1) and 1-methyl-4-(2-pyridylmethylthio)benzene (NS-mpy) (2) were synthesized and a series of their Cu(II) complexes, 3–10, prepared. The imidazole-containing complexes (3–6) have the form [Cu(NS-mim)2(solvent)2](X)2 where X = ClO4, BF4and [Cu(NS-mim)2(Y)2] where Y = Cl or Br and the pyridine-containing complexes (7–10) have the form [Cu(NS-mpy)2]X2 (where X = ClO4, BF4) and [Cu2(NS-mpy)2Y4] (where Y = Cl or Br). These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry. The X-ray structure of the imidazole-containing [Cu(NS-mim)2(DMF)2](ClO4)2 (3) was determined and it showed the copper(II) coordinated only by the nitrogen donors while the sulfurs remain uncoordinated. In comparison, the X-ray structure of the pyridine-containing [Cu2(NS-mpy)2(Cl)4] (9) shows a dinuclear copper(II) complex with the nitrogens and the sulfurs coordinated along with a terminal chloride and two μ-chloro atoms bridging the coppers. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 0.31 and 0.51 V versus SCE. The complexes were found to be active for the oxidation of di-tert-butyl catechol (DTBC) with the rate dependent on the ligand and the counterion present.

Graphical abstractTwo bidentate nitrogen and sulfur containing ligands were complexed to copper(II) salts resulting in the formation of novel mononuclear and binuclear complexes. The complexes were characterized by elemental analysis, electrochemistry and X-ray crystallography and their ability to catalyze the oxidation of catechols was studied.Figure optionsDownload full-size imageDownload as PowerPoint slide