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.