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 = ClO(4), BF(4) and [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)]X(2) (where X = ClO(4), BF(4)) and [Cu(2)(NS-mpy)(2)Y(4)] (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)](ClO(4))(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 [Cu(2)(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 mu-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. (C) 2008 Elsevier B.V. All rights reserved.