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

Abstract 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 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.