Some high-potential trithioether chelates of copper

Abstract The linear quadridentate ligand 1,8-bis(2′-quinolyl)-3,6-dithiaoctane and the three quinquedentate ligands 1,9-bis(2′-pyridyl)-2,5,8-trithianonane, 1,9-bis(6′-methyl-2′-pyridyl)-2,5,8-trithianonane and 1,11-bis(2′-quinolyl)-3,6,9-trithiaundecane have been prepared. The deep green-blue copper(II) chelates have been characterized by optical and ESR spectroscopy and cyclic voltammetry. The two pyridyl chelates have similar tetragonal coordination about the copper, with an equatorial N 2 S 2 donor set, plus the third thioether sulfur bound axially. The most marked consequence of the pyridine α-methylation is that the Cu 2+/+ reduction potential is raised by about 200 mV; otherwise, the E 1 2 is consonant with previously advanced models for correlating redox potentials with ligand structural features. The pyridyl copper(II) complexes have been isolated as the tetrafluoroborate salts, whereas the quinolyl-copper(II) chelates are rather redox unstable, in association with even more positive Cu 2+/+ E 1 2 values, similar to that for dibromine reduction.