SOME HIGH-POTENTIAL TRITHIOETHER CHELATES OF COPPER

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 N2S2 donor set, plus the third thioether sulfur bound axially. The most marked consequence of the pyridine alpha-methylation is that the Cu2+/+ reduction potential is raised by about 200 mV; otherwise, the E1/2 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 Cu2+/+E1/2 values, similar to that for dibromine reduction.