Transition metals in the þ2 oxidation state form complexes with octakis(benzylthio)tetraazaporphyrin [M{TAP(SBn) 8 }] (M ¼ Mn 2þ , Co 2þ , Ni 2þ , Cu 2þ , Zn 2þ and 2H þ ; Bn ¼ ACH 2 Ph; TAP ¼ tetraazaporphyrin) and were prepared via demetallation of the template-synthesized complex [Mg{TAP(SBn) 8 }] in ClCH 2 COOH, followed by insertion of the metal ions in a PhCl-DMF mixture. All compounds were characterized by u.v-vis, 1 H-n.m.r., e.s.r. and mass spectra, microanalyses and magnetic susceptibility data. PM3 geometry optimization showed near coplanar arrangement of five phenyl rings vis-a`-vis the TAP ring plane, while the remaining three phenyl rings lie bent over it. The Mn 2þ , Co 2þ and Cu 2þ complexes exhibited reversible one electron oxidation waves, that were observed at E 1/2 À0.33, À0.29 and 0.58 V versus Ag/AgCl respectively. They all exhibited an irreversible reduction wave at E p À1.1 V versus Ag/AgCl followed by appearance of an irreversible oxidation wave at E p 1.1-1.2 V versus Ag/AgCl. This has been interpreted in terms of reductive dissociation, leading to removal of the benzyl substituents, and subsequent oxidation of thiolate products. The Mn 2þ , Co 2þ and Cu 2þ complexes exhibited metal ion-based e.s.r. signals. The [Co{TAP(SBn) 8 }] complex in a homogeneous DMF solution was found to catalyze electroreduction/oxidation of nitrite ions. In the presence of a 1/5 molar quantity of the complex [Co{TAP(SBn) 8 }], the nitrite reduction peak was observed to be shifted by 0.1 V towards the positive potential side and the peak current rose by a factor of 1.33. Similarly a sharp rise in the anodic current, corresponding to oxidation of nitrite ions, was observed in the presence of the complex.
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