Electrochemical oxidation of the Ni(II) complex of 2-amino cyclopentene-1-dithiocarboxylate at a Pt electrode

Abstract

The electrochemical oxidation of 2-amino dithiocarboxylic acid (ACDA) and its nickel(II) complex has been studied in DMF at a platinum electrode. The oxidation of the ligand shows two oxidation peaks (+0.8 V and +1.1 V). The first oxidation peak is related to ring formation between two dithio groups with the elimination of one sulphur atom via two electron processes. The second peak is due to a two-electron transfer process by releasing a proton. The oxidation of the Ni(II) complex of ACDA, Ni(ACD)2, is usually irreversible and metal-based on a short time scale while on a long time scale a ligand-based oxidation predominates. Although the formally nickel(III) species could not be prepared and isolated chemically, they are readily formed from Ni(ACD)2 and the electrochemically generated ACD radical. It was found that the redox potential of the Ni(II) complex studied is substantially reduced relative to those of most synthetic complexes and is in the region of Ni(III)/Ni(II) potentials in the native proteins (−390 to −640 mV vs. SCE).