Electrochemical behaviour of 2,2′-bibenzimidazoles: Voltammetric, in situ UV–vis- and EPR-spectroelectrochemical and computational studies

Abstract

• The electrochemical properties of 2,2′-bibenzimidazole and its substituted analogues have been investigated by cyclic voltammetry, square-wave voltammetry and in situ UV–vis- and EPR-spectroelectrochemistry. • The nature of the formed in the electrochemical process radicals has been elucidated. • The formation of 2,2′- bibenzoimidazolylidene species and the mechanism of the electrochemical reduction process have been postulated. The electrochemical properties of 2,2′-bibenzimidazole and its substituted analogues 5,6-dimethyl-2,2′-bibenzimidazole, 5,5′,6,6′-tetramethyl-2,2′-bibenzimidazole as well as 1,1′-dimethyl-2,2′-bibenzimidazole were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV) combined with mechanistic studies by means of in situ UV–vis- and EPR-spectroelectrochemistry. The data obtained for N H derivatives suggest the formation of 2,2′-bibenzoimidazolylidene species via ECEC reaction mechanism consisting of two successive one-electron transfers accompanied by proton migration. The resulting species undergo further one-electron reduction with the formation of stable anion-radicals, whose structures have been identified by in situ UV–vis- and EPR-spectroelectrochemical measurements and supported by the computational study using density functional theory (DFT) calculations. In contrast to N H derivatives, the electrochemical reduction of N,N -dimethyl substituted derivative leads to radical anion and dianion species.