The influence of substitution on the reduction mechanism and stability of reduction intermediates in 1,1′-phenylene-, 1,1′-diphenylene- and 1,1′-polymethylene-bispyridinium dications

• Published in: Electrochimica acta 1992, Vol.37 (13), p.2481-2490
• Main Authors: Volke, J., Urban, J., Volkeová, V.
• Format: Article
• Language: English
• Subjects: bispyridinium dications; Chemistry; ditopic derivatives; Electrochemistry; electroreduction mechanism; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions; reduction intermediates
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/0013-4686(92)87088-H

Electrochemical investigations in aprotic solvents showed a great influence of substituents in the pyridine nuclei on the reduction of the title compounds and also a sensitivity of the mechanism towards the groups forming a linkage between the two pyridine nuclei: whether the 1,1′-linkage is formed by a polymethylene chain or by phenylene groups is important. It was found that a full delocalization of the doubly positive charge only occurs over the whole particle with 1,1′-bispyridinium dications in which the separation of the two nigrogen atoms is effected by means of phenylene groups. If compared with the polymethylene-linked derivatives the uptake of the first electron takes place at considerably more positive potentials ( ie at about −0.3 V vs. nce). The first reduction step is extremely sensitive towards even traces of hydroxyl ions (and water). An addition of N( nC 4H 9) 4OH leads to lowering or to disappearance of this wave. Spectral measurements in the uv-vis range proved that this is due not to a change in the electrochemical behaviour but, owing to the media, to a chemical change of the substance. On the other hand, in the 1,1′-bispyridinium dications where both nitrogen atoms are linked by several methylene groups (these compounds have two separated π-electron systems) the doubly positive charge is not delocalized over the whole particle. The electrochemical behaviour supports the assumption of two independent monovalent electroactive centres which are equivalent before the uptake of the primary electron. The electrochemical reduction of studied substances is strongly affected by oxygen and the mechanism of this effect is discussed.