Methyl- and methoxy-substituted di[1,4]benzodithiio[2,3-b:2,3-e]pyridines as new electron donor compounds: synthesis, molecular structure, electrochemical properties, and EPR studies

Abstract

Two new derivatives of di[1,4]benzodithiino[2,3-b:2,3-e]pyridine (5) tetrasubstituted with methyl (7) and methoxy (8) groups at the 2,3,9 and 10 positions have been prepared from 2,3,5,6-tetrachloropyridine, by cyclization reaction with the bidentate nucleophiles, 4,5-dimethyl- and 4,5-dimethoxy-benzene-1,2-dithiol. Cyclic voltammograms for the oxidation of both polyheterocyclic compounds 7 and 8 in CH₂Cl₂ exhibit two consecutive redox couples. The first pairs are due to the equilibria between the initial compounds and their radical cations, while in the second couples, the electrogenerated radical cations are in equilibrium with the corresponding dications. Radical cations of these molecules have been generated in fluid solution, by oxidation of the parent compounds with thallium(III) trifluoroacetate in trifluoroacetic acid in the case of 7, and by irradiation of a CH₂Cl₂ solution containing trifluoroacetic acid (10%) in the case of 8. Both species were analyzed by electron paramagnetic resonance (EPR). X-Ray analysis of the molecular structures of both 7 and 8 shows a stable chair-shaped conformation with interplanar angles between the phenyl rings and the pyridine ring of 139.9 and 141.4° for 7 and 133.7° for 8.