Electrochemical studies of some dithiadiazolylium cations; evidence for the dithiadiazolide anion, [PhCNSSN]–

Abstract

A series of para-substituted aryldithiadiazolylium salts [p-XC₆H₄[graphic omitted]][Y](X = H, Me, CF₃, MeO, MeS, NO₂, F, Cl, Br, CN or [graphic omitted]⁺; Y = Cl or AsF₆) and [p-XC₆H₄[graphic omitted]][AsF₆](X = H, Me, CF₃, MeO, MeS, NO₂, F, Cl, Br or [graphic omitted]⁺) has been prepared. An electrochemical study of both 1,2,3,5- and 1,3,2,4-dithiadiazolylium derivatives, as the hexafluoroarsenate(V) salts, showed reversible redox behaviour, forming the corresponding dithiadiazolyl radicals. The half-wave reduction potentials, E_½(red), for the two isomeric dithiadiazolylium cations showed linear free-energy relationships between E_½(red) and the Hammett value, σ_p, for the substituent group X; the σ_p values for [graphic omitted]⁺ and [graphic omitted]⁺ rings have been calculated at +0.537 ± 0.005 and +0.57 ± 0.02 respectively. A second reduction process was also observed for both 1,2,3,5- and 1,3,2,4-dithiadiazolylium cations, indicative of the formation of the dithiadiazolide anion, [p-XC₆H₄[graphic omitted]]^–; a preparative-scale reduction of (Ph[graphic omitted])₂ using sodium amalgam and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) provided a yellow air-sensitive solid, [Na(18-crown-6)][Ph[graphic omitted]].