Ethenediylidene-2,2′ -bis(1,3-dithiole) and butatriene-1,4-diylidene-2,2′-bis(1,3-dithiole)

This paper describes the synthesis and electrochemical behavior of dicationic salts of ethenediylidene‐2,2′ ‐bis(1,3‐dithiole) (3) and butatriene‐1,4‐diylidene‐2,2′ ‐bis(1,3‐dithiole) (4). These are expected as donor components for developing organic conducting and superconducting materials, on the grounds of high electron donating ability and of rigid skeletal structure with two and four cumulenic carbons inserted between two 1,3‐dithioles. These salts were obtained in good overall yields by several steps starting from (2‐morpholino‐4,5‐dimethyl or ‐diphenyl)‐1,3‐dithiolylium salt. From the 1H and 13C NMR, and electronic spectra it is suggested that the π conjugation between two 1,3‐dithiolylium ions through an acetylenic bond is less effective than that through an olefinic bond of the corresponding salts of ethanediylidene‐2,2′ ‐bis(1,3‐dithiole) (1) and 2‐butene‐1,4‐diylidene‐2,2′‐bis(1,3‐dithiole) (2). The cyclic voltammetric study shows that the corresponding radical cations, and in particular 3 and 4, are less stable even at −40°C, thus providing reasons for our current lack of success in isolation of 3 and 4. From comparison of the first redox potentials of neutral species, it is deduced that the donating ability increases in the order of TTF < 1 ⋍ 2 ≲ 3 ≪ 4.