EPR studies on the thiophenodithiazolyl radical, C4H2S3N˙

Abstract

Selective chlorination of thiophene-2,3-dithiol with SO₂Cl₂ generates the corresponding sulfenyl chloride, 2,3-C₄H₂S(SCl)₂. Subsequent condensation with Me₃SiN₃ yields the thiophenodithiazolylium salt [C₄H₂S₃N]Cl, [TDTA]Cl. The structure of the cation, TDTA⁺, was established by X-ray diffraction as both its AsF₆⁻ and HSO₄⁻ salts. Reduction of [TDTA]Cl with Ag powder yields the radical TDTA˙ which was characterised by X- and Q-band (9 and 34 GHz) EPR and ENDOR studies. The spin density distributions estimated from the EPR/ENDOR measurements were found to be in very good agreement with those determined by DFT (B3LYP/6-31G*) indicating that ca 10% of the spin density is delocalised onto the thiophene ring. Comparison of the spin density distributions in TDTA˙ and the isoelectronic trithiatriazapentalenyl radical C₂S₃N₃, TTTA˙, indicates that replacement of N by C–H leads to a localisation of the spin density on the dithiazolyl ring.