Studies on the electroactive heterocycles C₆S₈(0/2-) and C₆S₆O₂(0/2-) and related metal complexes

The properties of the carbon sulfide C₆S₈ (1) as well as its dioxo analogue C₆S₆O₂ (2) have been studied in the fully oxidized and fully reduced forms, i.e., 1⁰, 1,^2- 2⁰, 2^2-. A crystallographic study shows that compound 2 is a tricyclic species with a twisted 1,2-dithiin (unsaturated C₄S₂ ring) core. Reduction of 1 with 2 equiv of LiBHEt₃ gave C₆S₈^2- (1^2-), which was isolated as its PPh₄⁺ salt. A crystallographic study of this salt shows that reduction has resulted in cleavage of the S-S bond and that, in the solid state, the dihedral angle between the two rings is 180°. Both 1^2- and 2^2- undergo two sequential and reversible 1e^- oxidations near 0 V (vs Ag/AgCl), thus establishing that 1⁰ and 2⁰ are good oxidants relative to other disulfides. Treatment of (PPh₄)₂[C₆S₈] with [Ni(H₂O)₆]Cl₂ afforded the dark red (PPh₄)₂[Ni(C₆S₈)₂] (3). The analogous Pt complex (4) was also prepared. Crystallographic analysis of 3 shows that the nickel center is square planar, comprising two seven-membered NiS₂C₄ rings. The paramagnetism observed for solutions of 3 are attributed to the formation of a tetrahedral isomer.