New Carbon Sulfides Based on 4,5-Dimer capto-1,2-dithiole-3-thione (β-C₃S₅²⁻): [C₃S₅]_n, C₆S₈, and C₅S₇

This investigation centers on the preparation of new binary carbon sulfides based on the 1,2-dithiole-3-thione subunit as found in the precursor dithiolate C₃S₅^2-. Tricyclic C₆S₈, 1, was obtained in high yield by thermal elimination of H₂S from the dimercaptan β-C₃S₅H₂. A crystallographic study confirmed a tricyclic structure of idealized D_2h symmetry containing an unusual planar 1,4-dithiin unit. The crystals of 1 are monoclinic, space group P2₁/c, with a = 8.046(2), b = 9.797(3), c = 13.818(4) Å, V = 1048.3(9) ų, and Z = 4. The final R and R_w values were 0.036 and 0.042, respectively. The bicyclic carbon sulfide C₅S₇, 3, was prepared from reduction of C₄S₆, 2, with LiBEt₃H, followed by addition of thiophosgene. Oxidation of Cp₂Ti(β-C₃S₅) or Zn(β-C₃S₅)₂^2- with SO₂Cl₂ afforded [β-C₃S₅]_n, 4, an orange insoluble solid. Degradation of [β-C₃S₅]_n with dimethyl acetylenedicarboxylate (DMAD) afforded C₃S₅·2DMAD, 5, together with small amounts of C₃S_5•3DMAD, 6. The single-crystal X-ray structure of C₃S_5•-2DMAD revealed a folded 1,4-dithiin linked to a planar 1,3-dithiole. Crystals of 5 are monoclinic, space group Cc, with a = 18.760(4), b = 13.664(3), c = 7.880(2) Å, V = 1957(2) ų, and Z = 4. The least-squares refinement with anisotropic thermal parameters for all non-hydrogen atoms converged at R = 0.036 and R_w = 0.047. The DMAD treatment proceeds in a similar manner with [M(β-C₃S₅)₂]^2- (M = Zn, Ni) to yield [M(C₃S_5•DMAD)₂]^2-. The C₃S_5•DMAD ligand can subsequently be removed from the zinc complex by reaction with thiophosgene giving bicyclic C₄S_6•DMAD, which can also be obtained via Cp₂Ti(C₃S₅·DMAD).