Synthesis, redox properties, and molecular structure of 4,5-diethylthio-4-cyclopenten-1,3-dione: Cyclic voltammetric evidence for a kinetically stable radical anion

The preparation of the new disulfide compound 4,5-diethylthio-4-cyclopenten-l,3-dione (1) from 4,5-dichloro- 4-cyclopenten-l,3-dione and ethanethiol is described. The title compound has been isolated and characterized in solution by IR and NMR spectroscopies, and the solid-state structure solved by X-ray crystallography. 4,5-Diethylthio-4-cyclopenten-l,3-dione crystallizes in the triclinic space group P-l, a = 7.230(4) Å, b = 8.191(5) Å, c = 10.187(6) Å, α = 108.48(1)°, β = 97.75(1)°, γ = 105.90(1)°, V = 533.8(6) Å³, Z = 2, and d _calc = 1.346 Mg/m³; R = 0.0406, R _w = 0.0967 for 1394 reflections with I > 2σ(I). The redox properties of 4,5-diethylthio-4-cyclopenten-l,3-dione have been examined by cyclic voltammetry in CH₂C1₂ solution, where a reversible one-electron reduction was found. The reduction behavior of the diethylthio derivative is discussed relative to the closely related 4,5-bis(p-tolylthio)-4-cyclopenten-l,3-dione, whose radical anion exhibits quasi-reversible reduction behavior due to competitive C(dione ring)–S bond cleavage. The differences in the electrochemical behavior of the two disulfides are discussed with respect to the ancillary R group.