Quinoxaline-1,2,3-dithiazolyls - Synthesis, EPR characterization, and redox chemistry

Oxidation of quinoxalineaminothiol with SCl2 or S2Cl2/Cl-2 affords a series of compounds based on the quinoxaline-1,2,3-dithiazole framework QDTA. Und er highly oxidizing conditions, the 1,2,3-dithiazolyl ring is opened to aff ord the acyclic dichlorosulfimino-sulfenyl chlorides Cl-x-QDTA-Cl-3 (x = 0, 1, 2). Reduction of these "trichloro" compounds leads to ring closure. For x = 2, reduction using S2Cl2 affords the dithiazolylium chloride [Cl-2-QDT A][Cl]. For all values of x, reduction with iodide ion (3 mol equiv) afford s the corresponding dithiazolyl radical [Cl-x-QDTA]. The radicals can be is olated in good yield in crude form, but attempts to purify them by vacuum s ublimation lead to thermal degradation. The radicals have nonetheless been fully characterized by EPR spectroscopy, and the assignments of the observe d hyperfine coupling constants cross-matched with those obtained by computa tion at the B3LYP/6-31G** level. The structures of the trichloro compounds Cl-x-QDTA-Cl-3 (x = 1, 2) have been confirmed by X-ray crystallography. Cry stal data: Cl-QDTA-Cl-3, monoclinic, space group C2/c, a = 30.561(5) Angstr om, b = 4.9764(9) Angstrom, c = 22.247(4) Angstrom, beta = 131.822(14)degre es, V = 2521.4(8) Angstrom (3), Z = 8, R(F) = 0.043, and R-w(F) [I greater than or equal to sigma (I)] = 0.049; Cl-2-QDTA-Cl-3, orthorhombic, space gr oup Pnma, a = 18.627(12) Angstrom, b = 6.848(4) Angstrom, c = 10.926(7) Ang strom, V = 1393.7(15) Angstrom (3), Z = 4, R(F) = 0.047, and R-w(F) [I grea ter than or equal to 3 sigma (I)] = 0.060.