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

by Cordes, A. Wallace; Mingie, James R.; Oakley, Richard T.; Reed, Robert W.; Zhang, Hongzhou

Oxidation of quinoxalineaminothiol with SCl2 or S2Cl2/Cl-2 affords a series of compounds based on the quinoxaline-1,2,3-dithiazole framework QDTA. Under highly oxidizing conditions, the 1,2,3-dithiazolyl ring is opened to afford 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-QDTA][Cl]. For all values of x, reduction with iodide ion (3 mol equiv) affords the corresponding dithiazolyl radical [Cl-x-QDTA]. The radicals can be isolated in good yield in crude form, but attempts to purify them by vacuum sublimation lead to thermal degradation. The radicals have nonetheless been fully characterized by EPR spectroscopy, and the assignments of the observed hyperfine coupling constants cross-matched with those obtained by computation 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. Crystal data: Cl-QDTA-Cl-3, monoclinic, space group C2/c, a = 30.561(5) Angstrom, b = 4.9764(9) Angstrom, c = 22.247(4) Angstrom, beta = 131.822(14)degrees, 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 group Pnma, a = 18.627(12) Angstrom, b = 6.848(4) Angstrom, c = 10.926(7) Angstrom, V = 1393.7(15) Angstrom (3), Z = 4, R(F) = 0.047, and R-w(F) [I greater than or equal to 3 sigma (I)] = 0.060.

Canadian Journal of Chemistry-Revue Canadienne de Chimie
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