Characterization of organic polyselenide ions in N,N-dimethylacetamide

The reactivity of selenolate ions RSe− [R = Ph (1), PhCH2 (2)] towards solid selenium has been investigated by UV-visible spectrophotometry in N,N-dimethylacetamide. After the slow formation of RSe2−, further addition of Se yielded RSe3− and RSe4− species, which partly disproportionated (RSe3−, 30% RSe4−, 50%) into diselanes RSe2R (a) and polyselenide ions Se42− and Se62−, respectively. These equilibria were readily attained by the reactions between electrogenerated Sex2− ions (x = 4, 6) and substrates 1a and 2a. Visible spectra of RSe3− and RSe4− ions (380 < λ < 580 nm) were calculated [λmax = 420 (1), 400 nm (2)]. The formation of RSe2R as major products in the RSezR mixtures obtained by the nucleophilic reactions Se42− + PhCH2Br ( = 2.17) or CH3I ( = 2.48) on a preparative scale agrees with the disproportionation of intermediate RSey− ions.

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