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-dimet hylacetamide. After the slow formation of RSe2-, further addition of Se yie lded RSe3- and RSe4- species, which partly disproportionated (RSe3-, 30%; R Se4-, 50%) into diselanes RSe2R (a) and polyselenide ions Se-4(2-) and Se-6 (2-), respectively. These equilibria were readily attained by the reactions between electrogenerated Se-x(2-) ions (x=4, 6) and substrates 1a and 2a. Visible spectra of RSe3- and RSe4- ions (380 < lambda < 580 nm) were calcul ated [lambda (max)=420 (1), 400 nm (2)]. The formation of RSe2R as major pr oducts in the RSezR mixtures obtained by the nucleophilic reactions Se-4(2- )+PhCH2Br ((z) over bar =2.17) or CH3I ((z) over bar =2.48) on a preparativ e scale agrees with the disproportionation of intermediate RSey- ions.