Characterization of organic polyselenide ions in N,N-dimethylacetamide

Abstract

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 Se_x²⁻ ions (x = 4, 6) and substrates 1a and 2a. Visible spectra of RSe₃⁻ and RSe₄⁻ ions (380 < λ < 580 nm) were calculated [λ_max = 420 (1), 400 nm (2)]. The formation of RSe₂R as major products in the RSe_zR mixtures obtained by the nucleophilic reactions Se₄²⁻ + PhCH₂Br ( = 2.17) or CH₃I ( = 2.48) on a preparative scale agrees with the disproportionation of intermediate RSe_y⁻ ions.