Reactivity of Nucleophiles toward and the Site of Nucleophilic Attack on Bis(alkylthio) Selenides

Article abstract of DOI:10.1021/ja00389a039

Bis(alkylthio)selenides, RSSeSR (1), a class of compounds that occupy a key role as intermediates in the incorporation of inorganic selenium into biological systems, react quite readily with nucleophilic reagents.In principle, such reactions could take place at either sulfur (eq 3a) or at selenium (eq 3b).In the present work the reaction of a series of 1 having R groups of varying steric dimensions (n-Bu, i-Pr, t-Bu) with a group of common nucleophiles (thiolate, cyanide, and sulfite ions, phenyllithium, piperidine) has been examined.The results show that when R = t-Bu, reaction with the nucleophile at selenium occurs considerably faster than reaction at sulfur, but that when R is an n-alkyl group (n-Bu), reaction at sulfur is considerably faster than reaction at selenium.With R = i-Pr, the rates of reaction at the two sites are comparable.For reaction at sulfur, the retardation in rate accompanying a change in R from n-Bu to i-Pr to t-Bu parallels closely the decrease in rate with the same change in R that has been observed in other nucleophilic substitution at dicoordinate sulfur.As might be expected, an increase in steric dimensions of R has a considerably smaller effect on the rate of mechanism at selenium.Comparison of the rate of reaction of n-BuS^- with n-BuSSeSBu-n and n-BuSSBu-n shows that bis(n-alkylthio) selenides can be expected generally to be more than several orders of magnitude more reactive toward nucleophiles than the corresponding disulfide.