Study of the reductive Cleavage of Selenides with Nickel Boride. A Convenient Deselenization Procedure

Article abstract of DOI:10.1021/jo00251a028

The reductive deselenization of a variety of organoselenium compounds can be performed rapidly, conveniently, and in high yield by using nickel boride.The latter reagent was generated in situ by adding sodium borohydride to nickel chloride hexahydrate and the substrate selenide in THF-methanol at 0 deg C.Under these conditions, ca. 3-3.5 mol of borohydride was required to reduce all of the nickel salt to nickel boride and an excess of nickel boride was generally required to effect complete deselenization.Preformed nickel boride lost virtually all of its ability to cleave n-dodecyl phenyl selenide (2) after only 5 min, but continued to catalyze the decomposition of sodium borohydride.Deselenizing ability was not restored by the addition of hydrogen or further sodium borohydride to preformed nickel boride.Deuterium-labeling studies indicated that the hydrogen required for reductive deselenization originates from both the borohydride and the methanol solvent in a ratio of ca. 3:1.The use of sodium borodeuteride in methanol-d afforded 1-deuteriododecane of high isotopic purity, indicating that the procedure comprises a convenient method for preparing deuteriated products.The mechanism of nickel boride deselenization may involve transient nickel hydride or Ni(0) intermediates.The chemoselectivity of the reaction permits the cleavage of C-Se bonds in the presence of chlorides, nitriles, esters, sulfides, sulfones, ketones, and some olefins, but iodides and sulfinate esters undergo concomitant or preferential reduction.Electrochemical deselenization of 2 was studied and resulted in anodic oxidation of the selenide to 1-dodecene instead of cathodic reduction to n-dodecane.