[4099-46-1] · C6H18SeSi2 · Bis(trimethylsilyl) Selenide · (MW 225.34)
Physical Data: bp 45-46 °C/5.3 mmHg.
Solubility: sol Et2O and THF.
Handling, Storage, and Precautions: is an air-sensitive, colorless oil. Because of the strong odor and the release of toxic hydrogen selenide on exposure to moisture, handling of bis(trimethylsilyl) selenide should be performed in a well-ventilated hood. It can be stored at -20 °C in an argon-flushed glass vessel for about a month; after this time, amorphous selenium (red color) is gradually deposited on the vessel.
In the initial studies, bis(trimethylsilyl) selenide was synthesized by the following two methods: silylation of Sodium Selenide1 (or Lithium Selenide2) with Chlorotrimethylsilane (eq 1) or reaction of bromobenzene, Magnesium, and Selenium with chlorotrimethylsilane (eq 2).3
However, the former method requires the troublesome manipulation involved in preparing sodium selenide (or lithium selenide) in liquid ammonia1b and conducting the silylation in benzene (or diethyl ether). The latter method is inefficient and results in a low yield of the desired disilyl selenide. Thus a one-pot, high-yield procedure based on the Lithium Triethylborohydride reduction of elemental selenium has been developed, as depicted in eq 3.4 In this method, both preparation of Li2Se and silylation with Me3SiCl are performed in THF. Technically important is the use of selenium shot; if selenium powder is utilized, the yield of Li2Se decreases sharply. Moreover, addition of small amount of Boron Trifluoride Etherate (1.6 mol %) accelerates the silylation of Li2Se.5
Recently it has been reported that the reaction of Lithium Diselenide (Li2Se2) with 2 equiv of chlorotrimethylsilane affords bis(trimethylsilyl) selenide in 73% yield with the concomitant formation of elemental selenium (eq 4).5
Bis(trimethylsilyl) selenide reacts with equimolar amounts of n-Butyllithium to generate Me3SiSeLi, alkylation of which then provides trimethylsilyl alkyl selenides. Similar treatment of Me3SiSeR1 with BuLi / R2X successfully leads to unsymmetrical selenides in good yields (eq 5).6 Use of acid chlorides in place of alkyl halides results in the formation of selenoesters.
Direct conversion of aldehydes to selenoaldehydes has been achieved by treatment with bis(trimethylsilyl) selenide in the presence of a catalytic amount of butyllithium (eq 6).7a
A mechanistic proposal includes addition of Me3SiSeLi to aldehydes, followed by elimination of Me3SiOLi to generate selenoaldehydes, which undergo Diels-Alder reaction with dienes. Aldehydes bearing a conjugate diene unit provide intramolecular Diels-Alder adducts (eq 7).7b
Bis(trimethylsilyl) selenide is useful as a two-electron reducing agent for the reduction of sulfoxides, selenoxides, and telluroxides to corresponding sulfides, selenides, and tellurides, respectively (eq 8).4
Akiya Ogawa & Noboru Sonoda
Osaka University, Japan