[13465-77-5] · Cl6Si2 · Hexachlorodisilane · (MW 268.88)
(deoxygenation and desulfurization of phosphine oxides, phosphine sulfides, and amine oxides; reducing agent for nitro groups and sulfur diimides)
Physical Data: bp 144-145.5 °C; d 1.562 g cm-3.
Solubility: sol CHCl3, CH2Cl2, benzene, THF; reacts violently, producing toxic fumes, with H2O, alcohols.
Form Supplied in: neat as clear colorless liquid.
Handling, Storage, and Precautions: neat liquid and solutions react violently with water and protic solvents to produce HCl gas. Avoid contact with strong bases. Hexachlorodisilane is corrosive and should be handled and stored in a tightly sealed vessel under N2. Store cool. Vapor ignites in air when heated. Avoid prolonged and repeated exposure. Use in a fume hood.
Hexachlorodisilane has been shown to effect the stereospecific reduction of phosphine oxides to phosphines with inversion of configuration (eq 1),2 although short reaction times are required to prevent chemical racemization of the phosphine products under the reaction conditions. This protocol complements Trichlorosilane which, under appropriate conditions, reduces phosphine oxides with retention of configuration.2,3 Reductions of bridged bicyclic phosphine oxides4 and cyclic halophospholene oxides5 by hexachlorodisilane have also been reported.
In contrast to the deoxygenation of phosphine oxides by hexachlorodisilane, desulfurization of phosphine sulfides by this reagent occurs stereospecifically with retention of configuration (eq 2).6
Quinuclidine N-oxide was reduced by hexachlorodisilane (eq 3).2 Likewise, azo oxide,7 azo dioxide,8,9 and sulfoxide deoxygenations2 by the reagent were also reported. Treatment of aryl nitro compounds with hexachlorodisilane afforded products which suggested the possibility of a nitrene intermediate being involved (eq 4).10 Other disilanes were evaluated in the study, including hexamethyl- and hexaphenyldisilane, pentamethylphenoxy- and pentamethylphenyldisilane, as well as novel benzodisilacyclopentane (1).
Quinoxaline 1,4-dioxide derivatives were reduced by hexachlorodisilane to give the corresponding quinoxalines (eq 5).11 Also evaluated in the study were the reducing agents Iodotrimethylsilane, Trifluoroacetic Anhydride-Sodium Iodide, and Titanium(IV) Chloride-Zinc dust. Hexachlorodisilane, for its convenience and efficiency, was recommended by the authors as the reagent of choice for this transformation.
Dehydroxylation occurred upon treatment of the alkoxide of a 1-hydroxyimidazole derivative with hexachlorodisilane (eq 6).12 In the same report it was observed that nitrones are deoxygenated upon treatment with hexachlorodisilane, while C=N reduction occurs to yield hydroxylamines with Trichlorosilane (eq 7).
Chlorophosphanes or (trimethylsilyl)phosphanes are converted to trichlorosilylphosphanes upon treatment with hexachlorodisilane (eq 8).14
N-Trichlorosilyldiaminosulfanes were prepared upon treatment of sulfur diimides with hexachlorodisilane (eq 9).13 Likewise, the corresponding N-dichloromethylsilyldiaminosulfanes resulted by substituting 1,2-dimethyl-1,1,2,2-tetrachlorodisilane for hexachlorodisilane.
David P. Sebesta
University of Colorado, Boulder, CO, USA