[789-25-3] · C18H16Si · Triphenylsilane · (MW 260.43)
(reducing agent for esters, xanthates, and polychloroalkanes; protecting group for alcohols)
Physical Data: mp 47 °C; bp 152 °C/2 mmHg.
Solubility: sol most organic solvents.
Form Supplied in: white solid; commercially available.
Handling, Storage, and Precautions: this reagent is stable in air. Because the toxicogical properties are unknown, it should be handled in a well-ventilated fume hood. Contact with the eyes and skin should be avoided.
Ph3SiH is a useful reducing reagent under radical conditions. Esters are reduced to hydrocarbons at 140 °C by Ph3SiH in the presence of a radical generator, 1,1-Di-t-butyl Peroxide (DTBP) (eq 1).1
The best results are obtained with acetate esters compared with other esters, such as isobutyrate, pivalate, or benzoate. Acetates derived from primary, secondary, and tertiary alcohols are all reduced in high yield. Other silanes such as tripropylsilane and diphenylmethylsilane are not as effective, and other radical generators such as AIBN and dibenzoyl peroxide are not suitable for the deoxygenations.
This reaction can be applied to deoxygenation of carbohydrates. Thus both O-acetylfuranoses and -pyranoses can be converted to the corresponding deoxy sugars (eqs 2 and 3).2
Xanthates (eq 4)3 and perhaloalkanes4 are also reduced by Ph3SiH.
Ph3SiH in combination with Trifluoroacetic Acid has been used for ionic deoxygenation of tertiary alcohols (eq 5).5
Triphenylsilane is used in certain cases for the preparation of triphenylsilyl ethers, which serve as alcohol protecting groups.6 The triphenylsilyl group is considerably more stable (about 400 times) than the TMS group toward acidic hydrolysis.7
Gunma University, Japan