Organosilicon - Silyl Hydrides

Silyl Hydrides

The silicon to hydrogen bond is longer than the C–H bond (148 compared to 105 pm) and weaker (299 compared to 338 kJ/mol). Hydrogen is more electronegative than silicon hence the naming convention of silyl hydrides. The parent compound SiH₄ is called silane, and an example is phenylsilane. Silyl hydrides are very reactive and used as reducing agents for example PMHS.

In one study triethylsilylhydride is used in the conversion of an phenyl azide to an aniline :

In this reaction ACCN is a radical initiator and an aliphatic thiol transfers radical character to the silylhydride. The triethylsilyl free radical then reacts with the azide with expulsion of nitrogen to a N-silylarylaminyl radical which abstracts a proton from a thiol completing the catalytic cycle:

Aqueous workup then gives aniline.

Silyl hydrides can even take up the reduction of robust molecules such as carbon dioxide (to methane) :

Although it takes a very complex catalyst system.