Silyl hydride


Silicon hydrides are organosilicon compounds that contain a silicon–hydrogen bond. Examples include phenylsilane and triethoxysilane.

Bonding and structure

The silicon-to-hydrogen bond is longer than the C–H bond and weaker. Hydrogen is more electronegative than silicon, which results in the polarization of the Si-H bond to be the reverse of that for the C-H bond. Generally silyl hydrides are colourless with physical properties comparable to hydrocarbons. They can be pyrophoric, reflecting the great driving force for replacing Si-H bonds with Si-O bonds.

Reactions and applications

The dominant application of silicon hydrides is in the production of silicon films and coatings. Silane decomposes as follows:
This reaction is conducted by chemical vapor deposition, exploits the weakness of the Si-H bond.
The second most heavily produced silicon hydride is trichlorosilane, HSiCl3.

Hydrosilylation

Silyl hydrides adds across multiple bonds in alkenes, alkynes, imines, and carbonyls. in hydrosilylation. Many organosilicon compounds are prepared in this way. Illustrative is the crosslinking of vinyl-terminated siloxanes:

Laboratory reductants

In the laboratory, silyl hydrides are used as reducing agent. For example, PMHS. In one study triethylsilane is used in the conversion of a 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 grabs a proton from a thiol completing the catalytic cycle:
Silyl hydrides can reduce robust molecules such as carbon dioxide : Unfortunately such reactions are stoichiometric and practical means to regenerate the silicon hydrides are not available.
In the related silylmetalation, a metal replaces the hydrogen atom.

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