Hydrosilylation

Hydrosilylation
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Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds. Ordinarily the reaction is conducted catalytically and usually the substrates are unsaturated organic compounds. Alkenes and alkynes give alkyl and vinyl silanes; aldehydes and ketones give silyl ethers.

The catalytic transformation represents an important method for preparing organosilicon compounds. An idealized transformation is illustrated by the addition of triethylsilane to diphenylacetylene:[1]
Et3SiH + PhC?CPh > Et3Si(Ph)C=CH(Ph)

The reaction is similar to hydrogenation, and similar catalysts are sometimes employed for the two catalytic processes. In industry “Speier’s catalyst,” H2PtCl6 is important.[2] The mechanism usually assumes an intermediate metal complex that contains a hydride, a silyl ligand (R3Si), and the alkene or alkyne substrate.

Idealized mechanism for metal-catalysed hydrosilylation of an alkene.Contents [hide]
1 Asymmetric hydrosilylation
2 Surface hydrosilylation
3 References
4 Further reading

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Asymmetric hydrosilylation

Using chiral phosphines as spectator ligands, catalysts have been developed for catalytic asymmetric hydrosilation. A well studied reaction is the addition of trichlorosilane to styrene to give 1-phenyl-1-(trichlorosilyl)ethane:
Cl3SiH + PhCHCH2 > (Ph)(CH3)CHSiCl3

Nearly perfect enantioselectivities (ee’s) can be achieved using palladium catalysts supported by binaphthyl-substituted monophosphine ligands.[3]
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Surface hydrosilylation

Silicon wafer can be etched in hydrofluoric acid (HF) to remove the native oxide, and form a hydrogen-terminated silicon surface. Then the hydrogen-terminated surfaces can react with unsaturated compounds (such as terminal alkenes and alkynes), to form a stable monolayer on the surface. For example:

H:Si(100) + CH=CH(CH2)7CH3 > Si(100)-(CH2)9CH3

The hydrosilylation.