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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:
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. 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
4 Further reading
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.
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