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 compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s. Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

s and alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

s give alkyl and vinyl silanes; aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

s and ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s give silyl ethers. Hydrosilylation has been called the "most important application of platinum in homogeneous catalysis."

The catalytic transformation represents an important method for preparing organosilicon compounds
Organosilicon compounds are organic compounds containing carbon silicon bonds. Organosilicon chemistry is the corresponding science exploring their properties and reactivity.Like carbon, the organically bound silicon is tetravalent and tetrahedral...

. An idealized transformation is illustrated by the addition of triethylsilane
Triethylsilane is a silane with the molecular formula C6H16Si. It is a trialkylsilicon hydride compound with a reactive Si-H bond. This colorless liquid is often used in organic synthesis, specifically for the hydrosilation of olefins to give alkyl silanes...

 to diphenylacetylene
Diphenylacetylene is the chemical compound C6H5C≡CC6H5. The molecule consists of phenyl groups attached to both ends of an alkyne. It is a colorless crystalline material that is widely used as a building block in organic and as a ligand in organometallic chemistry.-Preparation:Several...

Et3SiH + PhC≡CPh → Et3Si(Ph)C=CH(Ph)

The reaction is similar to hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

, 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
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

, a silyl ligand (R3Si), and the alkene or alkyne substrate.

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
Trichlorosilane is a chemical compound containing silicon, hydrogen, and chlorine. At high temperatures, it decomposes to produce silicon, and therefore purified trichlorosilane is the principal source of ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce...

 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.

Surface hydrosilylation

Silicon wafer can be etched in hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....

(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 reaction can be initiated with UV light at room temperature, or with applied heat (typical reaction temperature 120-200 degrees C), under moisture and oxygen free conditions.

The resulting monolayer is stable and inert, and prevent oxidation of the base silicon layer. Surfaces of this kind could find applications in areas such as molecular electronics, biochemistry, and direct electronic sensing of biomolecules.

Further reading

  • Applied homogeneous catalysis with organometallic compounds : a comprehensive handbook : applications, developments. Boy Cornils; W A Herrmann. Publisher: Weinheim ; New York : Wiley-VCH, ©2000.
  • Hydrosilylation : a comprehensive review on recent advances. Bogdan Marciniec; et al. Publisher: Springer, ©2009.
  • Comprehensive handbook on hydrosilylation. Bogdan Marciniec. Publisher: Oxford [u.a.] : Pergamon Press, 1992.
  • Rhodium complexes as hydrosilylation catalysts. N.K. Skvortsov. // Rhodium Express. 1994. No 4 (May). P. 3 - 36 (Eng). ISSN 0869 - 7876
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