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 is usually assumes the intermediacy of a metal complex that contains a hydride, a silyl ligand (R₃Si), and the alkene or alkyne substrate.

[edit] 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 → PhCH(SiCl₃)CH₃

Nearly perfect enantioselectivities (ee's) can be achieved using palladium catalysts supported by binaphthyl-subsituted monophosphine ligands.^[3]

[edit] References

1. ^ James L. Fry, Ronald J. Rahaim Jr., Robert E. Maleczka Jr. "Triethylsilane", Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, 2007. DOI: 10.1002/ ISBN 047084289X .rt226.pub2.
2. ^ C. Elschenbroich, Organometallics (2006) Wiley and Sons-VCH: Weinheim. ISBN 978-3-29390-6
3. ^ T. Hayashi and K. Yamasaki, "C–E Bond Formation through Asymmetric Hydrosilylation of Alkenes", Comprehensive Organometallic Chemistry III, Robert H. Crabtree and D. Michael P. Mingos, Editors. Amsterdam: Elsevier, 2007