Hydrosilylation

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Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds. [1] 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. Hydrosilylation has been called the "most important application of platinum in homogeneous catalysis." [2]

Contents

Scope and mechanism

Idealized mechanism for metal-catalysed hydrosilylation of an alkene. HSi'n.png
Idealized mechanism for metal-catalysed hydrosilylation of an alkene.

Hydrosilylation of alkenes represents a commercially important method for preparing organosilicon compounds. The process is mechanistically similar to the hydrogenation of alkenes. In fact, similar catalysts are sometimes employed for the two catalytic processes.

The prevalent mechanism, called the Chalk-Harrod mechanism, assumes an intermediate metal complex that contains a hydride, a silyl ligand (R3Si), and the alkene substrate. Oxidative addition proceeds by the intermediacy of a sigma-complex, wherein the Si-H bond is not fully broken.

Hydrosilylation of alkenes usually proceeds via anti-Markovnikov addition, i.e., silicon is placed at the terminal carbon when hydrosilylating a terminal alkene [1] Variations of the Chalk-Harrod mechanism exist. Some cases involve insertion of alkene into M-Si bond followed by reductive elimination, the opposite of the sequence in the Chalk-Harrod mechanism. In certain cases, hydrosilylation results in vinyl or allylic silanes resulting from beta-hydride elimination. [3]

Alkynes also undergo hydrosilylation, e.g., the addition of triethylsilane to diphenylacetylene: [4]

Et3SiH + PhC≡CPh → Et3Si(Ph)C=CH(Ph)

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 + PhCH=CH2 → (Ph)(CH3)CHSiCl3

Nearly perfect enantioselectivities (ee's) can be achieved using palladium catalysts supported by binaphthyl-substituted monophosphine ligands. [5]

Surface hydrosilylation

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

Si-H + H2C=CH(CH2)7CH3 → Si-CH2CHH-(CH2)7CH3

The hydrosilylation reaction can be initiated with UV light at room temperature or with heat (typical reaction temperature 120-200 °C), under moisture- and oxygen-free conditions. [6] The resulting monolayer, which is stable and inert, inhibits oxidation of the base silicon layer, relevant to various device applications. [7]

Catalysts

Kartstedt's catalyst is often used in hydrosilylation. KartstedtCatalyst.png
Kartstedt's catalyst is often used in hydrosilylation.

Before introduction of platinum catalysts by Speier, hydrosilylation was not practiced widely. A peroxide-catalyzed process was reported in academic literature in 1947, [8] but the introduction of Speier's catalyst (H2PtCl6) was a big breakthrough.

Karstedt's catalyst was later introduced. It is a lipophilic complex that is soluble in the organic substrates of industrial interest. [9] Complexes and compounds that catalyze hydrogenation are often effective catalysts for hydrosilylation, e.g. Wilkinson's catalyst.

Related Research Articles

<span class="mw-page-title-main">Alkene</span> Hydrocarbon compound containing one or more C=C bonds

In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.

<span class="mw-page-title-main">Hydrogenation</span> Chemical reaction between molecular hydrogen and another compound or element

Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons.

<span class="mw-page-title-main">Trichlorosilane</span> Chemical compound

Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a siloxane polymer while giving off hydrochloric acid. Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds.

The Heck reaction is the chemical reaction of an unsaturated halide with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is a way to substitute alkenes.

<span class="mw-page-title-main">Wilkinson's catalyst</span> Chemical compound

Wilkinson's catalyst is the common name for chlorido­tris(triphenylphosphine)­rhodium(I), a coordination complex of rhodium with the formula [RhCl(PPh3)3], where 'Ph' denotes a phenyl group). It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so in tetrahydrofuran or chlorinated solvents such as dichloromethane. The compound is widely used as a catalyst for hydrogenation of alkenes. It is named after chemist and Nobel laureate Sir Geoffrey Wilkinson, who first popularized its use.

In organic chemistry, hydrocyanation is a process for conversion of alkenes to nitriles. The reaction involves the addition of hydrogen cyanide and requires a catalyst. This conversion is conducted on an industrial scale for the production of precursors to nylon.

<span class="mw-page-title-main">Alkyne metathesis</span>

Alkyne metathesis is an organic reaction that entails the redistribution of alkyne chemical bonds. The reaction requires metal catalysts. Mechanistic studies show that the conversion proceeds via the intermediacy of metal alkylidyne complexes. The reaction is related to olefin metathesis.

<span class="mw-page-title-main">Crabtree's catalyst</span> Chemical compound

Crabtree's catalyst is an organoiridium compound with the formula [C8H12IrP(C6H11)3C5H5N]PF6. It is a homogeneous catalyst for hydrogenation and hydrogen-transfer reactions, developed by Robert H. Crabtree. This air stable orange solid is commercially available and known for its directed hydrogenation to give trans stereoselectivity with respective of directing group.

<span class="mw-page-title-main">Chloroplatinic acid</span> Chemical compound

Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6
). Hexachloroplatinic acid is highly hygroscopic.

<span class="mw-page-title-main">Organosilicon chemistry</span> Organometallic compound containing carbon–silicon bonds

Organosilicon chemistry is the study of organometallic compounds containing carbon–silicon bonds, to which they are called organosilicon compounds. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Silicon carbide is an inorganic compound.

<span class="mw-page-title-main">Hydroamination</span> Addition of an N–H group across a C=C or C≡C bond

In organic chemistry, hydroamination is the addition of an N−H bond of an amine across a carbon-carbon multiple bond of an alkene, alkyne, diene, or allene. In the ideal case, hydroamination is atom economical and green. Amines are common in fine-chemical, pharmaceutical, and agricultural industries. Hydroamination can be used intramolecularly to create heterocycles or intermolecularly with a separate amine and unsaturated compound. The development of catalysts for hydroamination remains an active area, especially for alkenes. Although practical hydroamination reactions can be effected for dienes and electrophilic alkenes, the term hydroamination often implies reactions metal-catalyzed processes.

Hydrosilanes are tetravalent silicon compounds containing one or more Si-H bond. The parent hydrosilane is silane (SiH4). Commonly, hydrosilane refers to organosilicon derivatives. Examples include phenylsilane (PhSiH3) and triethoxysilane ((C2H5O)3SiH). Polymers and oligomers terminated with hydrosilanes are resins that are used to make useful materials like caulks.

<span class="mw-page-title-main">Metallacycle</span>

In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.

A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. Many kinds of FLPs have been devised, and many simple substrates exhibit activation.

<span class="mw-page-title-main">Organocobalt chemistry</span> Chemistry of compounds with a carbon to cobalt bond

Organocobalt chemistry is the chemistry of organometallic compounds containing a carbon to cobalt chemical bond. Organocobalt compounds are involved in several organic reactions and the important biomolecule vitamin B12 has a cobalt-carbon bond. Many organocobalt compounds exhibit useful catalytic properties, the preeminent example being dicobalt octacarbonyl.

Hydroacylation is a type of organic reaction in which an alkene is inserted into the a formyl C-H bond. The product is a ketone. The reaction requires a metal catalyst. It is almost invariably practiced as an intramolecular reaction using homogeneous catalysts, often based on rhodium phosphines.

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts.

Hydrophosphination is the insertion of a carbon-carbon multiple bond into a phosphorus-hydrogen bond forming a new phosphorus-carbon bond. Like other hydrofunctionalizations, the rate and regiochemistry of the insertion reaction is influenced by the catalyst. Catalysts take many forms, but most prevalent are bases and free-radical initiators. Most hydrophosphinations involve reactions of phosphine (PH3).

In organic chemistry, hydrovinylation is the formal insertion of an alkene into the C-H bond of ethylene. The more general reaction, hydroalkenylation, is the formal insertion of an alkene into the C-H bond of any terminal alkene. The reaction is catalyzed by metal complexes. A representative reaction is the conversion of styrene and ethylene to 3-phenybutene:

<span class="mw-page-title-main">Lanthanocene</span>

A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.

References

  1. 1 2 "Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009. doi : 10.1007/978-1-4020-8172-9
  2. Renner, H.; Schlamp, G.; Kleinwächter, I.; Drost, E.; Lüschow, H. M.; Tews, P.; Panster, P.; Diehl, M.; Lang, J.; Kreuzer, T.; Knödler, A.; Starz, K. A.; Dermann, K.; Rothaut, J.; Drieselman, R. (2002). "Platinum group metals and compounds". Ullmann's Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a21_075. ISBN   3527306730.
  3. Troegel, D.; Stohrer, J. (2011). "Recent Advances and Actual Challenges in Late Transition Metal Catalyzed Hydrosilylation of Olefins from an Industrial Point of View". Coord. Chem. Rev. 255 (13–14): 1440–1459. doi:10.1016/j.ccr.2010.12.025.
  4. James L. Fry, Ronald J. Rahaim Jr., Robert E. Maleczka, Jr. "Triethylsilane", Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, 2007. doi : 10.1002/047084289X.rt226.pub2
  5. Hayashi, T.; Yamasaki, K. (2007). "C–E Bond Formation through Asymmetric Hydrosilylation of Alkenes". In Crabtree, Robert H.; D. Michael P. Mingos (eds.). Comprehensive Organometallic Chemistry III. Amsterdam: Elsevier. doi:10.1016/B0-08-045047-4/00140-0. ISBN   978-0-08-045047-6.
  6. "Photoreactivity of Unsaturated Compounds with Hydrogen-Terminated Silicon (111)," R. L. Cicero, M. R. Linford, C. E. D. Chidsey, Langmuir 16, 5688-5695 (2000)
  7. Direct electrical detection of DNA Hybridization at DNA-modified silicon surfaces, W.Cai, J. Peck, D. van der Weide, and R.J. Hamers, Biosensors and Bioelectronics 19, 1013-1019 (2004)
  8. Sommer, L.; Pietrusza, E.; Whitmore, F. (1947). "Peroxide-catalyzed addition of trichlorosilane to 1-octene". J. Am. Chem. Soc. 69 (1): 188. doi:10.1021/ja01193a508.
  9. C. Elschenbroich, Organometallics (2006) Wiley and Sons-VCH: Weinheim. ISBN   978-3-527-29390-2

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