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Organosilicon compounds are organometallic compounds containing
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Silicon carbide is an '' inorganic'' compound.


History

In 1846 Von Ebelman's had synthesized Tetraethyl orthosilicate (Si(OC2H5)4). In 1863 Friedel and Crafts managed to make the first organosilieon compound with C-Si bonds which gone byound the syntheses of
orthosilicic acid Orthosilicic acid () is an inorganic compound with the formula . Although rarely observed, it is the key compound of silica and silicates and the precursor to other silicic acids . Silicic acids play important roles in biomineralization and ...
esters. The same year they also described a «polysilicic acid ether» in the preparation of ethyl- and methyl-o-silicic acid. The early extensive research in the field of organosilicon compounds was pioneerd in the beginning of 20th century by Frederic Kipping. He also had coined the term «silicone» (akin to
ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...
s) in relation to these materials in 1904. In recognition of Kipping's achievements the
Dow Chemical Company The Dow Chemical Company, officially Dow Inc., is an American multinational chemical corporation headquartered in Midland, Michigan, United States. The company is among the three largest chemical producers in the world. Dow manufactures plastics ...
had established an award in 1960s that is given for significant contributions into the silicon chemistry. In his works Kipping was noted for using
Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . ...
s to make alkylsilanes and arylsilanes and the prepartion of silicone oligomers and polymers for the first time.


Occurrence and applications

Organosilicon compounds are widely encountered in commercial products. Most common are antifoamers, caulks (sealant), adhesives, and coatings made from
silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cookin ...
s. Other important uses include agricultural and plant control
adjuvant In pharmacology, an adjuvant is a drug or other substance, or a combination of substances, that is used to increase the efficacy or potency of certain drugs. Specifically, the term can refer to: * Adjuvant therapy in cancer management * Analgesi ...
s commonly used in conjunction with
herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
s and
fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality ...
s.


Biology and medicine

Carbon–silicon bonds are absent in
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
, however enzymes have been used to artificially create carbon-silicon bonds in living microbes.
Silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is a ...
s, on the other hand, have known existence in
diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...
s. Silafluofen is an organosilicon compound that functions as a
pyrethroid A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums ('' Chrysanthemum cinerariaefolium'' and '' C. coccineum''). Pyrethroids are used as commercial and household insecticides. ...
insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed t ...
. Several organosilicon compounds have been investigated as pharmaceuticals.


Properties of Si–C, Si–O, and Si–F bonds

In most organosilicon compounds, Si is tetravalent with
tetrahedral molecular geometry In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−) = 109.4712206...° ≈ 109.5° when all four substituents a ...
. Carbon–silicon bonds compared to carbon–carbon bonds are longer (186 pm vs. 154 pm) and weaker with bond dissociation energy 451 kJ/ mol vs. 607 kJ/mol. The C–Si bond is somewhat polarised towards carbon due to carbon's greater electronegativity (C 2.55 vs Si 1.90). The Si–C bond can be broken more readily than typical C–C bonds. One manifestation of bond polarization in organosilanes is found in the Sakurai reaction. Certain alkyl silanes can be oxidized to an
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
in the Fleming–Tamao oxidation. Another manifestation is the β-silicon effect describes the stabilizing effect of a β-silicon atom on a carbocation with many implications for reactivity. Si–O bonds are much stronger (809 kJ/mol compared to 538 kJ/mol) than a typical C–O single bond. The favorable formation of Si–O bonds drives many
organic reaction Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical ...
s such as the
Brook rearrangement In organic chemistry the Brook rearrangement refers to any ,''n''carbon to oxygen silyl migration. The rearrangement was first observed in the late 1950s by Canadian chemist Adrian Gibbs Brook (1924–2013), after which the reaction is named. The ...
and Peterson olefination.


Preparation

The first organosilicon compound, tetraethylsilane, was prepared by
Charles Friedel Charles Friedel (; 12 March 1832 – 20 April 1899) was a French chemist and mineralogist. Life A native of Strasbourg, France, he was a student of Louis Pasteur at the Sorbonne. In 1876, he became a professor of chemistry and mineralogy at ...
and
James Crafts James Mason Crafts (March 8, 1839 – June 20, 1917) was an American chemist, mostly known for developing the Friedel–Crafts alkylation and acylation reactions with Charles Friedel in 1876. Biography James Crafts, the son of Royal Altamo ...
in 1863 by reaction of tetrachlorosilane with diethylzinc. The bulk of organosilicon compounds derive from organosilicon chlorides . These chlorides are produced by the "
Direct process The direct process, also called the direct synthesis, Rochow process, and Müller-Rochow process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and ...
", which entails the reaction of
methyl chloride Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, odorless, flammable gas. Methyl chloride is a crucial reagent in industria ...
with a silicon-copper alloy. The main and most sought-after product is dimethyldichlorosilane: :2 + Si → A variety of other products are obtained, including trimethylsilyl chloride and methyltrichlorosilane. About 1 million tons of organosilicon compounds are prepared annually by this route. The method can also be used for phenyl chlorosilanes.


Hydrosilylation

After the Direct Process, a second major method for the formation of Si-C bonds is hydrosilylation (also called hydrosilation). In this process, compounds with Si-H bonds (hydrosilanes) add to unsaturated substrates. Commercially, the main substrates are
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s. Other unsaturated functional groups—
alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...
s, imines,
ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...
s, and
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
s. An example is the hydrosilation of phenylacetylene: Hydrosilylation requires metal catalysts, especially those based on
platinum group metal The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered tog ...
s. In the related silylmetalation, a metal replaces the hydrogen atom.


Cleavage or Si-Si bonds

Hexamethyldisilane reacts with methyl lithium to give trimethylsilyl lithium: : Similarly, tris(trimethylsilyl)silyl lithium is derived from tetrakis(trimethylsilyl)silane: :


Functional groups

Silicon is a component of many functional groups. Most of these are analogous to organic compounds. The overarching exception is the rarity of multiple bonds to silicon, as reflected in the
double bond rule In chemistry, the double bond rule states that elements with a principal quantum number greater than 2 for their valence electrons ( period 3 elements and higher) tend not to form multiple bonds (e.g. double bonds and triple bonds). The double ...
.


Silanols, siloxides, and siloxanes

Silanols are analogues of alcohols. They are generally prepared by hydrolysis of silyl chlorides: : + → + HCl Less frequently silanols are prepared by oxidation of silyl hydrides, a reaction that uses a metal catalyst: :2 + → 2 Many silanols have been isolated including and . They are about 500x more acidic than the corresponding alcohols. Siloxides are the deprotonated derivatives of silanols: "" : + NaOH → + Silanols tend to dehydrate to give siloxanes: :2 → + Polymers with repeating siloxane linkages are called
silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cookin ...
s. Compounds with an Si=O double bond called silanones are extremely unstable.


Silyl ethers

Silyl ether Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protecting ...
s have the connectivity Si-O-C. They are typically prepared by the reaction of alcohols with silyl chlorides: : + ROH → + HCl Silyl ethers are extensively used as
protective group A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In ma ...
s for
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s. Exploiting the strength of the Si-F bond, fluoride sources such as tetra-n-butylammonium fluoride (TBAF) are used in deprotection of silyl ethers: : + + → + H-O-R +


Silyl chlorides

Organosilyl chlorides are important commodity chemicals. They are mainly used to produce
silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cookin ...
polymers as described above. Especially important silyl chlorides are dimethyldichlorosilane (), methyltrichlorosilane (), and trimethylsilyl chloride () are all produced by
direct process The direct process, also called the direct synthesis, Rochow process, and Müller-Rochow process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and ...
. More specialized derivatives that find commercial applications include dichloromethylphenylsilane, trichloro(chloromethyl)silane, trichloro(dichlorophenyl)silane, trichloroethylsilane, and phenyltrichlorosilane. Although proportionately a minor outlet, organosilicon compounds are widely used in
organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
. Notably trimethylsilyl chloride is the main silylating agent. One classic method called the Flood reaction for the synthesis of this compound class is by heating hexaalkyldisiloxanes with concentrated
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
and a sodium
halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a flu ...
.


Silyl hydrides

The silicon to hydrogen bond is longer than the C–H bond (148 compared to 105 pm) and weaker (299 compared to 338 kJ/mol). Hydrogen is more
electronegative Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
than silicon hence the naming convention of silyl ''hydrides''. Commonly the presence of the hydride is not mentioned in the name of the compound. Triethylsilane has the formula . Phenylsilane is . The parent compound is called silane.


Silenes

Organosilicon compounds, unlike their carbon counterparts, do not have a rich
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
chemistry. Compounds with silene Si=C bonds (also known as alkylidenesilanes) are laboratory curiosities such as the silicon benzene analogue silabenzene. In 1967, Gusel'nikov and Flowers provided the first evidence for silenes from pyrolysis of ''dimethylsilacyclobutane''. The first stable (kinetically shielded) silene was reported in 1981 by Brook. Disilenes have Si=Si double bonds and disilynes are silicon analogues of an alkyne. The first Silyne (with a silicon to carbon triple bond) was reported in 2010.


Siloles

Siloles, also called silacyclopentadienes, are members of a larger class of compounds called
metallole Metalloles are derivatives of cyclopentadiene in which the carbon atom at position 5, the saturated carbon, is replaced by a heteroatom. In contrast to its parent compound, the numbering of the metallole starts at the heteroatom. Some of these com ...
s. They are the silicon analogs of
cyclopentadiene Cyclopentadiene is an organic compound with the formula C5H6.LeRoy H. Scharpen and Victor W. Laurie (1965): "Structure of cyclopentadiene". ''The Journal of Chemical Physics'', volume 43, issue 8, pages 2765-2766. It is often abbreviated CpH beca ...
s and are of current academic interest due to their
electroluminescence Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting fro ...
and other electronic properties. Siloles are efficient in electron transport. They owe their low lying LUMO to a favorable interaction between the
antibonding In chemical bonding theory, an antibonding orbital is a type of molecular orbital that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more no ...
sigma Sigma (; uppercase Σ, lowercase σ, lowercase in word-final position ς; grc-gre, σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used a ...
silicon orbital with an
antibonding In chemical bonding theory, an antibonding orbital is a type of molecular orbital that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more no ...
pi orbital of the
butadiene 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two v ...
fragment.


Pentacoordinated silicon

Unlike carbon, silicon compounds can be coordinated to five atoms as well in a group of compounds ranging from so-called silatranes, such as phenylsilatrane, to a uniquely stable pentaorganosilicate: : The stability of hypervalent silicon is the basis of the
Hiyama coupling The Hiyama coupling is a palladium-catalyzed cross-coupling reaction of organosilanes with organic halides used in organic chemistry to form carbon–carbon bonds (C-C bonds). This reaction was discovered in 1988 by Tamejiro Hiyama and Yasuo Ha ...
, a coupling reaction used in certain specialized organic synthetic applications. The reaction begins with the activation of Si-C bond by
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ty ...
: : + R"-X + → R-R" + +


Various reactions

Certain
allyl In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, ...
silanes can be prepared from allylic
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
s such as 1 and monosilylcopper compounds, which are formed ''in situ'' by the reaction of the disilylzinc compound 2, with Copper Iodide, in: : In this reaction type, silicon polarity is reversed in a chemical bond with
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and a formal
allylic substitution An allylic rearrangement or allylic shift is an organic reaction in which the double bond in an allyl chemical compound shifts to the next carbon atom. It is encountered in nucleophilic substitution. In reaction conditions that favor a SN1 react ...
on the
benzoyl In organic chemistry, benzoyl (, ) is the functional group with the formula C6H5CO-. It can be viewed as benzaldehyde missing one hydrogen. The term "benzoyl" should not be confused with benzyl, which has the formula C6H5CH2. The benzoyl group ...
oxy group takes place.


Environmental effects

Organosilicon compounds affect bee (and other insect) immune expression, making them more susceptible to viral infection.


See also

*Compounds of carbon with period 3 elements: organoaluminum compounds,
organophosphorus compound Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective i ...
s,
organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulf ...
s *Compounds of carbon with other group 14 elements: organogermanium compounds,
organotin compound Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered ...
s,
organolead compound Organolead compounds are chemical compounds containing a chemical bond between carbon and lead. Organolead chemistry is the corresponding science. The first organolead compound was hexaethyldilead (Pb2(C2H5)6), first synthesized in 1858.''Main Gro ...
s *
Silylene Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
s, the
carbene In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" m ...
counterparts *
Silylenoid A silylenoid in organosilicon chemistry is a type of chemical compound with the general structure where R is any organic residue, X a halogen and M a metal. Silylenoids are the silicon pendants of carbenoid and both compounds have carbene or silyl ...
s, the carbenoid counterparts *
Decamethylsilicocene Decamethylsilicocene, (C5Me5)2Si, is a group 14 sandwich compound. It is an example of a main-group cyclopentadienyl complex; these molecules are related to metallocenes but contain p-block elements as the central atom. It is a colorless, air sens ...


References


External links

*Magnus Walter'
Selected Aspects of Organosilicon Chemistry
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*S. Marsden (Editor)
Contemporary organosilicon chemistry.
Thematic Series in the Open Access Beilstein Journal of Organic Chemistry. {{ChemicalBondsToCarbon