Organosilicon
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[[Image:OrganosiliconLogo.png|right|150px|Organosilicon compounds]]'''Organosilicon compounds''' are [[Organic chemistry|organic]] [[chemical compound|compounds]] containing [[carbon]] [[silicon]] [[chemical bond|bonds]]. '''Organosilicon chemistry''' is the corresponding science exploring their properties and reactivity.<ref>''Silicon in Organic Synthesis'' Colvin, E. Butterworth: London 1981</ref>
Like carbon, the organically bound silicon is [[tetravalent]] and [[tetrahedral molecular geometry|tetrahedral]]. Carbon-silicon bonds are not found in any [[biomolecule]].<ref>''Organosilicon Chemistry'' S. Pawlenko Walter de Gruyter New York 1986</ref> The first organosilicon compound, tetraethylsilane was discovered by [[Charles Friedel]] and [[James Crafts]] in 1863 by reaction of [[tetrachlorosilane]] with [[diethyl zinc]]. The carbosilicon [[silicon carbide]] is an ''[[inorganic chemistry|inorganic]]'' compound.
== Organosilanes ==
Carbon silicon bonds compared to carbon carbon bonds are longer (186 [[picometer|pm]] vs. 154 pm) and weaker with [[bond dissociation energy]] 451 [[kilojoule|kJ]]/[[mole (unit)|mol]] vs. 607 kJ/mol <ref>''Handbook of Chemistry and Physics'', 81st Edition CRC Press ISBN 0-8493-0481-4</ref>. The C–Si is somewhat polarized towards carbon due to its higher [[electronegativity]] (C 2.55 vs Si 1.90). One manifestation of bond polarization in organosilanes is found in the [[Sakurai reaction]]. In oxidative couplings silicon is represented by the [[Hiyama coupling]]. Certain alkyl silanes can be oxidized to an [[alcohol]] in the [[Fleming-Tamao oxidation]].
Certain [[allyl]] silanes can be prepared from allylic [[ester]] such as '''1''' and monosilylcopper compounds such as '''2''' in <ref>''Mechanistic insight into copper-catalysed allylic substitutions with bis(triorganosilyl) zincs. Enantiospecific preparation of -chiral silanes'' Eric S. Schmidtmann and Martin Oestreich [[Chem. Commun.]], '''2006''', 3643 - 3645, {{DOI|10.1039/b606589a}}</ref> <ref> By [[isotope labeling|isotopic]] [[desymmetrisation]] on the substrate (replacing hydrogen by [[isotope labeling|deuterium]]) it can be demonstated that the reaction proceeds not through the symmetrical π-allyl intermediate '''5''' which would give an equal mixture of '''3a''' and '''3b''' but through the Π-δ intermediate '''4''' resulting in '''3a''' only, through an [[oxidative addition|oxidative addition / reductive elimination]] step</ref>.
:
:[[Image:AllylSilaneSynthesis.png|400px|Allylic substitution forming a allyl silane]]
In this reaction type silicon polarity is reversed in a chemical bond with [[zinc]] and a formal [[allylic substitution]] on the [[benzoyl]]oxy group takes place.
The chemistry of [[silane]]s such as [[tetramethylsilane]] is comparable to that of [[alkane]]s in many aspects such as thermal stability. The [[Beta-silicon effect|β-silicon effect]] describes the stabilizing effect of a β-silicon atom on a carbocation with many implications for reactivity.
== Siloxides ==
More notably bonds of silicon to [[oxygen]] are much shorter and stronger (809 compared to 538 kJ/mol) than that of those of carbon to oxygen. The polarization in this bond increases towards oxygen. Examples are '''silyl acetals''' RR'Si(OR)2, the [[siloxane]]s and the polymeric [[polysiloxane]]s. [[Silyl ether]]s are extensively used as [[protective group]]s for [[alcohol]]s. Only silicon bonds to [[fluorine]] are stronger and that is why the fluorine source [[TASF reagent|TASF]] (or more commonly [[TBAF]]) is useful in deprotection. The favorable formation of Si–O bonds drive many [[organic reaction]]s such as the [[Brook rearrangement]] and [[Peterson olefination]].
Another manifestation is the highly explosive nature of the silicon pendant of [[pentaerytritol tetranitrate]] <ref>''The Sila-Explosives Si(CH2N3)4 and Si(CH2ONO2)4: Silicon Analogues of the Common Explosives Pentaerythrityl Tetraazide, C(CH2N3)4, and Pentaerythritol Tetranitrate, C(CH2ONO2)4'' Thomas M. Klapötke, Burkhard Krumm, Rainer Ilg, Dennis Troegel, and Reinhold Tacke [[J. Am. Chem. Soc.]]; '''2007'''; ASAP Web Release Date: 04-May-2007; (Article) {{DOI|10.1021/ja071299p}}</ref> <ref>''Sila-Explosives Offer A Better Bang'' Stephen K. Ritter [[Chemical & Engineering News]] May 7 '''2007'''[http://pubs.acs.org/cen/news/85/i20/8520news5.html Link]</ref>:
:[[Image:SilaExplosives.png|300px|Sila explosive Klapötke 2007]]
A single crystal of this compound, first synthesized in 2007 even detonates when in contact with a [[teflon]] spatula and in fact made full characterization impossible. Another contributor to its exothermic decomposition (inferred from much safer [[in silico]] experimentation) is the ability of silicon in its crystal phase to coordinate to two oxygen nitrito groups in addition to regular coordination to the four carbon atoms. This additional coordination would make formation of [[silicon dioxide]] (one of the decomposition products) more facile.
==Silyl halides==
Organosilyl halides are important [[reagent]]s in organic chemistry notably [[trimethylsilyl chloride]] Me<sub>3</sub>SiCl. A classic method called the '''Flood reaction''' for the synthesis of this compound class is by heating hexaalkyldisiloxanes R<sub>3</sub>SiOSiR<sub>3</sub> with concentrated [[sulfuric acid]] and a sodium [[halide]] <ref>''Preparation of Triethylsilicon Halides'' E. A. Flood [[J. Am. Chem. Soc.]]; '''1933'''; 55(4) pp 1735 - 1736; {{DOI|10.1021/ja01331a504}}</ref>. Other relevant silyl halides are '''dichloromethylphenylsilane''', '''dimethyldichlorosilane''', '''methyltrichlorosilane''', '''(4-aminobutyl)diethoxymethylsilane''', '''trichloro(chloromethyl)silane''', '''trichloro(dichlorophenyl)silane''', '''trichloroethylsilane''', '''trichlorophenylsilane''' and '''trimethylchlorosilane'''
== 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]] than silicon hence the naming convention of silyl hydrides. Silyl hydrides are very reactive and used as [[reducing agent]]s for example [[PMHS]].
In one study triethylsilylhydride is used in the conversion of an [[phenyl azide]] to an [[aniline]] <ref>''Radical Reduction of Aromatic Azides to Amines with Triethylsilane'' Luisa Benati, Giorgio Bencivenni, Rino Leardini, Matteo Minozzi, Daniele Nanni, Rosanna Scialpi, Piero Spagnolo, and Giuseppe Zanardi [[Elumalai Palani., ''J. Org. Chem''.]]; '''2006'''; 71(15) pp 5822 - 5825; (Note) {{DOI|10.1021/jo060824k}}</ref>:
:[[Image:AzideReductionByTriethylsilylhydride.png|400px|Azide Reduction By Triethylsilylhydride]]
In this reaction [[Azobis(cyclohexanecarbonitrile)|ACCN]] is a [[radical initiator]] and an [[aliphatic]] [[thiol]] transfers radical character to the silylhydride. The triethylsilyl [[free radical]] then reacts with the azide with expulsion of nitrogen to a N-silylarylaminyl radical which grabs a proton from a thiol completing the [[catalytic cycle]]:
:[[Image:AzideReductionMechanism.png|400px|Azide Reduction By Triethylsilylhydride mechanism]]
Aqueous workup then gives aniline.
Silyl hydrides can even take up the reduction of robust molecules such as [[carbon dioxide]] (to [[methane]]) <ref>''From Carbon Dioxide to Methane: Homogeneous Reduction of Carbon Dioxide with Hydrosilanes Catalyzed by Zirconium-Borane Complexes''
Tsukasa Matsuo and Hiroyuki Kawaguchi [[J. Am. Chem. Soc.]]; '''2006'''; 128(38) pp 12362 - 12363; {{DOI|10.1021/ja0647250}}</ref>:
:[[Image:Carbondioxidereduction.png|400px|Carbon dioxide reduction]]
Although it takes a very complex [[catalyst]] system.
===Hydrosilylation===
Silyl hydrides react with various unsaturated substrates such as [[alkene]]s, [[alkyne]]s, [[imine]]s, [[carbonyl]]s and [[oxime]]s to new organosilicon compounds in '''hydrosilylation'''. In the reaction of ''triphenylsilyl hydride'' with [[phenylacetylene]] the reaction product is a [[trans isomer|trans or cis]] or the [[geminal]] vinyl silane, for example <ref>''Effect of the synthetic method of Pt/MgO in the hydrosilylation of phenylacetylene'' Eulalia Ramírez-Oliva, Alejandro Hernández, J. Merced Martínez-Rosales, Alfredo Aguilar-Elguezabal, Gabriel Herrera-Pérez, and Jorge Cervantesa [[Arkivoc]] '''2006''' (v) 126-136 [http://www.arkat-usa.org/ARKIVOC/JOURNAL_CONTENT/manuscripts/2006/EL-1973AP%20as%20published%20mainmanuscript.pdf Link]</ref>:
:[[Image:HydrosilylationTriphenylsilylhydride.png|400px|Hydrosilylation with Triphenylsilyl hydride]]
In the related [[silylmetalation]], a metal replaces the hydrogen atom.
== Silenes ==
Organosilicon compounds unlike their carbon counterparts do not have a rich [[double bond]] chemistry due to the large difference in electronegativity. Existing compounds with [[organosilene]] Si=C bonds are laboratory curiosities such as the silicon benzene analogue [[silabenzene]], and Si=Si bond containing [[disilene]]s.
==Siloles==
'''Siloles''' are the silicon pendants of [[pyrrole]]s and of current academic interest due to their [[electroluminescence]] and other electronic properties <ref>Direct synthesis of 2,5-dihalosiloles [[Organic Syntheses]] '''2008''', 85, 53-63 http://www.orgsynth.org/orgsyn/pdfs/V85P0053.pdf</ref> <ref>''Synthesis of new dipyridylphenylaminosiloles for highly emissive organic electroluminescent devices'' Laurent Aubouy, Philippe Gerbier, Nolwenn Huby, Guillaume Wantz, Laurence Vignau, Lionel Hirsch and Jean-Marc Jano New J. Chem., '''2004''', 28, 1086 - 1090, {{DOI|10.1039/b405238b}}</ref>. Siloles are efficient in electron transport. They owe their low lying [[LUMO]] to a favorable interaction between the [[antibonding]] [[sigma bond|sigma]] silicon orbital with a [[antibonding]] [[pi orbital]] of the [[butadiene]] fragment.
==Hypercoordinated silicon==
Unlike carbon, silicon compounds can be coordinated to five atoms as well in a group of compounds ranging from so-called [[silatrane]]s to a uniquely stable pentaorganosilicate <ref>''Tetraalkylammonium pentaorganosilicates: the first highly stable silicates with five hydrocarbon ligands'' Sirik Deerenberg, Marius Schakel, Adrianus H. J. F. de Keijzer, Mirko Kranenburg, Martin Lutz, Anthony L. Spek, Koop Lammertsma, [[Chem. Commun.]], '''2002''', (4),348-349 {{DOI|10.1039/b109816k}}</ref>:
:[[Image:Pentaorganosilicate.png|200px|Pentaorganosilicate]]
== See also ==
* Compounds of carbon with [[period 3 element]]s: [[organoaluminum compound]]s, '''organosilicon compounds''', [[organophosphorus compound]]s, [[organosulfur compound]]s,
* Compounds of carbon with other [[carbon group|group 14]] elements: '''organosilicon compounds''', [[organogermanium compound]]s, [[organotin compound]]s, [[organolead compound]]s.
{{ChemicalBondsToCarbon}}
* [[silylene]]s, the [[carbene]] counterparts and [[silylenoid]]s the [[carbenoid]] counterparts.
== External links ==
* Magnus Walter's [http://users.ox.ac.uk/~mwalter/web_05/resources/sil_chem/org_silicon_chem.shtml Selected Aspects of Organosilicon Chemistry]
* [http://www.chem.wisc.edu/areas/reich/orgmet/silicon.htm Silicon in organic synthesis]
* [http://msds.chem.ox.ac.uk/ME/methyltrichlorosilane.html Safety data for methyltrichlorosilane] from the Chemistry Department at Oxford University.
== References ==
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[[Category:silicon compounds]]
[[Category:Organosilicon compounds| ]]
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