Silabenzene
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[[Image:silabenzenes.svg|thumb|right|300px|Unstable silabenzenes]]'''Silabenzene''' is a [[aromaticity#Heterocyclics|heteroaromatic]] compound containing a [[silicon]] atom instead of the [[carbon]] atom in [[benzene]], so silabenzene has been one of the most interesting targets of theoretical and synthetic-[[Organic chemistry|organic chemists]] considering the question of whether heavy [[benzene]]s exhibit [[aromatic]]ity. The chemical structure of silabenzene is shown to the right.
Although several [[aromatic|heteroaromatic]] compounds bearing [[nitrogen]], [[oxygen]], and [[sulfur]] atoms have been known since the early stages of [[organic chemistry]], silabenzene had been considered to be a transient, un-isolable compound and was detected only in low-temperature matrices for a long time. In recent years, however, a [[kinetic reaction control|kinetically stabilized]] silabenzene and other heavy [[aromatic]] compounds with [[silicon]] or [[germanium]] atoms have been reported.
==Synthesis==
Several attempts to synthesize stable silabenzenes have been reported from the late 1970s using well-known bulky substituents such as a [[butyl|tert-butyl]], a (1,1-dimethylethyl) group or a TMS ([[trimethylsilyl]]) group, but such silabenzenes readily react with themselves to give the corresponding [[dimer]] even at low temperature (below -100[[°C]]) due to the high reactivity of [[silicon]]-[[carbon]] ''π'' bonds. Following the synthesis of the [[naphthalene]] pendant 2-silanaphthalene, the first sila-aromatic compound, by Norihiro Tokitoh and Renji Okazaki in 1997, the same group reported thermally stable silabenzene in 2000 taking advantage of a new [[steric effects|steric]] [[protective group]].
[[Image:stablesilabenzene.png|frame|center|300px|Stable 2-silanaphthalene and silabenzene]]
In 2004, 1,2-disilabenzene was synthesized via formal [2+2+2] [[cycloaddition|cyclotrimerization]] of a disilyne (Si-Si triple bonded species) and [[phenylacetylene]].
==Properties and reactions==
Isolated silabenzene reacts with various reagents at 1,2- or 1,4-positions to give [[diene]]-type products, so the [[aromatic]]ity of the silabenzene is destroyed. It is different from [[benzene]], which reacts with [[electrophile]]ss to give not [[diene]]s but substituted benzenes, so benzene sustains its [[aromatic]]ity. [[Silicon]] is a [[metalloid|semi-metal]] [[chemical element|element]], so the Si-C ''π'' bond in the silabenzene is highly [[polar bond|polarized]] and easily broken. The silabenzene is also light-sensitive; [[Ultraviolet|UV]] irradiation gives the [[valence (chemistry)|valence]] [[isomer]], a silabenzvalene. The theoretical calculations and the [[Nuclear magnetic resonance|NMR]] [[chemical shift]]s of silabenzenes, though, show that silabenzene is an [[aromatic]] compound in spite of the different reactivity from [[benzene]] and other classical [[aromatic]] compounds.
== See also ==
* 6-membered aromatic rings with one carbon replaced by another group: [[borabenzene]],[[benzene]], '''silabenzene''', [[germanabenzene]],[[stannabenzene]], [[pyridine]], [[phosphorine]], [[pyrylium salt]]
==External links==
[[Category:Organosilicon compounds]]
[[Category:Heterocyclic compounds]]
[[Category:Simple aromatic rings]]