Pentalene

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| verifiedrevid = 381670614

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| ImageFile = Pentalene.svg

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| ImageFile1 = Pentalene-3D-balls.png

| ImageSize1 = 180

| PIN = Pentalene{{cite book |author=International Union of Pure and Applied Chemistry |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=The Royal Society of Chemistry |pages=209 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}

| OtherNames = Bicyclooctatetraene

| Section1 = {{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|??}}

| CASNo = 250-25-9

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| UNII = E5A3KT7S2A

| PubChem = 5460726

| SMILES = C1=CC2=CC=CC2=C1

| InChI = 1/C8H6/c1-3-7-5-2-6-8(7)4-1/h1-6H

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEBI = 33074

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| ChemSpiderID = 4574194

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| Section2 = {{Chembox Properties

| C=8|H=6

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Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings.{{cite journal | doi = 10.1002/anie.201307162 | title = Pentalenes-From Highly Reactive Antiaromatics to Substrates for Material Science | year = 2013 | last1 = Hopf | first1 = Henning | journal = Angewandte Chemie International Edition | volume = 52 | issue = 47 | pages = 12224–6 | pmid=24127399}} It has chemical formula {{chem2|C8H6}}. It is antiaromatic, because it has 4n π electrons where n is any integer. For this reason it dimerizes even at temperatures as low as −100 °C.{{cite book|last1=Carey|first1=Francis A.|last2=Sundberg|first2=Richard J.|title=Advanced Organic Chemistry: Part A Structure and Mechanisms|edition=2nd|year=1984|publisher=Plenum Press|location=New York, NY|isbn=0-306-41198-9}}{{cite journal | author1 = Bally T. | author2 = Chai S. | author3 = Neuenschwander M. | author4 = Zhu Z. | year = 1997 | title = Pentalene: Formation, Electronic, and Vibrational Structure | journal = J. Am. Chem. Soc. | volume = 119 | issue = 8 | pages = 1869–1875(7) | doi = 10.1021/ja963439t | url = http://www-chem.unifr.ch/tb/bally/pdf/pentalene.pdf | format = reprint | access-date = 2007-07-06 | archive-date = 2007-03-15 | archive-url = https://web.archive.org/web/20070315163804/http://www-chem.unifr.ch/tb/bally/pdf/pentalene.pdf | url-status = dead }} The derivative 1,3,5-tri-tert-butylpentalene was synthesized in 1973.{{cite journal | last1 = Hafner | first1 = K. | last2 = Süss | first2 = H. U. | year = 1973 | title = 1,3,5-Tri-tert-Butylpentalene. A Stabilized Planar 8π-Electron System | journal = Angew. Chem. Int. Ed. Engl. | volume = 12 | issue = 7| pages = 575–577 | doi = 10.1002/anie.197305751 }} Because of the tert-butyl substituents this compound is thermally stable. Pentalenes can also be stabilized by benzannulation for example in the compounds benzopentalene and dibenzopentalene.

Dilithium pentalenide was isolated in 1962, long before pentalene itself in 1997.{{cite journal | doi = 10.1021/ja00864a038 | title = The Pentalenyl Dianion | year = 1962 | last1 = Katz | first1 = Thomas J. | last2 = Rosenberger | first2 = Michael. | journal = Journal of the American Chemical Society | volume = 84 | issue = 5 | pages = 865}} It is prepared from reaction of dihydropentalene (pyrolysis of an isomer of dicyclopentadiene) with n-butyllithium in solution and forms a stable salt. In accordance with its structure proton NMR shows 2 signals in a 2 to 1 ratio. The addition of two electrons removes the antiaromaticity; it becomes a planar 10π-electron aromatic species and is thus a bicyclic analogue of the cyclooctatetraene (COT) dianion {{chem2|C8H8(2−)}}.

:Image:Pentalenide.svg

The dianion can also be considered as two fused cyclopentadienyl rings, and has been used as a ligand in organometallic chemistry to stabilise many types of mono- and bimetallic complexes, including those containing multiple metal-metal bonds, and anti-bimetallics with extremely high levels of electronic communication between the centers.{{cite journal | doi = 10.1016/j.ccr.2005.11.020 | title = The organometallic chemistry of pentalene | year = 2006 | last1 = Summerscales | first1 = Owen T. | last2 = Cloke | first2 = F. Geoffrey N. | journal = Coordination Chemistry Reviews | volume = 250 | issue = 9–10 | pages = 1122}}