Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings.[2] It has chemical formula 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.[3][4] The derivative 1,3,5-tri-tert-butylpentalene was synthesized in 1973.[5] 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.[2]

Preferred IUPAC name
Other names
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3D model (JSmol)
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  • InChI=1/C8H6/c1-3-7-5-2-6-8(7)4-1/h1-6H
  • c1c=c2ccc=c2c1
Molar mass 102.136 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Dilithium pentalenide was isolated in 1962, long before pentalene itself in 1997.[6] 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 C

Synthesis dilithium pentalenide

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.[7]

See alsoEdit


  1. ^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 209. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
  2. ^ a b Hopf, Henning (2013). "Pentalenes-From Highly Reactive Antiaromatics to Substrates for Material Science". Angewandte Chemie International Edition. 52 (47): 12224–6. doi:10.1002/anie.201307162. PMID 24127399.
  3. ^ Carey, Francis A.; Sundberg, Richard J. (1984). Advanced Organic Chemistry: Part A Structure and Mechanisms (2nd ed.). New York, NY: Plenum Press. ISBN 0-306-41198-9.
  4. ^ Bally T.; Chai S.; Neuenschwander M.; Zhu Z. (1997). "Pentalene: Formation, Electronic, and Vibrational Structure" (PDF). J. Am. Chem. Soc. 119 (8): 1869–1875(7). doi:10.1021/ja963439t. Archived from the original (reprint) on 2007-03-15. Retrieved 2007-07-06.
  5. ^ Hafner, K.; Süss, H. U. (1973). "1,3,5-Tri-tert-Butylpentalene. A Stabilized Planar 8π-Electron System". Angew. Chem. Int. Ed. Engl. 12 (7): 575–577. doi:10.1002/anie.197305751.
  6. ^ Katz, Thomas J.; Rosenberger, Michael. (1962). "The Pentalenyl Dianion". Journal of the American Chemical Society. 84 (5): 865. doi:10.1021/ja00864a038.
  7. ^ Summerscales, Owen T.; Cloke, F. Geoffrey N. (2006). "The organometallic chemistry of pentalene". Coordination Chemistry Reviews. 250 (9–10): 1122. doi:10.1016/j.ccr.2005.11.020.