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Pentalene

Pentalene

IUPAC name	Pentalene
Identifiers
CAS number	250-25-9
PubChem	5460726
ChEBI	33074
SMILES	c1cc2cccc2c1
InChI	InChI=1/C8H6/c1-3-7-5-2-6-8(7)4-1/h1-6H
Properties
Molecular formula	C₈H₆
Molar mass	102.13 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula C₈H₆ and CAS number 250-25-9. It is antiaromatic, because it has 4n pi electrons. For this reason it dimerizes even at temperatures as low as -100°C ^[1] ^[2]

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Dilithium pentalenide was isolated (1962) long before pentalene itself (1997) ^[3] 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 10 pi aromatic species and is thus a bicyclic analogue of the cyclooctatetraene (COT) dianion C₈H₈^2-.

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 ^[4]

References

^ Carey, Francis A.; Sundberg, Richard J.; (1984). Advanced Organic Chemistry Part A Structure and Mechanisms (2nd ed.). New York N.Y.: Plenum Press. ISBN 0-306-41198-9.
^ Bally T., Chai S., Neuenschwander M., Zhu Z. (1997). "Pentalene: Formation, Electronic, and Vibrational Structure". J. Am. Chem. Soc. 119: 1869-1875(7). doi:10.1021/ja963439t. Retrieved on 2007-07-06.
^ The Pentalenyl Dianion Thomas J. Katz, Michael Rosenberger J. Am. Chem. Soc.; 1962; 84(5); 865-866. doi:10.1021/ja00864a038
^ The Organometallic Chemistry of Pentalene Owen T. Summerscales, F. Geoffrey N. Cloke Coord. Chem. Rev.; 2006; 250; 1122-1140.