Fulvalene

Fulvalene
Names
	Other names Bicyclopentyliden-2,4,2',4'-tetraene ; 1,1'-Bi[cylopentadienylidene] ; Pentafulvalene ; Bicyclopentadienylidene ; [5,5']Bicyclopentadienylidene
Identifiers
CAS Number	91-12-3 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:51994 ;
ChemSpider	9083553 ;
PubChem CID	10908294;
CompTox Dashboard (EPA)	DTXSID10447902 ;
	InChI InChI=1S/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H Key: XEOSBIMHSUFHQH-UHFFFAOYSA-N ; InChI=1/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H Key: XEOSBIMHSUFHQH-UHFFFAOYAP;
	SMILES C=1\C=C/C(/C=1)=C2\C=C/C=C2;
Properties
Chemical formula	C10H8
Molar mass	128.174 g·mol−1
Density	1.129 g/ml
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Fulvalene (bicyclopentadienylidene) is the member of the fulvalene family with the molecular formula C₁₀H₈. It is of theoretical interest as one of the simplest non-benzenoid conjugated hydrocarbons. Fulvalene is an unstable isomer of the more common benzenoid aromatic compounds naphthalene and azulene. Fulvalene consists of two 5-membered rings, each with two double bonds, joined by yet a fifth double bond. It has D_2h symmetry.

History

An earlier attempt at synthesis of fulvalene in 1951 by Pauson and Kealy resulted in the accidental discovery of ferrocene.^[1] Its synthesis was first reported in 1958 by E. A. Matzner, working under William von Eggers Doering.^[2] In this method, cyclopentadienyl anion is coupled with iodine to the dihydrofulvalene. Double deprotonation of dihydrofulvalene with n-butyllithium gives the dilithio derivative, which oxidizes with oxygen. Fulvalene was spectroscopically observed at 77 K from photolysis of diazocyclopentadiene, which induces dimerization of cyclopentadiene-derived carbenes.^[3] The compound was isolated in 1986.^[4] It was found to be nonaromatic. Above −50 °C it dimerizes by a Diels-Alder reaction.

Perchlorofulvalene (C₄Cl₄C)₂ is quite stable in contrast to fulvalene itself.^[5]

^ T. J. Kealy, P. L. Pauson (1951). "A New Type of Organo-Iron Compound". Nature. 168 (4285): 1039–1040. Bibcode:1951Natur.168.1039K. doi:10.1038/1681039b0. S2CID 4181383.
^ Dissertation Abstracts Int'l 26-06 page 3270 6411876.
^ Demore, William B.; Pritchard, H. O.; Davidson, Norman (1959). "Photochemical Experiments in Rigid Media at Low Temperatures. II. The Reactions of Methylene, Cyclopentadienylene and Diphenylmethylene". Journal of the American Chemical Society. 81 (22): 5874–5879. doi:10.1021/ja01531a008.
^ Escher, André; Rutsch, Werner; Neuenschwander, Markus (1986). "Synthese von Pentafulvalen durch oxidative Kupplung von Cyclopentadienid mittels Kupfer(II)-chlorid". Helvetica Chimica Acta. 69 (7): 1644 - 1654. doi:10.1002/hlca.19860690719.
^ Mark, V. (1966). "Perchlorofulvalene". Organic Syntheses. 46: 93. doi:10.15227/orgsyn.046.0093.