A fulvalene is a

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

obtained by formally cross-conjugating two rings through a common

exocyclic In organic chemistry, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. Cyc ...

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

. The name is derived from the similarly structured

fulvenes Fulvenes are the class of hydrocarbon obtained by formally cross-conjugation, cross-conjugating one Cycloalkane, ring and methylidene through a common exocyclic alkene, double bond. The name is derived from fulvene, which has one pentagonal ring. ...

which lack one ring. Pentafulvalene (2) is also called simply

fulvalene 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 mor ...

, the parent structure of this class. Triapentafulvalene (3) is also known as

calicene Calicene or triapentafulvalene is a hydrocarbon of the fulvalene class with chemical formula C8H6, composed of a cyclopentadiene ring and a cyclopropene ring linked by a double bond. Its name is derived from the Latin ''calix'' meaning "goblet", ...

from the words ''calix'' or ''

chalice A chalice (from Latin 'cup', taken from the Ancient Greek () 'cup') is a drinking cup raised on a stem with a foot or base. Although it is a technical archaeological term, in modern parlance the word is now used almost exclusively for the ...

'' because of its wine-glass appearance. In general, the parent fulvalenes are very unstable; for instance, the parent

triafulvalene Triafulvalene or cyclopropenylidenecyclopropene is a fulvalene hydrocarbon with chemical formula C6H4, composed of two linked cyclopropene rings. Triafulvalene has never been isolated, since it can decompose via an isodesmic reaction. However, it ...

(1) has never been synthesized. On the other hand, stable fulvalenes can be obtained by proper

substitution Substitution may refer to: Arts and media *Substitution (poetry), a variation in poetic scansion * Substitution (theatre), an acting methodology Music *Chord substitution, swapping one chord for a related one within a chord progression *Tritone ...

or benzannulation. Several members should be stabilized taking into account a dipolar mesomeric form with for instance

sesquifulvalene Sesquifulvalene or pentaheptafulvalene is a hydrocarbon in the fulvalene class with chemical formula C12H10. It is composed of linked cyclopentadiene and cycloheptatriene rings. Properties In the ground state, which is a singlet state, the cent ...

4, which can be thought of as a

tropylium cation The tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of 7H7sup>+. Its name derives from the molecule tropine from which cycloheptatriene (tropylidene) was first synthesized in 1881. Salts of the tropylium cation ...

joined to a

cyclopentadienyl Cyclopentadienyl can refer to * Cyclopentadienyl anion, or cyclopentadienide, ** Cyclopentadienyl ligand * Cyclopentadienyl radical, • * Cyclopentadienyl cation, See also * Pentadienyl {{Chemistry index ...

anion (both stable and

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

). In this compound the dipolar structure is calculated to contribute 23% to the total structure.

Fulvalenes as a ligand

: Tungsten fulvalene complex Fulvalenes forms stable

organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

complexes that can be formally considered derivatives of the dianion C₁₀H₈²⁻, akin to two bonded

cyclopentadienyl anion Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pin ...

Ferrocene Ferrocene is an organometallic chemistry, organometallic compound with the formula . The molecule is a Cyclopentadienyl complex, complex consisting of two Cyclopentadienyl anion, cyclopentadienyl rings sandwiching a central iron atom. It is an o ...

was isolated from an attempted synthesis of pentafulvalene. Many compounds are known, especially for the early transition metals. The bond joining the two rings in some fulvalene complexes can break reversibly.Boese, R. J.; Cammack, K.; Matzger, A. J.; Pflug, K.; Tolman, W. B.; Vollhardt, K. P. C.; Weidman, T. W. "Photochemistry of (Fulvalene)tetracarbonyldiruthenium and Its Derivatives: Efficient Light Energy Storage Devices" Journal of the American Chemistry Society 1997, volume 119, p. 6757-6773.

References

{{Reflist Fulvalenes