Fulvenes Explained

Fulvenes are the class of hydrocarbon obtained by formally cross-conjugating one ring and methylidene through a common exocyclic double bond.

The name is derived from fulvene, which has one pentagonal ring. Other examples include methylenecyclopropene (triafulvene) and heptafulvene.

Subclasses

Several types of fulvenes are defined. They are:

• triafulvene
• pentafulvene
• heptafulvene
• nonafulvene

Preparation

Fulvenes are readily prepared by the condensation of cyclopentadiene and aldehydes and ketones:

C₅H₆ + R₂C=O → C₄H₄C=CR₂ + H₂OThiele is credited with discovering this reaction.^{[1] [2]}

Modern synthesis of fulvenes employ buffer systems.^{[3] [4]}

Ligand in organometallic chemistry

Fulvenes are common ligands and ligand precursors in organometallic chemistry.^[5] 2,3,4,5-Tetramethylfulvene, abbreviated Me₄Fv, results from the deprotonation of cationic pentamethylcyclopentadienyl complexes.^[6] Some Me₄Fv complexes are called tuck-in complexes.

Notes and References

1. Thiele, J. . Ueber Ketonreactionen bei dem Cyclopentadiën. . 33. 666–673. 1900. 10.1002/cber.190003301113.
2. 10.15227/orgsyn.047.0052. 6-(Dimethylamino)Fulvene. Hafner. K.. Vöpel. K. H. . Ploss. G.. König. C.. Organic Syntheses. 1967. 47. 52.
3. Coşkun. Necdet. Erden. Ihsan. 2011-11-11. An efficient catalytic method for fulvene synthesis. Tetrahedron. 67. 45. 8607–8614. 10.1016/j.tet.2011.09.036. 0040-4020. 3196336. 22021940.
4. Sieverding. Paul. Osterbrink. Johanna. Besson. Claire. Kögerler. Paul. 2019-01-18. Kinetics and mechanism of pyrrolidine buffer-catalyzed fulvene formation. J. Org. Chem.. 84. 2. 486–494. 10.1021/acs.joc.8b01660. 30540466. 0022-3263.
5. 10.1039/B707310K. Bioorganometallic fulvene-derived titanocene anti-cancer drugs. 2008. Strohfeldt. Katja. Tacke. Matthias. Chemical Society Reviews. 37. 6. 1174–87. 18497930.
6. Kreindlin, A. Z. . Rybinskaya, M. A. . Cationic and Neutral Transition Metal Complexes with a Tetramethylfulvene or Trimethylallyldiene Ligand. Russian Chemical Reviews . 73. 417–432. 2004. 10.1070/RC2004v073n05ABEH000842. 5. 2004RuCRv..73..417K .