Gourt Home::Gourt :: Ferrocene
| General | Discovered | 1951 | Systematic | bis(η5-cyclopentadienyl)iron(II) | Name | Ferrocene, iron cyclopentadienyl | Chemical formula | Fe(C5H5)2 (C10H10Fe) | Data | Formula weight | 186.04 amu | Melting point | 174–176°C (447–449 K) | Boiling point | 249°C (522 K) | Density | 1,490 g/m3 (20°C) | color | yellow-orange | Solubility | insoluble in water and soluble in organic solvents | Thermochemistry | ΔfH0gas | ΔfH0liquid | ΔfH0solid | S0solid | Safety | Ingestion | ? | Inhalation | ? | Skin | ? | Eyes | ? | More info | Hazardous Chemical Database |
|---|
Ferrocene Fe(C5H5)2 is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom and forming an organometallic sandwich compound.R. Dagani "Fifty Years of Ferrocene Chemistry" Chemical and Engineering News" (December 3, 2001) Volume 79, Number 49, pp. 37-38.
History
Ferrocene, like many synthetic chemical compounds, was first made unintentionally. In 1951, Pauson (often mistakenly spelled Paulson) and Kealy at Duquesne University described the reaction of cyclopentadienyl magnesium bromide and ferric chloride with the goal of oxidatively coupling the diene. Instead, they obtained a light orange powder of "remarkable stability." Ferrocene is more efficiently prepared by the reaction of sodium cyclopentadienyl with anhydrous ferrous chloride in etherial solvents.
Ferrocene's structure was confirmed by NMR spectroscopy and X-ray crystallography. Its distinctive "sandwich" structure led to an explosion of interest in compounds of d-block metals with hydrocarbons, and initiated the development of the now flourishing study of organometallic chemistry. Many other metals can be used in place of iron and many other hydrocarbons can be used instead of cyclopentadienyl.
In ferrocene, the six π-electrons of each aromatic cyclopentadienyl ring are shared with the central Fe2+ ion, giving it an inert gas electron configuration. This configuration makes ferrocene particularly stable.
Physical properties
Ferrocene is an air stable orange solid that readily sublimes in vacuum. As expected for a symmetric and uncharged species, ferrocene is soluble in normal organic solvents, such as benzene, but is insoluble in water.
Chemical properties
Ferrocene undergoes many reactions characteristic of aromatic compounds, notably Friedel-Crafts reactions. In an illustrative undergraduate experiment, ferrocene is acetylated upon treatment with acetic anhydride (or acetyl chloride) in the presence of phosphoric acid as a catalysts:
- Fe(C5H5)2 + (CH3CO)2O → Fe(C5H5)(C5H4C(O)CH3) + CH3CO2H
Ferrocene is readily deprotonated, e.g. by butyl lithium, to give 1,1'-dilithioferrocene, which in turn is a versatile nucleophile.
- Fe(C5H5)2 + 2 C4H9Li → Fe(C5H4Li)2 + 2 C4H10
- Fe(C5H4Li)2 + 2 (C6H5)2PCl → Fe(C5H4P(C6H5)2)2 + 2 LiCl
Unlike related organic compounds, ferrocene has one very special property - the ability to undergo one-electron oxidation at the low potential of ca. 0.4 V vs. a saturated calomel electrode (SCE). Oxidation is usually conducted using FeCl3 to give the blue-colored ferrocenium ion, which is often isolated as its [PF6− salt. Ferrocenium salts are a widely used oxidising agent, in part because the redox product ferrocene is so inert and readily separated from the products.N. G. Connelly, W. E. Geiger, "Chemical Redox Agents for Organometallic Chemistry" Chemical Reviews 1996, vol. 96, pp. 877-910.
Applications
Ferrocene has many applications:
Fuel additivesApplication of fuel additives
Ferrocene and its derivatives are anti-knock agents used in the fuel for petrol engines; they are considered to be safer than tetraalkyl lead additives. It is possible to buy at Halfords a petrol additive solution which contains ferrocene which can be added to unleaded petrol to enable it to be used in vintage cars which were designed to run on leaded petrol. For details of ferrocene as an antiknocking agent see United States Patent 4104036. Unfortuantely, the iron containing deposits formed from ferrocene can form a conductive coating on the sparkplug surfaces leading to sparkplug failure.
In diesel fuel ferrocene reduces the production of soot by the engine.
Medical
It has been found that ferrocenium salts have an anticancer activity, and an experimental drug has been reported which is a ferrocenyl version of tamoxifenThe idea is that the tamoxifen will bind to the estrogen binding site in a cell and the ferrocene will then have a cytotoxic effect.[http://pubs.acs.org/cen/science/8037/8037sci1.html Science PublicationS. Top, B. Dauer, J. Vaissermann and G. Jaouen, Journal of Organometallic Chemistry, 1997, 541, 355-361.S. Top, A. Vessières, G. Leclercq, J. Quivy, J. Tang, J. Vaissermann, M. Huché and G. Jaouen, Chemistry, 2003, 9, 5223-5236.
Synthetic chemistry
Ferrocene, being readily sublimed, can be used to deposit certain kinds of fullerenes.
Chiral ferrocenyl phosphines are employed in the synthesis of important pharmaceuticals.
1,1'-bis-diphenylphosphinoferrocene is a valuable ligand for palladium cross couplings. It is very useful because it prevents beta hydride elimination as it is a trans chelator, which prevents a vacant site cis to an alkyl being formed.
Variations
Many ferrocene derivatives are actively researched and may one day find technical applications. In a so-called penta(ferrocenyl)cyclopentadienyl ligand Y. Yu, A.D. Bond, P. W. Leonard, K. P. C. Vollhardt, G. D. WhitenerSyntheses, Structures, and Reactivity of Radial Oligocyclopentadienyl Metal Complexes: Penta(ferrocenyl)cyclopentadienyl and Congeners Angewandte Chemie International Edition Volume 45, Issue 11 , Pages 1794 - 1799 2006 Abstract, prepared via a Negishi coupling, a cyclopentadienyl ligand is fitted with five ferrocene substituents. This ferris wheel metallocene is a potentially useful ligand in organometallic catalysis.
The ultimate ferris wheel ferrocene, also prepared in a Negishi coupling, is hexaferrocenylbenzene, a benzene molecule with 6 of the above displayed substituents (R) Hexaferrocenylbenzene Yong Yu, Andrew D. Bond, Philip W. Leonard, Ulrich J. Lorenz, Tatiana V. Timofeeva, K. Peter C. Vollhardt, Glenn D. Whitener and Andrey A. Yakovenko Chemical Communications, 2006, 2572 - 2574 . X-ray crystallography of this compound shows that the cyclopentadienyl ligands are not in the plane of the benzene core but have alternating dihedral angles of +30° and −80°. Due to steric crowding the ferrocenyls are slightly bent with angles of 177° and have elongated C-Fe bonds. The quaternary cyclopentadienyl carbon atoms are also pyramidalized. Also, the benzene core has a chair conformation with dihedral angles of 14° and displays bond length alternation between 142.7 pm and 141.1 pm, both indications of steric crowding of the substituents.
References
Further reading
- Jaouen, G.,"Bioorganometallics: Biomolecules, Labeling, Medicine" Wiley-VCH: Weinheim, 2006 (discussion of biological role of ferrocene and related compounds)
- Kealy, T. J. and Pauson, P. L., "A New Type of Organo-iron Compound", Nature 1951, volume 168, pages 1039-40 (announcement of ferrocene, but with the incorrect structure).
- Pauson, P. L., "Ferrocene-how it all began", Journal of Organometallic Chemistry, 2001, 637-639, 3-6.
External links
For a full list of external links and suppliers see Chemical sources
"Ferrocene"
