Ferrocene
From Wikipedia, the free encyclopedia
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| General | |
|---|---|
| Systematic name | bis(η5-cyclopentadienyl)iron(II) |
| Name | Ferrocene, iron cyclopentadienyl |
| Chemical formula | 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 | |
| Related compounds | |
| Metallocenes | cobaltocene nickelocene chromacene |
| Sandwich compounds | bis(benzene)chromium |
| Safety | |
| More info | Hazardous Chemical Database |
Ferrocene is the chemical compound with the formula Fe(C5H5)2. Ferrocene is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compound are also known as sandwich compounds.[1]
Contents |
[edit] History
Ferrocene, like many chemical compounds, was first prepared unintentionally. In 1951, Pauson and Kealy at Duquesne University reported 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.[2] 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 anion are shared with the central Fe2+ ion, resulting in an inert gas electron configuration. This configuration makes ferrocene particularly stable.
[edit] 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.
[edit] 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 catalyst:
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- Fe(C5H5)2 + (CH3CO)2O → Fe(C5H5)(C5H4C(O)CH3) + CH3CO2H
- Fe(C5H5)(C5H4C(O)CH3) + (CH3CO)2O → Fe(C5H4C(O)CH3)2 + CH3CO2H
Ferrocene is readily deprotonated, e.g. by butyl lithium, to give 1,1'-dilithioferrocene, which in turn is a versatile nucleophile.
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- Fe(C5H5)2 + 2 C4H9Li → Fe(C5H4Li)2 + 2 C4H10
- Fe(C5H4Li)2 + 2 (C6H5)2PCl → Fe(C5H4P(C6H5)2)2 + 2 LiCl
Unlike classic organo-aromatic compounds, ferrocene has one very special property - the ability to undergo one-electron oxidation at a low potential, around. 0.4 V vs. a saturated calomel electrode (SCE). Oxidation is usually conducted using FeCl3 to give the blue-colored ferrocenium ion, [Fe(C5H5)2]+, 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.[3]
[edit] Applications of ferrocene and its derivatives
Ferrocene itself has few applications. The availability of countless derivatives, including both mono- and disubstituted derivatives. extends the range of possibilities.
[edit] 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.[4] It is possible to buy at Halfords retail shop in UK, 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-fueled engines, ferrocene reduces the production of soot.
[edit] Medical
Some ferrocenium salts exhibit anticancer activity, and an experimental drug has been reported which is a ferrocenyl version of tamoxifen[1]. The idea is that the tamoxifen will bind to the estrogen binding sites, resulting cytotoxicity effect.[5][6][7]
[edit] Materials chemistry
Ferrocene, being readily sublimed, can be used to deposit certain kinds of fullerenes.
[edit] As a ligand scaffold
Chiral ferrocenyl phosphines are employed as ligands for transition-metal catalyzed reactions. Some of them have found industrial applications in the synthesis of pharmaceuticals and agrochemicals.
1,1'-bis-diphenylphosphinoferrocene is a valuable ligand for palladium coupling reactions.
[edit] Variations
Because of the ease of substitution, many structurally unusual ferrocene derivatives have been prepared. For example, penta(ferrocenyl)cyclopentadienyl ligand [8], features a cyclopentadiene fitted with five ferrocene substituents.
In hexaferrocenylbenzene, all six positions on a benzene molecule have ferrocenyl substituents (R) [9]. X-ray diffraction analysis of this compound confirms that the cyclopentadienyl ligands are not co-planar with 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. [10]
[edit] References
- ^ R. Dagani "Fifty Years of Ferrocene Chemistry" Chemical and Engineering News" (December 3, 2001) Volume 79, Number 49, pp. 37-38.
- ^ J. Dunitz, L. Orgel, A. Rich (1956). "The crystal structure of ferrocene". Acta Crystallographica 9: 373–5. DOI:10.1107/S0365110X56001091.
- ^ N. G. Connelly, W. E. Geiger, "Chemical Redox Agents for Organometallic Chemistry" Chemical Reviews 1996, vol. 96, pp. 877-910.
- ^ Application of fuel additives
- ^ Science Publication
- ^ S. 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.
- ^ 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
- ^ 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 DOI:10.1039/b604844g
- ^ 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.
[edit] Further reading
- Kealy, T. J., Pauson, P. L., "A New Type of Organo-iron Compound", Nature 1951, volume 168, pages 1039-40; Miller, S. A., Tebboth, J. A., Tremaine, J. F., Journal of the Chemical Society 1952, 632-635 (announcement of ferrocene, but with the incorrect structure).
- Wilkinson, G., Rosenblum, M., Whiting, M. C., Woodward, R. B., "The Structure of Iron Bis-Cyclopentadienyl", Journal of the American Chemical Society 1952, volume 74, 2125-2126; Fischer, E. O., Pfab, W., Zeitschrift für Naturforschung B, 1952, volume 7, 377-379 (announcement of the correct 'sandwich' structure).
- Dunitz, J. D., Orgel, L. E., "Bis-Cyclopentadienyl - A Molecular Sandwich", Nature 1953, volume 171, 121-122 (crystallographic evidence supporting the revolutionary structure).
- Pauson, P. L., "Ferrocene-how it all began", Journal of Organometallic Chemistry, 2001, 637-639, 3-6.
- Jaouen, G.,"Bioorganometallics: Biomolecules, Labeling, Medicine" Wiley-VCH: Weinheim, 2006 (discussion of biological role of ferrocene and related compounds)
