Ferrocene
From Wikipedia, the free encyclopedia
| Ferrocene | |
|---|---|
 |
|
 |
|
| IUPAC name | bis(η5-cyclopentadienyl)iron(II) |
| Other names | ferrocene, iron cyclopentadienyl |
| Identifiers | |
| CAS number | [] |
| PubChem | |
| Properties | |
| Molecular formula | C10H10Fe |
| Molar mass | 186.04 g/mol |
| Appearance | light orange powder |
| Density | 1.49 g/cm3 (20 °C) |
| Melting point |
174-176 °C |
| Boiling point |
249 °C |
| Solubility in water | Insoluble in water, soluble in most organic solvents |
| Related Compounds | |
| Related compounds | cobaltocene, nickelocene, chromacene, bis(benzene)chromium |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
|
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 compounds 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 ethereal solvents.
Sir Geoffrey Wilkinson of Imperial College London shared a Nobel Prize for his work on ferrocene. 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 cyclopentadiene to form altered Cp ligands which are then attached to iron. For instance indene can be used in place of the cyclopentadiene to form bisbenzoferrocene.[3].
In addition it is possible by heating [Fe(η5-C5H5)(CO)2(η1-pyrrole)] in cyclohexane to form the pyridine version (azaferrocene) of ferrocene [Fe(η5-C5H5)(η5-C4H4N)].[4]. This compound on boiling under reflux in benzene is converted to ferrocene.[5]
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 or when heated. 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
[edit] Reaction with electrophiles
Ferrocene undergoes many reactions characteristic of aromatic compounds, enabling the preparation of derivatives (substituted ferrocenes). Most common substitution patterns are 1-substituted (one substituent on one ring), 1,1'-disubstituted (1 H of each ring is replaced by a substituent), and 1,2-disubstituted (two substituents on the same ring). For example the reaction of ferrocene, aluminium chloride and Me2NPCl2 in hot heptane forms dichloroferrocenyl phosphine,[6] while treatment with phenyldichlorophosphine under similar conditions forms P,P-diferrocenyl-P-phenyl phosphine.[7] In common with anisole the reaction of ferrocene with P4S10 forms a dithiadiphosphetane disulfide.[8]
A common undergraduate experiment is the Friedel-Crafts reaction of ferrocene with acetic anhydride (or acetyl chloride) in the presence of phosphoric acid as a catalyst:
[edit] Lithiation
Ferrocene is readily deprotonated, e.g. by butyl lithium, to give 1,1'-dilithioferrocene, which in turn is a versatile nucleophile. It has been reported that the reaction of 1,1'-dilithioferrocene with selenium diethyldithiocarbamate forms a strained ferrocenophane where the two Cp ligands are lined by the selenium atom.[9] This ferrocenophane can be converted to a polymer by a thermal ring-opening polymerization (ROP) to form poly(ferrocenyl selenide). Likewise by the reaction of silicon and phosphrous linked ferrocenophanes the poly(ferrocenylsilane)s and poly(ferrocenylphosphines)s can be obtained.[10][11]
-
- Fe(C5H5)2 + 2 C4H9Li → Fe(C5H4Li)2 + 2 C4H10
- Fe(C5H4Li)2 + 2 (C6H5)2PCl → Fe(C5H4P(C6H5)2)2 + 2 LiCl
[edit] Redox chemistry
Unlike the majority of aromatic hydrocarbons, ferrocene can undergo one-electron oxidation at a low potential, around. 0.4 V vs. a saturated calomel electrode (SCE) (N.B. electron rich aromatic amines such as aniline, the heterocycles pyrrole and thiophene can be oxidized with ease by electrochemical means). It is important to note that by adding groups to the Cp ligands attached to the iron that the redox potential of the resulting ferrocene can be altered, by the addition of an electron withdrawing group such as a carboxylic acid the potential can be shifted in the anodic direction while the addition of electron releasing groups such as methyl groups will shift the potential in the cathodic direction. For instance decamethylferrocene is much more easy to oxidise than ferrocene its self. It is the case that in non-aqueous electrochemistry that ferrocene is oftein used as an internal standard for redox potential.
Ferrocene can be oxidized using FeCl3 to give the blue-colored ferrocenium ion, [Fe(C5H5)2]+, which is often isolated as its [PF6]− salt. Ferrocenium salts are sometimes used as oxidizing agents, in part because the redox product ferrocene is so inert and readily separated from the products.[12]
[edit] Applications of ferrocene and its derivatives
Ferrocene itself has few applications. However, known synthetic methods allow the preparation of countless of derivatives, such as mono- and disubstituted ferrocenes, thus extending the range of applications.
[edit] Fuel additives
Ferrocene and its derivatives are antiknock agents used in the fuel for petrol engines; they are considered to be safer than tetraethyl lead, previously used.[13] 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.[14] Unfortunately, the iron containing deposits formed from ferrocene can form a conductive coating on the spark plug surfaces leading to spark plug 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.[15] The idea is that the tamoxifen will bind to the estrogen binding sites, resulting cytotoxicity effect.[16][17][18]
[edit] Materials chemistry
Ferrocene, being readily sublimed, can be used to deposit certain kinds of fullerenes, especially carbon nanotubes. Due to the fact that many organic reactions can be used to modify ferrocenes, it is the case that vinyl ferrocene can be made. The vinyl ferrocene can be made by a Wittig reaction of the aldehyde, a phosphonium salt and sodium hydroxide.[19] The vinyl ferrocene can be converted into a polymer which can be thought of as a ferrocnyl version of polystyrene (the phenyl groups are replaced with ferrocenyl groups).
[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(diphenylphosphino)ferrocene (dppf) is a diphosphine containing a ferrocene moiety; it 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 [20], features a cyclopentadiene fitted with five ferrocene substituents.
In hexaferrocenylbenzene, all six positions on a benzene molecule have ferrocenyl substituents (R) [21]. 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. [22]
[edit] References
- ^ R. Dagani (3 December 2001). "Fifty Years of Ferrocene Chemistry" (Subscription required). Chemical and Engineering News 79 (49): 37-38.
- ^ J. Dunitz, L. Orgel, A. Rich (1956). "The crystal structure of ferrocene". Acta Crystallographica 9: 373–5. DOI:10.1107/S0365110X56001091.
- ^ B.R. Waldbaum and R.C. Kerber, Inorg. Chim. Acta, 1999, 291, 109 - 126.
- ^ J. Zakrzewski and C. Gianotti, J. Organomet. Chem., 1990, 388,175 - 180.
- ^ A. Efraty, N. Jubran and A. Goldman, Inorg. Chem., 1982, 21, 868 - 873.
- ^ G.R. Knox, P.L. Pauson and D. Willison, Organometallics, 1992, 11, 2930 - 2933
- ^ G.P. Sollott, H.E. Mertwoy, S. Portnoy and J.L. Snead, J. Org. Chem., 1963, 28, 1090 - 1092.
- ^ M.R.StJ. Foreman, A.M.Z. Slawin and J.D. Woollins, J. Chem. Soc., Dalton Trans., 1996, 3653 - 3658.
- ^ Ron Rulkens, Derek P. Gates, David Balaishis, John K. Pudelski, Douglas F. McIntosh, Alan J. Lough, and Ian Manners, J. Am. Chem. Soc., 1997, 119, 10976
- ^ Paloma Gómez-Elipe, Rui Resendes, Peter M. Macdonald, and Ian Manners, J. Am. Chem. Soc., 1998, 120, 8348
- ^ Timothy J. Peckham, Jason A. Massey, Charles H. Honeyman, and Ian Manners, Macromolecules, 1999, 32, 2830
- ^ N. G. Connelly, W. E. Geiger (1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews 96: 877-910. DOI:10.1021/cr940053x.
- ^ Application of fuel additives
- ^ U.S. Patent 4104036
- ^ [1]
- ^ Ron Dagani (16 Sep 2002). "The Bio Side of Organometallics". Chemical and Engineering News 80 (37): 23-29.
- ^ S. Top, B. Dauer, J. Vaissermann and G. Jaouen (1997). "Facile route to ferrocifen, 1-[4-(2-dimethylaminoethoxy)]-1-(phenyl-2-ferrocenyl-but-1-ene), first organometallic analogue of tamoxifen, by the McMurry reaction". Journal of Organometallic Chemistry 541: 355-361. DOI:10.1016/S0022-328X(97)00086-7.
- ^ S. Top, A. Vessières, G. Leclercq, J. Quivy, J. Tang, J. Vaissermann, M. Huché and G. Jaouen (2003). "Synthesis, Biochemical Properties and Molecular Modelling Studies of Organometallic Specific Estrogen Receptor Modulators (SERMs), the Ferrocifens and Hydroxyferrocifens: Evidence for an Antiproliferative Effect of Hydroxyferrocifens on both Hormone-Dependent and Hormone-Independent Breast Cancer Cell Lines". Chemistry, a European Journal 9: 5223-5236. DOI:10.1002/chem.200305024.
- ^ Liu, Wan-yi; Xu, Qi-hai; Ma, Yong-xiang; Liang, Yong-min; Dong, Ning-li; Guan, De-peng,J. Organomet. Chem., 2001, 625, 128 - 132
- ^ Y. Yu, A.D. Bond, P. W. Leonard, K. P. C. Vollhardt, G. D. Whitener (2006). "Syntheses, Structures, and Reactivity of Radial Oligocyclopentadienyl Metal Complexes: Penta(ferrocenyl)cyclopentadienyl and Congeners". Angewandte Chemie International Edition 45 (11): 1794 - 1799. DOI:10.1002/anie.200504047.
- ^ 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 (2006). "Hexaferrocenylbenzene". Chemical Communications: 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
- Announcement of the discovery of ferrocene, but with wrong structure
- Kealy, T. J., Pauson, P. L. (1951). "A New Type of Organo-iron Compound". Nature 168: 1039-40. DOI:10.1038/1681039b0.
- Miller, S. A., Tebboth, J. A., Tremaine, J. F. (1952). "114. Dicyclopentadienyliron". Journal of the Chemical Society: 632-635. DOI:10.1039/JR9520000632.
- Announcement of the correct 'sandwich' structure
- Wilkinson, G., Rosenblum, M., Whiting, M. C., Woodward, R. B. (1952). "The Structure of Iron Bis-Cyclopentadienyl". Journal of the American Chemical Society 74: 2125-2126. DOI:10.1021/ja01128a527.
- Fischer, E. O., Pfab, W. (1952). "{{{title}}}". Zeitschrift für Naturforschung B 7: 377-379.
- Others
- Dunitz, J. D., Orgel, L. E. (1953). "Bis-Cyclopentadienyl - A Molecular Sandwich". Nature 171: 121-122. DOI:10.1038/171121a0.
- Pauson, P. L. (2001). "Ferrocene-how it all began". Journal of Organometallic Chemistry: 637-639.
- Gerard Jaouen (ed.) (2006). Bioorganometallics: Biomolecules, Labeling, Medicine. Weinheim: Wiley-VCH. ISBN 978-3-527-30990-0. (discussion of biological role of ferrocene and related compounds)
