Ferrocene

Short description: Organometallic compound: Fe(II) sandwiched between two cyclopentadienyl rings

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Names
Preferred IUPAC name

Ferrocene[1]

Other names

* Dicyclopentadienyl iron
* Bis(η5-cyclopentadienyl)iron
* Iron(II) cyclopentadienide

Identifiers

CAS Number

* 102-54-5 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:30672 N

ChemSpider |

* 7329 Y

PubChem CID

* 11985121

UNII |

* U96PKG90JQ Y

InChI

* InChI=1S/2C5H5.Fe/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2 Y

Key: KTWOOEGAPBSYNW-UHFFFAOYSA-N Y

* InChI=1/2C5H5.Fe/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2

Key: KTWOOEGAPBSYNW-UHFFFAOYAZ

SMILES

* [CH-]1C=CC=C1.[CH-]1C=CC=C1.[Fe+2]

Properties

Chemical formula

| C10H10Fe
Molar mass | 186.04 g/mol
Appearance  | light orange powder
Odor | camphor-like
Density | 1.107 g/cm3 (0 °C), 1.490 g/cm3 (20 °C)[2]
Melting point |  172.5 °C (342.5 °F; 445.6 K)[4]
Boiling point |  249 °C (480 °F; 522 K)

Solubility in water

| Insoluble in water, soluble in most organic solvents
log P | 2.04050 [3]
Structure

Point group

| D5d / D5h / D5

Molecular shape

| Metallocene

Dipole moment

| No Permanent Dipole moment due to rapid Cp rotations[5]
Hazards
NFPA 704 (fire diamond)  |

[7]

NIOSH (US health exposure limits):

PEL (Permissible)

| TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[6]

REL (Recommended)

| TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[6]

IDLH (Immediate danger)

| N.D.[6]
Related compounds

Related compounds

* Metallocene
* f-Block metallocene
* Actinocene
* Thorocene
* Protactinocene
* Uranocene
* Neptunocene
* Plutonocene
* Zirconocene
* Vanadocene
* Chromocene
* Bis(benzene)chromium
* Manganocene
* Nickelocene
* Cobaltocene
* Ruthenocene
* Rhodocene
* Osmocene
* Hassocene
* Stannocene
* Plumbocene

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)
Infobox references

Ferrocene is an organometallic compound with the formula Fe(C

2. The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, and is soluble in most organic solvents. It is remarkable for its stability: it is unaffected by air, water, strong bases, and can be heated to 400 °C without decomposition. In oxidizing conditions it can reversibly react with strong acids to form the ferrocenium cation Fe(C

5)+
2.[8] Ferrocene and the ferrocenium cation are sometimes abbreviated as Fc and Fc+
respectively.

The rapid growth of organometallic chemistry is often attributed to the excitement arising from the discovery of ferrocene and its many analogues, such as metallocenes.

## Contents

* 1 History
* 1.1 Discovery
* 1.2 Determining the structure
* 1.3 Understanding the structure
* 1.4 Impact
* 2 Structure and bonding
* 3 Synthesis
* 3.1 Industrial synthesis
* 3.2 Via Grignard reagent
* 3.3 Gas-metal reaction
* 3.4 Via alkali cyclopentadienide
* 4 Properties
* 5 Reactions
* 5.1 With electrophiles
* 5.2 Lithiation
* 5.3 Redox chemistry
* 6 Stereochemistry of substituted ferrocenes
* 7 Applications of ferrocene and its derivatives
* 7.1 Ligand scaffolds
* 7.2 Fuel additives
* 7.3 Pharmaceuticals
* 7.4 Solid rocket propellant
* 8 Derivatives and variations
* 8.1 Materials chemistry
* 9 See also
* 10 References
* 11 External links

## History

### Discovery

Ferrocene was discovered by accident twice. The first known synthesis may have been made in the late 1940s by unknown researchers at Union Carbide, who tried to pass hot cyclopentadiene vapor through an iron pipe. The vapor reacted with the pipe wall, creating a "yellow sludge" that clogged the pipe. Years later, a sample of the sludge that had been saved was obtained and analyzed by Eugene O. Brimm, shortly after reading Kealy and Pauson's article, and was found to consist of ferrocene.[8][9]

The second time was around 1950, when Samuel A. Miller, John A. Tebboth, and John F. Tremaine, researchers at British Oxygen, were attempting to synthesize amines from hydrocarbons and nitrogen in a modification of the Haber process. When they tried to react cyclopentadiene with nitrogen at 300 °C, at atmospheric pressure, they were disappointed to see the hydrocarbon react with some source of iron, yielding ferrocene. While they too observed its remarkable stability, they put the observation aside and did not publish it until after Pauson reported his findings.[8][10][11] In fact, Kealy and Pauson were provided with a sample by Miller et al., who confirmed that the products were the same compound.[9]

In 1951, Peter L. Pauson and Thomas J. Kealy at Duquesne University attempted to prepare fulvalene ((C

2) by oxidative dimerization of cyclopentadiene (C

6). To that end, they reacted the Grignard compound cyclopentadienyl magnesium bromide in diethyl ether with ferric chloride as an oxidizer.[8] However, instead of the expected fulvalene, they obtained a light orange powder of "remarkable stability", with the formula C
10H
10Fe.[9][12]

### Determining the structure

Pauson and Kealy's original (incorrect) notion of ferrocene's molecular structure.[12]

Pauson and Kealy conjectured that the compound had two cyclopentadienyl groups, each with a single covalent bond from the saturated carbon atom to the iron atom.[8] However, that structure was inconsistent with then-existing bonding models and did not explain the unexpected stability of the compound, and chemists struggled to find the correct structure.[11][13]

The structure was deduced and reported independently by three groups in 1952:[14]

* Robert Burns Woodward and Geoffrey Wilkinson deduced it by observing that ferrocene underwent reactions typical of aromatic compounds such as benzene[15]
* Ernst Otto Fischer deduced the structure (which he called "double cone") and also synthesized other metallocenes such as nickelocene and cobaltocene.[16][17][18]
* P. F. Eiland and R. Pepinsky confirmed the structure through X-ray crystallography and later by NMR.[11][19][20][21]

### Understanding the structure

The "sandwich" structure of ferrocene was shockingly novel, and required new theory to explain. Application of molecular orbital theory with the assumption of a Fe2+ centre between two cyclopentadienide anions C
5H−
5 resulted in the successful Dewar–Chatt–Duncanson model, allowing correct prediction of the geometry of the molecule as well as explaining its remarkable stability.[22][23]

### Impact

Ferrocene was not the first organometallic compound to be discovered. Zeise's salt K[PtCl
3(C

4)] * H2O was reported in 1831,[24][25] Edward Frankland synthesized diethylzinc and other similar compounds in 1848, Mond's discovery of Ni(CO)4 occurred in 1888,[26] and organolithium compounds were developed in the 1930s.[27] However, it can be argued that it was ferrocene's discovery that began organometallic chemistry as a separate area of chemistry. It also led to an explosion of interest in compounds of d-block metals with hydrocarbons.

The discovery was considered so significant that Wilkinson and Fischer shared the 1973 Nobel Prize for Chemistry "for their pioneering work, performed independently, on the chemistry of the organometallic, called sandwich compounds".[28]

## Structure and bonding

Mössbauer spectroscopy indicates that the iron center in ferrocene should be assigned the +2 oxidation state. Each cyclopentadienyl (Cp) ring should then be allocated a single negative charge. Thus ferrocene could be described as iron(II) bis(cyclopentadienide), Fe2+[C
5H−

The number of π-electrons on each ring is then six, which makes it aromatic according to Hückel's rule. These twelve π-electrons are then shared with the metal via covalent bonding. Since Fe2+ has six d-electrons, the complex attains an 18-electron configuration, which accounts for its stability. In modern notation, this sandwich structural model of the ferrocene molecule is denoted as Fe(η5

The carbon–carbon bond distances around each five-membered ring are all 1.40 Å, and the Fe–C bond distances are all 2.04 Å. From room temperature down to 164K, X-ray crystallography yields the monoclinic space group; the cyclopentadienide rings are a staggered conformation, resulting in a centrosymmetric molecule, with symmetry group D5d.[19] However, below 110 K, ferrocene crystallizes in an orthorhombic crystal lattice in which the Cp rings are ordered and eclipsed, so that the molecule has symmetry group D5h.[29] In the gas phase, electron diffraction[30] and computational studies[31] show that the Cp rings are eclipsed.

The Cp rings rotate with a low barrier about the Cp(centroid)–Fe–Cp(centroid) axis, as observed by measurements on substituted derivatives of ferrocene using 1H and 13C nuclear magnetic resonance spectroscopy. For example, methylferrocene (CH3C5H4FeC5H5) exhibits a singlet for the C5H5 ring.[32]

In solution, and at room temperature, eclipsed D5h ferrocene was determined to dominate over the staggered D5d conformer, as suggested by both Fourier-transform infrared spectroscopy and DFT calculations.[33]

## Synthesis

### Industrial synthesis

Industrially, ferrocene is synthesized by the reaction of iron(II) ethoxide with cyclopentadiene;[34] the iron(II) ethoxide needed is produced by the electrochemical oxidation of metallic iron in anhydrous ethanol. Since the reaction between iron(II) ethoxide and cyclopentadiene produces ethanol as a byproduct, the ethanol effectively serves as a catalyst for the overall reaction, with the net reaction being Fe + 2C5H6 → H2 + Fe(C5H5)2 (also see below)

### Via Grignard reagent

The first reported syntheses of ferrocene were nearly simultaneous. Pauson and Kealy synthesised ferrocene using iron(III) chloride and a Grignard reagent, cyclopentadienyl magnesium bromide. Iron(III) chloride is suspended in anhydrous diethyl ether and added to the Grignard reagent.[12] A redox reaction occurs, forming the cyclopentadienyl radical and iron(II) ions. Dihydrofulvalene is produced by radical-radical recombination while the iron(II) reacts with the Grignard reagent to form ferrocene. Oxidation of dihydrofulvalene to fulvalene with iron(III), the outcome sought by Kealy and Pauson, does not occur.[9]

### Gas-metal reaction

The Miller et al.[10] approach to ferrocene

The other early synthesis of ferrocene was by Miller et al.,[10] who reacted metallic iron directly with gas-phase cyclopentadiene at elevated temperature.[35] An approach using iron pentacarbonyl was also reported.[36]

Fe(CO)5 \+ 2 C5H6(g) → Fe(C5H5)2 \+ 5 CO(g) + H2(g)

### Via alkali cyclopentadienide

More efficient preparative methods are generally a modification of the original transmetalation sequence using either commercially available sodium cyclopentadienide[37] or freshly cracked cyclopentadiene deprotonated with potassium hydroxide[38] and reacted with anhydrous iron(II) chloride in ethereal solvents.

Modern modifications of Pauson and Kealy's original Grignard approach are known:

* Using sodium cyclopentadienide:  2 NaC5H5 \+  FeCl2 →  Fe(C5H5)2 \+  2 NaCl
* Using freshly-cracked cyclopentadiene:  FeCl2·4H2O  \+  2 C5H6 \+  2 KOH  →  Fe(C5H5)2 \+  2 KCl  \+  6 H2O
* Using an iron(II) salt with a Grignard reagent:  2 C5H5MgBr  \+  FeCl2 →  Fe(C5H5)2 \+  2 MgBrCl

Even some amine bases (such as diethylamine) can be used for the deprotonation, though the reaction proceeds more slowly than when using stronger bases:[37]

2 C5H6 \+  2 (CH3CH2)2NH  \+  FeCl2 →  Fe(C5H5)2 \+  2 (CH3CH2)2NH2Cl

Direct transmetalation can also be used to prepare ferrocene from other metallocenes, such as manganocene:[39]

FeCl2 \+  Mn(C5H5)2 →  MnCl2 \+  Fe(C5H5)2

## Properties

Crystals of ferrocene after purification by vacuum sublimation

Ferrocene is an air-stable orange solid with a camphor-like odor. As expected for a symmetric, uncharged species, ferrocene is soluble in normal organic solvents, such as benzene, but is insoluble in water. It is stable to temperatures as high as 400 °C.[40]

Ferrocene readily sublimes, especially upon heating in a vacuum. Its vapor pressure is about 1 Pa at 25 °C, 10 Pa at 50 °C, 100 Pa at 80 °C, 1000 Pa at 116 °C, and 10,000 Pa (nearly 0.1 atm) at 162 °C.[41][42]

## Reactions

### With electrophiles

Ferrocene undergoes many reactions characteristic of aromatic compounds, enabling the preparation of substituted derivatives. 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. Under conditions for a Mannich reaction, ferrocene gives N,N-dimethylaminomethylferrocene.

Important reactions of ferrocene with electrophiles and other reagents

Ferrocene itself can be used as the backbone of a ligand, e.g. 1,1'-bis(diphenylphosphino)ferrocene (dppf). Ferrocene can itself be oxidized to the ferrocenium cation (Fc+); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry.[13]

It is an aromatic substance and undergoes substitution reactions rather than addition reactions on the cyclopentadienyl ligands. For example, Friedel-Crafts acylation of ferrocene with acetic anhydride yields acetylferrocene[43] just as acylation of benzene yields acetophenone under similar conditions.

Protonation of ferrocene allows isolation of [Cp2FeH]PF6.[44]

In the presence of aluminium chloride, Me2NPCl2 and ferrocene react to give ferrocenyl dichlorophosphine,[45] whereas treatment with phenyldichlorophosphine under similar conditions forms P,P-diferrocenyl-P-phenyl phosphine.[46]

Ferrocene reacts with P4S10 forms a diferrocenyl-dithiadiphosphetane disulfide.[47]

### Lithiation

Ferrocene reacts with butyllithium to give 1,1′-dilithioferrocene, which is a versatile nucleophile. In combination with butyllithiium, tert-butyllithium produces monolithioferrocene.[48]

### Redox chemistry

Ferrocene undergoes a one-electron oxidation at around 0.4 V versus a saturated calomel electrode (SCE), becoming ferrocenium. This reversible oxidation has been used as standard in electrochemistry as Fc+/Fc = 0.64 V versus the standard hydrogen electrode,[49] however other values have been reported.[50] Ferrocenium tetrafluoroborate is a common reagent.[51] The remarkably reversible oxidation-reduction behaviour has been extensively used to control electron-transfer processes in electrochemical[52][53] and photochemical[54][55] systems.

The one-electron oxidized derivative of biferrocene has attracted much research attention.

Substituents on the cyclopentadienyl ligands alters the redox potential in the expected way: electron-withdrawing groups such as a carboxylic acid shift the potential in the anodic direction (i.e. made more positive), whereas electron-releasing groups such as methyl groups shift the potential in the cathodic direction (more negative). Thus, decamethylferrocene is much more easily oxidised than ferrocene and can even be oxidised to the corresponding dication.[56] Ferrocene is often used as an internal standard for calibrating redox potentials in non-aqueous electrochemistry.

## Stereochemistry of substituted ferrocenes

A planar chiral ferrocene derivative

Disubstituted ferrocenes can exist as either 1,2-, 1,3- or 1,1′- isomers, none of which are interconvertible. Ferrocenes that are asymmetrically disubstituted on one ring are chiral – for example [CpFe(EtC5H3Me)]. This planar chirality arises despite no single atom being a stereogenic centre. The substituted ferrocene shown at right (a 4-(dimethylamino)pyridine derivative) has been shown to be effective when used for the kinetic resolution of racemic secondary alcohols.[57] Several approaches have been developed to asymmetrically 1,1′-functionalise the ferrocene.[58]

## Applications of ferrocene and its derivatives

Ferrocene and its numerous derivatives have no large-scale applications, but have many niche uses that exploit the unusual structure (ligand scaffolds, pharmaceutical candidates), robustness (anti-knock formulations, precursors to materials), and redox (reagents and redox standards).

### Ligand scaffolds

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. For example, the diphosphine 1,1′-bis(diphenylphosphino)ferrocene (dppf) is a valued ligand for palladium-coupling reactions and Josiphos ligand is useful for hydrogenation catalysis.[59] They are named after the technician who made the first one, Josi Puleo.[60][61]

Josiphos ligand.[59]

### Fuel additives

Ferrocene and its derivatives are antiknock agents used in the fuel for petrol engines. They are safer than previously used tetraethyllead.[62] Petrol additive solutions containing ferrocene can be added to unleaded petrol to enable its use in vintage cars designed to run on leaded petrol.[63] The iron-containing deposits formed from ferrocene can form a conductive coating on spark plug surfaces. Ferrocene polyglycol copolymers, prepared by effecting a polycondensation reaction between a ferrocene derivative and a substituted dihydroxy alcohol, has promise as a component of rocket propellants. These copolymers provide rocket propellants with heat stability, serving as a propellant binder and controlling propellant burn rate.[64]

Ferrocene has been found to be effective at reducing smoke and sulfur trioxide produced when burning coal. The addition by any practical means, impregnating the coal or adding ferrocene to the combustion chamber, can significantly reduce the amount of these undesirable byproducts, even with a small amount of the metal cyclopentadienyl compound.[65]

### Pharmaceuticals

Ferrocene derivatives have been investigated as drugs,[66] with one compound ferrocerone approved for use in the USSR in the 1970s, though it is no longer marketed today.[67] Only one drug has entered clinical trials in recent years, Ferroquine (7-chloro-N-(2-((dimethylamino)methyl)ferrocenyl)quinolin-4-amine), an antimalarial,[68][69][70] which has reached Phase IIb trials.[71] Ferrocene-containing polymer-based drug delivery systems have been investigated.[72]

Ferroquine

The anticancer activity of ferrocene derivatives was first investigated in the late 1970s, when derivatives bearing amine or amide groups were tested against lymphocytic leukemia.[73] Some ferrocenium salts exhibit anticancer activity, but no compound has seen evaluation in the clinic.[74] Ferrocene derivatives have strong inhibitory activity against human lung cancer cell line A549, colorectal cancer cell line HCT116, and breast cancer cell line MCF-7.[75] An experimental drug was reported which is a ferrocenyl version of tamoxifen.[76] The idea is that the tamoxifen will bind to the estrogen binding sites, resulting in cytotoxicity.[76][77]

Ferrocifens are exploited for cancer applications by a French biotech, Feroscan, founded by Pr. Gerard Jaouen.

### Solid rocket propellant

Ferrocene and related derivatives are used as powerful burn rate catalysts in ammonium perchlorate composite propellant.[78]

## Derivatives and variations

Ferrocene analogues can be prepared with variants of cyclopentadienyl. For example, bisindenyliron and bisfluorenyliron.[61]

Various ferrocene derivatives where cyclopentadienyl has been replaced by related ligands

Carbon atoms can be replaced by heteroatoms as illustrated by Fe(η5-C5Me5)(η5-P5) and Fe(η5-C5H5)(η5-C4H4N) ("azaferrocene"). Azaferrocene arises from decarbonylation of Fe(η5-C5H5)(CO)2(η1-pyrrole) in cyclohexane.[79] This compound on boiling under reflux in benzene is converted to ferrocene.[80]

Because of the ease of substitution, many structurally unusual ferrocene derivatives have been prepared. For example, the penta(ferrocenyl)cyclopentadienyl ligand,[81] features a cyclopentadienyl anion derivatized with five ferrocene substituents.

Penta(ferrocenyl)cyclopentadienyl ligand Structure of hexaferrocenylbenzene

In hexaferrocenylbenzene, C6[(η5-C5H4)Fe(η5-C5H5)]6, all six positions on a benzene molecule have ferrocenyl substituents (R).[82] 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. 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.

The synthesis of hexaferrocenylbenzene has been reported using Negishi coupling of hexaiodidobenzene and diferrocenylzinc, using tris(dibenzylideneacetone)dipalladium(0) as catalyst, in tetrahydrofuran:[82]

The yield is only 4%, which is further evidence consistent with substantial steric crowding around the arene core.

### Materials chemistry

Strands of an uncharged ferrocene-substituted polymer are tethered to a hydrophobic silica surface. Oxidation of the ferrocenyl groups produces a hydrophilic surface due to electrostatic attractions between the resulting charges and the polar solvent.[83]

Ferrocene, a precursor to iron nanoparticles, can be used as a catalyst for the production of carbon nanotubes.[84] The vinylferrocene can be made by a Wittig reaction of the aldehyde, a phosphonium salt, and sodium hydroxide.[85] The vinyl ferrocene can be converted into a polymer (polyvinylferrocene, PVFc), a ferrocenyl version of polystyrene (the phenyl groups are replaced with ferrocenyl groups). Another polyferrocene which can be formed is poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate), PFcMA. In addition to using organic polymer backbones, these pendant ferrocene units have been attached to inorganic backbones such as polysiloxanes, polyphosphazenes, and polyphosphinoboranes, (-PH(R)-BH2-)n, and the resulting materials exhibit unusual physical and electronic properties relating to the ferrocene / ferrocinium redox couple.[83] Both PVFc and PFcMA have been tethered onto silica wafers and the wettability measured when the polymer chains are uncharged and when the ferrocene moieties are oxidised to produce positively charged groups. The contact angle with water on the PFcMA-coated wafers was 70° smaller following oxidation, while in the case of PVFc the decrease was 30°, and the switching of wettability is reversible. In the PFcMA case, the effect of lengthening the chains and hence introducing more ferrocene groups is significantly larger reductions in the contact angle upon oxidation.[83][86]

## See also

* Josiphos ligands

## References

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10. ↑ 10.0 10.1 10.2 "114. Dicyclopentadienyliron". J. Chem. Soc.: 632–635. 1952. doi:10.1039/JR9520000632.
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17. ↑ "Zur Kristallstruktur der Di-Cyclopentadienyl-Verbindungen des zweiwertigen Eisens, Kobalts und Nickels". Zeitschrift für Naturforschung B 7 (7): 377–379. 1952. doi:10.1515/znb-1952-0701.
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24. ↑ "Von der Wirkung zwischen Platinchlorid und Alkohol, und von den dabei entstehenden neuen Substanzen" (in de). Annalen der Physik 97 (4): 497–541. 1831. doi:10.1002/andp.18310970402. Bibcode: 1831AnP....97..497Z. https://zenodo.org/record/1423546.
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29. ↑ "Low-temperature crystallization of orthorhombic ferrocene: structure analysis at 98 K". Acta Crystallographica Section B 38 (6): 1741–1745. 1982. doi:10.1107/s0567740882007080. ISSN 0567-7408.
30. ↑ "The Determination of Barriers to Internal Rotation by Means of Electron Diffraction. Ferrocene and Ruthenocene". Acta Chem. Scand. 22: 2653–2670. 1968. doi:10.3891/acta.chem.scand.22-2653.
31. ↑ "The equilibrium structure of ferrocene". ChemPhysChem 7 (1): 245–249. January 2006. doi:10.1002/cphc.200500339. PMID 16404766.
32. ↑ "Dynamic NMR studies of ring rotation in substituted ferrocenes and ruthenocenes". J. Org. Chem. 403 (1–2): 195–208. 1991. doi:10.1016/0022-328X(91)83100-I.
33. ↑ Wang, Feng; Mohammadi, Narges; Best, Stephen P.; Appadoo, Dominique; Chantler, Christopher T. (2021). "Dominance of eclipsed ferrocene conformer in solutions revealed by the IR spectra between 400 and 500 cm-1" (in en). Radiation Physics and Chemistry 188: 109590. doi:10.1016/j.radphyschem.2021.109590. Bibcode: 2021RaPC..18809590W. https://linkinghub.elsevier.com/retrieve/pii/S0969806X21002401.
34. ↑ "Iron, bis(eta5-2,4-cyclopentadien-1-yl)-". https://pubchem.ncbi.nlm.nih.gov/compound/7611.
35. ↑ "Bis-cyclopentadienyl Compounds of Nickel and Cobalt". J. Am. Chem. Soc. 76 (7): 1970–1974. 1954. doi:10.1021/ja01636a080.
36. ↑ "Cyclopentadienyl and Arene Metal Compounds". Progress in Inorganic Chemistry. 1. 1959. pp. 1–124. doi:10.1002/9780470166024.ch1. ISBN 978-0-470-16602-4.
37. ↑ 37.0 37.1 "Ferrocene". Organic Syntheses 36: 31. 1956. doi:10.15227/orgsyn.036.0031.
38. ↑ The Synthesis and Characterization of Inorganic Compounds. New Jersey: Prentice-Hall. 1970. ISBN 9780138799328. https://archive.org/details/synthesischaract0000joll.
39. ↑ "On manganese cyclopentadienide and some chemical reactions of neutral bis-cyclopentadienyl metal compounds". J. Inorg. Nucl. Chem. 2 (2): 95–113. 1956. doi:10.1016/0022-1902(56)80004-3.
40. ↑ Organic Chemistry (9th ed.). USA: John Wiley & Sons. 2006.
41. ↑ "New Static Apparatus and Vapor Pressure of Reference Materials: Naphthalene, Benzoic Acid, Benzophenone, and Ferrocene". Journal of Chemical & Engineering Data 51 (2): 757. 2006. doi:10.1021/je050502y.
42. ↑ "Recommended vapor pressure and thermophysical data for ferrocene". Journal of Chemical Thermodynamics 57: 530–540. 2013. doi:10.1016/j.jct.2012.07.023.
43. ↑ "Acetylation of Ferrocene: A Chromatography Experiment for Elementary Organic Laboratory". J. Chem. Educ. 43 (2): 73. 1966. doi:10.1021/ed043p73. Bibcode: 1966JChEd..43...73B.
44. ↑ "Protonation of Ferrocene: A Low-Temperature X-ray Diffraction Study of [Cp2 FeH](PF6 ) Reveals an Iron-Bound Hydrido Ligand". Angewandte Chemie 56 (43): 13372–13376. October 2017. doi:10.1002/anie.201704854. PMID 28834022.
45. ↑ "Ferrocene derivatives. 27. Ferrocenyldimethylphosphine". Organometallics 11 (8): 2930–2933. 1992. doi:10.1021/om00044a038.
46. ↑ "Unsymmetrical Tertiary Phosphines of Ferrocene by Friedel–Crafts Reactions. I. Ferrocenylphenylphosphines". J. Org. Chem. 28 (4): 1090–1092. 1963. doi:10.1021/jo01039a055.
47. ↑ "2,4-Diferrocenyl-1,3-dithiadiphosphetane 2,4-disulfide; structure and reactions with catechols and [PtCl2(PR3)2](R = Et or Bun)". J. Chem. Soc., Dalton Trans. (18): 3653–3657. 1996. doi:10.1039/DT9960003653.
48. ↑ Carl A. Busacca, Magnus C. Eriksson, Nizar Haddad, Z. Steve Han, Jon C. Lorenz, Bo Qu, Xingzhong Zeng, Chris H. Senanayake (2013). "Practical Synthesis of Di-tert-Butyl-Phosphinoferrocene". Organic Syntheses 90: 316. doi:10.15227/orgsyn.090.0316.
49. ↑ "Electrochemical considerations for determining absolute frontier orbital energy levels of conjugated polymers for solar cell applications". Advanced Materials 23 (20): 2367–2371. May 2011. doi:10.1002/adma.201004554. PMID 21462372. Bibcode: 2011AdM....23.2367C.
50. ↑ Vitaly V Pavlishchuk, Anthony W Addison (January 2000), "Conversion constants for redox potentials measured versus different reference electrodes in acetonitrile solutions at 25°C" (in German), Inorganica Chimica Acta 298 (1): pp. 97–102, doi:10.1016/S0020-1693(99)00407-7, https://linkinghub.elsevier.com/retrieve/pii/S0020169399004077, retrieved 2022-07-26
51. ↑ "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews 96 (2): 877–910. March 1996. doi:10.1021/cr940053x. PMID 11848774.
52. ↑ "The ferrocene effect: enhanced electrocatalytic hydrogen production using meso-tetraferrocenyl porphyrin palladium(II) and copper(II) complexes". Dalton Transactions 44 (33): 14646–14655. September 2015. doi:10.1039/C5DT02191J. PMID 26213204. https://eprint.ncl.ac.uk/fulltext.aspx?url=214473/2DD72927-25BC-4809-8636-5FDB014D7CB0.pdf&pub_id=214473.
53. ↑ "Selective electrochemical generation of benzylic radicals enabled by ferrocene-based electron-transfer mediators". Chemical Science 9 (2): 356–361. January 2018. doi:10.1039/C7SC04032F. PMID 29732109.
54. ↑ "Photosensitization by Ferrocene. Photochemistry of Higher Electronic Excited States". Journal of the American Chemical Society 87 (7): 1626–1627. 1965-04-01. doi:10.1021/ja01085a048. ISSN 0002-7863.
55. ↑ "Synthesis and properties of a meso- tris–ferrocene appended zinc(II) porphyrin and a critical evaluation of its dye sensitised solar cell (DSSC) performance" (in en). RSC Advances 4 (43): 22733–22742. 2014-05-23. doi:10.1039/C4RA03105A. ISSN 2046-2069. Bibcode: 2014RSCAd...422733S. https://eprint.ncl.ac.uk/fulltext.aspx?url=199647/CED25CA5-111E-4500-8188-DCFC5D4D7190.pdf&pub_id=199647.
56. ↑ "Isolation and structural and electronic characterization of salts of the decamethylferrocene dication". Science 353 (6300): 678–682. August 2016. doi:10.1126/science.aaf6362. PMID 27516596. Bibcode: 2016Sci...353..678M.
57. ↑ "Effective Kinetic Resolution of Secondary Alcohols with a Planar-Chiral Analogue of 4-(dimethylamino)pyridine. Use of the Fe(C5Ph5) Group in Asymmetric Catalysis". J. Am. Chem. Soc. 119 (6): 1492–1493. 1997. doi:10.1021/ja963835b.
58. ↑ "The syntheses and catalytic applications of unsymmetrical ferrocene ligands". Chemical Society Reviews 33 (5): 313–328. June 2004. doi:10.1039/B316819K. PMID 15272371.
59. ↑ 59.0 59.1 "Solvias Josiphos ligands: From discovery to technical applications". Topics in Catalysis 19: 3–16. 2002. doi:10.1023/a:1013832630565.
60. ↑ Privileged Chiral Ligands and Catalysts. Weinheim: Wiley-VCH Verlag. 2011. ISBN 978-3-527-63521-4.
61. ↑ 61.0 61.1 Ferrocenes: Ligands, Materials and Biomolecules. Hoboken, NJ: J. Wiley. 2008. ISBN 978-0-470-03585-6.
62. ↑ "Application of fuel additives". International Conference on Automotive Technology. Istanbul. 26 November 2004. http://www.osd.org.tr/14.pdf.
63. ↑ Chao TS, "Iron-containing motor fuel compositions and method for using same", US patent 4104036, published 1978-08-01, assigned to Atlantic Richfield Co
64. ↑ Dewey FM, "Ferrocene Polyglycols", US patent 3598850, issued Aug. 10, 1971, assigned to U.S. Air Force.
65. ↑ Kerley RV, "Coal Combustion Process and Composition", US patent 3927992, issued December 23, 1975, assigned to Ethyl Corporation.
66. ↑ "Bioorganometallic chemistry of ferrocene". Chemical Reviews 104 (12): 5931–5985. December 2004. doi:10.1021/cr0101510. PMID 15584693.
67. ↑ "Organometallic compounds in drug discovery: Past, present and future". Drug Discovery Today: Technologies 37: 117–124. December 2020. doi:10.1016/j.ddtec.2019.06.001. PMID 34895650. https://hal.archives-ouvertes.fr/hal-02169801/file/Organometallic Compounds in Drug Discovery Past, Present and futur.pdf.
68. ↑ "The antimalarial ferroquine: from bench to clinic". Parasite 18 (3): 207–214. August 2011. doi:10.1051/parasite/2011183207. PMID 21894260.
69. ↑ "Ferrocene-based antimalarials". Future Medicinal Chemistry 4 (6): 783–797. April 2012. doi:10.4155/fmc.12.26. PMID 22530641.
70. ↑ "Ferroquine and its derivatives: new generation of antimalarial agents". European Journal of Medicinal Chemistry 101: 534–551. August 2015. doi:10.1016/j.ejmech.2015.07.009. PMID 26188909.
71. ↑ "A randomized, double-blind, phase 2b study to investigate the efficacy, safety, tolerability and pharmacokinetics of a single-dose regimen of ferroquine with artefenomel in adults and children with uncomplicated Plasmodium falciparum malaria". Malaria Journal 20 (1): 222. May 2021. doi:10.1186/s12936-021-03749-4. PMID 34011358.
72. ↑ "Redox-stimuli-responsive drug delivery systems with supramolecular ferrocenyl-containing polymers for controlled release". Coordination Chemistry Reviews 364: 51–85. June 2018. doi:10.1016/j.ccr.2018.03.013. ISSN 0010-8545.
73. ↑ "Application of ferrocene and its derivatives in cancer research". New Journal of Chemistry 35 (10): 1973. 2011. doi:10.1039/c1nj20172g.
74. ↑ "Ferrocenes as potential anticancer drugs. Facts and hypotheses". Russ. Chem. Bull. 63 (11): 2405–2422. 2014. doi:10.1007/s11172-014-0756-7.
75. ↑ Yong J, Lu C, "Ferrocene Derivative, Preparation Method and Use Thereof.", US patent 9738673, issued August 22, 2017, assigned to Xiamen Institute of Rare Earth Materials.
76. ↑ 76.0 76.1 "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 (21): 5223–5236. November 2003. doi:10.1002/chem.200305024. PMID 14613131.
77. ↑ "The Bio Side of Organometallics". Chemical and Engineering News 80 (37): 23–29. 16 September 2002. doi:10.1021/cen-v080n037.p023. http://pubs.acs.org/cen/science/8037/8037sci1.html.
78. ↑ "Ferrocene Burn Rate Catalyst". https://www.rocketmotorparts.com/index.aspx?pageid=1577809&prodid=15759228.
79. ↑ "An improved photochemical synthesis of azaferrocene". J. Organomet. Chem. 388 (1–2): 175–179. 1990. doi:10.1016/0022-328X(90)85359-7.
80. ↑ "Chemistry of some η5-pyrrolyl- and η1-N-pyrrolyliron complexes". Inorg. Chem. 21 (3): 868–873. 1982. doi:10.1021/ic00133a006.
81. ↑ "Syntheses, structures, and reactivity of radial oligocyclopentadienyl metal complexes: penta(ferrocenyl)cyclopentadienyl and congeners". Angewandte Chemie 45 (11): 1794–1799. March 2006. doi:10.1002/anie.200504047. PMID 16470902.
82. ↑ 82.0 82.1 "Hexaferrocenylbenzene". Chemical Communications (24): 2572–2574. June 2006. doi:10.1039/b604844g. PMID 16779481. https://zenodo.org/record/896672.
83. ↑ 83.0 83.1 83.2 "Polymers with pendant ferrocenes". Chemical Society Reviews 45 (19): 5216–5231. October 2016. doi:10.1039/C6CS00196C. PMID 27156979.
84. ↑ "Carbon nanotube reactor: Ferrocene decomposition, iron particle growth, nanotube aggregation and scale-up". Chem. Eng. Sci. 65 (10): 2965–2977. 2010. doi:10.1016/j.ces.2010.01.019.
85. ↑ "Solvent-free synthesis of ferrocenylethene derivatives". J. Organomet. Chem. 625: 128–132. 2001. doi:10.1016/S0022-328X(00)00927-X.
86. ↑ "Ferrocene Polymers for Switchable Surface Wettability". Organometallics 32 (20): 5873–5878. 2013. doi:10.1021/om400468p.

## External links

* Ferrocene at The Periodic Table of Videos (University of Nottingham)
* NIOSH Pocket Guide to Chemical Hazards (Centers for Disease Control and Prevention)

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Iron compounds

Fe(-II)|

* Na2Fe(CO)4

Fe(0)|

* Fe(CO)5
* Fe2(CO)9
* Fe3(CO)12
* Fe(CO)3CH3COC2H2C6H6

Fe(I)|

* FeH

| Organoiron(I) compounds|

* (C5H5FeCO)2(CO)2

|

Fe(0,II)|

* Fe3C

Fe(II)|

* FeBr2
* FeCl2
* FeF2
* FeI2
* FeH2
* FeMoO4
* FeO
* Fe(OH)2
* FeS
* FeSO4
* FeSe
* FeSeO4
* FeSi2
* FeTiO3
* FeCO3
* FeC2O4
* Fe(C2H3O2)2
* Fe(C3H5O3)2
* FeC6H6O7
* FeC12H22O14
* Fe2CrO4
* Fe3(PO4)2
* H2Fe(CO)4
* Fe(HCO3)2
* Mg2FeH6

| Organoiron(II) compounds|

* Fe(C5H5)2
* Fe(C5H4P(C6H5)2)2
* C4H4Fe(CO)3
* C4H6Fe(CO)3

|

Fe(0,III)|

* Fe3P

Fe(II,III)|

* Fe3O4
* Fe3S4

Fe(III)|

* FeBr3
* FeCl3
* FeF3
* FeI3
* Fe(NO3)3
* Fe(acac)3
* FeOCl
* FeO(OH)
* FePO4
* Fe4(P2O7)3
* Fe2(CrO4)3
* Fe2(C2O4)3
* Fe2O3
* Fe2S3
* Fe2(SO4)3
* FeBO3
* FeB

| Organoiron(III) compounds|

* Fe(C5H5)2BF4
* C6H8O7⋅xFe3+⋅yNH3

|

Fe(VI)|

* K2FeO4
* BaFeO4

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