Cobaltocene

Last updated
Cobaltocene
Skeletal formula of cobaltocene Cobaltocene.svg
Skeletal formula of cobaltocene
Ball-and-stick model of cobaltocene Cobaltocene-3D-balls.png
Ball-and-stick model of cobaltocene
Names
IUPAC names
Cobaltocene
Bis(η5-cyclopentadienyl)cobalt
Other names
Cp2Co
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.013.692
EC Number
  • 215-061-0
PubChem CID
RTECS number
  • GG0350000
UNII
Properties
[Co(η5-C5H5)2]
Molar mass 189.12 g/mol
AppearanceDark purple solid
Melting point 171–173 °C (340–343 °F; 444–446 K)
Insoluble
Structure
sandwich
zero
Thermochemistry
236 J K−1 mol−1
+237 kJ/mol (uncertain)
−5839 kJ/mol
Hazards
Safety data sheet External SDS
GHS pictograms GHS-pictogram-flamme.svg GHS-pictogram-silhouette.svg [1]
GHS Signal word Danger [1]
H228, H317, H351 [1]
P210, P261, P280, P363, P405, P501 [1]
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeCobaltocene
2
1
0
Related compounds
Related metallocenes
Ferrocene
Nickelocene
Rhodocene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cobaltocene, known also as bis(cyclopentadienyl)cobalt(II) or even "bis Cp cobalt", is an organocobalt compound with the formula Co(C5H5)2. It is a dark purple solid that sublimes readily slightly above room temperature. Cobaltocene was discovered shortly after ferrocene, the first metallocene. Due to the ease with which it reacts with oxygen, the compound must be handled and stored using air-free techniques.

Contents

Synthesis

Vacuum sublimated cobaltocene under nitrogen atmosphere Cobaltocene crystals.png
Vacuum sublimated cobaltocene under nitrogen atmosphere

Cobaltocene is prepared by the reaction of sodium cyclopentadienide (NaC5H5) with anhydrous cobalt(II) chloride in THF solution. Sodium chloride is cogenerated, and the organometallic product is usually purified by vacuum sublimation. [2]

Structure and bonding

In Co(C5H5)2 the Co centre is "sandwiched" between two cyclopentadienyl (Cp) rings. The Co–C bond lengths are about 2.1 Å, slightly longer than the Fe–C bond in ferrocene. [3]

Co(C5H5)2 belongs to a group of organometallic compounds called metallocenes or sandwich compounds. [4] Cobaltocene has 19 valence electrons, one more than usually found in organotransition metal complexes such as its very stable relative ferrocene. (See 18-electron rule.) This additional electron occupies an orbital that is antibonding with respect to the Co–C bonds. Consequently, the Co–C distances are slightly longer than the Fe–C bonds in ferrocene. Many chemical reactions of Co(C5H5)2 are characterized by its tendency to lose this "extra" electron, yielding an 18-electron cation known as cobaltocenium:

The otherwise close relative of cobaltocene, rhodocene does not exist as a monomer, but spontaneously dimerizes by formation of a C–C bond between Cp rings.

Reactions

Redox properties

Co(C5H5)2 is a common one-electron reducing agent in the laboratory. [5] In fact, the reversibility of the Co(C5H5)2 redox couple is so well-behaved that Co(C5H5)2 may be used in cyclic voltammetry as an internal standard. Its permethylated analogue decamethylcobaltocene (Co(C5Me5)2) is an especially powerful reducing agent, due to inductive donation of electron density from the 10 methyl groups, prompting the cobalt to give up its "extra" electron even more so. These two compounds are rare examples of reductants that dissolve in non-polar organic solvents. The reduction potentials of these compounds follow, using the ferrocene-ferrocenium couple as the reference:

Half-reaction E0 (V)
Fe(C
5
H
5
)+
2
+ e ⇌ Fe(C5H5)2
0.00 (by definition)
Fe(C
5
Me
5
)+
2
+ e ⇌ Fe(C5Me5)2
−0.59
Co(C
5
H
5
)+
2
+ e ⇌ Co(C5H5)2
−1.33
Co(C
5
Me
5
)+
2
+ e ⇌ Co(C5Me5)2
−1.94

The data show that the decamethyl compounds are around 600 mV more reducing than the parent metallocenes. This substituent effect is, however, overshadowed by the influence of the metal: changing from Fe to Co renders the reduction more favorable by over 1.3 volts.

Carbonylation

Treatment of Co(C5H5)2 with carbon monoxide gives the cobalt(I) derivative Co(C5H5)(CO)2, concomitant with loss of one Cp ligand. This conversion is conducted near 130 °C with 500 psi of CO. [2] [6]

See also

Related Research Articles

Metallocene Compounds typically consisting of two cyclopentadienyl anions bound to a metal center.

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
5
H
5
, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization.

Ferrocene is an organometallic compound with the formula Fe(C
5
H
5
)
2
. The molecule consists of two cyclopentadienyl rings bound on opposite sides of 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
H
5
)+
2
.

Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction. This dimer can be restored by heating to give the monomer.

Cyclopentadienyl complex class of chemical compounds

A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups. Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (η5-) bonding mode. The metal–cyclopentadienyl interaction is typically drawn as a single line from the metal center to the center of the Cp ring.

Nickelocene chemical compound

Nickelocene is the organonickel compound with the formula Ni(η5-C5H5)2. Also known as bis(cyclopentadienyl)nickel or NiCp2, this bright green paramagnetic solid is of enduring academic interest, although it does not yet have any known practical applications.

Titanocene dichloride chemical compound

Titanocene dichloride is the organotitanium compound with the formula (η5-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.

Hapticity coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms.

Hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

Chromocene chemical compound

Chromocene is the organochromium compound with the formula [Cr(C5H5)2]. Like structurally related metallocenes, chromocene readily sublimes in a vacuum and is soluble in non-polar organic solvents. It is more formally known as bis(η5-cyclopentadienyl)chromium(II).

Sandwich compound chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands

In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands. The arenes have the formula CnHn, substituted derivatives (for example Cn(CH3)n) and heterocyclic derivatives (for example BCnHn+1). Because the metal is usually situated between the two rings, it is said to be "sandwiched". A special class of sandwich complexes are the metallocenes.

Organouranium chemistry

Organouranium chemistry is the science exploring the properties, structure and reactivity of organouranium compounds, which are organometallic compounds containing a carbon to uranium chemical bond. The field is of some importance to the nuclear industry and of theoretical interest in organometallic chemistry.

In organometallic chemistry, a transition metal indenyl complex is a coordination compound that contains one or more indenyl ligands. The indenyl ligand is formally the anion derived from deprotonation of indene. The η5-indenyl ligand is related to the η5cyclopentadienyl anion (Cp), thus indenyl analogues of many cyclopentadienyl complexes are known. Indenyl ligands lack the 5-fold symmetry of Cp, so they exhibit more complicated geometries. Furthermore, some indenyl complexes also exist with only η3-bonding mode. The η5- and η3-bonding modes sometimes interconvert.

Sodium cyclopentadienide chemical compound

Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pink owing to traces of oxidized impurities.

Organoiron chemistry is the chemistry of iron compounds containing a carbon-to-iron chemical bond. Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate. Iron adopts oxidation states from Fe(−II) through to Fe(VII). Although iron is generally less active in many catalytic applications, it is less expensive and "greener" than other metals. Organoiron compounds feature a wide range of ligands that support the Fe-C bond; as with other organometals, these supporting ligands prominently include phosphines, carbon monoxide, and cyclopentadienyl, but hard ligands such as amines are employed as well.

Rhodocene, formally known as bis(η5-cyclopentadienyl)rhodium(II), is a chemical compound with the formula [Rh(C5H5)2]. Each molecule contains an atom of rhodium bound between two planar aromatic systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has (haptic) covalent rhodium–carbon bonds. The [Rh(C5H5)2] radical is found above 150 °C or when trapped by cooling to liquid nitrogen temperatures (−196 °C). At room temperature, pairs of these radicals join via their cyclopentadienyl rings to form a dimer, a yellow solid.

Manganocene chemical compound

Manganocene or bis(cyclopentadienyl)manganese(II) is an organomanganese compound with the formula [Mn(C5H5)2]n. It is a thermochromic solid that degrades rapidly in air. Although the compound is of little utility, it is often discussed as an example of a metallocene with ionic character.

Decamethylferrocene chemical compound

Decamethylferrocene or bis(pentamethylcyclopentadienyl)iron(II) is a chemical compound with formula Fe(C
5
(CH
3
)
5
)
2
or C
20
H
30
Fe
. It is a sandwich compound, whose molecule has an iron(II) cation Fe2+ attached by coordination bonds between two pentamethylcyclopentadienyl anions (Cp*, (CH
3
)
5
C
5
). It can also be viewed as a derivative of ferrocene, with a methyl group replacing each hydrogen atom of its cyclopentadienyl rings. The name and formula are often abbreviated to DmFc, Me
10
Fc
or FeCp*
2
.

Vanadocene chemical compound

Vanadocene, bis(η5-cyclopentadienyl) vanadium, is the organometallic compound with the formula V(C5H5)2, commonly abbreviated Cp2V. It is a violet crystalline, paramagnetic solid. Vanadocene has relatively limited practical use, but it has been extensively studied.

Decamethylcobaltocene chemical compound

Decamethylcobaltocene is an organocobalt compound with the formula Co(C5(CH3)5)2, abbreviated CoCp
2
. It is a dark brown solid. This compound is used as a strong reducing agent in organometallic chemistry.

Cyclopentadienyliron dicarbonyl iodide chemical compound

Cyclopentadienyliron dicarbonyl iodide is an organoiron compound with the formula (C5H5)Fe(CO)2I. It is a dark brown solid that is soluble in common organic solvents. (C5H5)Fe(CO)2I, or FpI as it is often known, is an intermediate for the preparation of other organoiron compounds such as in ferraboranes.

Magnesocene, also known as bis(cyclopentadienyl)magnesium(II) and sometimes abbreviated as MgCp2, is an organometallic compound with the formula Mg(η5-C5H5)2. It is an example of an s-block main group sandwich compound, structurally related to the d-block element metallocenes, and consists of a central magnesium atom sandwiched between two cyclopentadienyl rings.

References

  1. 1 2 3 4 "Bis(cyclopentadienyl)cobalt(II)". American Elements . Retrieved 2018-08-24.
  2. 1 2 King, R. B. (1965). Organometallic Syntheses. 1. New York, NY: Academic Press.
  3. Antipin, M. Yu.; Boese, R.; Augart, N.; Schmid, G. (1993). "Redetermination of the cobaltocene crystal structure at 100 K and 297 K: Comparison with ferrocene and nickelocene". Struct. Chem. 4 (2): 91–101. doi:10.1007/BF00677370.
  4. Elschenbroich, C.; Salzer, A. (1992). Organometallics: A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN   978-3-527-28165-7.
  5. Connelly, N. G.; Geiger, W. E. (1996). "Chemical Redox Agents for Organometallic Chemistry". Chem. Rev. 96 (2): 877–910. doi:10.1021/cr940053x. PMID   11848774.
  6. King, R. B.; Stone, F. G. A. (1967). "Cyclopentadienyl Metal Carbonyls and Some Derivatives". Inorganic Syntheses. 7: 99–115. doi:10.1002/9780470132388.ch31. ISBN   9780470132388.