Bis(cyclooctatetraene)iron is an
organoiron compound with the formula Fe(C
8H
8)
2, abbreviated Fe(COT)
2. It is an air-sensitive black solid that is soluble in
diethyl ether
Diethyl ether, or simply ether, is an organic compound with the chemical formula , sometimes abbreviated as . It is a colourless, highly Volatility (chemistry), volatile, sweet-smelling ("ethereal odour"), extremely flammable liquid. It belongs ...
and
aromatic
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
s. The compound decomposes in solution after a few days even under inert atmosphere.
It has no known practical applications but has been studied as a soluble source of Fe(0).
Preparation
The laboratory synthesis of Fe(COT)
2, using
Schlenk techniques, involves reduction of
ferric acetylacetonate by
triethylaluminium
Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important comp ...
in the presence of 1,3,5,7-
cyclooctatetraene
1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as nnulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of ...
:
[
:Fe(C5H7O2)3 + 2 C8H8 + 3 Al(C2H5)3 → Fe(C8H8)2 + 3 Al(C2H5)2(C5H7O2) + C2H4 + C2H6
]
Structure
According to analysis by single crystal X-ray crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
, the two cyclooctatetraene rings bind differently to the Fe center, leading to the description Fe(''η''4-C8H8)(''η''6-C8H8). One cyclooctatetraene ring binds to Fe with two adjacent double bonds. This interaction is similar to that in (''η''4-C8H8)Fe(CO)3. The two planar groups formed by carbon atoms 1,2,7,8 and carbon atoms 3,4,5,6,7 form a dihedral angle of 33°. The second cyclooctatetraene ring binds through three double bonds. The shape and coordination of the lower ring is similar to that in (''η''6-C8H8)Mo(CO)3. The non-coordinated double bond has a similar bond length as an ordinary double bond.[{{cite journal, first1=G. , last1=Allergra, first2= A., last2= Colmbo , first3=A. , last3=Immirzi , first4=I. W. , last4=Bassi , title=The Crystal Structure of Bis(cyclooctatetraene)iron , journal= J. Am. Chem. Soc., volume= 90, issue=16 , date=1968 , pages=4454–4456 , doi=10.1021/ja01018a046]
In solution, Fe(C8H8)2 is a fluxional molecule
In chemistry and molecular physics, fluxional (or non-rigid) molecules are molecules that undergo dynamics such that some or all of their atoms interchange between symmetry-equivalent positions. Because virtually all molecules are fluxional in som ...
such that its 1H NMR spectrum consists of a singlet at room-temperature.[
]
References
Organoiron compounds
Sandwich compounds
Iron(0) compounds