Bis(cyclooctatetraene)iron

Bis(cyclooctatetraene)iron is an organoiron compound with the formula Fe(C8H8)2, abbreviated Fe(COT)2. It is an air-sensitive black solid that is soluble in diethyl ether and aromatic solvents. The compound decomposes in solution after a few days even under inert atmosphere.[2] It has no known practical applications but has been studied as a soluble source of Fe(0).

Bis(cyclooctatetraene)iron
Identifiers
3D model (JSmol)
Properties
C16H16Fe
Molar mass 264.149 g·mol−1
Density 1.42 (from structure)
Structure
Monoclinic
Cc or C2/c
a = 15.13, b = 10.68, c = 13.98
α = 90°, β = 99.5°, γ = 90°[1]
12
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Preparation

The laboratory synthesis of Fe(COT)2, using Schlenk techniques, involves reduction of ferric acetylacetonate by triethylaluminium in the presence of 1,3,5,7-cyclooctatetraene:[2]

Fe(C5H7O2)3 + 2 C8H8 + 3 Al(C2H5)3 → Fe(C8H8)2 + 3 Al(C2H5)2(C5H7O2) + ​3⁄2 C2H4 + ​3⁄2 C2H6

Structure

According to analysis by single crystal X-ray crystallography, the two cyclooctatetraene rings bind differently to the Fe center, leading to the description Fe(η4-C8H8)(η6-C8H8). One cyclooctatetraene ring binds to Fe with two adjacent double bonds. This interaction is similar to that in (η4-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 (η6-C8H8)Mo(CO)3. The non-coordinated double bond has a similar bond length as an ordinary double bond.[3]

In solution, Fe(C8H8)2 is a fluxional molecule such that the room-temperature 1H NMR spectrum consists of a singlet.[3]

References
  1. Allegra, G.; Colombo, A.; Immirzi, A.; Bassi, I. W. (July 1968). "The crystal structure of bis(cyclooctatetraene)iron". Journal of the American Chemical Society. 90 (16): 4455–4456. doi:10.1021/ja01018a046.
  2. Gerlach, D. H.; Schunn, R. A. (1974). "Bis(1,3,5,7-cyclooctatetraene)iron(0)". Inorg. Synth. 15: 1–4. doi:10.1002/9780470132463.ch1.
  3. Allergra, G.; Colmbo, A.; Immirzi, A.; Bassi, I. W. (1968). "The Crystal Structure of bis(cyclooctatetraene)iron,". J. Am. Chem. Soc. 90 (16): 4454–4456. doi:10.1021/ja01018a046.
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