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
CAS Number	12184-52-0
3D model (JSmol)	Interactive image
PubChem CID	10923395
InChI InChI=1S/2C8H8.Fe/c2*1-2-4-6-8-7-5-3-1;/h2*1-8H;/b2*2-1-,3-1?,4-2?,5-3-,6-4-,7-5?,8-6?,8-7-; Key: MXSLSXKBFNCQNV-MZLYQNCSSA-N
SMILES C\1=C\C=C/C=C\C=C1.C\1=C\C=C/C=C\C=C1.[Fe]
Properties
Chemical formula	C16H16Fe
Molar mass	264.149 g·mol−1
Density	1.42 (from structure)
Structure
Crystal structure	Monoclinic
Space group	Cc or C2/c
Lattice constant	a = 15.13, b = 10.68, c = 13.98 α = 90°, β = 99.5°, γ = 90°[1]
Formula units (Z)	12
Related compounds
Related compounds	Tris(cyclooctatetraene)triiron
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.^[1]

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