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Diiron nonacarbonyl
Diiron nonacarbonyl
Diiron nonacarbonyl
Sample of diiron nonacarbonyl
IUPAC name
Other names Iron enneacarbonyl
CAS number 15321-51-4 Yes check.svgY
Molecular formula Fe2C9O9
Molar mass 363.78 g/mol
Appearance orange crystals
Density 2.08 g/cm3
Melting point

decomposes at 100 °C

Boiling point


Solubility in water insoluble
Dipole moment 0 D
Main hazards Toxic
Related compounds
Related iron carbonyls Iron pentacarbonyl
Triiron dodecacarbonyl
Related compounds Dimanganese decacarbonyl
Dicobalt octacarbonyl
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Diiron nonacarbonyl is an inorganic compound with the formula Fe2(CO)9. This metal carbonyl is an important reagent in organometallic chemistry and of occasional use in organic synthesis.[1] It is a more reactive source of Fe(0) than Fe(CO)5 and less dangerous to handle because it is nonvolatile. This micaceous orange solid is virtually insoluble in all common solvents.


Synthesis and structure

Following the original method,[2] photolysis of an acetic acid solution of Fe(CO)5 produces Fe2(CO)9 in good yield:[3][4]

2 Fe(CO)5 → Fe2(CO)9 + CO

Fe2(CO)9 consists of a pair of Fe(CO)3 centers linked by three bridging CO ligands. The iron atoms are equivalent and octahedral molecular geometry. Elucidation of the structure of Fe2(CO)9 proved to be challenging because its low solubility inhibits growth of crystals. The Mößbauer spectrum reveals one quadrupole doublet, consistent with the D3h-symmetric structure.


Fe2(CO)9 is a precursor to compounds of the type Fe(CO)4L and Fe(CO)3(diene). Such syntheses are typically conducted in THF solution. In these conversions, it is proposed that small amounts of Fe2(CO)9 dissolve according the following reaction:[5]

Fe2(CO)9 → Fe(CO)5 + Fe(CO)4(THF)

Cyclobutadieneiron tricarbonyl is prepared using Fe2(CO)9. Fe2(CO)9 has also been employed in the synthesis of cyclopentadienones via a net [2+3]-cycloaddition from dibromoketones, known as the Noyori [3+2] reaction.[6]

Low temperature UV/vis photolysis of Fe2(CO)9 yields the Fe2(CO)8 unsaturated complex, producing both CO-bridged and unbridged isomers. [7]


Fe2(CO)9 is a source of CO, although it is nonvolatile and insoluble.


  1. ^ Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  2. ^ Edmund Speyer, Hans Wolf "Über die Bildungsweise von Eisen-nonacarbonyl aus Eisen-pentacarbonyl" Berichte der deutschen chemischen Gesellschaft, 1924 volume 60, p. 1424-1425. doi:10.1002/cber.19270600626
  3. ^ King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8.
  4. ^ E. H. Braye, W. Hübel "Diiron Enneacarbonyl" Inorganic Syntheses 1966, volume VIII, p. 178-181. doi:10.1002/9780470132395.ch46.
  5. ^ F. Albert Cotton, Jan M. Troup "Reactivity of diiron nonacarbonyl in tetrahydrofuran. I. Isolation and characterization of pyridinetetracarbonyliron and pyrazinetetracarbonyliron" J. Am. Chem. Soc., 1974, volume 96, pp 3438–3443. doi:10.1021/ja00818a016
  6. ^ R. Noyori, R.; Yokoyama, K.; Hayakawa, Y. (1988), "Cyclopentanones from α, α'-Dibromoketones and Enamines: 2,5-Dimethyl-3-Phenyl-2-Cyclopenten-1-one", Org. Synth.,  ; Coll. Vol. 6: 520  
  7. ^ Susan C. Fletcher, M.; Poliakoff, J.; J.; Turner.; Structure and Reactions of Fe2(CO)8: An IR Spectroscopic study using 13C Photolysis with plane-polarized light, and matrix isolation. Inorg. Chem. 25 3597, 1986


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