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Diiron nonacarbonyl

Diiron nonacarbonyl
IUPAC name Diiron nonacarbonyl
Other names Iron enneacarbonyl
CAS number 15321-51-4
Molecular formula Fe2CO9
Molar mass 363.78 g/mol
Appearance orange crystals
Density 2.85 g/cm3
Melting point

decomposes at 100 °C

Boiling point


Solubility in water insoluble
Dipole moment 0 D
Main hazards CO source
R-phrases 11-23/25
S-phrases 16-28-36/37/39-45
Related Compounds
Related compounds Fe(CO)5
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Diiron nonacarbonyl (referred to as diiron enneacarbonyl in the older literature) is the chemical 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. One of the strangest properties of this micaceous, orange solid is that it is virtually insoluble in all known solvents.



Photolysis of Fe(CO)5, typically in acetic acid solution, produces Fe2(CO)9 in good yield:[2]

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. Elucidation of the structure of Fe2(CO)9 has proven to be challenging because of its very low solubility, which prevents growth of crystals. The Mößbauer spectrum reveals one quadrupole doublet, consistent with the D3h-symmetric structure.


Fe2(CO)9 is primarily employed as 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:

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.[3]


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. ^ King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8
  3. ^ 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. 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Diiron_nonacarbonyl". A list of authors is available in Wikipedia.
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