Diiron nonacarbonyl


Diiron nonacarbonyl
Diiron nonacarbonyl
Diiron nonacarbonyl
Sample of diiron nonacarbonyl
IUPAC name
Diiron nonacarbonyl, tri-μ-carbonyl-bis(tricarbonyliron)(Fe—Fe)
Other names
Iron enneacarbonyl
  • 15321-51-4 checkY
3D model (JSmol)
  • Interactive image
  • 4807522 checkY
ECHA InfoCard 100.035.765 Edit this at Wikidata
EC Number
  • 239-359-5
  • 6096993
  • DTXSID50934700 Edit this at Wikidata
  • InChI=1S/9CO.2Fe/c9*1-2;; checkY
  • InChI=1/9CO.2Fe/c9*1-2;;
  • O=C1[Fe]2(=C=O)(=C=O)(=C=O)C(=O)[Fe]1(=C=O)(=C=O)(=C=O)C2=O
Molar mass 363.78 g/mol
Appearance orange crystals
Density 2.08 g/cm3
Melting point decomposes at 100 °C
Boiling point decomposes
0 D
Main hazards Toxic
GHS pictograms GHS02: FlammableGHS05: CorrosiveGHS06: Toxic
GHS Signal word Danger
Related compounds
Related iron carbonyls
Iron pentacarbonyl
Triiron dodecacarbonyl
Related compounds
Dimanganese decacarbonyl
Dicobalt octacarbonyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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. Although older textbooks show an Fe-Fe bond consistent with the 18 electron rule (8 valence electrons from Fe, two each from the terminal carbonyls, one each from the bridging carbonyls and one from the other Fe atom in the metal-metal bond), theoretical analyses have consistently indicated the absence of a direct Fe-Fe bond:[5] this latter model proposes an Fe-C-Fe three-center-two-electron "banana bond" for one of the bridging carbonyls. The minor isomer has been crystallized together with C60. 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 to the following reaction:[6]

Fe2(CO)9 → Fe(CO)5 + Fe(CO)4(THF)

Oxidative addition of allyl bromide to diiron nonacarbonyl gives the allyl iron(II) derivaive:[7]

Fe2(CO)9 + BrCH2CH=CH2 → FeBr(CO)3(C3H5) + CO + Fe(CO)5

Cyclobutadieneiron tricarbonyl is prepared similarly using 3,4-dichlorocyclobutene:[8]

C4H4Cl2 + 2 Fe2(CO)9 → (C4H4)Fe(CO)3 + 2 Fe(CO)5 + 2 CO + 2 FeCl2.

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.[9]

Low temperature UV/vis photolysis of Fe2(CO)9 yields the Fe2(CO)8 unsaturated complex, producing both CO-bridged and unbridged isomers.[10]


  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 (1924). "Über die Bildungsweise von Eisen-nonacarbonyl aus Eisen-pentacarbonyl". Berichte der deutschen chemischen Gesellschaft. 60: 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 (1966). "Diiron Enneacarbonyl". Inorg. Synth. Inorganic Syntheses. 8: 178. doi:10.1002/9780470132395.ch46. ISBN 978-0-470-13239-5.
  5. ^ Jennifer C. Green, Malcolm L. H. Green, Gerard Parkin "The occurrence and representation of three-centre two-electron bonds in covalent inorganic compounds" Chem. Commun. 2012, 11481-11503. doi:10.1039/c2cc35304k
  6. ^ 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
  7. ^ Putnik, Charles F.; Welter, James J.; Stucky, Galen D.; d'Aniello, M. J.; Sosinsky, B. A.; Kirner, J. F.; Muetterties, E. L. (1978). "Metal clusters in catalysis. 15. A Structural and Chemical Study of a Dinuclear Metal Complex, Hexacarbonylbis(.eta.3-2-propenyl)diiron(Fe-Fe)". Journal of the American Chemical Society. 100 (13): 4107–4116. doi:10.1021/ja00481a020.
  8. ^ Pettit, R.; Henery, J. (1970). "Cyclobutadieneiron Tricarbonyl". Organic Syntheses. 50: 21. doi:10.15227/orgsyn.050.0021.
  9. ^ R. Noyori; Yokoyama, K.; Hayakawa, Y. (1988). "Cyclopentanones from α, α'-Dibromoketones and Enamines: 2,5-Dimethyl-3-Phenyl-2-Cyclopenten-1-one". Organic Syntheses.; Collective Volume, 6, p. 520
  10. ^ Susan C. Fletcher; Martyn Poliakoff; James J. Turner (1986). "Structure and Reactions of Fe2(CO)8: An IR Spectroscopic study using 13C Photolysis with plane-polarized light, and matrix isolation". Inorg. Chem. 25 (20): 3597. doi:10.1021/ic00240a014.