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Diiron nonacarbonyl

Names
IUPAC name Diiron nonacarbonyl, tri-μ-carbonyl-bis(tricarbonyliron)(Fe—Fe)
Other names Iron enneacarbonyl
Identifiers
CAS Number	15321-51-4
3D model (JSmol)	Interactive image
ChemSpider	4807522
ECHA InfoCard	100.035.765
EC Number	239-359-5
PubChem CID	6096993
CompTox Dashboard (EPA)	DTXSID50934700
InChI InChI=1S/9CO.2Fe/c9*1-2;;Key: JCXLZXJCZPKTBW-UHFFFAOYSA-N InChI=1/9CO.2Fe/c9*1-2;;Key: JCXLZXJCZPKTBW-UHFFFAOYAN
SMILES O=C12(=C=O)(=C=O)(=C=O)C(=O)1(=C=O)(=C=O)(=C=O)C2=O
Properties
Chemical formula	Fe2C9O9
Molar mass	363.78 g/mol
Appearance	orange crystals
Density	2.08 g/cm
Melting point	decomposes at 100 °C
Solubility in water	insoluble, does not react with water
Structure
Dipole moment	0 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Toxic, flammable
GHS labelling:
Pictograms
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 , 100 kPa). Y verify (what is  ?) Infobox references

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

Synthesis and structure

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

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: 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 D_3h-symmetric structure.

Reactions

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

Fe₂(CO)₉ ⇌ Fe(CO)₅ + Fe(CO)₄(THF)

Alkene complexes arise by direct reaction of a suspension in warm benzene:

Fe₂(CO)₉ + RCH=CRH → Fe(CO)₅ + Fe(CO)₄(RCH=CRH)

In related reaction (benzylideneacetone)iron tricarbonyl, with the formula (C₆H₅CH=CHC(O)CH₃)Fe(CO)₃ is prepared by the reaction of diiron nonacarbonyl with benzylideneacetone. This complex is a source of the Fe(CO)₃ fragment. Oxidative addition of allyl bromide to diiron nonacarbonyl gives the allyl iron(II) derivative:

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

Cyclobutadieneiron tricarbonyl is prepared similarly using 3,4-dichlorocyclobutene perhaps according to the following idealized equation:

C₄H₄Cl₂ + Fe₂(CO)₉ → (C₄H₄)Fe(CO)₃ + FeCl₂ + 6 CO

Fe₂(CO)₉ has also been employed in the synthesis of cyclopentadienones via a net -cycloaddition from dibromoketones, known as the Noyori reaction.

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

Safety

Metal carbonyls are typically treated as if they are highly toxic.

References

1. Dewar, J., & Jones, H. O. (1907). On a New Iron Carbonyl, and on the Action of Light and of Heat on the Iron Carbonyls. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 79(527), 66–80. doi:10.1098/rspa.1907.0015
2. Diiron nonacarbonyl, reactivity
3. Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7
4. Edmund Speyer; Hans Wolf (1924). "Über die Bildungsweise von Eisen-nonacarbonyl aus Eisen-pentacarbonyl". Berichte der Deutschen Chemischen Gesellschaft. 60 (6): 1424–1425. doi:10.1002/cber.19270600626.
5. ^ King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8.
6. E. H. Braye; W. Hübel (1966). "Diiron Enneacarbonyl". Inorganic Syntheses. 8: 178–181. doi:10.1002/9780470132395.ch46.
7. 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
8. Cotton, F. Albert; Troup, Jan M. (1974). "Reactivity of diiron nonacarbonyl in tetrahydrofuran. I. Isolation and Characterization of Pyridinetetracarbonyliron and Pyrazinetetracarbonyliron". Journal of the American Chemical Society. 96 (11): 3438–3443. Bibcode:1974JAChS..96.3438C. doi:10.1021/ja00818a016.
9. Weiss, E.; Stark, K.; Lancaster, J. E.; Murdoch, H. D. (1963). "π-Olefin-eisentetracarbonyl-Komplexe mit Liganden der Malein-, Fumar-, Acryl-, Methacryl- und Zimtsäure-Reihe". Helvetica Chimica Acta. 46: 288–297. doi:10.1002/hlca.19630460128.
10. Domingos, A. J. P.; Howell, J. A. S.; Johnson, B. F. G.; Lewis, J. (1990). "Reagents for the Synthesis of η-Diene Complexes of Tricarbonyliron and Tricarbonylruthenium". Inorg. Synth. Inorganic Syntheses. Vol. 28. pp. 52–55. doi:10.1002/9780470132593.ch11. ISBN 9780470132593.
11. 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.
12. Pettit, R.; Henery, J. (1970). "Cyclobutadieneiron Tricarbonyl". Organic Syntheses. 50: 21. doi:10.15227/orgsyn.050.0021.
13. 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; Collected Volumes, vol. 6, p. 520.
14. Susan C. Fletcher; Martyn Poliakoff; James J. Turner (1986). "Structure and Reactions of Fe₂(CO)₈: An IR Spectroscopic Study Using C Photolysis with Plane-Polarized Light, and Matrix Isolation". Inorg. Chem. 25 (20): 3597. doi:10.1021/ic00240a014.

• Iron carbonyl complexes
• Chemical compounds containing metal–metal bonds
• Iron(0) compounds