Diiron nonacarbonyl

Diiron nonacarbonyl

Names
IUPAC name Diiron nonacarbonyl, tri-μ-carbonyl-bis(tricarbonyliron)(Fe—Fe)
Other names Iron enneacarbonyl
Identifiers
CAS Number	15321-51-4
ChemSpider	4807522
Jmol interactive 3D	Image
InChI InChI=1S/9CO.2Fe/c9*1-2;; Key: JCXLZXJCZPKTBW-UHFFFAOYSA-N InChI=1/9CO.2Fe/c9*1-2;; Key: JCXLZXJCZPKTBW-UHFFFAOYAN
SMILES [Fe].[Fe].[C-]#[O+].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-]
Properties
Chemical formula	Fe2C9O9
Molar mass	363.78 g/mol
Appearance	orange crystals
Density	2.08 g/cm^3
Melting point	decomposes at 100 °C
Boiling point	decomposes
Solubility in water	insoluble
Structure
Dipole moment	0 D
Hazards
Main hazards	Toxic
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 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 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)

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.^[7]

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

References

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. 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, p. 520
8. 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.