Triiron dodecacarbonyl

Triiron dodecarbonyl is the organoiron compound with the formula Fe₃(CO)₁₂. It is a dark green solid that sublimes under vacuum. It is soluble in nonpolar organic solvents to give intensely green solutions. Most low-nuclearity clusters are pale yellow or orange. Hot solutions of Fe₃(CO)₁₂ decompose to an iron mirror, which can be pyrophoric in air. The solid decomposes slowly in air, and thus samples are typically stored cold under an inert atmosphere.^[1] It is a more reactive source of iron(0) than iron pentacarbonyl.

Triiron dodecacarbonyl

Names
IUPAC names dodecarbonyltriiron, tetra-μ-carbonyl-1:2κ4C,1:3κ2C,2:3κ2C-octacarbonyl-1κ3C,2κ3C,3κ2C-triangulo-triiron(3 Fe—Fe)
Other names Iron tetracarbonyl trimer
Identifiers
CAS Number	17685-52-8 Y
3D model (JSmol)	Interactive image
ChemSpider	22439569
ECHA InfoCard	100.037.864
EC Number	241-668-5
PubChem CID	519467
InChI InChI=1S/12CO.3Fe/c12*1-2;;; Key: HLYRMDDXFDINCB-UHFFFAOYSA-N
SMILES [C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[C-]#[O+].[Fe].[Fe].[Fe]
Properties
Chemical formula	Fe3(CO)12
Molar mass	503.66 g/mol
Appearance	dark black/green crystals
Melting point	165 °C (329 °F; 438 K)
Boiling point	decomposes
Solubility in water	insoluble
Structure
Point group	C2v
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H228, H302, H312, H331, H332, H371
Related compounds
Other cations	Triruthenium dodecacarbonyl Triosmium dodecacarbonyl
Related iron carbonyls	Iron pentacarbonyl Diiron nonacarbonyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis

It was one of the first metal carbonyl clusters synthesized. It was occasionally obtained from the thermolysis of Fe(CO)₅:

3 Fe(CO)₅ → Fe₃(CO)₁₂ + 3 CO

Traces of the compound are easily detected because of its characteristic deep green colour. UV-photolysis of Fe(CO)₅ produces Fe₂(CO)₉, not Fe₃(CO)₁₂.

The usual synthesis of Fe₃(CO)₁₂ starts with the reaction of Fe(CO)₅ with base:^[2]

3 Fe(CO)₅ + (C₂H₅)₃N + H₂O → [(C₂H₅)₃NH][HFe₃(CO)₁₁] + 3 CO + CO₂

followed by oxidation of the resulting hydrido cluster with acid:

[(C₂H₅)₃NH][HFe₃(CO)₁₁] + HCl + CO → Fe₃(CO)₁₂ + H₂ + [(C₂H₅)₃NH]Cl

The original synthesis by Walter Hieber et al. entailed the oxidation of H₂Fe(CO)₄ with manganese dioxide. The cluster was originally formulated incorrectly as "Fe(CO)₄".^[3]

Structure

Saturated solution of Fe₃(CO)₁₂ in mesitylene.

Elucidation of the structure of Fe₃(CO)₁₂ proved to be challenging because the CO ligands are disordered in the crystals. Early evidence for its distinctive C_2v structure came from Mössbauer spectroscopic measurements that revealed two quadrupole doublets with similar isomer shifts but different (1.13 and 0.13 mm s⁻¹) quadrupolar coupling constants.

Fe₃(CO)₁₂ consists of a triangle of iron atoms surrounded by 12 CO ligands. Ten of the CO ligands are terminal and two span an Fe---Fe edge, resulting in C_2v point group symmetry. By contrast, Ru₃(CO)₁₂ and Os₃(CO)₁₂ adopt D_3h-symmetric structures, wherein all 12 CO ligands are terminally bound to the metals. In solution Fe₃(CO)₁₂ is fluxional, resulting in equivalencing all 12 CO groups on the ¹³C NMR timescale.^[4]

The anion [HFe₃(CO)₁₁]⁻ is structurally related to Fe₃(CO)₁₂, with the hydride replacing one bridging CO ligand. The bonding in the Fe-H-Fe subunit is described using concepts developed for diborane.

Reactions

Solutions of Fe₃(CO)₁₂ reacts with triphenylphosphine to give (triphenylphosphine)iron tetracarbonyl (and some bis(triphenylphosphine)iron tricarbonyl).^[5]

Fe₃(CO)₁₂ + 3 P(C₆H₅)₃ → 3 Fe(CO)₄(P(C₆H₅)₃)

Heating Fe₃(CO)₁₂ gives a low yield of the carbido cluster Fe₅(CO)₁₅C. Such reactions proceed via disproportionation of CO to give CO₂ and carbon.

Fe₃(CO)₁₂ forms "ferroles" upon reaction with heterocycles such as thiophenes.

Fe₃(CO)₁₂ reacts with thiols and disulfides to give thiolate-bridged complexes, such as methylthioirontricarbonyl dimer:^[6]

2 Fe₃(CO)₁₂ + 3 (CH₃)₂S₂ → 3 [Fe(CO)₃SCH₃]₂ + 6 CO. These complexes are studied as hydrogenase mimics.^[7]

Safety

Fe₃(CO)₁₂ is hazardous as a source of carbon monoxide. Solid samples, especially when finely divided, and residues from reactions can be pyrophoric, which can ignite the organic solvents used for such reactions.

References

1. Elschenbroich, C.; Salzer, A. ”Organometallics: A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
2. McFarlane, W.; Wilkinson, G. W. (1966). Triiron dodecacarbonyl. Inorganic Syntheses. Vol. 8. pp. 181–3. doi:10.1002/9780470132395.ch47. ISBN 978-0-470-13239-5.
3. Hieber, W.; Leutert, F. (1932). "Über Metallcarbonyle. XII. Die Basenreaktion des Eisenpentacarbonyls und die Bildung des Eisencarbonylwasserstoffs (Metal carbonyls. XII. The Reaction of Iron Pentacarbonyl with Bases and the Formation of Iron Hydrocarbonyl)". Zeitschrift für anorganische und allgemeine Chemie. 204: 145–64. doi:10.1002/zaac.19322040115.{{cite journal}}: CS1 maint: multiple names: authors list (link)
4. Farrugia, Louis J. (1997). "Dynamics and Fluxionality in Metal Carbonyl Clusters: Some Old and New Problems". Journal of the Chemical Society, Dalton Transactions (11): 1783–1792. doi:10.1039/A608514H.
5. Clifford, A. F.; Mukherjee, A. K. (1966). "Iron Carbonyl Complexes of Triphenylphosphine, Triphenylarsine, and Triphenylstibine". Inorganic Syntheses. Vol. VIII. pp. 185–191. doi:10.1002/9780470132395.ch49. ISBN 978-0-470-13239-5.
6. King, R. B. "Organosulfur Derivatives of Metal Carbonyls. I. The Isolation of Two Isomeric Products in the Reaction of Triiron Dodecacarbonyl with Dimethyl Disulfide" J. Am. Chem. Soc. 1962, vol. 84, 2460. doi:10.1021/ja00871a045
7. Synthesis, Purification, and Characterization of a μ-(1,3-Propanedithiolato)-hexacarbonyldiiron Laboratory Experiment or Mini-Project for Inorganic Chemistry or Integrated Laboratory Carmen F. Works 836 Journal of Chemical Education Vol. 84 No. 5 May 2007 Abstract