Triiron dodecacarbonyl

Chembox new
ImageFile = Fe3(CO)12.png ImageSize = 150px
ImageName = Triiron dodecacarbonyl
IUPACName = dodecarbonyltriiron,
tetra-μ-carbonyl-1:2κ⁴"C",1:3κ²"C",2:3κ²"C"-
octacarbonyl-1κ³"C",2κ³"C",3κ²"C"-"triangulo"
-triiron(3 "Fe"—"Fe")
OtherNames = Iron tetracarbonyl trimer
Section1 = Chembox Identifiers
SMILES =
CASNo = 17685-52-8
Section2 = Chembox Properties
Formula = Fe₃CO₁₂
MolarMass = 503.66 g/mol
Appearance = dark green crystals
Density = ? g/cm³, ?
Solubility = insoluble
MeltingPt = 165 °C
BoilingPt = decompose °C (? K)
Section3 = Chembox Structure
Dipole =
Section7 = Chembox Hazards
ExternalMSDS =
MainHazards =
Section8 = Chembox Related
Function = compounds
OtherFunctn = Fe(CO)₅
Fe₂(CO)₉
Mn₂(CO)₁₀

Triiron dodecarbonyl is the chemical compound with the formula Fe₃(CO)₁₂. It was one of the first metal carbonyl clusters synthesized. [Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7] It is a more reactive source of iron(0) than is iron pentacarbonyl.

General properties

Fe₃(CO)₁₂ is a dark green solid, which sublimes under a good vacuum, albeit with significant decomposition. 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.

ynthesis

It was occasionally obtained from the thermolysis of Fe(CO)₅::3 Fe(CO)₅ → Fe₃(CO)₁₂ + 3 COTraces 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.

An efficient synthesis of Fe₃(CO)₁₂ proceeds via the reaction of Fe(CO)₅ with base: [cite journal | author = McFarlane, W.; Wilkinson, G. W. | title = Triiron dodecacarbonyl | journal = Inorganic Syntheses | year = 1966 | volume = 8 | pages = 181–3 | doi = 10.1002/9780470132395.ch47] :3 Fe(CO)₅ + (C₂H₅)₃N + H₂O → [(C₂H₅)₃NH] [HFe₃(CO)₁₁] + 3 CO + CO₂followed by oxidation of the resulting hydride with acid:: [(C₂H₅)₃NH] [HFe₃(CO)₁₁] + HCl + CO → Fe₃(CO)₁₂ + H₂ + [(C₂H₅)₃NH] Cl

The original synthesis, by Walter Hieber, entailed the reaction of H₂Fe(CO)₄ with MnO₂. The cluster was formulated merely as "Fe(CO)₄". [cite journal| author=Hieber, W.; Leutert, F.| title=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)|journal= Zeitschrift für anorganische und allgemeine Chemie|year= 1932| volume= 204| pages =145–64| doi=10.1002/zaac.19322040115]

tructure

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. Overall, it can be appreciated that these three clusters formally arise from condensation of three 16-electron M(CO)₄ fragments, akin to the condensation of CH₂ units into cyclopropane.

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.

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

Like most metal carbonyls, Fe₃(CO)₁₂ undergoes substitution reactions, making, for example, Fe₃(CO)₁₁{P(C₆H₅)₃} upon reaction with triphenylphosphine.

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 reacts with 1,3-Propanedithiol to form air-stable µ-(1,3-Propanedithiolato)-hexacarbonyldiiron in which both thiol sulfur atoms form a bridge between two iron atoms. This compound is a model compound for certain all-iron hydrogenases ["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 [http://jchemed.chem.wisc.edu/Journal/Issues/2007/May/abs836.html Abstract] ] .

afety

Like all metal carbonyls Fe₃(CO)₁₂ is hazardous as a source of volatile iron and 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