Triiron dodecarbonyl is the
organoiron compound with the
formula Fe
3(CO)
12. It is a dark green solid that
sublimes
Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...
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 Fe
3(CO)
12 decompose to an iron mirror, which can be
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
in air.The solid decomposes slowly in air, and thus samples are typically stored cold under an inert atmosphere. It is a more reactive source of iron(0) than
iron pentacarbonyl
Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula . Under standard conditions Fe( CO)5 is a free-flowing, straw-colored liquid with a pungent odour. Older samples appear darker. This compound is a common precursor ...
.
Synthesis
It was one of the first
metal carbonyl
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe ...
cluster
may refer to:
Science and technology Astronomy
* Cluster (spacecraft), constellation of four European Space Agency spacecraft
* Asteroid cluster, a small asteroid family
* Cluster II (spacecraft), a European Space Agency mission to study th ...
s synthesized. It was occasionally obtained from the
thermolysis of
Fe(CO)5:
:3 Fe(CO)
5 → Fe
3(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 Fe
3(CO)
12.
The usual synthesis of Fe
3(CO)
12 starts with the reaction of Fe(CO)
5 with base:
:3 Fe(CO)
5 +
(C2H5)3N + H
2O →
2H5)3NH">C2H5)3NHHFe
3(CO)
11] + 3 CO + CO
2
followed by oxidation of the resulting
hydride, hydrido cluster with acid:
:
2H5)3NH">C2H5)3NHHFe
3(CO)
11] + HCl + CO → Fe
3(CO)
12 + H
2 +
2H5)3NH">C2H5)3NHl
The original synthesis by
Walter Hieber et al. entailed the oxidation of H
2Fe(CO)
4 with
manganese dioxide
Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cel ...
. The cluster was originally formulated incorrectly as "Fe(CO)
4".
Structure
left, 140px, Saturated solution of Fe3(CO)12 in .">mesitylene.
Elucidation of the structure of Fe
3(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.
Fe
3(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 Fe
3(CO)
12 is
fluxional, resulting in equivalencing all 12 CO groups on the
13C NMR timescale. Overall, it can be appreciated that these three clusters formally arise from condensation of three 16-electron M(CO)
4 fragments, akin to the theoretical condensation of three
methylene (:CH
2) molecules into
cyclopropane.
The anion
3(CO)11">Fe3(CO)11sup>− is structurally related to Fe
3(CO)
12, with the
hydride
In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of ...
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, Fe
3(CO)
12 undergoes substitution reactions, making, for example, Fe
3(CO)
11 upon reaction with
triphenylphosphine
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...
.
Heating Fe
3(CO)
12 gives a low yield of the
carbido cluster Fe
5(CO)
15C. Such reactions proceed via
disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term ca ...
of CO to give
CO2 and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
.
Fe
3(CO)
12 forms "ferroles" upon reaction with heterocycles such as
thiophenes.
Fe
3(CO)
12 reacts with
thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s and
disulfide
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
s to give
thiolate-bridged complexes, such as
methylthioirontricarbonyl dimer
Methylthioirontricarbonyl dimer, also known as methanethiolatoirontricarbonyl dimer, is an organometallic compound with the formula Fe2(SCH3)2(CO)6. It is a red volatile solid that is classified as a transition metal thiolate complex. It exists ...
:
:2 Fe
3(CO)
12 + 3 (CH
3)
2S
2 → 3
3SCH3">e(CO)3SCH3sub>2 + 6 CO. These complexes are studied as
hydrogenase mimics.
[''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
The ''Journal of Chemical Education'' is a monthly peer-reviewed academic journal available in both print and electronic versions. It is published by the Division of Chemical Education of the American Chemical Society and was established in 1924 ...
Vol. 84 No. 5 May 2007''
Abstract
/ref>
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
{{Iron compounds
Carbonyl complexes
Iron complexes
Organoiron compounds
Chemical compounds containing metal–metal bonds
Iron(0) compounds