Diiron nonacarbonyl is an
organometallic compound
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
Fe
2(CO)
9. This
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 c ...
is an important reagent in
organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...
and of occasional use in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
. It is a more reactive source of Fe(0) than
Fe(CO)5. This micaceous orange solid is virtually
insoluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubi ...
in all common
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s.
Synthesis and structure
Following the original method,
photolysis
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
of an acetic acid solution of Fe(CO)
5 produces Fe
2(CO)
9 in good yield:
[King, R. B. Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. .]
:2 Fe(CO)
5 → Fe
2(CO)
9 + CO
Fe
2(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
In organic chemistry, a bent bond, also known as a banana bond, is a type of covalent chemical bond with a geometry somewhat reminiscent of a banana. The term itself is a general representation of electron density or configuration resembling a ...
" for one of the bridging carbonyls. The minor isomer has been crystallized together with C
60. The iron atoms are equivalent and
octahedral molecular geometry
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The o ...
. Elucidation of the structure of Fe
2(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
Fe
2(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
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
solution. In these conversions, it is proposed that small amounts of Fe
2(CO)
9 dissolve according to the following reaction:
:Fe
2(CO)
9 → Fe(CO)
5 + Fe(CO)
4(THF)
Oxidative addition of allyl bromide to diiron nonacarbonyl gives the
allyl
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, ...
iron(II) derivaive:
:Fe
2(CO)
9 + BrCH
2CH=CH
2 → FeBr(CO)
3(C
3H
5) + CO + Fe(CO)
5
Cyclobutadieneiron tricarbonyl
Cyclobutadieneiron tricarbonyl is an organoiron compound with the formula Fe(C4H4)(CO)3. It is a yellow solid that is soluble in organic solvents. It has been used in organic chemistry as a precursor for cyclobutadiene, which is an elusive specie ...
is prepared similarly using 3,4-dichlorocyclobutene:
:C
4H
4Cl
2 + 2 Fe
2(CO)
9 → (C
4H
4)Fe(CO)
3 + 2 Fe(CO)
5 + 2 CO + 2 FeCl
2.
Fe
2(CO)
9 has also been employed in the synthesis of cyclopentadienones via a net
+3cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity" ...
from dibromoketones, known as the Noyori
+2reaction.
Low temperature UV/vis photolysis of Fe
2(CO)
9 yields the Fe
2(CO)
8 unsaturated complex, producing both CO-bridged and unbridged isomers.
Safety
Metal carbonyls are typically treated as if they are highly toxic.
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References
{{Iron compounds
Carbonyl complexes
Iron complexes
Organoiron compounds
Iron(0) compounds