Iron tetracarbonyl dihydride is the
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 H
2Fe(CO)
4. This compound was the first
transition metal hydride
Transition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions. The term "hydride" is used loo ...
discovered. The complex is stable at low temperatures but decomposes rapidly at temperatures above –20 °C.
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Preparation
Iron tetracarbonyl dihydride was first produced by Hieber and Leutert from 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 to ...
, which is first converted to HFe(CO):
:Fe(CO)5 + 2 OH− → HFe(CO) + HCO
:HFe(CO) + H+ → H2Fe(CO)4
Since the compound is thermally labile and sensitive to light, ideal conditions in 1930's Munich called for winter nights. The early method was called the "polar night synthesis."
As recommended by Hieber and Leutert, the compound can be purified by trap-to-trap distillation.
Structure and properties
In iron tetracarbonyl hydride the Fe(CO)4 group has C''2v'' molecular symmetry with a geometry intermediate between octahedral
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...
and tetrahedral
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
. Viewed as an octahedral complex, the hydride ligands are ''cis''. Viewed as a tetrahedral Fe(CO)4 complex, the hydrides occupy adjacent faces of the tetrahedron. Although the structure of tetracarbonyliron with the hydrogen atoms bound as a single H2 ligand has been proposed as an intermediate in some rearrangement reactions, the stable state for the compound has the two atoms as independent ligands.
Reactions
Iron tetracarbonyl dihydride undergoes rapid ligand substitutions by phosphorus ligands:
:H2Fe(CO)4 + PPh3 → H2Fe(CO)3PPh3
The substitution mechanism is proposed to entail transient formation of a 16e− formyl intermediate.water-gas shift reaction
Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
(WGSR). The slow step in the WGSR is the proton transfer from water to the iron hydride anion.[Crabtree, R.H. Mingos D.M.P. 2007. Comprehensive Organometallic Chemistry III From Fundamentals to Applications. Elsevier Ltd.]
:HFe(CO) + H2O → H2Fe(CO)4 + OH−
See also
* Potassium tetracarbonyliron hydride
* Collman's reagent
Further reading
*
*
References
{{DEFAULTSORT:Iron Tetracarbonyl Hydride
Carbonyl complexes
Iron complexes
Metal hydrides