Vanadium hexacarbonyl is the
inorganic compound with the
formula V(CO)
6. It is a blue-black volatile solid. This highly reactive species is noteworthy from theoretical perspectives as a rare isolable
homoleptic
In inorganic chemistry, a homoleptic chemical compound is a metal compound with all ligands identical. The term uses the " homo-" prefix to indicate that something is the same for all. Any metal species which has more than one type of ligand is he ...
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 ...
that is paramagnetic. Most species with the formula M
''x''(CO)
''y'' follow the
18-electron rule, whereas V(CO)
6 has 17 valence electrons.
Synthesis
Traditionally V(CO)
6 is prepared in two-steps via the intermediacy of . In the first step, VCl
3 is reduced with metallic
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
under 200 atm CO at 160 °C. The solvent for this reduction is typically
diglyme
Diglyme, or bis(2-methoxyethyl) ether, is a solvent with a high boiling point. It is an organic compound which is the dimethyl ether of diethylene glycol. (The name ''diglyme'' is a portmanteau of ''diglycol methyl ether''.) It is a colorless li ...
, CH
3OCH
2CH
2OCH
2CH
2OCH
3. This tri
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be ...
solubilizes sodium salts, akin to the behavior of a
crown ether
In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Impo ...
:
:4 Na + VCl
3 + 6 CO + 2 diglyme →
a(diglyme)2V(CO)
6] + 3 NaCl
The resulting anion is oxidized with acid:
:2 + 2 H
3PO
4 → 2 V(CO)
6 + H
2 + 2
Reactions
Vanadium hexacarbonyl is thermally unstable. Its primary reaction is reduction to the monoanion , salts of which are well studied. It is also susceptible to substitution by tertiary
phosphine ligand A metal-phosphine complex is a In coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. ...
s, often leading to
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 can ...
.
V(CO)
6 reacts with sources of the
cyclopentadienyl anion to give the orange
four-legged piano stool complex (C
5H
5)V(CO)
4 (m.p. 136 °C). Like many charge-neutral organometallic compounds, this half-sandwich species is volatile. In the original preparation of this species, C
5H
5HgCl was employed as the source of .
Structure
V(CO)
6 adopts an
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 ...
coordination geometry and is isostructural with
chromium hexacarbonyl
Chromium carbonyl, also known as chromium hexacarbonyl, is the chemical compound with the formula Cr( CO)6. At room temperature the solid is stable to air, although it does have a high vapor pressure and sublimes readily. Cr(CO)6 is zerovalent ...
, even though they have differing valence electron counts. High resolution X-ray crystallography indicates that the molecule is slightly distorted with two (''axial'') shorter V–C distances of 1.993(2) Å vs. four (equatorial) 2.005(2) Å. Even though V(−I) is a larger ion than V(0), the V–C distances in are 0.07 Å shorter than in the neutral precursor.
References
Further reading
* Original synthesis:
{{Carbonyl complexes
Vanadium compounds
Carbonyl complexes