Tungsten hexacarbonyl (also called tungsten carbonyl) is the chemical compound with the formula W(CO)
6. This complex gave rise to the first example of a dihydrogen complex.
[Kubas, G. J., Metal Dihydrogen and σ-Bond Complexes, Kluwer Academic/Plenum Publishers: New York, 2001.]
This colorless compound, like its
chromium and
molybdenum analogs, is noteworthy as a volatile, air-stable derivative of
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
in its zero oxidation state.
Preparation, properties, and structure
W(CO)
6 is prepared by the
reduction of
tungsten hexachloride under a pressure of
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
. The compound is relatively air-stable. It is sparingly soluble in nonpolar organic solvents. Tungsten carbonyl is widely used in
electron beam-induced deposition Electron-beam-induced deposition (EBID) is a process of decomposing gaseous molecules by an electron beam leading to deposition of non-volatile fragments onto a nearby substrate. The electron beam is usually provided by a scanning electron microsco ...
technique - it is easily vaporized and decomposed by the electron beam providing a convenient source of tungsten atoms.
W(CO)
6 adopts an
octahedral 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 oc ...
consisting of six rod-like CO
ligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
s radiating from the central W atom with
dipole moment 0
D.
Reactivity
All reactions of W(CO)
6 commence with displacement of some CO ligands in W(CO)
6. W(CO)
6 behaves similarly to the Mo(CO)
6 but tends to form compounds that are kinetically more robust.
left, 144px, Cyclopentadienyltungsten tricarbonyl dimer ((C
5H
5.)
2W
2(CO)
6) is produced from W(CO)
6.
Treatment of tungsten hexacarbonyl with
sodium cyclopentadienide
Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are p ...
followed by oxidation of the resulting NaW(CO)
3(C
5H
5) gives
cyclopentadienyltungsten tricarbonyl dimer.
One derivative is the
dihydrogen complex
Dihydrogen complexes are coordination complexes containing intact H2 as a ligand. They are a subset of sigma complexes. The prototypical complex is W(CO)3( PCy3)2(H2). This class of compounds represent intermediates in metal-catalyzed reactions ...
W(CO)
3 (C6H11)3sub>2(H
2).
Three of these CO ligands can be displaced by acetonitrile.
W(CO)
6 has been used to desulfurize organosulfur compounds and as a precursor to catalysts for
alkene metathesis
Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds. Because of the relative simplicity of olefin metathesis, it often create ...
.
Safety and handling
Like all metal carbonyls, W(CO)
6 is a dangerous source of volatile metal as well as CO.
References
{{Tungsten compounds
Organotungsten compounds
Carbonyl complexes
Octahedral compounds
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