Hexa(''tert''-butoxy)ditungsten(III) is a
coordination complex
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...
of
tungsten
Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
(III). It is one of the
homoleptic alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...
s of tungsten. A red, air-sensitive solid, the complex has attracted academic attention as the precursor to many
organotungsten derivatives. It an example of a charge-neutral complex featuring a W≡W bond, arising from the coupling of a pair of d
3 metal centers.
Preparation
W
2(O-''t''-Bu)
6 was first prepared by treating tungsten(III) dialkylamides with tert-butanol.
W
2(O-''t''-Bu)
6 can also be synthesized from NaW
2Cl
7(THF)
5 and
NaO-''t''-Bu.
:NaW
2Cl
7(THF)
5 + 6 NaO-''t''-Bu → W
2(O-''t''-Bu)
6 + 7 NaCl + 5 THF
Structure
As verified by
X-ray crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
, the two tungsten(III) centers are joined by a
triple bond
A triple bond in chemistry is a chemical bond between two atoms involving six Electron pair bond, bonding electrons instead of the usual two in a covalent bond, covalent single bond. Triple bonds are stronger than the equivalent covalent bond, sin ...
. Each W(III) is pseudotetrahedral. The W
2O
6 core adopts a staggered, ethane-like conformation, similar to that for its dimolybdenum analogue. The molecule has inversion symmetry.
Reactions
Hydrolysis
This compound hydrolyzes at 200 °C to give WO
2:
:
With carbon dioxide
Carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
reacts reversibly with to form green 2:1 adduct featuring two alkyl carbonate ligands.
:
With carbon monoxide
Carbon monoxide react with to give . In this adduct, the carbonyl ligand
bridges
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somet ...
between two W(III) atoms.. This compound can further react with
''i''-PrOH to generate W
4(μ-CO)
2(O-''i''-Pr)
12. The higher nuclearity of this isopropoxide can be attributed to the smaller size of the isopropoxyl ligands.
With alkynes
reacts with alkynes to give RC≡W(O-''t''-Bu)
3, tetrahedral alkylidyne complexes. In these complexes, tungsten is electrophilic and the alkylidyne carbon is nucleophilic.
: (R can be Me, Et, Pr)
The reaction proceed in minutes near room temperature. The rate increases in the following order: 4-octyne, 3-hexyne, 2-butyne. The resulting alkylidyne compounds are colorless solids that sublime near room temperature. does not react with
diphenylacetylene
Diphenylacetylene is the chemical compound C6H5C≡CC6H5. The molecule consists of two phenyl groups attached to a C2 unit. A colorless solid, it is used as a building block in organic synthesis and as a Transition metal alkyne complex, ligand in ...
or
bis(trimethylsilyl)acetylene. These results are attributed to unfavorable electronic and steric effects, respectively. On the other hand, reacts with two equivalents of EtC≡CPh, EtC≡CSiMe
3, and EtC≡C–CH=CH
2 to form corresponding alkylidyne complexes. Thus, reacts more easily with asymmetric substitute acetylenes than symmetric ones.
The reactions with alkynes initially afford adducts with a bridging ("μ-perpendicular") alkyne with elongated WW bonds and CC (alkyne) bonds. This intermediate is analogue to other
dimetallatetrahedranes. These adducts convert into RC≡W(O-''t''-Bu)
3. The resulting alkylidyne complexes RC≡W(O-''t''-Bu)
3 catalyze
alkyne metathesis reactions.
Besides simple metathesis reactions, W
2(O-''t''-Bu)
6 also reacts with 3-hexyne in a 1:1 molar ratio to form a triangular tritungsten complex compound
3(O-''t''-Bu)5(μ-O)(μ-CEt)Osub>2. This reaction has a two steps mechanism; first is the C≡C and W≡W metathesis reaction and follow by formal addition of carbyne (W≡C) to alkoxide (W
2):
W
2(O-''t''-Bu)
6 + RC≡CR → 2
C≡W(O-''t''-Bu)3
:
also reacts with EtC≡CC≡CEt to form (''t''-Bu-O)
3W≡CC≡W(O-''t''-Bu)
3:
This compound, however, does not act as a metathesis catalyst.
also reacts with ''trans''-Pt(C≡CH)
2(PMe
2Ph)
2 to form (''t''-Bu-O)
3W≡C–C≡W(O-''t''-Bu)
3 and ''trans''-(PMe
2Ph)
2Pt
2W2(O-''t''-Bu)5sub>2.
With nitriles
With excess amount of nitrile, N≡W(O-''t''-Bu)
3 is formed along with RC≡CR. The reaction initially gives a 1:1 mixture of the alkylidyne RC≡W(O-''t''-Bu)
3 and nitride N≡W(O-''t''-Bu)
3:
:
Although W
2(O-''t''-Bu)
6 reacts with nitriles, it doesn’t react with nitrogen (N≡N).
When C≡C and C≡N bond both exist, W
2(O-''t''-Bu)
6 reacts more rapidly with C≡N than C≡C bond. Here’s an example of W
2(O-''t''-Bu)
6 reacting with EtC≡CCN in the presence of quinuclidine:
:
On the other hand, the metathesis catalyst MeC≡W(O-''t''-Bu)
3 reacts more rapidly with C≡C than C≡N bond. Similar reaction with EtC≡CCN and quinuclidine produce different product:
:
With nitroso
and
nitrosobenzene combine to give
(O-''t''-Bu)2(NPh)sub>2(μ-O)(μ-O-''t''-Bu)
2. This reaction undergoes two oxidative additions to form W=N bonds. However, researchers couldn't figure out where the one missing oxygen went. This reaction is the first discovered reaction of a nitroso with metal multiple bonds.
With allenes
Allene
In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon atoms (, where R is hydrogen, H or some organyl group). Allenes are classified as diene#Classes, cumulated dienes ...
s react with the ditungsten complex forming adducts, e.g.,
:
Further reaction with
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
was also demonstrated.
See also
*
Hexa(tert-butoxy)dimolybdenum(III)
References
{{tungsten compounds
Alkoxides
Tungsten compounds