Английская Википедия:Hexa(tert-butoxy)ditungsten(III)
Шаблон:Chembox Hexa(tert-butoxy)ditungsten(III) is a coordination complex of tungsten(III). It is one of the homoleptic alkoxides 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 d3 metal centers.
Preparation
W2(O-t-Bu)6 was first prepared by treating tungsten(III) dialkylamides with tert-butanol.[1]
W2(O-t-Bu)6 can also be synthesized from NaW2Cl7(THF)5 and NaO-t-Bu.[2]
- NaW2Cl7(THF)5 + 6 NaO-t-Bu → W2(O-t-Bu)6 + 7 NaCl + 5 THF
Structure
As verified by X-ray crystallography, the two tungsten(III) centers are joined by a triple bond. Each W(III) is pseudotetrahedral. The W2O6 core adopts a staggered, ethane-like conformation, similar to that for its dimolybdenum analogue. The molecule has inversion symmetry.[3]
Reactions
Hydrolysis
This compound hydrolyzes at 200 °C to give WO2:
With carbon dioxide
Carbon dioxide reacts reversibly with Шаблон:Chem2 to form green 2:1 adduct featuring two alkyl carbonate ligands.
With carbon monoxide
Carbon monoxide react with Шаблон:Chem2 to give Шаблон:Chem2. In this adduct, the carbonyl ligand bridges between two W(III) atoms.. This compound can further react with i-PrOH to generate W4(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
Шаблон:Chem2 reacts with alkynes to give RC≡W(O-t-Bu)3, tetrahedral alkylidyne complexes.[4] In these complexes, tungsten is electrophilic and the alkylidyne carbon is nucleophilic.[5] [6]
- Шаблон:Chem2 (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. Шаблон:Chem2 does not react with diphenylacetylene or bis(trimethylsilyl)acetylene. These results are attributed to unfavorable electronic and steric effects, respectively. On the other hand, Шаблон:Chem2 reacts with two equivalents of EtC≡CPh, EtC≡CSiMe3, and EtC≡C–CH=CH2 to form corresponding alkylidyne complexes. Thus, Шаблон:Chem2 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.[7]
Besides simple metathesis reactions, W2(O-t-Bu)6 also reacts with 3-hexyne in a 1:1 molar ratio to form a triangular tritungsten complex compound [W3(O-t-Bu)5(μ-O)(μ-CEt)O]2.[8] 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 (W2):
W2(O-t-Bu)6 + RC≡CR → 2[RC≡W(O-t-Bu)3]
Шаблон:Chem2 also reacts with EtC≡CC≡CEt to form (t-Bu-O)3W≡CC≡W(O-t-Bu)3:
Шаблон:Chem2 This compound, however, does not act as a metathesis catalyst.
Шаблон:Chem2 also reacts with trans-Pt(C≡CH)2(PMe2Ph)2 to form (t-Bu-O)3W≡C–C≡W(O-t-Bu)3 and trans-(PMe2Ph)2Pt[C2W2(O-t-Bu)5]2.[9]
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:[5]
Although W2(O-t-Bu)6 reacts with nitriles, it doesn’t react with nitrogen (N≡N).
When C≡C and C≡N bond both exist, W2(O-t-Bu)6 reacts more rapidly with C≡N than C≡C bond. Here’s an example of W2(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
- Шаблон:Chem2 and nitrosobenzene combine to give [W(O-t-Bu)2(NPh)]2(μ-O)(μ-O-t-Bu)2. This reaction undergoes two oxidative additions to form W=N bonds. However, they couldn’t figure out where the one missing oxygen went. This reaction is the first discovered reaction of a nitroso with metal multiple bonds.[10]
With allenes
Allenes react:with the ditungsten complex forming adducts, e.g.,
- {{chem2|W2(O\st\sBu)6 + H2C\dC\dCH2 → :Шаблон:Chem2
Further reaction with carbon monoxide was also demonstrated.
See also
References
