Hexa(tert-butoxy)ditungsten(III)

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Hexa(tert-butoxy)ditungsten(III)
W2(OC(CH3)3)6.svg
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/6C4H9O.2W/c6*1-4(2,3)5;;/h6*1-3H3;;/q6*-1;2*+3
    Key: YKZVERBZIZOWIZ-UHFFFAOYSA-N
  • CC(C)(C)O[W](#[W](OC(C)(C)C)(OC(C)(C)C)OC(C)(C)C)(OC(C)(C)C)OC(C)(C)C
Properties
C24H54O6W2
Molar mass 806.37 g·mol−1
Appearancered solid
Density 1.651 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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.

Contents

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:

W2(O−t−Bu)6 + 2 H2O → 2 WO2 + 4 HO−t−Bu + 2 CH2=C(CH3)2

With carbon dioxide

Carbon dioxide reacts reversibly with W2(O−t−Bu)6 to form green 2:1 adduct featuring two alkyl carbonate ligands.

W2(O−t−Bu)6 + 2 CO2 ⇌ W2(O−t−Bu)4(O2CO−t−Bu)2

With carbon monoxide

Carbon monoxide react with W2(O−t−Bu)6 to give W2(O−t−Bu)6CO. 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

W2(O−t−Bu)6 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]

W2(O−t−Bu)6 + RC≡CR → 2 RC≡W(O−t−Bu)3 (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. W2(O−t−Bu)6 does not react with diphenylacetylene or bis(trimethylsilyl)acetylene. These results are attributed to unfavorable electronic and steric effects, respectively. On the other hand, W2(O−t−Bu)6 reacts with two equivalents of EtC≡CPh, EtC≡CSiMe3, and EtC≡C–CH=CH2 to form corresponding alkylidyne complexes. Thus, W2(O−t−Bu)6 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]

W2(O−t−Bu)6 + RC≡W(O−t−Bu)3 → W3(O−t−Bu)5(μ−O)(μ−CEt)O

W3(O−t−Bu)5(μ−O)(μ−CEt)O → [W3(O−t−Bu)5(μ−O)(μ−CEt)O]2

W2(O−t−Bu)6 also reacts with EtC≡CC≡CEt to form (t-Bu-O)3W≡CC≡W(O-t-Bu)3:

W2(O−t−Bu)6 + EtC≡CC≡CEt → (t−Bu−O)3W≡CC≡W(O−t−Bu)3 + EtC≡CEt This compound, however, does not act as a metathesis catalyst.

W2(O−t−Bu)6 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]

W2(O−t−Bu)6 + RC≡N → RC≡W(O−t−Bu)3 + N≡W(O−t−Bu)3

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:

W2(O−t−Bu)6 +EtC≡CCN + 12L → EtC≡CC≡W(O−t−Bu)3L + N≡W(O−t−Bu)3

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:

W2(O−t−Bu)6 + EtC≡CCN + 12 L → NCC≡W(O−t−Bu)3L + EtC≡CMe

With nitroso

W2(O−t−Bu)6 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 → :W2(O−t−Bu)6(HC2=C=CH2)

Further reaction with carbon monoxide was also demonstrated.

See also

References

  1. ↑ Chisholm, M. H.; Extine, M. (September 1975). "New Metalloorganic Compounds of Tungsten(III)". Journal of the American Chemical Society. 97 (19): 5625–5627. doi:10.1021/ja00852a074. ISSN   0002-7863.
  2. ↑ Broderick, Erin M.; Browne, Samuel C.; Johnson, Marc J. A.; Hitt, Tracey A.; Girolami, Gregory S. (2014-05-02), Girolami, Gregory S.; Sattelberger, Alfred P. (eds.), "Dimolybdenum and Ditungsten Hexa(Alkoxides)", Inorganic Syntheses (1 ed.), Wiley, pp. 95–102, doi:10.1002/9781118744994.ch18, ISBN   978-1-118-74487-1 , retrieved 2024-03-08
  3. ↑ Chisholm, Malcolm H.; Gallucci, Judith C.; Hollandsworth, Carl B. (2006-03-06). "Crystal and Molecular Structure of W2(OBut)6 and Electronic Structure Calculations on Various Conformers of W2(OMe)6". Polyhedron. Special issue in honour of Michael B. Hursthouse. 25 (4): 827–833. doi:10.1016/j.poly.2005.07.010. ISSN   0277-5387.
  4. ↑ Schrock, Richard R. (2006-06-02). "Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)". Angewandte Chemie International Edition. 45 (23): 3748–3759. doi:10.1002/anie.200600085. ISSN   1433-7851. PMID   16703641.
  5. 1 2 Listemann, Mark L.; Schrock, Richard R. (January 1985). "Multiple metal carbon bonds. 35. A General Route to tri-tert-butoxytungsten alkylidyne complexes. Scission of acetylenes by ditungsten hexa-tert-butoxide". Organometallics. 4 (1): 74–83. doi:10.1021/om00120a014. ISSN   0276-7333.
  6. ↑ Schrock, Richard R.; Listemann, Mark L.; Sturgeoff, Lynda G. (July 1982). "Metathesis of Tungsten-Tungsten Triple Bonds with Acetylenes and Nitriles to give alkylidyne and nitrido complexes". Journal of the American Chemical Society. 104 (15): 4291–4293. doi:10.1021/ja00379a061. ISSN   0002-7863.
  7. ↑ Mortreux, André; Petit, Francis; Petit, Michèle; Szymanska-Buzar, Teresa (1995-02-23). "Reactions of W(CCMe3)(OCMe3)3 with Terminal Alkynes: Metathesis and Polymerization". Journal of Molecular Catalysis A: Chemical. 96 (2): 95–105. doi:10.1016/1381-1169(94)00004-2. ISSN   1381-1169.
  8. ↑ Cotton, F. Albert; Schwotzer, Willi; Shamshoum, Edwar S. (October 1983). "A new type of triangular tritungsten cluster compound from reaction of 3-hexyne with hexa-tert-butoxyditungsten". Organometallics. 2 (10): 1340–1343. doi:10.1021/om50004a014. ISSN   0276-7333.
  9. ↑ Cotton, F. Albert; Murillo, Carlos A.; Walton, Richard A., eds. (2005). "Multiple Bonds Between Metal Atoms". SpringerLink. doi:10.1007/b136230. ISBN   978-0-387-25084-7.
  10. ↑ Cotton, F. Albert; Shamshoum, Edwar S. (May 1984). "Oxidative addition of nitrosobenzene fragments across the triply bonded ditungsten hexa-tert-butoxide molecule. The preparation and structure of the tungsten-tert-butoxy complex [W(OCMe3)2(NPh)]2(.mu.-O)(.mu.-OCMe3)2". Journal of the American Chemical Society. 106 (11): 3222–3225. doi:10.1021/ja00323a026. ISSN   0002-7863.
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