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Hexa(tert-butoxy)ditungsten(III)

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Hexa(tert-butoxy)ditungsten(III)
Identifiers
3D model (JSmol)
ChemSpider
  • 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
Appearance red 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.

Preparation

Hexa(tert-butoxy)ditungsten(III) was first prepared by treating tungsten(III) dialkylamides with tert-butanol.[1]. It was

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

These needle-like red crystals are highly unstable under oxygen and water and can be dissolved in most organic solvents such as diethyl ether and pentane. They are found in dimers with two tungsten(III) bond with each other to form triple bonds. These two W(III) form pseudotetrahedral center and adopt a staggered, ethane-like conformation, similar to its dimolybdenum analogue. The structure of the compound was investigated by Chisholm and his team using single crystal X-ray diffraction. The investigation was performed in a C-centered monoclinic crystal. In C2/c space group, there is one half inversion center molecule and one whole molecule in general position. There are several orientations for each position which leads to the length of WW ranging from 1.74 to 2.53 Å. The orientation of t-butyl groups in each W are one direct away from WW (distal) and two over WW (proximal). This arrangement had been calculated as the best to minimize the steric repulsing effect.[3]


Reactions

Hydrolysis

This compound hydrolyzes at 200oC 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:

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.

With alkynes

W2(O−t−Bu)6 react with alkynes or nitriles to generate RC≡W(O-t-Bu)3 or both RC≡W(O-t-Bu)3 and N≡W(O-t-Bu)3. RC≡W(O-t-Bu)3 is important catalyst for alkyne metathesis[4] while N≡W(O-t-Bu)3 is a catalyst for nitrogen exchange of nitriles. The C≡W bond in RC≡W(O-t-Bu)3 was concluded to behave as polarized C(-)≡W(+).[5] In the metathesis reaction, tungsten is electrophilic and alkylidyne carbon is nucleophilic.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.</ref>:

W2(O−t−Bu)6 + RC≡CR → 2 RC≡W(O−t−Bu)3

Where R can be Me, Et, Pr.

The reaction happens at around 25 ″C in less than an hour. The rate increases in the following order: 4-octyne, 3-hexyne, 2-butyne. The resulting alkylidyne compounds are all colorless and sublime at room temperature. W2(O−t−Bu)6 does not react with PhC≡CPh or Me3SiC≡CSiMe3. It is because of unfavorable electronic and steric effects, respectively. Instead, it can react with two equivalents of EtC≡CPh, EtC≡CSiMe3, or EtC≡C–CH=CH2 to form corresponding alkylidyne complexes. W2(O−t−Bu)6 reacts more easily with asymmetric substitute acetylenes than symmetric ones.

This reaction includes an alkyne adduct on the μ-perpendicular site to increase both the length of WW bonds and CC (alkyne) bonds. This intermediate can be analogue as a dimetallatetrahedranes and further react into RC≡W(O-t-Bu)3 with internal redox reaction. The resulting RC≡W(O-t-Bu)3 is a catalyst for metathesis reactions. RC≡W(O-t-Bu)3 can react with normal alkynes for metathesis reactions and also with terminal alkynes for both metathesis reactions and polymerizations.[6]

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.[7] 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.[8]

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.[9]

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. ^ a b 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. ^ 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.
  7. ^ 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.
  8. ^ 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.
  9. ^ 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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