Hexakis(trimethylphosphine)tungsten
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| Identifiers | |
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3D model (JSmol) |
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| Properties | |
| C18H54P6W | |
| Molar mass | 640.31 |
| Appearance | yellow crystalline solid |
| Structure | |
| Cubic | |
| Im3m | |
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Other cations |
Mo(PMe3)6 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Hexakis(trimethylphosphine)tungsten is a tungsten(0) organometallic compound with the formula W(P(CH3)3)6. It is a yellow crystalline solid, soluble in organic solvents. Much of the most interesting and varied chemistry occurs from its dissociated variants, such as W(PMe3)5.
Synthesis and equilibrium
W(PMe3)6 is a relatively difficult zero-valent, homoleptic trimethylphosphine complex to synthesize and isolate. It equilibrates with PMe3 and the metallacycle W(PMe3)4(η2-CH2PMe2)H:
tungsten_in_solution.png)
The equilibrium constant at 30 °C is about 17.8 M, and the rightwards reaction has ΔH° = 9.3 kcal/mol (39 kJ/mol) and ΔS° = 37 eu (150 J K−1 mol−1). Thus W(PMe3)6 solutions decompose in about 2 hours, unless the equilibrium is driven to the left by an excess of PMe3.[1]
Naive attempts to prepare W(PMe3)6 by co-condensation of tungsten with PMe3, or reduction of WCl6 with alkali metals, only form W(PMe3)4(η2-CH2PMe2)H.[2] Parkin and Rabinovich first recognized in 1990 that these attempts, using only stoichiometric PMe3 and slow extraction procedures, must necessarily fight the equilibrium. Simple room-temperature reduction with Na-K alloy gives the homoleptic complex when excess PMe3 is the solvent:[1]
tungsten.png)
Crystal properties
In the solid state, W(PMe3)6 is stable at room temperature for at least two weeks. The complex was crystallographically characterized, demonstrating W-P bond lengths of 2.455 ± 0.01 Å (245.5 ± 1.0 pm) and P-W-P bond angles of 90° and 180°.
Reactivity
Metal complexes of the form M(PMe3)n contain very electron-rich and highly-reactive metal centers as a result of the combination of the strong σ-donating and π-accepting nature of the PMe3 ligand.[3] These complexes have been shown to be capable of activating C-H and other otherwise unreactive σ bonds via oxidative addition, often forming cyclometalated products.[1]
W(PMe3)6 possesses an 18-electron valence count, and as such demonstrates somewhat limited reactivity.
Diphosphene metathesis
W(PMe3)6 can catalyze the metathesis of phosphorus-phosphorus double-bonds. Interaction of the appropriate dichlorophosphane with W(PMe3)6 leads to dechlorination and formation of symmetrical and unsymmetrical diphosphenes: [4][5]
The resultant phosphorus-tungsten species can also catalyze the exchange of diphosphene end-groups.
Metal-germanium triple bonds
The W(PMe3)4(η2-CH2PMe2)H species formed upon the dissolution of W(PMe3)6 can participate in a Ge-Cl bond heterolysis and form a metal-germanium triple bond:[3]
References
- 1 2 3 Rabinovich, Daniel; Parkin, Gerard (1990). "Hexakis(trimethylphosphine)tungsten(0): synthesis, structure, and reactivity". Journal of the American Chemical Society. 112 (13): 5381–5383. doi:10.1021/ja00169a073. ISSN 0002-7863.
- ↑ Green, Malcolm L. H.; Parkin, Gerard; Chen, Mingqin; Prout, Keith (1986-01-01). "The chemistry of [W(PMe3)4(η2-CH2PMe2)H]: synthesis of hydroxy-hydrido, fluoro-hydrido, and silyl-hydrido derivatives and the dimerisation of ethylene and propene giving η4-diene derivatives. Crystal structure of [W(PMe3)4H2(OH2)F]F". Journal of the Chemical Society, Dalton Transactions (10): 2227–2236. doi:10.1039/DT9860002227. ISSN 1364-5447.
- 1 2 Filippou, Alexander C.; Weidemann, Nils; Philippopoulos, Athanassios I.; Schnakenburg, Gregor (2006-09-11). "Activation of Aryl Germanium(II) Chlorides by [Mo(PMe 3 ) 6 ] and [W(η 2 ‐CH 2 PMe 2 )H(PMe 3 ) 4 ]: A New Route to Metal–Germanium Triple Bonds". Angewandte Chemie International Edition. 45 (36): 5987–5991. doi:10.1002/anie.200602061. ISSN 1433-7851.
- ↑ Dillon, Keith B.; Fox, Mark A.; Gibson, Vernon C.; Goodwin, Helen P.; Sequeira, Leila J. (2017-02-15). "Platinum(II) complexes of some unsymmetrical diphosphenes". Journal of Organometallic Chemistry. 830: 113–119. doi:10.1016/j.jorganchem.2016.10.005. ISSN 0022-328X.
- ↑ Dillon, Keith B.; Gibson, Vernon C.; Sequeira, Leela J. (1995-01-01). "Transition-metal catalysed metathesis of phosphorus–phosphorus double bonds". Journal of the Chemical Society, Chemical Communications (23): 2429–2430. doi:10.1039/C39950002429. ISSN 0022-4936.