Hexakis(trimethylphosphine)tungsten is a tungsten(0) organometallic compound with the formula W(P(CH<sub>3</sub>)<sub>3</sub>)<sub>6</sub>. It is a yellow crystalline solid soluble in organic solvents.
Compared to other zerovalent homoleptic trimethylphosphine complexes, W(PMe<sub>3</sub>)<sub>6</sub> was less straightforward to synthesize and isolate. Previous attempts to prepare W(PMe<sub>3</sub>)<sub>6</sub> by co-condensation (a modification of metal vapor synthesis) of tungsten with PMe<sub>3</sub> and reduction of WCl<sub>6</sub> with alkali metal reducing agents only formed the cyclometalated W(PMe<sub>3</sub>)<sub>4</sub>(÷<sup>2</sup>-CH<sub>2</sub>PMe<sub>2</sub>)H.
W(PMe<sub>3</sub>)<sub>6</sub> was first isolated in 1990 by Parkin and Rabinovich. It was prepared by the reduction of WCl<sub>6</sub> with Na(K) alloy, using PMe<sub>3</sub> as a reactive solvent.
Previous attempts to synthesize W(PMe<sub>3</sub>)<sub>6</sub> placed the Na(K) alloy in a glass ampoule in a liquid nitrogen bath, condensed PMe<sub>3</sub> into the ampoule, then added WCl<sub>6</sub>. Following this addition, the ampoule warmed to room temperature and stirred at room temperature for 2 weeks. Parkin and Rabinovich modified this preparation by simply stirring a mixture of WCl<sub>6</sub> and Na(K) alloy in PMe<sub>3</sub> at room temperature for 10 days.
The complex was crystallographically characterized, demonstrating W-P bond lengths of and P-W-P bond angles of 90ð and 180ð.
W(PMe<sub>3</sub>)<sub>6</sub> demonstrates ÃÂHð = and ÃÂSð = 37 eu (150 J K<sup>âÂÂ1</sup> mol<sup>âÂÂ1</sup>) for the dissociation of PMe<sub>3</sub>.
In the solid state, W(PMe<sub>3</sub>)<sub>6</sub> is stable at room temperature for at least two weeks. However, it is unstable in solution, and rapidly converts to an equilibrium mixture between W(PMe<sub>3</sub>)<sub>4</sub>(÷<sup>2</sup>-CH<sub>2</sub>PMe<sub>2</sub>)H and PMe<sub>3</sub> with K<sub>eq</sub> = 17.8 M at 30 ðC.
Metal complexes of the form M(PMe<sub>3</sub>)<sub>n</sub> contain very electron-rich and highly-reactive metal centers as a result of the combination of the strong ÃÂ-donating and ÃÂ-accepting nature of the PMe<sub>3</sub> ligand. These complexes have been shown to be capable of activating C-H and other otherwise unreactive ÃÂ-bonds via oxidative addition, often forming cyclometalated products.
W(PMe<sub>3</sub>)<sub>6</sub> possesses an 18-electron valence count, and as such demonstrates somewhat limited reactivity. Much of the most interesting and varied chemistry occurs from its dissociated variants, such as W(PMe<sub>3</sub>)<sub>5</sub>.
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W(PMe<sub>3</sub>)<sub>6</sub> can catalyze the metathesis of phosphorus-phosphorus double-bonds. Interaction of the appropriate dichlorophosphane with W(PMe<sub>3</sub>)<sub>6</sub> leads to dechlorination and formation of symmetrical and unsymmetrical diphosphenes.The resultant phosphorus-tungsten species can also catalyze the exchange of diphosphene end-groups.
The W(PMe<sub>3</sub>)<sub>4</sub>(÷<sup>2</sup>-CH<sub>2</sub>PMe<sub>2</sub>)H species formed upon the dissolution of W(PMe<sub>3</sub>)<sub>6</sub> can participate in a Ge-Cl bond heterolysis and form a metal-germanium triple bond.