Hexakis(trimethylphosphine)tungsten

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.

Hexakis(trimethylphosphine)tungsten

Identifiers
CAS Number	127594-80-3
3D model (JSmol)	Interactive image
ChemSpider	9138493
PubChem CID	10963280
InChI InChI=1S/6C3H9P.W/c6*1-4(2)3;/h6*1-3H3; Key: VLOHEZVDOMZCNC-UHFFFAOYSA-N
SMILES C[P+](C)(C)[W-6]([P+](C)(C)C)([P+](C)(C)C)([P+](C)(C)C)([P+](C)(C)C)[P+](C)(C)C
Properties
Chemical formula	C18H54P6W
Molar mass	640.31
Appearance	yellow crystalline solid
Structure
Crystal structure	Cubic
Space group	Im3m
Related compounds
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

Synthesis and characterization

Compared to other zerovalent homoleptic trimethylphosphine complexes, W(PMe₃)₆ was less straightforward to synthesize and isolate. Previous attempts to prepare W(PMe₃)₆ by co-condensation (a modification of metal vapor synthesis) of tungsten with PMe₃ and reduction of WCl₆ with alkali metal reducing agents only formed the cyclometalated W(PMe₃)₄(η²-CH₂PMe₂)H.^[1]

W(PMe₃)₆ was first isolated in 1990 by Parkin and Rabinovich.^[2] It was prepared by the reduction of WCl₆ with Na(K) alloy, using PMe₃ as a reactive solvent.

Previous attempts to synthesize W(PMe₃)₆ placed the Na(K) alloy in a glass ampoule in a liquid nitrogen bath, condensed PMe₃ into the ampoule, then added WCl₆. 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 WCl₆ and Na(K) alloy in PMe₃ at room temperature for 10 days.

Synthesis of W(PMe₃)₆.

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°.

W(PMe₃)₆ demonstrates ΔH° = 9.3 kcal/mol (39 kJ/mol) and ΔS° = 37 eu (150 J K⁻¹ mol⁻¹) for the dissociation of PMe₃.

Stability

In the solid state, W(PMe₃)₆ 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(PMe₃)₄(η²-CH₂PMe₂)H and PMe₃ with K_eq = 17.8 M at 30 °C.

Equilibrium mixture between W(PMe₃)₄(η²-CH₂PMe₂)H and PMe₃.

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.^[2]

W(PMe₃)₆ 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(PMe₃)₅.

Synthesis of symmetrical and unsymmetrical diphosphenes

Sources:^[4][5]

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.

The resultant phosphorus-tungsten species can also catalyze the exchange of diphosphene end-groups.

Formation of 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]