# Hexa(tert-butoxy)ditungsten(III)

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 d$^3$ metal centers.

## Preparation

W$_2$(O-t-Bu)$_6$ was first prepared by treating tungsten(III) dialkylamides with tert-butanol.
W$_2$(O-t-Bu)$_6$ can also be synthesized from NaW$_2$Cl$_7$(THF)$_5$ and NaO-t-Bu.
    NaW$_2$Cl$_7$(THF)$_5$ + 6 NaO-t-Bu → W$_2$(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 W$_2$O$_6$ core adopts a staggered, ethane-like conformation, similar to that for its dimolybdenum analogue. The molecule has inversion symmetry.

## Reactions
### Hydrolysis

This compound hydrolyzes at 200 °C to give WO$_2$:
    W$_2$(O−t−Bu)$_6$ + 2 H$_2$O → 2 WO$_2$ + 4 HO−t−Bu + 2 CH$_2$=C(CH$_3$)$_2$

### With carbon dioxide

Carbon dioxide reacts reversibly with W$_2$(O−t−Bu)$_6$ to form green 2:1 adduct featuring two alkyl carbonate ligands.
    W$_2$(O−t−Bu)$_6$ + 2 CO$_2$ ⇌ W$_2$(O−t−Bu)$_4$(O$_2$CO−t−Bu)$_2$

### With carbon monoxide

Carbon monoxide react with W$_2$(O−t−Bu)$_6$ to give W$_2$(O−t−Bu)$_6$CO. In this adduct, the carbonyl ligand bridges between two W(III) atoms.. This compound can further react with i-PrOH to generate W$_4$(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

W$_2$(O−t−Bu)$_6$ reacts with alkynes to give RC≡W(O-t-Bu)$_3$, tetrahedral alkylidyne complexes. In these complexes, tungsten is electrophilic and the alkylidyne carbon is nucleophilic.
    W$_2$(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. W$_2$(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, W$_2$(O−t−Bu)$_6$ reacts with two equivalents of EtC≡CPh, EtC≡CSiMe$_3$, and EtC≡C–CH=CH$_2$ to form corresponding alkylidyne complexes. Thus, W$_2$(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.
Besides simple metathesis reactions, W$_2$(O-t-Bu)$_6$ also reacts with 3-hexyne in a 1:1 molar ratio to form a triangular tritungsten complex compound [W$_3$(O-t-Bu)$_5$(μ-O)(μ-CEt)O]$_2$. 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 (W$_2$):
W$_2$(O-t-Bu)$_6$ + RC≡CR → 2[RC≡W(O-t-Bu)$_3$]
W$_2$(O−t−Bu)$_6$ + RC≡W(O−t−Bu)$_3$ → W$_3$(O−t−Bu)$_5$(μ−O)(μ−CEt)O
    W$_3$(O−t−Bu)$_5$(μ−O)(μ−CEt)O → [W$_3$(O−t−Bu)$_5$(μ−O)(μ−CEt)O]$_2$
W$_2$(O−t−Bu)$_6$ also reacts with EtC≡CC≡CEt to form (t-Bu-O)$_3$W≡CC≡W(O-t-Bu)$_3$:
W$_2$(O−t−Bu)$_6$ + EtC≡CC≡CEt → (t−Bu−O)$_3$W≡CC≡W(O−t−Bu)$_3$ + EtC≡CEt This compound, however, does not act as a metathesis catalyst.
W$_2$(O−t−Bu)$_6$ also reacts with trans-Pt(C≡CH)$_2$(PMe$_2$Ph)$_2$ to form (t-Bu-O)$_3$W≡C–C≡W(O-t-Bu)$_3$ and trans-(PMe$_2$Ph)$_2$Pt[C$_2$W$_2$(O-t-Bu)$_5$]$_2$.

### 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)$_3$:
    W$_2$(O−t−Bu)$_6$ + RC≡N → RC≡W(O−t−Bu)$_3$ + N≡W(O−t−Bu)$_3$
Although W$_2$(O-t-Bu)$_6$ reacts with nitriles, it doesn’t react with nitrogen (N≡N).
When C≡C and C≡N bond both exist, W$_2$(O-t-Bu)$_6$ reacts more rapidly with C≡N than C≡C bond. Here’s an example of W$_2$(O-t-Bu)$_6$ reacting with EtC≡CCN in the presence of quinuclidine:
    W$_2$(O−t−Bu)$_6$ +EtC≡CCN + 12L → EtC≡CC≡W(O−t−Bu)$_3$L + 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:
    W$_2$(O−t−Bu)$_6$ + EtC≡CCN + 12 L → NCC≡W(O−t−Bu)$_3$L + EtC≡CMe

### With nitroso

W$_2$(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, researchers couldn't figure out where the one missing oxygen went. This reaction is the first discovered reaction of a nitroso with metal multiple bonds.

### With allenes

Allenes react with the ditungsten complex forming adducts, e.g.,
    W$_2$(O−t−Bu)$_6$ + H$_2$C=C=CH$_2$ → W$_2$(O−t−Bu)$_6$(HC$_2$=C=CH$_2$)
Further reaction with carbon monoxide was also demonstrated.