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 Wâ¡W bond, arising from the coupling of a pair of d<sup>3</sup> metal centers.
W<sub>2</sub>(O-t-Bu)<sub>6</sub> was first prepared by treating tungsten(III) dialkylamides with tert-butanol.
W<sub>2</sub>(O-t-Bu)<sub>6</sub> can also be synthesized from NaW<sub>2</sub>Cl<sub>7</sub>(THF)<sub>5</sub> and NaO-t-Bu.
As verified by X-ray crystallography, the two tungsten(III) centers are joined by a triple bond. Each W(III) is pseudotetrahedral. The W<sub>2</sub>O<sub>6</sub> core adopts a staggered, ethane-like conformation, similar to that for its dimolybdenum analogue. The molecule has inversion symmetry.
This compound hydrolyzes at 200 ðC to give WO<sub>2</sub>:
Carbon dioxide reacts reversibly with to form green 2:1 adduct featuring two alkyl carbonate ligands.
Carbon monoxide react with to give . In this adduct, the carbonyl ligand bridges between two W(III) atoms.. This compound can further react with i-PrOH to generate W<sub>4</sub>(ü-CO)<sub>2</sub>(O-i-Pr)<sub>12</sub>. The higher nuclearity of this isopropoxide can be attributed to the smaller size of the isopropoxyl ligands.
reacts with alkynes to give RCâ¡W(O-t-Bu)<sub>3</sub>, tetrahedral alkylidyne complexes. In these complexes, tungsten is electrophilic and the alkylidyne carbon is nucleophilic.
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. does not react with diphenylacetylene or bis(trimethylsilyl)acetylene. These results are attributed to unfavorable electronic and steric effects, respectively. On the other hand, reacts with two equivalents of EtCâ¡CPh, EtCâ¡CSiMe<sub>3</sub>, and EtCâ¡CâÂÂCH=CH<sub>2</sub> to form corresponding alkylidyne complexes. Thus, reacts more easily with asymmetric substitute acetylenes than symmetric ones.
The reactions with alkynes initially afford adducts with a bridging ("ü-perpendicular") alkyne with elongated WW bonds and CC (alkyne) bonds. This intermediate is analogue to other dimetallatetrahedranes. These adducts convert into RCâ¡W(O-t-Bu)<sub>3</sub>. The resulting alkylidyne complexes RCâ¡W(O-t-Bu)<sub>3</sub> catalyze alkyne metathesis reactions.
Besides simple metathesis reactions, W<sub>2</sub>(O-t-Bu)<sub>6</sub> also reacts with 3-hexyne in a 1:1 molar ratio to form a triangular tritungsten complex compound [W<sub>3</sub>(O-t-Bu)<sub>5</sub>(ü-O)(ü-CEt)O]<sub>2</sub>. This reaction has a two steps mechanism; first is the Câ¡C and Wâ¡W metathesis reaction and follow by formal addition of carbyne (Wâ¡C) to alkoxide (W<sub>2</sub>):
W<sub>2</sub>(O-t-Bu)<sub>6</sub> + RCâ¡CR â 2[RCâ¡W(O-t-Bu)<sub>3</sub>]
also reacts with EtCâ¡CCâ¡CEt to form (t-Bu-O)<sub>3</sub>Wâ¡CCâ¡W(O-t-Bu)<sub>3</sub>:
This compound, however, does not act as a metathesis catalyst.
also reacts with trans-Pt(Câ¡CH)<sub>2</sub>(PMe<sub>2</sub>Ph)<sub>2</sub> to form (t-Bu-O)<sub>3</sub>Wâ¡CâÂÂCâ¡W(O-t-Bu)<sub>3</sub> and trans-(PMe<sub>2</sub>Ph)<sub>2</sub>Pt[C<sub>2</sub>W<sub>2</sub>(O-t-Bu)<sub>5</sub>]<sub>2</sub>.
With excess amount of nitrile, Nâ¡W(O-t-Bu)<sub>3</sub> is formed along with RCâ¡CR. The reaction initially gives a 1:1 mixture of the alkylidyne RCâ¡W(O-t-Bu)<sub>3</sub> and nitride Nâ¡W(O-t-Bu)<sub>3</sub>:
Although W<sub>2</sub>(O-t-Bu)<sub>6</sub> reacts with nitriles, it doesnâÂÂt react with nitrogen (Nâ¡N).
When Câ¡C and Câ¡N bond both exist, W<sub>2</sub>(O-t-Bu)<sub>6</sub> reacts more rapidly with Câ¡N than Câ¡C bond. HereâÂÂs an example of W<sub>2</sub>(O-t-Bu)<sub>6</sub> reacting with EtCâ¡CCN in the presence of quinuclidine:
On the other hand, the metathesis catalyst MeCâ¡W(O-t-Bu)<sub>3</sub> reacts more rapidly with Câ¡C than Câ¡N bond. Similar reaction with EtCâ¡CCN and quinuclidine produce different product:
and nitrosobenzene combine to give [W(O-t-Bu)<sub>2</sub>(NPh)]<sub>2</sub>(ü-O)(ü-O-t-Bu)<sub>2</sub>. 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.
Allenes react with the ditungsten complex forming adducts, e.g.,
Further reaction with carbon monoxide was also demonstrated.