Triisobutylaluminium
Encyclopedia
Triisobutylaluminium is an organoaluminium compound with the formula Al(CH2CH(CH3)2)3. This a colorless pyrophoric liquid is mainly used to make linear primary alcohol
s and α-olefins.
ic, however, it was discovered to exist in equilibrium with its dimer. To allow for the dimer to form, there is an appreciable increase in the length of the bonds between Al and the bridging alkyl ligand. There is also evidence of restricted rotation of the bridging isobutyl groups in the dimer. The equilibrium constant, KD, is 3.810 at 20 °C.
by this route.
In the second step isobutylene
adds to the diisobutylaluminium to give TiBA.
3Al + 3 RCH=CH2 → (RCH2CH3)3Al + 3 iC4H8
Like most organoaluminium compounds, TiBA reacts violently with water and air and must be handled with care.
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s and α-olefins.
Structure
Triisobutylaluminium was thought to be exclusively monomerMonomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
ic, however, it was discovered to exist in equilibrium with its dimer. To allow for the dimer to form, there is an appreciable increase in the length of the bonds between Al and the bridging alkyl ligand. There is also evidence of restricted rotation of the bridging isobutyl groups in the dimer. The equilibrium constant, KD, is 3.810 at 20 °C.
Synthesis
Trialkylaluminium compounds are available industrially through the reactions of aluminium powder, hydrogen gas, and the desired alkenes. The synthesis of TiBA requires two steps; the first step produces diisobutylaluminium hydrideDiisobutylaluminium hydride
Diisobutylaluminium hydride, DIBAL, DIBAL-H or DIBAH, is a reducing agent with the formula 2, where i-Bu represents isobutyl...
by this route.
- 6 iBu3 + 2 Al + 3 H2 → 6 iBu2AlH
In the second step isobutylene
Isobutylene
Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene , one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas.-Uses:...
adds to the diisobutylaluminium to give TiBA.
- 6 iBu2AlH + 6 (C4H8) → 6 iBu3Al
Reactions
α-olefins are readily eliminated from β-branched trialkylaluminium compounds. Trialkylaluminium compounds are used in the industrial production of polymers. In the most common of these compounds, TIBA, a substantial level of Al – H bonds are present at equilibrium. The greater stability of unbranched trialkylaluminium compounds relative to branched trialkylaluminium compounds in TIBA forms the basis for a general synthesis of triethyl- and higher linear trialkylaluminium materials from triisobutylaluminium.3Al + 3 RCH=CH2 → (RCH2CH3)3Al + 3 iC4H8
Like most organoaluminium compounds, TiBA reacts violently with water and air and must be handled with care.
Further reading
- Keisuke Suzuki, Tetsuya Nagasaws, Encyclopedia of Reagents for Organic Synthesis, Triisobutylaluminum, 2009