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Structure

Triisobutylaluminium exists in equilibrium with its dimer. The equilibrium constant, KD, is 3.810 at 20 °C.²

2 Al(CH2CH(CH3)2)3 ↽ − ⇀ {\displaystyle {\ce {<=>>}}} [Al(CH2CH(CH3)2)3]2

In the dimer, the bridging carbon-aluminium bond is elongated and exhibits evidence of restricted rotation. For the sake of simplicity, TiBA is written as the monomer in this article.

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 hydride (written as a monomer):

4 CH2=C(CH3)2 + 2 Al + 3 H2 → 2 HAl(CH2CH(CH3)2)2

In the second step isobutylene adds to the diisobutylaluminium to give TiBA:

CH2=C(CH3)2 + HAl(CH2CH(CH3)2)2 → Al(CH2CH(CH3)2)3

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.

Al(CH2CH(CH3)2)3 + 3 RCH=CH2 → Al(CH2CH2R)3 + 3 CH2=C(CH3)2

Safety

Like most organoaluminium compounds, TiBA reacts violently with water and air.³

Further reading

• Keisuke Suzuki, Tetsuya Nagasaws, Encyclopedia of Reagents for Organic Synthesis, Triisobutylaluminum, 2009

References

1. Michael J. Krause, Frank Orlandi, Alfred T. Saurage, Joseph R. Zietz Jr. "Aluminum Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a01_543 /wiki/Doi_(identifier) ↩

2. Smith, Martin B. (1970). "The Monomer-Dimer Equilibria of Liquid Ammonium Alkyls II Triisobutylaluminum". Journal of Organometallic Chemistry. 22 (2): 273–281. doi:10.1016/S0022-328X(00)86043-X. /wiki/Doi_(identifier) ↩

3. Sigma-Aldrich. "Triisobutylaluminum". MilliporeSigma. Merck Group. Retrieved 2021-03-15. /wiki/Sigma-Aldrich ↩