Triisobutylaluminium

Triisobutylaluminium

Monomeric form
Names
IUPAC name Triisobutylaluminum
Other names Aluminumtriisobutanide; TIBA
Identifiers
CAS Number	100-99-2 Y
3D model (Jmol)	Interactive image
ECHA InfoCard	100.002.643
UNII	09P2THV2X4 Y
SMILES CC(C)C[Al](CC(C)C)CC(C)C
Properties[1]
Chemical formula	C12H27Al
Molar mass	198.33 g·mol−1
Appearance	Colorless liquid
Density	0.786 g/mL at 25 °C
Melting point	4 to 6 °C (39 to 43 °F; 277 to 279 K)
Boiling point	86 °C (187 °F; 359 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Triisobutylaluminium (TiBA) is an organoaluminium compound with the formula Al(CH₂CH(CH₃)₂)₃. This colorless pyrophoric liquid is mainly used to make linear primary alcohols and α-olefins.^[2]

Structure

Triisobutylaluminium was thought to be exclusively monomeric, 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, K_D, is 3.810 at 20 °C.^[3]

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 by this route.

6 iBu₃ + 2 Al + 3 H₂ → 6 iBu₂AlH

In the second step isobutylene 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.

(iC₄H₉)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.^[1]

References

Further reading

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