Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the Chemical formula aluminum2(Ethyl group)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important compound, closely related to trimethylaluminium.
Structure and bonding
The structure and bonding in Al
2R
6 and
diborane are analogous (R = alkyl). Referring to Al
2Me
6, the Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively. The Al center is tetrahedral.
The carbon atoms of the bridging ethyl groups are each surrounded by five neighbors: carbon, two hydrogen atoms and two aluminium atoms. The ethyl groups interchange readily intramolecularly. At higher temperatures, the dimer cracks into monomeric AlEt
3.
Synthesis and reactions
Triethylaluminium can be formed via several routes. The discovery of an efficient route was a significant technological achievement. The multistep process uses aluminium,
hydrogen gas, and
ethylene, summarized as follows:
[
]
- 2 Al + 3 H2 + 6 C2H4 → Al2Et6
Because of this efficient synthesis, triethylaluminium is one of the most available organoaluminium compounds.
Triethylaluminium can also be generated from ethylaluminium sesquichloride (Al2Cl3Et3), which arises by treating aluminium powder with chloroethane. Reduction of ethylaluminium sesquichloride with an alkali metal such as sodium gives triethylaluminium:[Krause, M. J; Orlandi, F; Saurage, A T.; Zietz, J R, "Organic Aluminum Compounds" Wiley-Science 2002.]
- 6 Al2Cl3Et3 + 18 Na → 3 Al2Et6 + 6 Al + 18 NaCl
Reactivity
The Al–C bonds of triethylaluminium are polar bond to such an extent that the carbon is easily protonation, releasing ethane:[Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ]
- Al2Et6 + 6 HX → 2 AlX3 + 6 EtH
For this reaction, even weak acids can be employed such as terminal and alcohols.
The linkage between the pair of aluminium centres is relatively weak and can be cleaved by (L) to give with the formula AlEt3L:
- Al2Et6 + 2 L → 2 LAlEt3
Applications
Precursors to fatty alcohols
Triethylaluminium is used industrially as an intermediate in the production of , which are converted to . The first step involves the oligomerization of ethylene by the Aufbau reaction, which gives a mixture of trialkylaluminium compounds (simplified here as octyl groups):[
]
- Al2(C2H5)6 + 18 C2H4 → Al2(C8H17)6
Subsequently, these trialkyl compounds are oxidized to aluminium , which are then hydrolysed:
- Al2(C8H17)6 + 3 O2 → Al2(OC8H17)6
- Al2(OC8H17)6 + 6 H2O → 6 C8H17OH + 2 Al(OH)3
Co-catalysts in olefin polymerization
A large amount of TEAL and related aluminium alkyls are used in Ziegler-Natta catalysis. They serve to activate the transition metal catalyst both as a reducing agent and an alkylation. TEAL also functions to scavenge water and oxygen.
Reagent in organic and organometallic chemistry
Triethylaluminium has niche uses as a precursor to other organoaluminium compounds, such as diethylaluminium cyanide:
