326. Aluminum Alkyls

Description and references

Highly reactive compounds of the form R3Al, trialkylaluminum; [RnAlX3n]2, n = 1, 2, alkylaluminum halide; or R3Al2X3, alkylaluminum sesquihalide. (The sesquihalides are actually equilibrium mixtures of R3Al2X3, [R2AlX]2 and [RAlX2]2.) First prepn of aluminum alkyls: ethylaluminum sesquiiodide [(C2H5)3Al2I3] prepd by Hallwachs, Schaferik, Ann. 109, 207 (1859); trimethylaluminum, [(CH3)3Al]2, and triethylaluminum, [(C2H5)3Al]2, prepd by Buckton, Odling, Ann. Suppl. 4, 109 (1865). The alkylaluminum halides are prepd from alkyl halides and aluminum, or by halogenation of trialkylaluminums. The trialkylaluminums are prepd from aluminum, hydrogen and olefins; this improved “direct synthesis” was developed by Ziegler and co-workers. Comprehensive reviews of prepn, properties and chemistry: Schultz in Adv. Chem. Ser. 23, entitled “Metal-Organic Compounds,” M. Sittig, Ed. (ACS, Washington DC, 1959) pp 163-171; Ziegler in ACS Monograph Series no. 147, entitled “Organometallic Chemistry,” H. Zeiss, Ed. (Reinhold, New York, 1960) pp 194-269; Kster, Binger, Adv. Inorg. Chem. Radiochem. 7, 263-348 (1965); T. Mole, E. A. Jeffery, Organoaluminum Compounds (Elsevier, New York, 1972) 465 pp; Wade, Banister in Comprehensive Inorganic Chemistry vol 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 1058-1064.

Derivative

Trialkylaluminum compounds.

Properties

Colorless liquids at room temperature. Must be stored in an inert atm; sensitive to oxidation and hydrolysis in air; the lighter trialkylaluminums ignite spontaneously in air. The low mol wt, linear-chain alkyl compounds exist as dimers; the branched-chain alkyl compounds exist primarily as monomers. Among the industrially important trialkyl aluminums are triethylaluminum, dimeric liq, d25 0.832, bp760 194°, bp13 100° and triisobutylaluminum, primarily monomeric liq, d25 0.781; bp10 86°, mp 6°.

Derivative

Alkylaluminum halides.

Properties

Low melting solids or colorless, volatile liquids. Strongly associated forming dimers; held together by bridging halogen bonds. Less sensitive than trialkylaluminums to oxidation upon exposure to air. Halogen aluminum bonds cleaved by water, alcohol. Industrially important halides include chlorodiethylaluminum, [(C2H5)2AlCl]2, liq, d25 0.961, bp50 127°, bp17 100°, bp1.9 60° and dichloroethylaluminum, [C2H5AlCl2]2, solid, d50 1.207, mp 32°, bp50 113°, bp30 100°, bp5 60°.

Use

Catalyst; with compds of early transition metals as Ziegler-Natta polymerization catalysts; intermediates in organic syntheses.