The reactions of trialkylaluminium R 3 Al (R=Me, Et) with 2,4-pentanediols [(CH 3 ) 2 (OH)CCH 2 C(CH 3 ) 2 OH (A̱)], [(CH 3 ) 2 (OH)CCH 2 CH(OH)CH 3 (Ḇ)] and 2,5-dimethyl-2,5-hexanediol (C̱) were studied. Sterically hindered 2,4-pentanediols (A̱, Ḇ) react with alkylaluminium compounds to form mainly cyclic compounds 1̱–3̱ of a formula R 5 Al 3 [diol(−2H)] 2 possessing one central five-coordinated aluminium atom and two terminal four-coordinated aluminium atoms. All the compounds were characterised by means of NMR spectra, elemental analysis and molecular weight determination. The molecular structure of the solid Me 5 Al 3 [O(CH 3 ) 2 CCH 2 C(CH 3 ) 2 O] 2 1̱ was determined by X-ray diffraction analysis. Substituted at terminal carbon atoms 2,5-dimethyl-2,5-hexanediol (C̱) forms organoaluminium oligomers exclusively. The influence of the diol carbonchain lengths and its substituents on the yield of the cyclic complexes and organoaluminium oligomers are discussed.