Reactions of methyl- and ethylaluminium compounds with alkoxyalcohols. The influence of alkoxyalcohol substituents on the structure of the complexes formed

Dimeric dimethylaluminium compounds {[Me2Al(μ-OCH2CH2OnPr)]2 (1), [Me2Al(μ-OCH(CH3)CH2OtBu)]2 (3), [Me2Al(μ-OCH2CH2CH2OEt)]2 (5), [Me2Al(μ-OCH2CH2CH(Me)OMe)]2 (7), [Me2Al(μ-OCH2CH2C(Me)2OMe)]2 (9)} and dichloroaluminium compounds {[Cl2Al(μ-OCH2CH2OnPr)]2 (2), [Cl2Al(μ-OCH(CH3)CH2OtBu)]2 (4), [Cl2Al(μ-OCH2CH2CH2OEt)]2 (6), [Cl2Al(μ-OCH2CH2CH(Me)OMe)]2 (8), [Cl2Al(μ-OCH2CH2C(Me)2OMe)]2 (10)} have been prepared. The molecular structures of compounds 2, 3, 6, 8, 9 and 10 have been determined by X-ray crystallography. All these compounds exist in the solid state as dimers with chelating ether-alkoxide ligands and five-coordinate aluminium atoms. Dichloroaluminium derivatives (compounds 2, 4, 6, 8 and 10) exist as five-coordinate isomers also in solution, while dimethylaluminium ones (compounds 1, 3, 5, 7 and 9) exist as an equilibrium mixture between four- and five-coordinate isomers. An increase of aluminium Lewis acidity in dichloroaluminium derivatives in comparison with dimethylaluminium ones results in substantial shortening of AlO distances. The R2Al⋯O(ether)R′ distance is mainly determined by the steric repulsion between the OR′ group and the two alkyl substituents on aluminium. The influence of electronic properties of R′ on Cl2Al⋯O(ether)R′ interaction was illustrated for compound 2 in comparison with literature data for analogous complexes.