Steric effects in alkylalane dioldiates: [tBuAl(OC(CH3)2CH2C(CH3)2O)]2 a new (monoalkyl)alane O,O′-chelate complex

The dependence of the structure of alkylalane dioldiates on the steric bulk of the substituents on the aluminium, as well as steric hindrances of diol moiety is reported. Reactions of R3Al [where R=iBu, tBu] with 2,4-dimethylpentane-2,4-diol, butane-1,4-diol and propane-1,3-diol lead to the formation of alkylalane dioldiates, [tBuAl(OC(CH3)2CH2C(CH3)2O)]2 (1), iBu5Al3[(OC(CH3)2CH2C(CH3)2O)]2 (2) [tBu2Al(O(CH2)4OH)]2 (3), iBu5Al3(O(CH2)4O)2 (4) and tBu5Al3(O(CH2)3O)2 (5). The molecular structures of 1 and 3 have been determined by single crystal X-ray diffraction. In the reactions of iBu3Al with diols the trinuclear complexes of the general formula [R5Al3(diol(2H))2] (2 and 4) are formed irrespective of the diol moiety steric hindrances. tBu3Al reacts with diols to yield the products depending on the length of diol backbone and steric hindrances of the diol moiety. The interaction of the sterically crowded 2,4-dimethylpentane-2,4-diol with tBu3Al gives the new (monoalkyl)alane O,O′-chelate complex 1. In the case of unhindered aliphatic diols like butane-1,4-diol and propane-1,3-diol, the compound 3 with the strong intra-molecular hydrogen bonding interaction and the trimetallic compound 5 were obtained, respectively.