The influence of the steric repulsion of ligands on the structure of alkylaluminium and alkylgallium 2,3-dimethylbutane-2,3-diolates (pinacolates) has been studied. Reaction of Me 3Al and pinacol afforded the compound Me 5Al 3[OC(CH 3) 2C(CH 3) 2O] 2 ( 1) possessing two diolate ligands. The treatment of pinacol with the more sterically hindered t Bu 3Al resulted in the formation of aluminium tripinacolate t Bu 3Al 3[OC(CH 3) 2C(CH 3) 2O] 3 ( 2) as the only product. In contrast, the reaction of the less reactive t Bu 3Ga with pinacol stopped at the stage of the compound t Bu 3Ga 2[OC(CH 3) 3C(CH 3) 2O] [OC(CH 3) 3C(CH 3) 2OH] ( 3), which is an intermediate product of the reaction of 1,2-diols with group 13 trialkyls. Compounds 1, 2 and 3 were crystallographically characterised.