The propylene dimerization to 2,3-dimethylbutenes (DMB) by homogeneous catalysts prepared in situ by an alternative method based on the reaction of bis(alpha -nitroacetophenonate)nickel(II) [Ni(naph)(2)] with different organoaluminum compounds, in the presence of a bulky and basic alkyl phosphine such as tricyclohexylphosphine (PCy3), was described. In particular, the influence of the nature of the organoaluminum co-catalyst as well as of the reaction temperature was studied. The catalysts prepared according to this procedure displayed higher activity at room temperature and in hydrocarbon medium as compared with those obtained by oxidative addition of alpha -nitroacetophenone to bis(1,5-cyclooctadiene)nickel(0) [Ni(cod)(2)] in the presence of the same phosphine ancillary ligand, turnover frequencies up to 24 800 h-l being achieved when methylalumoxane (MAO) was used as co-catalyst. Moreover, regio-selectivity values to DMB within the C-6 cut higher than 82% were observed under the above conditions. Finally, the regio-selectivity was scarcely influenced by decreasing the reaction temperature below 25 degreesC, thus allowing to work at room temperature.