Selective propylene dimerization to 2,3-dimethylbutenes by homogeneous catalysts obtained from bis(alpha-nitroacetophenonate)nickel(II), tricyclohexylphosphine and different organoaluminum compounds

The propylene dimerization to 2,3-dimethylbutenes (DMB) by homogeneous cata lysts prepared in situ by an alternative method based on the reaction of bi s(alpha -nitroacetophenonate)nickel(II) [Ni(naph)(2)] with different organo aluminum compounds, in the presence of a bulky and basic alkyl phosphine su ch as tricyclohexylphosphine (PCy3), was described. In particular, the infl uence of the nature of the organoaluminum co-catalyst as well as of the rea ction temperature was studied. The catalysts prepared according to this procedure displayed higher activit y at room temperature and in hydrocarbon medium as compared with those obta ined by oxidative addition of alpha -nitroacetophenone to bis(1,5-cycloocta diene)nickel(0) [Ni(cod)(2)] in the presence of the same phosphine ancillar y ligand, turnover frequencies up to 24 800 h-l being achieved when methyla lumoxane (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 con ditions. Finally, the regio-selectivity was scarcely influenced by decreasi ng the reaction temperature below 25 degreesC, thus allowing to work at roo m temperature. (C) 2001 Elsevier Science B.V. All rights reserved.