Selective dimerization of propylene to 2,3-dimethylbutenes by homogeneous catalysts prepared from halogeno(β-dithioacetylacetonato)nickel(II) complexes containing a highly hindered alkyl phosphine ligand and different aluminium co-catalysts

Halogeno(β-dithioacetylacetonato)nickel(II) complexes with different alkyl phosphine ligands have been studied in the selective propylene dimerization to 2,3-dimethylbutenes (DMB) in the presence of different organoaluminium compounds. When basic and bulky phosphine ligands, such as tricyclohexyl-(PCy3) and triisopropyl-phosphine ( P i Pr 3 ) were used in combination with suitable co-catalysts, such as Et3Al2Cl3, Et2AlCl and EtAlCl2/methylalumoxane (MAO), the best results in terms of productivity (up to ∼36,000 h−1) and yield to DMB (up to 68%) were obtained. A detailed analysis of the composition of C9 cut in some selected experiments allowed to evaluate the octane characteristics of the reaction mixture offering both interesting applicative perspectives and mechanistic information.