A series of poly-salen type Ni(II) and Co(II) complexes were prepared, and the catalytic behavior in the dimerization of propylene has been studied in combination with aluminum co-catalysts and phosphine ligands. The effects of various reaction factors, such as the type of phosphine ligand and the P/Ni ratio, the type of aluminum co-catalyst and its quantity, particularly the nature of the nickel and cobalt complexes, were also examined. The results indicated that the productivity of the catalytic system was strongly dependent on the steric character of poly-salen ligand in the Ni(H) and Co(II) complexes. It was also found that reaction temperature deeply affected the performance of the catalytic system in the presence of phosphine ligand and alkyl aluminum promoter, and higher regioselectivities to 2,3-dimethylbutenes (2,3DMB) in the dimers were observed with incorporation of bulky and basic PCy3 into the nickel and cobalt catalysts. An extremely high activity in the propylene dimerization (TOF up to 221,000 h(-1)) was obtained with the 2b system under suitable conditions, which was much higher than that obtained with the corresponding monomeric salen system. However, it seemed difficult to realize recycling of the catalysts owing to the restrict dependence of catalytic activity with its solubility, at least under the adopted conditions. (C) 2002 Elsevier Science B.V. All rights reserved.