Studies On The Dimerization Of Propylene By Novel Nickel-based And Cobalt-based Catalysts

A series of late transtion complexes based on specified-structure imine ligands have been a novel family of catalysts for olefin polyerization since 1995 owing to their dramatically high and unique catalytic performance. On the basis of extremely high reactivity of such late transtion catalysts in the activition of olefin as well as the essential relationship between polymerization and oligomeriztion, we would explore the catalytic behaivor of a series of nickel and cobalt complexes coordinated with N,O and O,O multi-dentate chelating on the dimerization of propylene. Moreover, the effect of various factors on the catalytic process, particularly the nature of ligands in nickel and cobalt precursors and the type of phosphine ligands, would be carefully investigated in our paper.Primarily, the catalytic systems based on neutral nickel salicylaldiminato complexes and neutral nickel (β-ketoiminato) complexes for the dimerization of propoylene were described. The catalytic activity and selectivity of the former system might be strongly improved by varying the nature of salicylaldiminato ligands, the type of phosphine ligands and aluminum co-catalysts as well as the reaction conditions. According to well-known process to produce the active nickel intermediates, both bis(salicylaldiminate) nickel complexes and bis(β-ketoiminato) nickel complexes were treated with aluminun activitor and/or phosphine ligands in order to in situ form the active nickel species for propylene oligomerization, which would avoid to suffer of the multi-step synthesis of the neutral nickel precatalysts and make it easier to modulate the catalytic system. Extremely high productivity upto 250000 h-1 as well as a good regioselectivity to 2,3-DMB in dimers (-65 %) were achieved in either the bis(salicylaldiminate) nickel system or the bis(p-ketoiminato) nickel system under proper reaction conditions.The application of a series of salen-like nickel and cobalt complexes in the activation of propylene was also studied in the present paper. It was found that the salen nickel and cobalt catalysts exibihted different catalytic behavior as compared with the nickel catalysts based on bidentate N,O coordination, and significant productivity in the dimerization of propylene was obtained for the salen-like systems only in the presence of large excess of phosphine ligands. It was also found that the catalytic productivity was closely depended on both steric and electronic characteristics of salen ligands. High activity and certain selectivity of desired product could be detected through changing the nature of phosphine ligands and reaction temperatures in the case of salen-like systems characterized by bulky substituents and electron-withdrawing groups. Activity was confirmed for propylene dimerization with serval N2O2 type and N4 type nickel precursors when treated with Al co-catalysts, and low productivity was detected even in the presence of large excess of phosphine ligands in a 1\4 type nickel system, which characterized by extremely hindrance around the nickel center.A series of novel poly-salen nickel and cobalt complex was prepared and the catalytic performance in the dimerization of propylene was investigated. Significant of productivity was ascertained with treatment of aluminum promoters, and the catalytic activity was remarkably increased when phosphine lignads was added. The poly-salen system exihibited much higher productivity than the corresponding salen one under identical reaction conditions. However, it seemed difficult to recycle the poly-salen nickel catalyst owing to its restrict relationship between the activity and solubility in the reaction mediums, at least under the adopted conditions.For the first time, the catalytic behavior of bis(salicylaldehyde) nickel catalysts was studied in the dimerization of propylene. The active nickel species for the activation of proplyene was in situ generated when treated with alkyl aluminum. Theproductivity might be enhanced as H atom on the phenolic ring substituted with bulky...