Ni-Al二元催化体系的原位核磁共振研究

THE IN SITU NMR STUDIES OF Ni-Al BINARY CATALYST SYSTEM

1.概述 本世纪50年代Ziegler-Natta催化体系的发现使均相络合催化研究得到突飞猛进的发展。各种各样的Ziegler-Natta催化剂已广泛被用于烯烃聚合的工业生产中。与此同时对此催化剂的作用机理和催化活性物种也做了大量的研究。在提出的许多机理中,虽然金属氢化物机理在理论上已越来越多地被人们所接受,但仍需有新的更使人信服的实验来证实。 1971年Jones在研究Ni（acac）2和Et2AlOEt组成的催化剂催化丙烯齐聚反应时提出了氢化物机理;1979年Keim在用镍络合物作为丙烯齐聚催化剂时。

The in situ 1H NMR spectra and susceptibility measurements have been carried out in NMR sample tube for propene oligomerization catalyzed by t wo - component catalyst systems Ni ( acac ) 2 - AlEt 3 and Ni ( acac ) 2 -Et2AlOEt in benzene-d6 solvent respectively. From these 1H NMR spectra and results of susceptibility determination it can be concluded that ligand exchange between Ni ( acac ) 2 and aluminium alkyls occurred and the valence of nickel did not change. When propene is introduced, three Ni-H signals were observed, the chemical shifts being -12.37ppm, -28.52ppm and -40.98ppm respectively. These two catalyst systems gave the same results. This indicated that the same reaction mechanism was followed whether t riethylalumini-um or diethylaluminium ethoxide was used as the cocatalyst at Al/Ni ratios less than 1. In both cases there existed the similar active species nickel hydride as a transient intermediate. It had enough long lifetime and catalytic activity under the experimental conditions, so as to be detected by auto-stack technique. This success directly testified the existence of nickel hydride and would be a strong support to the metal hydride mechanism.