Effect Of The Structures Of Series Dendritic Bridging Nickel Complexes On The Ethylene Oligomerization

Three new dendritic bridging nickel complexes(complex 1, complex 2, and complex 3) were synthetized from three 1.0-generation poly(amidoamine) dendrimers(1,4-butanediamine, 1,6-hexanediamine or 1,8-octanediamine as core respectively), salicylaldehyde and nickel choride hexahydrate via Schiff base condensation and coordination reaction. The structures of three dendrimers, the resulting dendritic ligands and nickel complexes were characterized by FT-IR, UV, 1H-NMR and ESI-MS. Furthermore, not only investigated the catalytic properties of these three dendritic catalysts in the ethylene oligomerization, we also explored the impact of the bridging groups between the tertiary amine nitrogens in dendritic catalysts on catalytic properties.Three dendritic nickel complexes were evaluated as precursors in ethylene oligomerization, using methylaluminoxane(MAO) as cocatalyst. The results showed that, three dendritic catalysts have reached their maximum values, followed by 9.52×104, 1.02×105 and 1.03×105 g ·(mol Ni · h)-1 at 30 min, 35℃, 0.5MPa and Al/Ni ratio of 700. And the amount of C8 were 19.62%, 20.69% and 40.12%. We found that the catalytic activity of complex 3 was higher than that of complex 2, and catalytic activity of complex 2 was higher than that of complex 1. Meanwhile, the selectivity for C8 of complex 3 supassed that of complex 2 and complex 1.Three dendritic nickel complexes were also evaluated in ethylene oligomerization, using ethylaluminum sesquichloride(EASC) as cocatalyst. The results showed the alkyl-toluenes were dominant products. Three dendritic catalysts have reached their maximum values, followed by 9.25×105, 1.42×106 and 2.49×106 g ·(mol Ni · h)-1 at 15 min, 25℃, 0.5MPa and Al/Ni ratio of 900. And the amount of C11 were 43.06%, 64.36% and 49.13%. It can be concluded that the catalytic activity of complex 3 was higher than complex 2, and the catalytic activity of complex 2 was higher than complex 1 under the same condition. In addition, the selectivity for C11 of the complex 2 exceeded that of complex 3 and complex 1.