Cobalt complexes based on dendritic PAMAM bridged salicylaldimine ligands: Synthesis, characterization and performance in ethylene oligomerization
Two novel dendritic poly(amido-amine) (PAMAM) bridged salicylaldimine ligands were synthesized by Schiff base reaction using 1.0 generation dendritic PAMAM as bridged groups. The cobalt complex with 1,4-butanediamine as core (C1) and the cobalt complex with 1,6-hexanediamine as core (C2) based on dendritic PAMAM bridged salicylaldimine ligands were prepared by metallic coordination reaction, respectively. The structures of the ligands and the dendritic cobalt complexes were characterized by fourier transform infrared (FTIR), ultraviolet spectra (UV), hydrogen nuclear magnetic resonance (1H NMR) and electrospray ionization mass spectra (ESI-MS). The complexes C1 and C2 were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO), diethylaluminum chloride (Et2AlCl), ethylaluminium dichloride (EtAlCl2) and ethylaluminum sesquichloride (EASC). The dendritic cobalt complexes exhibited the highest activity and selectivity for high carbon oligomers with EASC as activator. Under the conditions of 1.0 MPa, 25°C and Al/Co molar ratio 1500, the catalytic activity and selectivity for C10–C20 using C1 were 3.44×106 g·(mol Co·h)−1 and 76.53% after activation with EASC, and the catalytic activity and selectivity for C10–C20 using C2 were 3.42×106 g·(mol Co·h)−1 and 84.50%, respectively.
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