Selective ethylene oligomerization bearing hyperbranched bispyridylamine chromium catalyst

Two new hyperbranched bispyridylamine ligands and multinuclear chromium complexes were synthesized with 1.0?G hyperbranched macromolecules, 2-chloropyridine, 2-chloro-4-methylpyridine and CrCl₃(THF)₃ as raw materials. The structures of hyperbranched ligands and chromium complexes were characterized by UV, FT-IR, ¹H NMR, ESI-MS, and elemental analysis. These hyperbranched chromium complexes were evaluated as catalyst precursors by using MAO as activator in the oligomerization of ethylene. Effects of reaction temperature, reaction pressure, Al/Cr molar ratio, concentration of catalyst, solvent, and the structure of catalysts on the catalytic activity and product selectivity were investigated. The oligomerization results showed that with increase of reaction temperature, reaction pressure, and Al/Cr molar ratio, the catalytic activity increased and then decreased; the catalytic activity continuously decreased as the amount of catalyst increased. The products were mainly based on C₆ and C₈. Under optimized conditions, the catalytic system of hyperbranched NNN/Cr(III)/MAO led to activity of 1.26?×?10⁵ g/(mol·Cr·h) and 63.34% selectivity for C₆ and C₈.