Synthesis, catalytic performance for ethylene oligomerization, and reaction mechanism of imino phthalocyanine nickel catalysts

Salicylaldiminato and pyridinimine phthalocyanine ligands, along with their corresponding nickel catalysts were synthesized and characterized by 1 H NMR, FT-IR, UV-Vis, elemental analysis, ICP-MS, and TG-DTA. The catalytic performance of imine phthalocyanine nickel-based catalysts in ethylene oligomerization was investigated. Ethylene oligomerization results indicated that under the optimal reaction conditions, the activity of the salicylaldiminato phthalocyanine nickel catalyst (12.54 × 10 5 g/(mol Ni·h)) was greater than that of the pyridinimine phthalocyanine nickel catalyst (10.06 × 10 5 g/(mol Ni·h)), and the products of the two catalysts were mainly butene as well as minor amounts of hexene and octene. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the imine phthalocyanine nickel-based catalysts were calculated using density functional theory (DFT). The results showed that the salicylaldiminato phthalocyanine nickel catalyst had larger energy gap value. To further investigate the micro reaction process of ethylene oligomerization, the reaction mechanism of ethylene oligomerization was proposed. The DFT calculation of the catalytic cycle process was carried out by selecting a reasonable molecular model of imine phthalocyanine nickel catalyst. The molecular model of the salicylaldiminato phthalocyanine nickel catalyst had a lower ethylene insertion barrier and β -H elimination barrier, indicating that this molecular model was more conducive to ethylene oligomerization.