Syntheses and Catalytic Behavior of Dendritic Macrocyclic Schiff-Base Nickel (II) Complexes in Ethylene Oligomerization

Graphical Dendritic macrocyclic Schiff base ligands with 1.0G dendrimer PAMAM and terephthalaldehyde were synthesized in different solvents. And the corresponding nickel complexes were also synthesized to be used for ethylene oligomerization. Two synthesized complexes displayed higher catalytic activity and higher selectivity for low-carbon olefin compared with dendritic salicylaldehyde-imine nickel (II) catalyst because of the steric hindrance of dendritic ring. The functionalized dendrimers play an important role in catalytic application. A dendritic Schiff base macrocyclic compound was designed and synthesized with the 1.0 generation dendrimer polyamidoamine (1.0G PAMAM) and terephthalaldehyde for ethylene oligomerization. The role of solvent in the synthesized process of dendritic macrocyclic Schiff base ligand was studied. Surprisingly, intermolecular or intramolecular cyclization occurred and formed bicyclic Schiff base ligand ( Ligand 1 ) and polycyclic Schiff base ligand ( Ligand 2 ). And their corresponding nickel complexes ( Catalyst 1 and Catalyst 2 ) were also synthesized with NiCl 2 (DME) as material to be used for ethylene oligomerization. The effects of the reaction parameters and the chemical structure of the ligand on the catalytic behavior were investigated with methyl-aluminoxane (MAO) as cocatalyst, and Catalyst 1 and Catalyst 2 displayed the high catalytic activity and the high selectivity for low-carbon olefin in ethylene oligomerization. Catalyst 2 based on Ligand 2 had a higher catalytic activity of 9.12×10 4 g (mol Ni h) −1 in ethylene oligomerization because of large dendritic ring in the ligand for ethylene diffusion and mass transfer. Moreover, two synthesized nickel complexes based on dendritic macrocyclic Schiff base ligand had a higher catalytic activity compared with the corresponding dendritic salicylaldehydeimine nickel (II) catalyst.