Catalytic performance of nickel(II) complexes bearing 1,10-phenanthroline based ligands in homogeneous ethylene oligomerization

Abstract

A comparative study of catalytic activity of nickel(II) complexes bearing 1,10-phenanthroline (phen) based ligands in homogeneous ethylene oligomerization process has been performed. It was found that activated by methylaluminoxane (MMAO-12), [NiBr2(phen)] complex oligomerizes ethylene with the moderate activity (66.2 × 103 molC2H4∙molNi−1∙h−1) to the wide range (C4–C20) of even-numbered olefins, with a selectivity for linear alpha-olefins of 43%. The insertion of the carbonyl groups at the 5- and 6-position of 1,10-phenanthroline leads to an increase in catalytic activity up to 81.4 × 103 molC2H4∙molNi−1∙h−1. The presence of hydroxyl groups at the same positions causes a decrease in activity to 15.5 × 103 molC2H4∙molNi−1∙h−1. The steric hindrances near the metal center caused by the methyl groups at 2- and 9-position of 2,9-dimethyl-1,10-phenanthroline result in a decrease in the activity to (26.8–52.2) × 103 molC2H4∙molNi−1∙h−1 and increasing of the selectivity to butenes to 80–96%. The use of activated by MMAO-12 organonickel sigma-complex [NiBr(Mes)(phen)] (where Mes = 2,4,6-trimethylphenyl) bearing Ni–C bond increases the oligomerization activity – the activated complex dimerizes ethylene to mainly butenes with activity of 83.5 × 103 molC2H4∙molNi−1∙h−1. At the same time, this sigma-complex in combination with Et3Al2Cl3 and EtAlCl2 served as activators exhibits higher oligomerization activity – (348.1–394.5) × 103 molC2H4∙molNi−1∙h−1, and lower selectivity to butenes – 58–61%.