Synthesis and characterization of nickel(II) complexes bearing 2-(imidazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles and their polymerization of norbornene

Abstract

Series of 2-R 1-6-(1-R 2-4,5-diphenyl-1H-imidazol-2-yl)pyridine (R 1 = R 2 = H, L1; R 1 = Me, R 2 = H, L2; R 1 = H, R 2 = Me, L3; R 1 = R 2 = Me, L4), 2-(6-R 1-pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (R 1 = H, L5; R 1 = Me, L6) and 2-(pyridin-2-yl)phenanthro[9,10-d]oxazole ( L7) were synthesized and used to prepare their corresponding dihalonickel complexes ( C1– C9). All organic compounds and nickel complexes were characterized by elemental and spectroscopic analyses. Molecular structures of C1, C4, C5 and C8 were confirmed by the single-crystal X-ray diffraction analysis. The single-crystal X-ray analysis revealed complex C1 as a distorted octahedral geometry, complex C4 as a distorted square pyramidal geometry, complex C5 as a distorted trigonal bipyramidal configuration, and complex C8 as a tetrahedral geometry. Upon activation with methylaluminoxane (MAO), the nickel complexes showed good activity towards norbornene polymerization through main additional and minor ring-opening metathesis. The reaction parameters such as norbornene concentration, reaction temperature and different coordinate environments caused by the ligands affected their catalytic performances.