Highly active nickel(II) and palladium(II) complexes bearing N,N,P tridentate ligand for vinyl addition polymerization of norbornene

A series of nickel (II) complexes (1a-4a) and palladium (II) complexes (1b-4b) bearing N,N,P tridentate ligands derived from amino-alkyl phosphines and 2-pyridinecarboxaldehyde and 2-quinolinecarboxaldehyde were synthesized and characterized. X-ray diffraction analysis revealed that complexes 1a, 4a, and 2b adopted square-pyramidal geometry, trigonal bipyramid, and distorted square-planar geometry, respectively. Activated by methylaluminoxane (MAO), all the complexes were highly active for norbornene polymerization in a vinyl addition fashion, affording high molecular weight polymers with narrow molecular weight distributions. The activities of palladium complexes are particularly notable; the highest activity reached 2.45 × 10⁸ g PNB (mol of Ni)⁻¹ h⁻¹. The activities of the complexes were affected by the ligand structure as well as the reaction parameters such as polymerization temperature, time, and cocatalyst loading.