Neutral Nickel(II) Complexes Bearing Aryloxide Imidazolin-2-imine Ligands for Efficient Copolymerization of Norbornene and Polar Monomers

A series of novel aryloxide imidazolin-2-imine bidentate neutral Ni­(II) complexes with different substituents on the imidazolin-2-imine ligand were synthesized and characterized. The complex Ni2 bearing a 2,6-diisopropylphenyl substituent adopted an almost square planar geometry, while the bulkier 2,6-bis­(diphenylmethyl)-4-methylphenyl substituent ligated complex Ni3 was obtained in an allyl adduct base-free η3 coordination mode. In the presence of B­(C6F5)3, these Ni­(II) complexes exhibited remarkably high activity (up to 2.7 × 107 g of PNB (mol of Ni)−1 h–1) and particularly good thermal stability toward the addition polymerization of norbornene. Most importantly, these catalysts were able to promote the direct copolymerization of norbornene with various polar monomers with high activity (∼105 g (mol of Ni)−1 h–1), reasonable comonomer incorporation (0.14–3.08%), and high copolymer molecular weight (M n up to 2.0 × 105). The strategy of installing a strongly electron donating imidazolin-2-imine ligand on the nickel complex demonstrates a great advantage for the copolymerization of an olefin with polar monomers.