Rational design of aldimine imidazolidin-2-imine/guanidine nickel catalysts for norbornene (Co)polymerizations with enhanced catalytic performance

The development of late transition metal catalysts bearing novel ligand platforms is a convenient pathway to obtain prospective systems with enhanced catalytic performance, however, it remains a challenge in the field of olefin (co)polymerizations. In this contribution, a new family of [N,N]-type of bidentate aldimine imidazolidin-2-imine/guanidine ligands and their nickel complexes Ni1–Ni7 bearing a distinct six-membered chelate ring were successfully synthesized, and characterized. All of the nickel catalysts were active for norbornene polymerization with high activity of up to 7.44 × 10⁵ g mol^–1 h⁻¹. These catalysts also copolymerized norbornene and 1-alkenes (1-dodecene and 1-octadecene) while keeping high activities to produce various norbornene-based high-molecular-weight (M_n = 5.75–36.0 kg mol⁻¹) cyclic olefin copolymers (COCs) with adjustable 1-alkene incorporations (1.44–13.30 mol%) and a wide range of T_g values (102.2–271.4 °C). Moreover, with the decoration of bulky N-aryl substituents, these nickel catalysts exhibited strong tolerance towards polar monomer to promote the direct copolymerization of norbornene and methyl 10-undecenoate with high activity (up to 9.88 × 10⁴ g mol^–1 h⁻¹), and furnished polar functionalized COCs with a high molecular weight (M_n up to 72.4 kg mol⁻¹) and reasonable polar monomer incorporations (0.19–0.45 mol%). These nickel complexes are rare examples and also promising candidates as catalysts for the efficient synthesis of various COCs.