“…They could tolerate functional groups such as ester and copolymerize ethylene with functional olefins, even the more challenging 1,1-disubstituted monomer methyl methacrylate (MMA) [76], so these catalysts were extensively studied by different research groups [34,77], including the installation of sterically bulky substituents to block the metal center and/or the design of new electron-donating ligands to reduce the electrophilicity of the metal center. A series of [N,O]-type nickel catalysts based on various new ligands, including βketoiminato [78], five-membered anilinonaphthoquinone [79][80][81], six-membered anilinoanthraquinone [82,83], anilinobenzoic acid methyl ester [84], 2-iminopyridine-N-oxide [85], imidazolin-2-imine [86,87], imine/phosphine-oxide [88,89], and cation-tunable nickel catalysts [90], have been further investigated in the copolymerization of ethylene/norbornene with polar monomers and alternating copolymerization of ethylene and CO [91]. Detailed mechanistic investigations have also been reported to indicate related insertion copolymerization [76].…”