Precise Control of Ethylene Polymerization via Nickel( <scp>II</scp> ) Catalysts with Tunable <i>ortho</i> ‐Coordinating Groups: From Living Polymerization to Functionalized Polyolefins

Comprehensive Summary The preparation of polyethylene with well‐defined microstructures and precise molecular weights has been a long‐standing challenge in olefin polymerization. Despite the complexity of this task, the rational modification of transition metal catalysts continues to be the primary strategy for addressing these limitations. Here, we reported the synthesis of a series of multifunctional amine‐imine nickel(II) complexes bearing ortho ‐substituents (X = –SO₂Ph, –COOMe, –POMe₂) on the ligand framework and systematically investigated the influence of adjacent functionalities on ethylene (co)polymerization performance. In ethylene polymerization, these nickel(II) complexes demonstrated high activities (up to 7.00 × 10 5 g PE ·mol Ni –1 ·h –1 ), affording polyethylene with high molecular weights ( M n up to 4.75 × 10 5 g·mol –1 ) and tunable branched microstructures (70–108/1000C). The resulting polymers displayed excellent elastomeric properties with a high tensile stress‐at‐break of 34.0 MPa and strain‐at‐break of 1032%. Notably, the complex containing POMe 2 achieved controlled living polymerization of ethylene, exhibiting precise molecular weight control and narrow dispersity ( Đ ≤ 1.10). In addition, these nickel(II) complexes successfully mediated the copolymerization of ethylene with 10‐undecenoate and 10‐undecenoic acid to prepare the functionalized polyolefins. These results suggest that the incorporation of ortho ‐coordinating groups may hinder the toxicity of polar functional groups to the metal center, thereby enhancing the catalyst's tolerance to polar substrates.