High-Performance Neutral Phosphine-Sulfonate Nickel(II) Catalysts for Efficient Ethylene Polymerization and Copolymerization with Polar Monomers

Abstract

Low-cost and earth-abundant nickel catalysts are of great interest for olefin copolymerization with polar monomers to generate highly desirable functionalized polyolefins. However, nickel catalysts usually suffer from poor thermal stability and low copolymer molecular weight. In this work, by combination of design strategies of sterics and electronics, a family of sterically demanding aliphatic/aromatic-substituted phosphine-sulfonate neutral nickel complexes 1–4 {[κ2(P,O)-(menthyl)ArP(C6H4SO2O)]NiMe(pyr)} (1: Ar = (MeO)3C6H2; 2: Ar = 2-(2′,6′-(MeO)2C6H3)C6H4; 3: Ar = 2-(C6H5)C6H4; 4: Ar = 2-(2′,6′-F2C6H3)C6H4) with different sterics and electronics were synthesized and fully characterized by comprehensive NMR spectroscopy, single-crystal X-ray diffraction, and elemental analysis. Among these nickel catalysts, catalysts 1 and 4 are in favor of generating polyethylenes with high molecular weights (up to 224.0 kg mol–1) in high activities (up to 1.6 × 106 g mol–1 h–1) and good thermal stabilities (up to 90 °C), while catalysts 2 and 3 suffer from low thermal stability. More remarkably, the preferred catalysts 1 and 4 are also efficient for ethylene copolymerization with a broad scope of polar monomers including vinyl trimethoxysilane, various allyl monomers, 6-chloro-1-hexene, 6-bromo-1-hexene, methyl 10-undecenoate, and hydroxymethyl norbornene. These copolymerizations exhibit moderate to high activities (up to 18.0 × 104 g mol–1 h–1), high molecular weights (23.9–165.5 kg mol–1), and relatively low incorporations (<2.4 mol %).