Monoarylmethyl Substituents Dictate Stability and Chain Transfer Behavior in Late Transition Metal Pyridine-Imine Catalytic Systems
Mengya Ma, Shengyu Dai
Abstract
Pyridine-imine Ni(II) and Pd(II) catalysts are pivotal in ethylene polymerization and copolymerization, offering tunable ligand architectures for precise control over catalytic performance. This study explores flexible monoarylmethyl-substituted pyridine-imine Ni(II)/Pd(II) catalysts, demonstrating their efficacy in ethylene oligomerization and co-oligomerization with methyl acrylate (MA). The Ni(II) catalysts, activated by diethylaluminum chloride, exhibited high activity (up to 2.66 × 10 6 g/(mol Ni·h)) and produced highly branched ethylene oligomers (83–124 branches/1000C) with low molecular weights (844–2159 g/mol). Conversely, Pd(II) catalysts, activated by NaBArF, showed moderate activity (1.07–15.97 × 10 4 g/(mol Pd·h)) and generated ethylene oligomers with higher branching densities (64–163 branches/1000C). Notably, the Pd(II) systems achieved efficient MA incorporation (4.66–18.26 mol %) in co-oligomerization, yielding hyperbranched functionalized products. In comparison with classical ethyl nickel and palladium catalysts, the monoarylmethyl catalysts demonstrated higher polymerization activity and produced higher-molecular-weight ethylene oligomers. Furthermore, when compared to the previously reported rigid phenyl- and dibenzhydryl-nickel and palladium catalysts, the flexible benzyl catalysts in this work exhibited comparable polymerization activity while generating more highly branched ethylene oligomers.