Investigations of flexible cycloalkyl substituents on pyridine‐imine based nickel(II)‐ and palladium(II)‐catalyzed ethylene oligomerization

Abstract

AbstractCycloalkyls show rich conformational change. According to our previous work, the flexible cycloalkyl substituted α‐diimine system generated polyethylene with good elastic properties and much higher branching densities. In this contribution, we introduce the cycloalkyls into the pyridine‐imine catalytic system. A series of novel pyridine‐imine ligands and the corresponding nickel(II) and palladium(II) complexes with cycloalkyl and phenyl substituents for ethylene oligomerization were designed, synthesized and characterized. The nickel(II) complexes with cycloalkyl substituent showed high oligomerization activity (up to 5.90 × 106 g mol−1 h−1) and generated ethylene oligomers with low to moderate branching density (17–57/1000C). The palladium(II) complexes showed moderate oligomerization activity (up to 8.33 × 103 g mol−1 h−1) and can yield high branching density (107–187/1000C) oligomers. In addition, compared to the catalyst with rigid phenyl substituent, the catalysts with flexible cycloalkyl substituents exhibited higher oligomerization activity and yielded ethylene oligomers with higher branching density under the same conditions. © 2023 Society of Industrial Chemistry.