Versatile PNPO ligands for palladium and nickel catalyzed ethylene polymerization and copolymerization with polar monomers

Abstract

Asymmetric PO-type ligands are versatile platforms for palladium and nickel catalyzed ethylene polymerization as well as copolymerization of ethylene with polar monomers. In this work, a series of phosphinoamine phosphoramidate/phosphoramide ligands and the corresponding palladium/nickel catalysts were prepared, characterized and investigated in ethylene polymerization as well as copolymerization of ethylene with various polar monomers. The palladium and nickel complexes exhibited high activities in ethylene (co) polymerization, generating high-molecular-weight polyethylenes and copolymers of ethylene and polar monomers. The introduction of electron-donating substituents in the palladium catalytic system can significantly increase polymer molecular weights while maintaining high ethylene (co)polymerization activities. The less electronic donating substituents in the nickel catalysts led to increased catalytic activities in both ethylene polymerization and copolymerization with polar monomers. These results demonstrate the importance of ligand electronic effect in tuning the properties of nickel and palladium catalysts in ethylene polymerization and copolymerization reactions.