Well-defined phosphino-phenolate neutral nickel(ii) catalysts for efficient (co)polymerization of norbornene and ethylene

Abstract

Phosphino-phenolate neutral nickel catalysts 1–3/B(C₆F₅)₃, without the help of any organoaluminum compound, were found to be efficient catalytic systems for norbornene polymerization and its copolymerization with norbornene derivatives. The amount of B(C₆F₅)₃ required for achieving a high efficiency (3 equiv.) was markedly lower compared to previous reports, and high molecular weight polymers were obtained (>10⁶ g mol⁻¹). Efficient incorporation of polar monomers NBC, NBA, and NBM was also achieved in a controllable fashion, yielding high molecular weight copolymers. Catalysts 1–3 were highly active for ethylene polymerization as single component catalysts, with an activity of up to 10⁷ g mol_Ni⁻¹ h⁻¹, and catalyst 3 was more readily initiated at lower temperature. Catalysts 1–3 were also efficient in incorporating norbornene (up to 30%) into the polyethylene backbone. Bisligated phosphino-phenolate nickel complex 4 and salicylaldimine complex 5 were also studied for comparison, which further verified the unique performance of catalysts 1–3. Preliminary NMR analyses were conducted to explore the norbornene polymerization mechanism.