Norbornene homopolymerization and copolymerization with ethylene by phosphine-sulfonate nickel catalysts

Abstract

A series of phosphine-sulfonate nickel and palladium complexes [(o-R₂-PC₆H₄SO₃)M(allyl)] (1a, R = Ph, M = Ni; 1b, R = o-MeO-C₆H₄, M = Ni; 1c, R = Cy, M = Ni, 2, R = Cy, M = Pd) were synthesized and characterized. The reaction of B(C₆F₅)₃ with complex 1c led to the isolation of complex [(o-Cy₂-PC₆H₄SO₃·B(C₆F₅)₃)Ni(allyl)] (3c). In the X-ray structure of 3c, the binding of B(C₆F₅)₃ to a sulfonate oxygen was observed. The X-ray analysis also suggests a zwitterionic resonance structure of 3c. In norbornene homopolymerization, 1a–1c showed very low activity. The addition of B(C₆F₅)₃ to the system led to an up to 4000 fold increase in the catalytic activity. Under optimized conditions, an activity of up to 1.2 × 10⁷ g mol⁻¹ h⁻¹ was observed for the B(C₆F₅)₃ adduct of 1c. Interestingly, the palladium analogue 2 was not active at all with or without the addition of B(C₆F₅)₃ under the same conditions. In ethylene homopolymerization, the addition of B(C₆F₅)₃ led to an increase in the activity and a decrease in the molecular weight, which is probably due to the reduction of electron density from the nickel center upon B(C₆F₅)₃ binding. In ethylene-norbornene copolymerization, complex 1c showed good activity with up to 10.1% of norbornene incorporation. Interestingly, a decrease in the activity was observed with the addition of B(C₆F₅)₃.