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

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.