Homo- and Copolymerization of Ethylene with Norbornene Catalyzed by Vanadium(III) Phosphine Complexes.

Herein, we report the homo- and co-polymerization of ethylene (E) with norbornene (NB) catalyzed by vanadium(III) phosphine complexes of the type VCl(PMePh) [n = 2 (), 1 ()] and VCl(PR) [R = phenyl (Ph, ), cyclohexyl (Cy, ), -butyl (Bu, )]. In the presence of EtAlCl and ClCCOOEt (ETA), - exhibit good activities for the polymerization of ethylene, affording linear, semicrystalline PEs with a melting temperature of approximately 130 °C. Mainly alternating copolymers with high comonomer incorporation were obtained in the E/NB copolymerization. A relationship was found between the electronic and steric properties of the phosphine ligands and the catalytic performance. Overall, the presence of electron-withdrawing ligand substituents increases the productivity, complexes with aryl phosphine (weaker σ-donor character) exhibiting a higher (co)polymerization initiation rate than those with alkyl phosphines (stronger σ-donor character). Steric effects also seem to play a key role since and , having large size phosphines (PCy θ = 170° and PBu θ = 182°, respectively) are more active than (PMePh θ = 122°). In this case, the larger size of PBu and PCy likely compensates for their higher donor strength compared to PMePh.