Indirect Substituent Effects upon the Olefin Polymerization Reactivity of Titanium(IV) Chelating σ-Aryl Catalysts

The surprising impact of substituents that are seemingly remote from the active site upon the olefin polymerization characteristics of group 4 catalysts supported by pyridine-2-phenolate-6-(sigma-aryl) ancillary ligands are described. Excellent ethylene polymerization activities (up to 22 kg mmol(-1) h(-1) (mol/L C2)(-1)) with borate cocatalysts are observed at 100 degrees C. On the basis of an X-ray crystal structure, a steric origin is proposed for the effect, which influences polymerization behavior by modulating catalyst conformation. However, excessively bulky substituents adjacent to the catalytic center can counteract this effect and give diminished efficiencies.