Oscillating non-metallocenes-from stereoblock-isotactic polypropylene to isotactic polypropylene via zirconium and hafnium dithiodiphenolate catalysts

Octahedral group 4 complexes of a new bulky tetradentate dithiodiphenolate {OSSO}-type ligand that oscillate between two enantiomeric C₂- symmetric conformations are described. The dibenzyl Zr and Hf complexes led to active catalysts in propylene polymerization. Polypropylene having predominantly stereoblock-isotactic microstructure or predominantly isotactic microstructure could be obtained by varying the polymerization conditions. Long isotactic blocks of 50 to more than 100 repeat units were formed at-10 °C in liquid propylene. Zr and Hf complexes of an {OSSO} ligand bearing bulky phenolates oscillate between two C₂-symmetric conformations. Controlling the relative rates of monomer insertion and catalyst flip affects the polypropylene microstructure, making it stereoblock-isotactic or isotactic, as demonstrated by catalyst signatures on the polymer backbone.