Backbone stiffening in [OOOO]-type complexes and the effect on polymerization performance

Zr and Hf bis(phenolate-ether) catalysts ([OOOO]-catalysts; see Figure A),1-2 originally patented by SYMYX3 and later acquired by Dow,4 comprise one of few homogeneous catalyst classes capable of working at high temperatures while still maintaining a high molecular weight capability. We conducted a systematic study on the C3-linked [OOOO] subfamily of catalysts, comparing the unsubstituted C3-linked with their rac- and meso-1,3-disubstituted derivatives. This study reveals the importance that stiffening the catalyst backbone via introduction of 1,3-dimethyl substituents has on catalyst performance. In particular, the molar mass capability of the stiffened catalysts is dramatically increased. Other recent attempts to increase the olefin polymerization performance of known catalyst classes by limiting catalyst backbone flexibility include (a) introduction of a 4,5-triptycene substituent pattern in metallocenes and (b) closure in the backbone of Salan-catalysts. A pattern emerges that emphasizes that limiting catalyst flexibility is key to high-performance, especially when high temperature conditions are desired. This research forms part of the research programme of DPI, project #835.