Chiral zirconium complexes with bianiline-based N4-donor ligands

Syntheses of new tetradentate ligands, containing a bianiline backbone and two additional heterocyclic N-donors, and of chiral zirconium complexes containing these ligands as dianions are reported. Crystal structures of some of these complexes show a preference for coordinating the two remaining ligands in a trans- rather than cis-orientation. Nevertheless, these complexes are moderately active in MAO-activated olefin polymerization in toluene solution at 50 degreesC. With propene, partly isotactic polypropene (55% mmmm) is obtained. These observations indicate that in cationic species generated in these reaction systems, the growing polymer chain and the olefin substrate occupy cis-coordination sites, while the heterocyclic N ligands adopt a screw-like trans orientation suitable to favor one of the enantiofacial orientations of the entering olefin substrate.