Polymerization of α-olefins promoted by zirconium complexes bearing bis(phenoxy-imine) ligands with ortho-phenoxy halogen substituents

New fluorinated bis(phenoxy-imine)zirconium complexes bearing halogen substituents in the ortho and para positions of the phenolate rings, bis[N-(3,5-dibromosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (1) and bis[N-(3,5-dichlorosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (2) have been synthesized and used as precatalysts in the polymerization of propylene and 1-hexene. Their catalytic behaviour was compared with that of the analogous fluorinated zirconium complexes bearing alkyl groups in the same positions of the phenolate rings to investigate the effects produced by the introduction of additional electron-withdrawing halogen substituents. Complexes 1 and 2 produce stereoirregular, slightly syndiotactic enriched polypropylenes showing enhanced catalytic activities and an improved primary regioselectivity. Both catalysts promote efficiently the oligomerization of 1-hexene to atactic and regioregular oligomers. Interestingly for both the studied monomers it is possible to control the molecular weights and the structures of end groups of the produced polymeric chains by an appropriate choice of the cocatalyst. Functionalization reactions of the unsaturated polymeric chains selectively produced are also reported.

Graphical abstractTwo new zirconium complexes (1 and 2) have been synthesized and used as precatalysts in the polymerization of propylene and 1-hexene. Both complexes promote efficiently the polymerization of propylene to regioregular slightly syndiotactic polymers and the oligomerization of 1-hexene to atactic and regioregular oligomers. By an appropriate choice of the cocatalyst, unsaturated polymeric chains can be selectively produced and subsequently functionalizated. Figure optionsDownload full-size imageDownload as PowerPoint slide