Zirconium and Titanium Complexes Supported by Tridentate LX2 Ligands Having Two Phenolates Linked to Furan, Thiophene, and Pyridine Donors: Precatalysts for Propylene Polymerization and Oligomerization

Abstract

Zirconium and titanium complexes with tridentate bis(phenolate)−donor (donor = pyridine, furan and thiophene) ligands have been prepared and investigated for applications in propylene polymerization. The ligand framework has two “X-type” phenolates connected to the flat heterocyclic “L-type” donor at the 2,6- or 2,5- positions via direct ring−ring (sp2−sp2) linkages. The zirconium and titanium dibenzyl complexes have been prepared by treatment of the neutral bis(phenol)−donor ligands with M(CH2Ph)4 (M = Ti, Zr) with loss of 2 equiv of toluene. Titanium complexes with bis(phenolate)pyridine and -furan ligands and zirconium complexes with bis(phenolate)pyridine and -thiophene ligands have been characterized by single-crystal X-ray diffraction. The solid-state structures of the bis(benzyl)titanium complexes are roughly C2-symmetric, while the zirconium derivatives display Cs and C1 symmetry. The bis(phenolate)pyridine titanium complexes are structurally affected by the size of the substituents (CMe3 or CEt3) ortho to the oxygens, the larger group leading to a larger C2 distortion. Both titanium and zirconium dibenzyl complexes were found to be catalyst precursors for the polymerization of propylene upon activation with methylaluminoxane (MAO). The activities observed for the zirconium complexes are particularly notable, exceeding 106 g polypropylene/mol Zr·h in some cases. The bis(phenolate)pyridine titanium analogues are about 103 times less active, but generate polymers of higher molecular weight. When activated with MAO, the titanium bis(phenolate)furan and bis(phenolate)thiophene systems were found to promote propylene oligomerization.