Phenoxy-Amidine (FA) Titanium and Zirconium Complexes: Synthesis, Structure, and Use in Olefin Polymerization

Herein, we report the synthesis of a series of new bis(phenoxy-amidine) dichloro and bis(dimethylamido) Ti and Zr complexes [(FA)₂MX₂]. In the solid state, all the structures showed a distorted octahedral geometry around the metal center with the same O-trans, N-cis, X-cis configuration. Remarkably, NMR spectroscopic study of (FA)₂MX₂ complexes in solution shows that all complexes exist only as a C₂-symmetric isomer. The direct alkylation of (L4)₂TiCl₂ and (L4)₂ZrCl₂ by two equivalents of PhCH₂MgCl and/or Me₃SiCH₂MgCl yielded the corresponding dialkyl complexes without alkylation of the amidine moieties. The (FA)₂Ti and Zr complexes are active in ethylene polymerization upon activation by MAO at 25-50 °C in toluene, at 5 bar ethylene pressure, providing linear (ultra) high-molecular-weight PE (M_w up to 2,154,000 g·mol^-1 for the soluble fraction), yet with very broad distributions (M_w/M_n = 14-408), testifying an abundant multisite behavior. Complexes with ^tBu substituents on the ligand aryloxy ring showed better polymerization productivity (up to 230 kg_PE·mol_cat^-1·h^-1). The (L4)₂MX₂ complexes, upon activation with MAO, are also slightly active toward styrene (2 to 39 kg_PS·mol_cat^-1·h^-1 at 25-100 °C) giving polystyrenes with an atactic microstructure and molecular weight characteristics (Đ = 1.77-1.86) indicative of a single-site behavior.