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) 2 MX 2 ]. 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) 2 MX 2 complexes in solution shows that all complexes exist only as a C 2 -symmetric isomer. The direct alkylation of (L4) 2 TiCl 2 and (L4) 2 ZrCl 2 by two equivalents of PhCH 2 MgCl and/or Me 3 SiCH 2 MgCl yielded the corresponding dialkyl complexes without alkylation of the amidine moieties. The (FA) 2 Ti 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 t Bu substituents on the ligand aryloxy ring showed better polymerization productivity (up to 230 kg PE ·mol cat –1 ·h – 1 ). The (L4) 2 MX 2 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.