Tridentate [N,N,O] Schiff-base group 4 metal complexes: Synthesis, structural characterization and reactivity in olefin polymerization

New complexes LTiCl3(1), LZrCl3(2) and LHfCl3(3) (L = (E)-2-tert-butyl-6[(quinoline-8-ylimino)methyl]phenolate) have been synthesized and fully characterized by multinuclear NMR, mass spectrometry and X-ray diffractometry. The three isostructural complexes show distorted octahedral geometries. Complexes 1–3 were tested as catalysts for ethylene polymerization under a variety of experimental conditions. Reasonable productivities were achieved after activation by methylaluminoxane (MAO) under moderate temperature and pressure conditions (e.g., 50 °C and 6 atm). Complexes 1–3 were also tested as precatalysts for the polymerization of propene. Interestingly, polymerization by 1-MAO at −20 °C afforded an isotactic polypropylene containing 5% isolated regioirregular units in threo configuration. This very unusual microstructure implicates that both primary and secondary monomer insertions occur with the same enantioface selectivity, at variance with what is observed in the case of metallocene catalysts.

Graphical abstractThe three completely characterized octahedral complexes, LTiCl3(1), LZrCl3(2) and LHfCl3(3)(L = (E)-2-tert-butyl-6[(quinoline-8-ylimino)methyl]phenolate were tested as catalysts for ethylene and propylene polymerization under a variety of experimental conditions. Titanium complex 1, activated by MAO afforded, at low temperature, an isotactic polypropylene ([mm] = 80%) containing 5% isolated regioirregular units in threo configuration.The analysis of the stereoerrors present in the methyl region of its 13C NMR spectrum are consistent with an “enantiomorphic site” mechanism of steric control and suggest that that both primary and secondary monomer insertions occur with the same enantioface selectivity. Figure optionsDownload full-size imageDownload as PowerPoint slide