New (Anilidomethyl)pyridine Titanium(IV) and Zirconium(IV) Catalyst Precursors for the Highly Chemo- and Stereoselective cis-1,4-Polymerization of 1,3-Butadiene

Group 4 metals complexes bearing anilidomethylpyridine ligands have been synthesized and characterized by nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. All complexes, after activation by using AliBu2H and methylalumoxane (MAO) were tested in 1,3-butadiene and α-olefins polymerization. The zirconium complexes showed higher activity with respect to the titanium homologous. Polymerization of ethylene resulted, in all cases in the production of high molecular weight linear polyethylene. Propylene polymerization tests provided substantially atactic polypropylene. 1,3-Butadiene polymerizations produced cis-1,4 polybutadiene, and in the case of zirconium complexes polymers with a content of cis-1,4 units higher a 99.9% were provided. Activity and stereoselectivity of the catalysts were related to the steric features of the complexes.