C1-Symmetric Pentacoordinate Anilidopyridylpyrrolide Zirconium(IV) Complexes as Highly Isospecific Olefin Polymerization Catalysts

Two new anilinepyridinepyrrole ligand precursors bearing bulky substituents on the carbon bridging the pyridine and the aniline moieties were synthesized and used to prepare the corresponding zirconium complexes with general formula [-NNN-]Zr(NMe2)2. NMR spectra analysis of the obtained complexes indicated a C1-symmetry in solution. Both complexes were tested as precatalysts for ethylene and R-olefins polymerization upon activation with AliBu2H as alkylating agent and MAO as ionizing activator. Linear polyethylene and highly isotactic polypropylene and poly(1-hexene) were obtained with good productivities. In particular, the features of the obtained polypropylene samples, in terms of isotacticity ([mmmm] up to 95%), molecular weight (Mw up to 950 kg/mol) and melting point (Tm up to 150 C), were remarkable. The activity and the isospecificity of this class of catalysts were found to depend strongly on the steric bulk of the substituents on the carbon bridging the pyridine and aniline moieties.