Isospecific Propylene Polymerization by C1-Symmetric Me2Si(C5Me4)(2-R-Ind)MCl2 (M = Ti, Zr) Complexes

Novel C1-symmetric group 4 ansa-metallocene complexes Me2Si(C5Me4)(2-R-Ind)MCl2 (R = H, M = Ti (5a), Zr (5b); R = Me, M = Ti (6a), Zr (6b)) were prepared from the reaction of dilithium salt of the corresponding ligands Me2Si(C5Me4H)(2-R-IndH) (R = H, Me) with appropriate group 4 metal halides. Crystal structures of 5a, 6a, and 6b determined by X-ray diffraction studies reveal chiral C1-symmetric nature irrespective of the type of metal and ligand. The complexes 5a, 5b, 6a, and 6b were tested for the polymerization of propylene in the presence of methylaluminoxane (MAO) at various temperatures. All of them exhibit good activity and afford moderate to high isotactic polypropylenes. In the case of titanocenes (5a and 6a), polymerization activity, molecular weight, and isotacticity of polypropylene sharply increase as the polymerization temperature decreases, while the increase of polymerization activity and the decrease of isotacticity and molecular weight of polypropylene were observed upon increasing the p...