Isospecific propylene polymerization by C-1-symmetric Me2Si(C5Me4)(2-R-Ind)MCl2 (M = Ti, Zr) complexes

Abstract

Novel Cl-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 C-1-symmetric nature irrespective of the type of metal ana 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 polymerization temperature in the case of zirconocenes (5b and 6b). The effect of a 2-Me substituent at the indenyl ring on propylene polymerization was apparent in terms of polymerization activity and molecular weight of polypropylene, especially for zirconocenes, but was minor for titanocenes.