Isospecific Propylene Polymerization with a Novel 2-Substituted Bis(indenyl) <i>ansa</i>-Zirconocene

Abstract

The preparation and crystal structure of the first group 4 ansa -metallocene with an oxygen atom directly bonded to the 2-position of an η 5 -indenyl moiety, rac -[ethylenebis(2-( tert -butyldimethylsiloxy)indenyl)]zirconium dichloride ( 3 ), is reported. In combination with methylaluminoxane (MAO), complex 3 polymerizes propylene to highly isotactic crystalline polypropylene ( T m = 148 °C; M w = 19 000; M w / M n = 2.4). Under similar conditions, the propylene polymerization activity of 3 /MAO exceeds that of the conventional ansa -metallocene catalyst system (dimethylsilyl)bis(4,5,6,7-tetrahydroindenyl)zirconium dichloride ( 4 )/MAO by a factor of 2 (5300 vs 2300 kg of PP/mol of Zr/h; T p = 20 °C; P (C 3 H 6 ) = 2.0 bar; [Al]:[Zr] = 3 000:1). Complex 3 crystallizes in the unusual indenyl-backward conformation. The molecular structure is consistent with the expected C 2 symmetry.