Isospecific propylene polymerization with a novel 2-substituted bis(indenyl) ansa-zirconocene

The preparation and crystal structure of the first group 4 ansa-metallocene with an oxygen atom directly bonded to the 2-position of an eta(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 degrees C; M(w) = 19 000; M(w)/M(m) = 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 degrees C; P(C3H6) = 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.