The ethylene bridged novel pseudo $C_s$ symmetric ansa-zirconocene complexes, (1-fluorenyl-2-cyclopentadienylethane)zirconium dichloride, (2) and (1-fluorenyl-2-tetramethylcyclopentadienylethan-e)zirconium dichloride, (3) were synthesized and their crystal structures have been determined by X-ray diffraction. In combination with MAO(methylaluminoxane), complex 2 has shown high propylene polymerization activity and afforded polypropylene with good syndiotacticity. In contrast, 3/MAO system produced nearly atactic polypropylene with low molecular weight and exhibited low activity on propylene polymerization. 2/MAO system was also more active in propylene polymerization than known complex, $iPr(Flu)(Cp)ZrCl_2/MAO$, (4) system under identical conditions but lower syndiotacticity. Complex 3 has existed as a hindered form which was probably attributed to the nonbonded steric interaction between both ring β-substituents and equatorial Cl atoms.
