C-2v-symmetric ethylenebis(9-fluorenyl)zirconium dichloride (1) and its C-2-symmetric bis[9-(1-methyl)fluoreny1] derivative (2) have been synthesized in good yields using a convenient synthetic route. Precursor 1 activated with triphenylcarbenium tetrakis(pentafluorophenyl)borate (3) catalyzes propylene polymerization with a constant activity of (6.28 +/- 1.63) x 10(7) g of PP/((mol of Zr).[C3H6]. h) between -20 and +70 degrees C. The polypropylene is ideally atactic and has the same ($) over bar M(W) of (6.03 +/- 1.19) x 10(5). The above system catalyzes ethylene polymerization with a maximum activity of 1.4 x 10(10) g of PE/((mol of Zr).[C2H4]. h) at -20 degrees C which decreases exponentially with an increase of T-p. All the polyethylenes produced between -20 and +50 degrees C have the same ($) over bar M(W) of (5.57 +/- 0.49) x 10(5). In contrast, precursor 2 catalyzed the formation of anisotactic polypropylene of low stereoregularity. Molecular mechanics calculations indicated that substituents on the fluorenyl rings have little effect on both diastereomeric ratios in the synthesis and stereoselectivities in the polymerization.