Symmetrical and lopsided zirconocene pro‐catalysts

Me 2 C[1‐Cp‐9‐Flu]ZrCl 2 derivatives with H‐, CH 3 ‐and (CH 3 ) 3 C‐ substituents β to the Cp bridgehead carbon atom as well as complexes having mono‐ or di‐substituted fluorenyl ligands (R = CH 3 ‐, (CH 3 ) 3 C‐, CH 3 O‐, CH 3 OCH 2 ‐, (CH 3 ) 3 CC≡C‐, (CH 3 ) 2 N‐, F‐, and Cl‐) have been investigated as propylene polymerization pro‐catalysts. Steric effects from the β‐Cp substituents determine the iso‐, hemi‐iso‐, and syndio‐specificities of the catalysts. The relative stereospecificities of Me 2 Si[1‐Cp‐3 t‐Bu ‐9‐Flu]ZrCl 2 and rac ‐Me 2 Si[1‐Ind‐3‐ t ‐Bu] 2 ZrCl 2 are in accord with molecular models. The more un‐symmetrical the catalysts are the more m and mm stereosequences there are in s‐PP. The m dyads also increase with the concentration of Me 2 C[1‐Cp‐9‐Flu‐2‐OMe]ZrCl 2 .