A number of novel C-1-symmetric metallocenes based on substituted fluorenyl and indenyl ligands, [dimethylsilyl(2,7-di-tert-butyl-9-eta(5)-fluorenyl)(1-eta(5)-indenyl)] zirconium dichloride (3), [dimethylsilyl(1,1,4,4,7,7,10,10-octamethyl-1,2,3,4,7,8,9,10-octahydrodi benzo[b,h]-9-eta(5)-fluorenyl)(1-eta(5)-indenyl)]zirconium dichloride (5), and [dimethylsilyl(1,1,4,4,7,7,10,10-octamethyl-1,2,3,4,7,8,9,10-octahydrodi benzo[b,h]9-)eta(5)-fluorenyl)(2-methyl-1-eta(5)-indenyl)] zirconium dichloride, and the analogue complexes with a Ph2Si bridge (4, 6, and 8) have been synthesized and used for alternating ethene/propene copolymerizations and compared to the unsubstituted complexes 1 and 2. With growing sterical demand of the substituents, the activities of the catalysts at moderate temperatures decrease strongly, but a very high-temperature stability is achieved. Usage of catalyst species with a Ph2Si instead of a Me2Si bridge leads to higher activities and molar masses. The percentages of alternating triads are high for all catalysts and are decreasing with growing polymerization temperature. Surprisingly, the catalysts with the bulky substitution at the fluorene ring (5-8) yield at 15 and 0 degrees C copolymers with a lower alternating part than at 30 degrees C.