New polycyclic cyclopentadiene compounds having the formula (II) wherein the various substituents and symbols R1, R2, R3, R4, R5, R6, R7, Z1 and Z2 and "n" have the meaning specified in the description. These compounds can form metallocene complexes with transition metals, which have shown unusual properties in the (co)polymerization of ethylene and alpha-olefins in general.