Solvent stabilized transition metal cations are excellent initiators for the polymerization of cyclopentadiene. The product yield is - in first approximation - directly proportional to the reaction time. Partial substitution of the solvent molecules by ligands with different donor strength and charge allows the synthesis of initiators with tailor made activity. The presence of a metal-metal multiple bond seems not to be of significant importance for the catalytic activity of the initiator systems. The crucial point for the activity of the complexes described here is the presence of labile and therefore easily replacable ligands in equatorial coordination sites.