PREFORMED CATALYTIC SYSTEM COMPRISING A RARE EARTH METAL METALLOCENE

The present invention relates to a catalytic system based at least on a preformation monomer selected from the group consisting of 1, 3-dienes, ethylene, α-monoolefins and mixtures thereof, on a metallocene of formula {P(Cp)(Flu)LnG} and on an organometallic compound as cocatalyst, Ln denoting a metal atom which is a rare earth metal, G denoting a group comprising the borohydride moiety BH4 or denoting a halogen atom X selected from the group consisting of chlorine, fluorine, bromine and iodine, Cp denoting a cyclopentadienyl group of formula C5H4, Flu denoting a fluorenyl group of formula C13H8, P being a group that bridges the two Cp and Flu groups, and comprising a silicon or carbon atom. Such a catalytic system has improved stability of the catalytic activity over time, in particular during storage.