The present invention relates to compounds in which a transition metal is complexed by at least two ligand systems and at least two of the systems are reversibly joined to one another by at least one bridge comprising a donor and an acceptor, wherein at least one fluorenyl ligand is present and at least one substituent on the acceptor group is an alkyl or aryl radical. The invention further relates to the use of these compounds having a donor-acceptor interaction as polymerization catalysts for preparing high molecular weight elastomers.