Abstract: Catalyst systems which are suitable for the polymerization of olefinically unsaturated hydrocarbons contain, as active components, A) an amidinato metal complex of the general formula A  where M is a metal from group IIIb, IVb, Vb or VIb of the Periodic Table of Elements or a metal from the lanthanide group, X is a negative leaving atom or a negative leaving group, and the radicals X may be identical or different if (n−m)>1, R1, R2 and R3 are each a C-organic or Si-organic radical, n is the valency of M in the metal complex A and m is from 1 to 5, with the proviso that n−m≧0, and, if required, B) an acceptor compound for the substituent X of the component A as an activator.

Abstract: Catalyst systems which are suitable for the polymerization of olefinically unsaturated hydrocarbons contain, as active components,A) an amidinato metal complex of the formula A ##STR1## where M is a metal from group IIIb, IVb, Vb or VIb of the Periodic Table of Elements or a metal from the lanthanide group,X is a negative leaving atom or a negative leaving group, and the radicals X may be identical or different if (n-m)>1,R.sup.1, R.sup.2 and R.sup.3 are each a C-organic or Si-organic radical,n is the valency of M in the metal complex A andm is from 1 to 5, with the proviso that n-m.gtoreq.0,and,B) an activator in a molar ratio of activator B to metal complex A of from 0.5:1 to 10,000:1.