Catalytic systems of the Ziegler-Natta type

Catalyst systems of the Ziegler-Natta type containing, as active components, a) a titanium-containing solids component which contains titanium, magnesium, halogen and a norbornadienecarboxylic ester of the general formula I as an electron donor, in which R and R denote C1-C8-alkyl groups or 5-membered to 7-membered cycloalkyl groups which in turn may carry C1-C10-alkyl groups, b) an aluminium component and c) a further electron donor component. These catalyst systems are suitable in particular for the preparation of polypropylene and copolymers of propylene with minor amounts of other alpha ,ss-unsaturated olefin compounds having 2 to 8 C atoms.