Mono, di and tetranuclear ansa zirconocene complexes have been synthesized and characterized. After activation with methylalumoxane (MAO) these catalysts were used for the homogeneous and heterogeneous polymerization of ethylene. The properties of the catalysts and the produced polymers were compared. The multinuclear catalysts show a different performance than the corresponding mononuclear derivatives. The tetranuclear catalysts have the lowest activities because of steric crowding. (C) 2002 Elsevier Science B.V. All rights reserved.