Polyethylene with extremely narrow polydispersity obtained from the new catalyst systems Nb(η 5 -C 5 Me 5 )(η 4 -diene)Cl 2 –MAO and Nb(η 5 -C 5 Me 5 )(η 4 -diene) 2 –MAO

Niobium complexes Nb(η5-C5Me5)(η4-diene)Cl2(diene = buta-1,3-diene 1a, isoprene 1b, or 2,3-dimethylbuta-1,3-diene 1c) and Nb(η5-C5Me5)(η4–2,3-dimethylbuta-1,3-diene)23 in the presence of a large excess of methylaluminoxane (MAO)were found to be active catalysts for the polymerization of ethylene to give polyethylen with narrow polydispersities (Mw/Mn as low as 1.05).