tetrakis(dimethylamido)zirconium or -hafnium gave the corresponding (chelate ligand)MX3 systems in a variety of cases. Some of these gave very active ethene polymerization catalysts upon activation with methylalumoxane. Six of the neutral aminoalkylpyridines were characterized by X-ray diffraction, as were eight of the zirconium or hafnium complexes and two aluminum chelate complex systems.