The complexation of 2-hydroxy-1,4-naphtho-quinone and 3-hydroxy-2-methyl-4-pyrone with zirconium tetrachloride yielded complexes containing bidentate alkoxide ligands. In the presence of MAO or TIBA these complexes were found to be active for ethylene polymerization, producing polymers with high molecular weight. Both catalytic systems were also shown to be active when supported on silica or on MAO-modified silica. (C) 2003 Elsevier B.V. All rights reserved.