Thirty-one complexes of bis-(benzimidazole, benzothiazole, and benzoxazole) compounds with Zr(IV) metal centers were synthesized, characterized, activated with methylaluminoxane (MAO), and then tested for catalytic ethylene polymerization. The activities of the various catalysts were found to be functions of the heteroatoms in the ligand frameworks and the structure around the active metal center. The highest activity was obtained with 38/MAO (424 kg E/mol cat. h). The produced polyethylenes showed high molecular weights (41/MAO, 1.9 x 10(6) g/mol) and broad molecular weight distributions (38/MAO, M-omega = 9.64 x 10(5) g/mol, PD = 23). This could result from different interactions of the MAO counter ion with the heteroatoms of the catalyst ligand generating different active sites.