The structures of intermediates generated by the activation of 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) chloride (1) with various cocatalysts, methylalumoxane (MAO), trimethylaluminum (TMA), and TMA in combination with B(C6F5)3and Ph3CB(C6F5)4, is studied by 1H and 2HNMR spectroscopy. The 1/AlMe3system exhibits a higher catalytic activity in ethylene polymerization than the 1/MAO system. The activity of the latter decreases sharply with a decrease in the amount of AlMe3in MAO. Neutral Fe(II) complexes rather than cationic intermediates are suggested to be active components in both catalytic systems.