In the present study, binary systems based on 2,6-bis(imino)pyridine iron and zirconocene complexes were evaluated in the polymerization of ethylene using different catalyst molar ratios and methylaluminoxane as the cocatalyst. The catalyst activity and polydispersity were evaluated, supported by electrochemical data of isolated and binary systems. The results indicated that in binary systems, each complex solely forms an active species. The combination effect was shown to be dependent on the nature of the complexes and on the ratio between them. For an equal molar ratio, a synergistic effect occurs on the catalyst activity. A redox reaction between the complexes was detected, which led to a decrease in the concentration of active species for the other ratios. In addition, it was found that such combined systems can produce polyethylene with a broad polydispersity with bimodal patterns and higher cristallinity than isolated systems. (C) 2016 Elsevier B.V. All rights reserved.