A series of sterically and electronically modulated iminopyridyl Ni(Il) bimetallic catalysts of the general formula [(2,6-C5H3NX)-C=N-(Z)-N=C-(2,6-C5H3NX)][NiBr2](2) {Z = (2,6-C6H2R2)(2)CH(4-C6H4Y); R = Me, Et, iPr; Y = H, NO2, OCH3, X = H, Me, Ph} have been synthesized. When activated with methylaluminoxane or common alkyl aluminums such as ethyl aluminum sesquichloride (EASC), all catalysts oligomerize/polymerize ethylene with activities exceeding 10(6) g-product/(mol-Ni h bar) at 30 degrees C to yield C-4 as a major product. Among the cocatalysts used, EASC records the best activity. The effect of electronic modification of the complexes on catalytic activity was studied by using UV-vis spectroscopy and cyclic voltammetry. The cooperative effect due to two metal centers of bimetallic complexes was evidenced by comparing the molecular weight of polymer and the C-13 NMR spectra of poly(1-hexene) obtained by its monometallic analogue. (C) 2008 Elsevier B.V. All rights reserved.