MgCl2/i-butylaluminum 2-ethyl-1-hexoxide, i-BumAl(OR)(n), prepared by the dealcoholysis of the MgCl2/2-ethyl-1-hexanol adduct with i-Bu3Al, was investigated as an activator for bis(phenoxy-imine)Ti complexes. The complexes with MgCl2/i-BumAl(OR)(n) displayed very high ethylene polymerization activities comparable to those obtained with methylalumoxane (MAO) activation. In addition, the activities obtained were comparable to or exceeded that found for the Cp2TiCl2/MAO catalyst system under identical conditions. Moreover, the catalyst systems produced narrow molecular weight distribution polyethylenes displaying good morphology. These are the first examples of MAO- or borate-free, highly active, single-site catalysts based on a transition metal complex and a MgCl2-based activator. (C) 2003 Elsevier Science (USA). All rights reserved.