The immobilization of the soluble precatalysts [(ArN=C(Me))(2)C5H3N]FeCl2, where Ar=2,4,6-trimethylphenyl (A) or 2,6-diisopropylphenyl (B), on supports derived from a spherical MgO2-alcohol adduct yields active supported systems for ethylene polymerization. The activity of the supported catalysts and the resultant polymer properties are strongly dependent on the method of preparation. The highest activities are obtained using supports obtained by pretreatment of the MgCl2-alcohol adduct with triethylaluminium (TEA). In addition, it was found that precatalyst A, having less steric bulk at the ortho-aryl position of the ligand, gave higher activity than precatalyst B, in line with the different behaviours of these precatalysts. in homogeneous polymerization, while precatalyst B gave polyethylene with lower polydispersity. (c) 2005 Elsevier B.V. All rights reserved.