Manganese(II) halogeno complexes containing a neutral tris(3,5-diisopropyl-l-pyrazolyl)methane (referred to as Ll') ligand have been examined on their catalytic performance in ethylene polymerization and ethylene/l-hexene copolymerization. The activities of [Mn(Cl-2)(Ll')] (a) and [Mn(Br)(Ll')](Br) (b) activated by Al(i-Bu)(3)/(Ph3C)[B(C6F5)4] for ethylene polymerization go up to 1600 and 840 kg mol(cat)(-1) h(-1) with a bimodal molecular weight distribution (MwMn) of 4.1 and 4.2, respectively. These results are different from the corresponding manganese(II) complexes with hydrotris(pyrazolyl)borate anion. (c) 2007 Elsevier B.V. All rights reserved.