The polymerization of ethylene with titanium complexes bearing one bulky imidazolin-2-iminato ligand (L) in the presence of MAO and/or TTPB as cocatalysts have been explored. The complex LTiCl3 and its methylated forms were prepared to shed light on the nature of the active polymerization species. With some of these complexes, the best catalytic activity was obtained at an Al:Ti ratio of 8.