The synthesis of mixed (aryloxo)(imidazolin-2-iminato)titanium dichloride complexes is presented. Full characterization of the complexes, including solid-state X-ray diffraction analysis of four complexes, is reported. Their catalytic activity in the polymerization of ethylene, propylene, 1-hexene, and 1-octene was studied. The different substituents at the aryloxo moiety were found to have a substantial impact on the reactivity of the complexes, indicating the need for a balance of steric and electronic effects. The complex (1,3-di-tert-butylimidazolin-2-iminato)(2,6-di-tert-butyl-4-methylphenoxide)titanium dichloride (1) was found to be the most active in the polymerization of ethylene, whereas the complex (1,3-di-tert-butylimidazolin-2-iminato)(2,6-di-tert-butylphenoxide)titanium dichloride (2) was found to be the most active in the polymerization of propylene. Interestingly, all complexes were more active in the polymerization of propylene than in that of ethylene.