Monocyclopentadienyl titanium imidazolin-2-iminato complexes [Cp'Ti(L)X-2] la (Cp' = cyclopentadienyl, L = 1,3-di-tert-butylirriidazolin-2-imide, X=Cl), 1b (X= CH3); 2 (Cp' = cyclopentadienyl, L = 1,3-diisopropylimidazolin-2-imide, X=Cl); 3 (Cp'= tert-butylcyclopentadienyl, L = 1,3-di-tert-butylimidazolin-2-imide, X = Cl), upon activation with methylaluminoxane (NIAO) were active for the polymerization of ethylene and propylene and the copolymerization of ethylene and 1-hexene. Catalysts derived from imidazolin-2-iminato tropidinyl titanium complex 4 = [(Trop)Ti(L)Cl-2] (Trop = tropidinyl, L 1,3-di-tert-butylimidazolin-2-imide) were much less active. Narrow polydispersities were observed for ethylene and propylene polymerization, but the copolymerization of ethylene/hexene led to bimodal molecular weight distributions. The productivity of catalysts derived from the dialkyl complex 1b activated with [Ph3C][B(C6F5)(4)] or B(C6F5)(3) were less active for ethylene/hexene copolymerization but yielded ethylene/hexene copolymers of narrower molecular weight distributions than those derived from la/MAO. (C) 2008 Wiley Periodicals, Inc.