A family of titanium complexes of the general formula [N-(3,5-di-tertbutylsalicylidene)-2-alkylsulfanylanilinato]Ti(IV)Cl-3 5a-f was prepared from the reaction of TiCl4 with the potassium salts of the corresponding ligands. These complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 5b and 5e were further confirmed by single-crystal X-ray analyses. Complexes 5a-f (except for 5c) exhibited good to high catalytic activities in ethylene copolymerization with cycloolefins such as norbornene, cyclopentene, dicyclopentadiene in the presence of modified methylaluminoxane. The reaction conditions and the steric hindrance of the alkyl substituents on sulfur atom in the precatalysts influenced strongly the copolymerization behaviors and the structures of the resultant copolymers. Complex 5c with bulky tert-butylthio sidearm showed both low catalytic activity and comonomer incorporation ratio. The n-alkylthio complexes 5a, 5d-f all exhibited good ethylene copolymerization capabilities with cycloolefins, which is superior to the corresponding phenylthio complex 5g. (c) 2008 Wiley Periodicals, Inc.