Three new titanium complexes bearing salicylidenimine ligands-bis[(salicylidene)-2,3,5,6-tetrafluoroanilinato] titanium (IV) dichloride (1), bis[(3,5-di-tertbutylsalicylidene)-2,3,5,6-tetrafluoroanilinato]titanium (IV) dichloride (2), and bis[(3,5-di-tert-butylsalicylidene)-4-trifluoromethyl-2,3,5,6-tetrafluor oanilinato]titanium(IV) dichloride (3)-were synthesized. The catalytic activities of 1-3 for ethylene polymerization were studied with poly(methylaluminoxane) (MAO) as a cocatalyst. Complex 1 was inactive in ethylene polymerization. Complex 2 at a molar ratio of cocatalyst to pre catalyst of Al-MAO/Ti = 400-1600 showed very high activity in ethylene polymerization comparable to that of the most efficient metallocene complexes and titanium compounds with phenoxy imine and indolide imine chelating ligands. It gave linear high-molecular-weight polyethylene [weight-average molecular weight (M-w) greater than or equal to 1,700,000. weight-average molecular weight/number-average molecular weight (M-w/M-n) = 4-5] with a melting point of 142degreesC. The ability of the 2/MAO system to copolymerize ethylene with hexene-1 in toluene was analyzed. No measurable incorporation of the comonomer was observed at 1:1 and 2:1 hexene-1/ethylene molar ratios. However, the addition of hexene-1 had a considerable stabilizing effect on the ethylene consumption rate and lowered the melting point of the resultant polymer to 132degreesC. The 2/MAO system exhibited low activity for propylene polymerization in a medium of the liquid monomer. The polymer that formed was high-molecular-weight atactic polypropylene (M-w similar to 870,000, M-w/M-n = 9-10) showing elastomeric behavior. The activity of 3/MAO in ethylene polymerization was approximately 70 times lower than that of the 2/MAO system. (C) 2005 Wiley Periodicals, Inc.