Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been explored in ethylene (co)polymerization using a series of Cp*MCl2(O-2,6-R2C6H3) [M = Ti (1), Zr (2), Hf (3); R Ph (a), Bu-t (b), Pr-i (C)] in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 2a, 3a,b were prepared and identified, and the Structures for 2-3a,b were determined by X-ray crystallography as a distorted tetrahedral geometry around the metal center. The catalytic activity in ethylene polymerization was affected by the centered metal employed [Ti > Zr > Hf]; the complexes containing 2,6-diphenylphenoxy ligand (1-3a) showed higher catalytic activities than the complexes containing 2,6-di-tert-butylphenoxy analogues (1-3b). The molecular weights in the resultant polymers prepared by the Zr and the Hf analogues were lower than those prepared by the Ti-Ph (1a) and the Ti-Pr-i (1c) analogues. Although the copolymerizations of ethylene with 1-octene afforded the copolymers With uniform molecular weight distributions (except 1b), both the catalytic activities and the 1-octene incorporation were highly affected by the centered metal employed: the Ti-Pr-i analogue(1c) seems to be the most suited in terms of both the catalytic activity and the 1-octene incorporation. The attempted copolymerization of ethylene with 2-methyl-1-pentene using 2a,b and 3a-MAO catalysts afforded linear polyethylene. (C) 2009 Elsevier B.V. All rights reserved.