In this research, we describe the application of the complexes o-C6H4(NSiMe3)(2)ZrCl2 (1), o-C6H4(NSiMe3)(2)TiBr2 (2), o-C6H4(NSiMe3)(2)TiCl2 (3), C2H4(NSiMe3)(2)ZrCl2 (4), in the ethylene polymerization with different Al/M ratios and temperatures. These complexes presented significant catalytic activities in the presence of methyaluminoxane, (MAO) as cocatalyst and toluene as solvent, producing high molecular weight linear polyethylenes. Zirconium complexes were more active at 60 degrees C and titanium complexes at 40 degrees C. Zirconium complex (1) showed the best values of activity (347 kg PE/mol Zr h atm) for Al/Zr ratio of 340 and 60 degrees C of temperature. In ethylene-1-hexene copolymerization, the best result was also reached with catalyst 1, at the same conditions. (C) 2008 Wiley Periodicals, Inc.