Imidovanadium complexes with cyclopentadienyl (Cp) ligands-(Cp)V( NC6H4Me-4)Cl-2, (1), (Cp)V( N'Bu)Cl-2 (2), and ((BuCp)-Bu-t)V( (NBu)-Bu-t)Cl-2 (3;(BuCp)-Bu-t = tert-butylcyclopentadienyl)-were synthesized through the reaction of imidovanadium trichloride with (trimethylsilyl)cyclopentadiene derivatives. The molecular structure of 3 was determined by X-ray crystallography. The monocyclopentaclienyl complex 1 exhibited moderate activity in combination with methylaluminoxane [MAO; 10.3 kg of polyethylene (mol of V)(-1) h(-1) atm(-1)], whereas similar complexes with bulky 'Bu groups, 2 and 3, were less active. (2-Methyl-8-quinolinolato)imidovanadium complexes, V( NR)(O<^>N)Cl-2, (R = (C6H3Pr2)-Pr-i-2,6 (4) or n-hexyl (5), (ON)-N-boolean AND = 2-methyl-8-quinolinolato), were obtained from the reaction of imidovanadium trichloride with 2-methyl-8-quinolinol. Upon activation with modified MAO, complex 4 showed moderate activities for the polymerization of ethylene at room temperature. The complex 5/MAO system also exhibited moderate activity at 0 degrees C. The polyethylenes obtained by these complexes had considerably high melting points, which indicated the formation of linear polyethylene. Moreover, the 5/dried MAO system showed propylene polymerization activities and produced polymers with considerably high molecular weights and narrow molecular weight distributions. (c) 2005 Wiley Periodicals, Inc.