A series of N,N,N-tridentate vanadium(III) complexes were tested after activation with methyl aluminoxane (MAO) for ethene oligomerization and polymerization. Variations in the catalyst structure as well as the influence of physical parameters were investigated and the properties of the obtained oligomeric products were determined. Methods of altering the Schulz-Flory distribution of the oligomeric products were investigated. The product properties of the polymers and oligomers obtained with the vanadium(III) complexes and the structurally identical iron(II) complexes were compared. Depending on their substitution pattern, the N,N,N-tridentate vanadium(III) catalysts exhibit high productivities and selectivities towards a-olefin oligomerization products under mild conditions when activated with MAO whereas the corresponding iron complexes produce higher molecular weight materials. The synthesis of these new vanadium(III)- and iron(II)-diiminepyridyl complexes was reported earlier. (C) 2004 Elsevier B.V. All rights reserved.