In work, employing quantum/molecular mechanical calculations, we describe the main steps of ethene polymerization reactions catalyzed by a cationic Ni(II) complex, bearing a cyclophane alpha-diimine ligand. The combination of Density Functional Theory (DFT) and Molecular Mechanics (MM), within the ONIOM approach, was employed to evaluate the molecular structures and energies involved in ethene polymerization. All intermediate and transition state structures, obtained along these elementary step reactions, were treated as representative molecular arrangements of the polymerization process. The steric environment and the electronic influence imposed by the cyclophane ligand were evaluated for all intermediate and transition state structures, and correlated to that observed with the analogous bulky diimine ligand, bis[N-(2,6-diisopropylphenyl)imino]acenaphthene, present in the Brookhart's catalyst. (C) 2012 Elsevier B.V. All rights reserved.