Arene-ruthenium complexes of type [RuCl2(p-cymene)(cyclo-alkylamine)], where alkyl is pentyl (1), hexyl (2), heptyl (3) or octyl (4), were successful synthetized and applied as pre-catalysts in ROMP of norbornene (NBE). From experiments as a function of temperature and NBE loads, the yields increased with increasing cyclo-alkyl ring size (4 > 3 > 2 > 1). This was associated with steric-electronic features of the amine ligands. The highest yields of polyNBE were obtained with [NBE]/[Ru] molar reaction ratio = 5000/1 in the presence of EDA at 50 degrees C for 60 min, with molecular weight range of 3.6-5.9 x 10(4) g mol(-1) and D of 1.6-2.3. Characterization data obtained from CHN elemental analysis, spectroscopic techniques (FTIR, UV-vis, and H-1- and C-13(H-1} NMR), cyclic voltammetry, computational studies, and single crystal diffraction for complexes 2 and 4 were useful for understanding the pre-catalyst behavior. Thermodynamic parameters from DFT-calculation corroborate a ROMP process via a dissociative mechanism.