Complexes of the type [RuCl2(PPh3)(2)(N-III)(2)], where N-III = 4-X-pyridines [X = C(O)NH2(isonicotinamide), H (pyridine), CH3 (4-picoline) or NH2 (4-amino-pyridine)] were investigated for catalysis of norbornene via ring-opening metathesis polymerization (ROMP). The results show that the yields are greater than 70% in CHCl3 when [NBE]/[Ru] = 3000 (M-n similar to 10(4) to 10(5) and M-w/M-n similar to 1.2-2.0) at 50 +/- 1 degrees C for 5 min. Considering the complex with isonicotinamide under similar conditions but for [NBE]/[Ru] = 5000, the yield reaches 94% of isolated polymer with M-w/M-n = 1.2. The behavior of the amine complexes were observed by P-31{H-1} and H-1 NMR analyses leading to the conclusion that a five-coordinated diamine-monophosphine complex is the active initiator. This 16-electron complex becomes inert when Nul is a good a-donor ligand, such as pyridine, 4-picoline or 4-amino-pyridine. Consequently, there is a decrease in catalytic activity since the subsequent step represents the exit of an amine ligand in order that the ROMP reaction can occur successfully. (c) 2005 Elsevier B.V. All rights reserved.