Development of easily accessible ruthenium-based catalysts for metathesis polymerization using 4-X-pyridines as ancillary ligands

Complexes of the type [RuCl2(PPh3)2(NIII)2], where NIII = 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 (Mn ∼ 104 to 105 and Mw/Mn ∼ 1.2-2.0) at 50 ± 1 °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 Mw/Mn = 1.2. The behavior of the amine complexes were observed by 31P{1H} and 1H NMR analyses leading to the conclusion that a five-coordinated diamine-monophosphine complex is the active initiator. This 16-electron complex becomes inert when NIII is a good σ-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.