Ring Opening Metathesis Polymerization (ROMP) of Norbornenes by (Arylimido)Niobium(V)–Alkylidene Catalysts, Nb(CHSiMe<sub>3</sub>)(NAr)[OC(CF<sub>3</sub>)<sub>3</sub>](PMe<sub>3</sub>)<sub>2</sub>

Effects of arylimido ligands on the ring-opening metathesis polymerization (ROMP) norbornene (NBE), norbornadiene (NBD), and tetracyclododecene (TCD) were investigated using a series (arylimido)niobium(V)–alkylidene complex catalysts, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2 [Ar = 2,6-Me2C6H3 (1), 2-MeC6H4 (2), 2,6-Cl2C6H3 (3)]. The catalytic activity in ROMP NBE for 1 was higher than 2 3 (toluene at 25 °C, initial concentration 0.44 mmol/mL), increased 50 °C. Further increase (TOF 236 s–1) observed with addition 1.0 equiv. PMe3, that analogous vanadium(V)–alkylidene. These complexes (1-3) could also catalyze NBD TCD activities NBE. dichlorophenylimido analogue (3) showed highest TCD, whereas NBD.