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

Effects of arylimido ligands on the ring-opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD), and tetracyclododecene (TCD) were investigated using a series of (arylimido)niobium(V) _ alkylidene complex catalysts, Nb(CHSiMe 3 )(NAr)[OC(CF 3 ) 3 ](PMe 3 ) 2 [Ar ＝ 2,6-Me 2 C 6 H 3 ( 1 ), 2-MeC 6 H 4 ( 2 ), 2,6-Cl 2 C 6 H 3 ( 3 )]. The catalytic activity in ROMP of NBE for 1 was higher than for 2 and 3 (toluene at 25 °C, initial NBE concentration 0.44 mmol/mL), and the activity increased at 50 °C. Further increase in the activity (TOF 236 s –1 ) was observed using 3 with addition of 1.0 equiv. of PMe 3 , and activity was higher than that for the analogous vanadium(V) _ alkylidene. These complexes ( 1 - 3 ) could also catalyze ROMP of NBD and TCD and the activities were higher than that for the ROMP of NBE. The dichlorophenylimido analogue ( 3 ) showed the highest activity for the ROMP of TCD, whereas 1 showed higher activity than 2 and 3 for the ROMP of NBD.