Efficient ring-opening metathesis polymerization of norbornene by vanadium-alkylidenes generated in situ from V(NAr)Cl 2(L) (L: ketimide, aryloxo)

Abstract

Ring-opening metathesis polymerization (ROMP) of norbornene (NBE) using a catalyst system consisting of V(N-2,6-Me 2C 6H 3)Cl 2(N = C t Bu 2) ( 1a), MeMgBr, and PMe 3 proceeded at a remarkable rate, and the catalytic activities (TON values, TON = turnover number) were low when MeLi or AlMe 3 was used in place of MeMgBr. The activities increased upon increasing the polymerization temperature, and were dependent upon the molar ratio(s) of the catalyst component(s) employed. The resultant polymers prepared at 25 °C under the optimized conditions possessed high molecular weights with unimodal molecular weight distributions ( M n = 1.31–1.66 × 10 6, M w/ M n = 1.40–1.59), and contained a mixture of cis/ trans olefinic double bonds. The effects of anionic donor ligands (L) and substituents on the arylimido ligands on the activity in the ROMP using V(NAr)Cl 2(L) [Ar = 2,6-Me 2C 6H 3 ( 1), 2,6- i Pr 2C 6H 3 ( 2); L = N = C t Bu 2 ( a), N = C(CH 2SiMe 3) t Bu ( b), O-2,6-Me 2C 6H 3 ( c), O-2,6- i Pr 2C 6H 3 ( d), O-2,6- t Bu 2-4-MeC 6H 2 ( e)]-MeMgBr-PMe 3 were explored; both 1a and 1c showed the remarkable activities, and the observed trends were similar to those observed in ethylene polymerization using V(NAr)Cl 2(L)-MAO catalyst systems.