Vanadium(V) Arylimido Alkylidene N‑Heterocyclic Carbene Alkyl and Perhalophenoxy Alkylidenes for the Cis, Syndiospecific Ring Opening Metathesis Polymerization of Norbornene

Vanadium­(V) arylimido alkylidene N-heterocyclic carbene (NHC) alkyl complexes of the type, V­(N-2,6-R2C6H3)­(CHSiMe3)­(CH2SiMe3)­(NHC), [R = Me (1a–c), Cl (2a,b); NHC = 1,3-bis­(2,6-dimethylphenyl)­imidazol-2-ylidene (IXy, a), 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IDipp, b), 1,3-bis­(cyclohexyl)­imidazol-2-ylidene (ICy, c)], and the perhalophenoxy substituted alkylidenes, V­(N-2,6-Cl2C6H3)­(CHSiMe3)­(OC6X5)­(IXy) [X = F (3), Cl (4)], have been prepared. The catalytic activities in the ring opening metathesis polymerization (ROMP) of norbornene (NBE) by 1a–c and 2a,b increased by addition of C6X5OH (1.0 equiv). The perhalophenoxides 3 and 4 exhibited superior activities with turnover frequencies (TOFs) up to 208 s–1. The resultant polymers possessed high molecular weights (M n up to 9.56 × 105) with cis-syndiotactic stereoregularity up to 98%.