Vanadium(V) Arylimido Alkylidene N‑Heterocyclic
Carbene Alkyl and Perhalophenoxy Alkylidenes for the Cis, Syndiospecific
Ring Opening Metathesis Polymerization of Norbornene
posted on 2021-06-28, 20:33authored byYuta Kawamoto, Iris Elser, Michael R. Buchmeiser, Kotohiro Nomura
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 (Mn up to 9.56 × 105) with cis-syndiotactic stereoregularity up to 98%.