Vanadium(V) Arylimido Alkylidene N‑Heterocyclic Carbene Alkyl and Perhalophenoxy Alkylidenes for the Cis, Syndiospecific Ring Opening Metathesis Polymerization of Norbornene
journal contribution
posted on 2021-06-28, 20:33 authored by Yuta Kawamoto, Iris Elser, Michael R. Buchmeiser, Kotohiro NomuraVanadium(V)
arylimido alkylidene <i>N</i>-heterocyclic
carbene (NHC) alkyl complexes of the type, V(N-2,6-R<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)(CHSiMe<sub>3</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)(NHC), [R = Me (<b>1a</b>–<b>c</b>), Cl
(<b>2a</b>,<b>b</b>); NHC = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene
(IXy, <b>a</b>), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene
(IDipp, <b>b</b>), 1,3-bis(cyclohexyl)imidazol-2-ylidene (ICy, <b>c</b>)], and the perhalophenoxy substituted alkylidenes, V(N-2,6-Cl<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)(CHSiMe<sub>3</sub>)(OC<sub>6</sub>X<sub>5</sub>)(IXy) [X = F (<b>3</b>), Cl (<b>4</b>)],
have been prepared. The catalytic activities in the ring opening metathesis
polymerization (ROMP) of norbornene (NBE) by <b>1a</b>–<b>c</b> and <b>2a</b>,<b>b</b> increased by addition
of C<sub>6</sub>X<sub>5</sub>OH (1.0 equiv). The perhalophenoxides <b>3</b> and <b>4</b> exhibited superior activities with turnover
frequencies (TOFs) up to 208 s<sup>–1</sup>. The resultant
polymers possessed high molecular weights (<i>M</i><sub>n</sub> up to 9.56 × 10<sup>5</sup>) with <i>cis</i>-syndiotactic stereoregularity up to 98%.
