Ring-opening polymerizations of THF using V(NR)(CH2SiMe3)(OAr)2 [R = 2,6-Me2C6H3, 1-adamantyl (Ad), Ph; Ar = 2,6-Me2C6H3, C6F5] proceeded in a living manner in the presence of [Ph3C][B(C6F5)4], affording high molecular weight polymers with low PDI (M w/M n) values: the observed activity (initiation efficiency) was affected by the arylimido and aryloxo ligands employed. A new vanadium(V)-alkylidene, V(CHSiMe3)(NAd)(OC6F5)(PMe3)2, prepared from V(NAd)(CH2SiMe3)2(OC6F5) by α-hydrogen elimination in n-hexane in the presence of PMe3 at 25 °C, exhibited remarkable catalytic activity for ring-opening metathesis polymerization of norbornene: the activity at 25 °C was higher than those by the reported vanadium(V)-alkylidenes and ordinary Mo(CHCMe2Ph)(N-2,6- i Pr2-C6H3)(O t Bu)2.

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at 25 °C) for additional explanation. These materials are available free of charge via the Internet at http://pubs.acs.org.

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