(Arylimido)Vanadium(V)-Alkylidenes Containing Chlorinated Phenoxy Ligands: Thermally Robust, Highly Active Catalyst in Ring-Opening Metathesis Polymerization of Cyclic Olefins

A series of (imido)vanadium(V)-alkylidene complexes containing pentachlorophenoxy ligand of type, V(CHSiMe3)-(N-2,6-R2C6H3)(OC6Cl5)(PMe3)(2) [R = H, Cl, F, CH3], have been prepared, and the structure of V(CHSiMe3)(N-2,6-Me2C6H3)-(OC6Cl5)(PMe3)(2) was determined by X-ray crystallographic analysis. Ring-opening metathesis polymerization (ROMP) of cyclic olefins such as norbornene (NBE), cyclopentene (CPE), cycloheptene (CHPE), and cis-cyclooctene (COE) using these alkylidene catalysts have been explored, and V(CHSiMe3)(N-2,6- Cl2C6H3)(OC6Cl5)(PMe3)(2) showed higher activities in the ROMP of CPE, CHPE, and COE than those of the reported V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6F5)(PMe3)(2). The activity in the ROMP of COE increased at high temperature until 120 degrees C, and the ROMPs of CHPE and COE proceeded without chain-transfer or termination (nor catalyst decomposition); the (quasi) living nature thus maintained even at 80 degrees C. The activities in the ROMPs of CHPE and COE (at 25 degrees C) increased upon addition of 1.0 equiv of B(C6F5)(3), whereas the activity in the ROMP of NBE became negligible upon the addition. The order in the activity in the ROMP of cyclic olefins displayed as COE CHPE < CPE NBE, which is different from not only that in the ring strain energy but also that reported in the ROMPs using ruthenium-carbene catalysts.