(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 °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 °C. The activities in the ROMPs of CHPE and COE (at 25 °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.