Syntheses of Various (Arylimido)vanadium(V)–Dialkyl Complexes Containing Aryloxo and Alkoxo Ligands, and Ring-Opening Metathesis Polymerization Using a Vanadium(V)–Alkylidene Complex

Abstract

Treatment of V(NAr)(CH2SiMe3)3 (1, Ar = 2,6-Me2C6H3) with 1.0 equiv of various alcohols in n-hexane at 25 °C cleanly afforded the corresponding dialkyl complexes of the type V(NAr)(CH2SMe3)2(OR) [R = 2,6-Me2C6H3 (2a), 2,6-iPr2C6H3 (2b), C6F5 (2c), tBu (2d), CMe(CF3)2 (2e), yield 90−93%]. In contrast, the reactions with R′N(H)Me (R′ = Ph, cyclohexyl) or 2,6-Me2C6H3SH did not take place even if the reactions were attempted in C2D2Cl4 at 50 °C. Complexes 2a and 2b showed high catalytic activities for the ring-opening metathesis polymerization (ROMP) of norbornene in the presence of PMe3, and the activity increased at high temperature (80 °C). A vanadium(V)−alkylidene complex, V(CHSiMe3)(NAr)(O-2,6-iPr2C6H3)(PMe3)x (3, x = 0.89), has been isolated when the C6D6 solution containing 2b was heated at 80 °C in the presence of PMe3 (5.0 equiv). Complex 3 showed remarkable catalytic activity for the ROMP of norbornene, and the polymerization at 25 °C proceeded in a living manner.