Synthesis of (adamantylimido)vanadium(V)-alkyl complexes containing aryloxo ligands and their use as the catalyst precursors for ring-opening metathesis polymerization of norbornene, and ring-opening polymerization of tetrahydrofuran

Abstract

Various (adamantylimido)vanadium(V) dialkyl complexes containing aryloxo ligands, V(NAd)(CH 2SiMe 3) 2(OAr) [Ad = 1-adamantyl ( 1); Ar = Ph ( a), 4-FC 6H 4 ( b), 2,6-F 2C 6H 3 ( c), 2,6-Me 2C 6H 3 ( d), C 6F 5 ( e)], have been prepared and identified. These complexes were employed as the catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of PMe 3 at 80 °C. The activity was strongly affected by the aryloxo substituent and increased in the order: C 6H 5 < 4-FC 6H 4 < 2,6-Me 2C 6H 3 << 2,6-F 2C 6H 3, C 6F 5. The same trend was observed in the ROMPs by the arylimido–aryloxo analogues, V(NAr′)(CH 2SiMe 3) 2(OAr) ( 2a– e; Ar′ = 2,6-Me 2C 6H 3), under the same conditions, and the activities by the arylimido analogues were generally higher than the adamantylimido analogues in most case. The (imido)vanadium(V) complexes containing O-2,6-F 2C 6H 3 ( 1, 2c) or OC 6F 5 ( 1, 2e) exhibited high catalytic activities, and these results strongly suggest that electronic as well as steric factors play a role. Living ring-opening polymerization of THF proceeded in the presence of V(NAd) (CH 2SiMe 3)(OAr) 2 (Ar = 2,6-Me 2C 6H 3, C 6F 5) and [Ph 3C][B(C 6F 5) 4], affording high molecular weight polymers with narrow molecular weight distributions (ex. M n = 2.11 × 10 5, M w / M n = 1.18).