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

Various (adamantylimido)vanadium(V) dialkyl complexes containing aryloxo ligands, V(NAd)(CH2SiMe3)2(OAr) [Ad = 1-adamantyl (1); Ar = Ph (a), 4-FC6H4 (b), 2,6-F2C6H3 (c), 2,6-Me2C6H3 (d), C6F5 (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 PMe3 at 80 °C. The activity was strongly affected by the aryloxo substituent and increased in the order: C6H5 < 4-FC6H4 < 2,6-Me2C6H3 << 2,6-F2C6H3, C6F5. The same trend was observed in the ROMPs by the arylimido–aryloxo analogues, V(NAr′)(CH2SiMe3)2(OAr) (2a–e; Ar′ = 2,6-Me2C6H3), 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-F2C6H3 (1,2c) or OC6F5 (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) (CH2SiMe3)(OAr)2 (Ar = 2,6-Me2C6H3, C6F5) and [Ph3C][B(C6F5)4], affording high molecular weight polymers with narrow molecular weight distributions (ex. Mn = 2.11 × 105, Mw/Mn = 1.18).