Reactions of (Arylimido)vanadium(V)–Trialkyl Complexes with Phenols: Effects of Arylimido Ligands and Phenols for Formation of the Vanadium Phenoxides

Reactions of a series of (arylimido)vanadium(V) trialkyl complexes, V(NAr′)(CH_2SiMe_3)_3 (Ar′ = C_6H_5, 2-MeC_6H_4, 2,6-Me_2C_6H_3, 2,6-Cl_2C_6H_3), with various phenols (ArOH, Ar = 2,6-F_2C_6H_3, 2,6-Cl_2C_6H_3, 2,6-Me_2C_6H_3, 2,6-^iPr_2C_6H_3, 2-^tBuC_6H_4, 2,6-^tBu_2C_6H_3; 1.0 equiv) affording V(NAr′)(CH_2SiMe_3)_2(OAr) were conducted in C_6D_6 at 25 °C, and the effects of both arylimido ligands and phenols on the substitution rate were explored. Sterically hindered arylimido ligands showed lower reactivity, and the reaction proceeded in the order: Ar′ = 2,6-Me_2C_6H_3 < 2,6-Cl_2C_6H_3 < 2-MeC_6H_4< C_6H_5. This order is somewhat different from that obtained from the chemical shifts in V(NAr′)(CH_2SiMe_3)_3 in the ^(51)V NMR spectra. The conversions with various disubstituted phenols increased in the order: 2,6-^iPr_2C_6H_3OH < 2,6-Me_2C_6H_3OH < 2,6-Cl_2C_6H_3OH < 2,6-F_2C_6H_3OH, irrespective of the kind of arylimido ligands. The reactions of V(NAr′)(CH_2SiMe_3)_3 with 2,6-^tBu_2C_6H_3OH (1.0 or 3.0 equiv) did not take place even upon heating at 60 °C. These results suggest that the reactions proceed via coordination of ArOH toward vanadium, and the reactivity is highly dependent on steric bulk of both the arylimido ligand and the phenol.