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 ₂ SiMe ₃ ) ₃ (Ar' = C ₆ H ₅ , 2-MeC ₆ H ₄ , 2,6-Me ₂ C ₆ H ₃ , 2,6-Cl ₂ C ₆ H ₃ ), with various phenols (ArOH, Ar = 2,6-F ₂ C ₆ H ₃ , 2,6-Cl ₂ C ₆ H ₃ , 2,6-Me ₂ C ₆ H ₃ , 2,6- ⁱ Pr ₂ C ₆ H ₃ , 2- ^t BuC ₆ H ₄ , 2,6- ^t Bu ₂ C ₆ H ₃ ; 1.0 equiv) affording V(NAr')(CH ₂ SiMe ₃ ) ₂ (OAr) were conducted in C ₆ D 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 ₂ C ₆ H ₃ < 2,6-Cl ₂ C ₆ H ₃ < 2-MeC ₆ H ₄ < C ₆ H ₅ . This order is somewhat different from that obtained from the chemical shifts in V(NAr')(CH ₂ SiMe ₃ ) ₃ in the ⁵¹ V NMR spectra. The conversions with various disubstituted phenols increased in the order: 2,6- ⁱ Pr ₂ C ₆ H ₃ OH < 2,6-Me ₂ C ₆ H ₃ OH < 2,6-Cl ₂ C ₆ H ₃ OH < 2,6-F ₂ C ₆ H ₃ OH, irrespective of the kind of arylimido ligands. The reactions of V(NAr')(CH ₂ SiMe ₃ ) ₃ with 2,6- ^t Bu ₂ C ₆ H ₃ OH (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.
Competing Interests: The authors declare no competing financial interest.