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.