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′)­(CH2SiMe3)3 (Ar′
= C6H5, 2-MeC6H4, 2,6-Me2C6H3, 2,6-Cl2C6H3), with various phenols (ArOH, Ar = 2,6-F2C6H3, 2,6-Cl2C6H3, 2,6-Me2C6H3, 2,6-iPr2C6H3, 2-tBuC6H4, 2,6-tBu2C6H3; 1.0 equiv)
affording V­(NAr′)­(CH2SiMe3)2(OAr) were conducted in C6D6 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-Me2C6H3 < 2,6-Cl2C6H3 < 2-MeC6H4 <
C6H5. This order is somewhat different from
that obtained from the chemical shifts in V­(NAr′)­(CH2SiMe3)3 in the 51V NMR spectra.
The conversions with various disubstituted phenols increased in the
order: 2,6-iPr2C6H3OH < 2,6-Me2C6H3OH < 2,6-Cl2C6H3OH < 2,6-F2C6H3OH, irrespective of the kind of
arylimido ligands. The reactions of V­(NAr′)­(CH2SiMe3)3 with 2,6-tBu2C6H3OH (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.