Unique Reactivity of (Arylimido)vanadium(V)–Alkyl Complexes with Phenols: Fast Phenoxy Ligand Exchange in the Presence of Vanadium(V)–Alkyls

Abstract

Reactions of the aryloxo-modified (arylimido)vanadium(V) mono- or dialkyl complexes, V(NAr)(CH2SiMe3)2(OAr) or V(NAr)(CH2SiMe3)(OAr)2 (Ar = 2,6-Me2C6H3), with various phenols in C6D6 have been explored. The reaction of V(NAr)(CH2SiMe3)2(OAr) (1a) with ArOH in C6D6 did not take place at 25 °C even after 24 h, and the reaction affording V(NAr)(CH2SiMe3)(OAr)2 (2a) was complete after 50 h at 60 °C. In contrast, the reaction of 1a with C6F5OH took place rapidly at 25 °C, affording another monophenoxide, V(NAr)(CH2SiMe3)2(OC6F5) (1b), in addition to formation of the corresponding bis(phenoxide), V(NAr)(CH2SiMe3)(OAr)(OC6F5) (2b). The immediate ligand exchange was also observed when V(NAr)(CH2SiMe3)(OAr)2 (2a) was added to C6F5OH at 25 °C, affording 2b exclusively without reaction with the vanadium(V)–alkyl bond: further, subsequent reaction of 2b with C6F5OH or ArOH did not take place or was very slow at 25 °C. The exchange of 1a (in C6D6 at 25 °C) with various phenols (Ar′OH) proceeded in the order Ar′ = C6F5 > 4-FC6H4 > C6H5 > 2,6-F2C6H3 ≫ 2,6-Me2C6H3 (too slow or no reaction). The results clearly suggest that the reactions proceeded by coordination of phenols on the vanadium metal center.