Addition of stoichiometric quantities of trifluoromethanesulfonic (triflic) acid to solutions of VIVO(salen) (H2-salen = N,N′-ethylenebis(salicylideneamine)) in dichloromethane produces the μ-oxo dinuclear vanadium(IV) complex [(salen)VIVOVIV(salen)]2+ ([VIVOVIV]2+). Addition of significant excesses of triflic acid converts the dimer into [VIV(salen)]2+. In dichloromethane solutions containing 0.1 M tetrabutylammonium tetrafluoroborate, the [VIVOVIV]2+ complex undergoes disproportionation and dissociation reactions to produce a solution containing an equimolar mixture of VIVO(salen), [VIII(salen)]+, and [VIVOVV]3+. The oxophilic [VIII(salen)]+ complex reacts with O2 to accomplish a four-electron reduction of O2: 2[VIII(salen)]+ + O2 → 2[VVO(salen)]+. These reactions can be exploited to carry out catalytic electroreductions of O2 to H2O in acidified dichloromethane solutions of VIVO(salen) at unusually positive potentials.
ASJC Scopus subject areas