Addition of stoichiometric quantities of trifluoromethanesulfonic (triflic) acid to solutions of (VO)-O-IV(salen) (H-2-salen = N,N'-ethylenebis(salicylideneamine)) in dichloromethane produces the mu-oxo dinuclear vanadium(IV) complex [(salen)(VOVIV)-O-IV(salen)](2+) ([(VOVIV)-O-IV](2+)). Addition of significant excesses of triflic acid converts the dimer into [V-IV(salen)](2+). In dichloromethane solutions containing 0.1 M tetrabutylammonium tetrafluoroborate, the [(VOVIV)-O-IV]2+ complex undergoes disproportionation and dissociation reactions to produce a solution containing an equimolar mixture of (VO)-O-IV(salen), [V-III(salen)](+), and [(VOVV)-O-IV](3+). The oxophilic [V-III(salen)](+) complex reacts with O-2 to accomplish a four-electron reduction of O-2: 2[V-III(salen)](+) + O-2 --> 2[(VO)-O-V(salen)](+). These reactions can be exploited to carry out catalytic electroreductions of O-2 to H2O in acidified dichloromethane solutions of (VO)-O-IV(salen) at unusually positive potentials.