E. Tsuchida et al., Catalysis of the electroreduction of O-2 to H2O by vanadium-salen complexes in acidified dichloromethane, INORG CHEM, 38(16), 1999, pp. 3704-3708
Addition of stoichiometric quantities of trifluoromethanesulfonic (triflic)
acid to solutions of (VO)-O-IV(salen) (H-2-salen = N,N'-ethylenebis(salicy
lideneamine)) 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 tetr
afluoroborate, the [(VOVIV)-O-IV]2+ complex undergoes disproportionation an
d dissociation reactions to produce a solution containing an equimolar mixt
ure of (VO)-O-IV(salen), [V-III(salen)](+), and [(VOVV)-O-IV](3+). The oxop
hilic [V-III(salen)](+) complex reacts with O-2 to accomplish a four-electr
on reduction of O-2: 2[V-III(salen)](+) + O-2 --> 2[(VO)-O-V(salen)](+). Th
ese reactions can be exploited to carry out catalytic electroreductions of
O-2 to H2O in acidified dichloromethane solutions of (VO)-O-IV(salen) at un
usually positive potentials.