High-valent chromium-oxo complex acting as an efficient catalyst precursor for selective two-electron reduction of dioxygen by a ferrocene derivative.

Efficient catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) produced hydrogen peroxide (H2O2) using a high-valent chromium(V)–oxo corrole complex, [(tpfc)CrV(O)] (tpfc = tris(pentafluorophenyl)corrole) as a catalyst precursor in the presence of trifluoroacetic acid (TFA) in acetonitrile (MeCN). The facile two-electron reduction of [(tpfc)CrV(O)] by 2 equiv of Me8Fc in the presence of excess TFA produced the corresponding chromium(III) corrole [(tpfc)CrIII(OH2)] via fast electron transfer from Me8Fc to [(tpfc)CrV(O)] followed by double protonation of [(tpfc)CrIV(O)]− and facile second-electron transfer from Me8Fc. The rate-determining step in the catalytic two-electron reduction of O2 by Me8Fc in the presence of excess TFA is inner-sphere electron transfer from [(tpfc)CrIII(OH2)] to O2 to produce the chromium(IV) superoxo species [(tpfc)CrIV(O2•–)], followed by fast proton-coupled electron transfer reduction of [(tpfc)CrIV(O2•–)] by Me8Fc to yield H2O2, accompanied by regener...