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

Shuo Liu, Kentaro Mase, Curt Bougher, Scott D. Hicks, Mahdi M. Abu-Omar, Shunichi Fukuzumi

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

Efficient catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) produced hydrogen peroxide (H 2O2) 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)Cr III(OH2)] to O2 to produce the chromium(IV) superoxo species [(tpfc)CrIV(O2•-)], followed by fast proton-coupled electron transfer reduction of [(tpfc)Cr IV(O2•-)] by Me8Fc to yield H2O2, accompanied by regeneration of [(tpfc)Cr III(OH2)]. Thus, although the catalytic two-electron reduction of O2 by Me8Fc was started by [(tpfc)Cr V(O)], no regeneration of [(tpfc)CrV(O)] was observed in the presence of excess TFA, regardless of the tetragonal chromium complex being to the left of the oxo wall. In the presence of a stoichiometric amount of TFA, however, disproportionation of [(tfpc)CrIV(O)]- occurred via the protonated species [(tpfc)CrIV(OH)] to produce [(tpfc)Cr III(OH2)] and [(tpfc)CrV(O)].

Original languageEnglish
Pages (from-to)7780-7788
Number of pages9
JournalInorganic Chemistry
Volume53
Issue number14
DOIs
StatePublished - 21 Jul 2014

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