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Proton-coupled electron-transfer reduction of dioxygen catalyzed by a saddle-distorted cobalt phthalocyanine

Title
Proton-coupled electron-transfer reduction of dioxygen catalyzed by a saddle-distorted cobalt phthalocyanine
Authors
Honda T.Kojima T.Fukuzumi S.
Ewha Authors
Shunichi Fukuzumi
SCOPUS Author ID
Shunichi Fukuzumiscopus
Issue Date
2012
Journal Title
Journal of the American Chemical Society
ISSN
0002-7863JCR Link
Citation
vol. 134, no. 9, pp. 4196 - 4206
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
Proton-coupled electron-transfer reduction of dioxygen (O 2) to afford hydrogen peroxide (H 2O 2) was investigated by using ferrocene derivatives as reductants and saddle-distorted (α- octaphenylphthalocyaninato)cobalt(II) (Co II(Ph 8Pc)) as a catalyst under acidic conditions. The selective two-electron reduction of O 2 by dimethylferrocene (Me 2Fc) and decamethylferrocene (Me 10Fc) occurs to yield H 2O 2 and the corresponding ferrocenium ions (Me 2Fc + and Me 10Fc +, respectively). Mechanisms of the catalytic reduction of O 2 are discussed on the basis of detailed kinetics studies on the overall catalytic reactions as well as on each redox reaction in the catalytic cycle. The active species to react with O 2 in the catalytic reaction is switched from Co II(Ph 8Pc) to protonated Co I(Ph 8PcH), depending on the reducing ability of ferrocene derivatives employed. The protonation of Co II(Ph 8Pc) inhibits the direct reduction of O 2; however, the proton-coupled electron transfer from Me 10Fc to Co II(Ph 8Pc) and the protonated [Co II(Ph 8PcH)] + occurs to produce Co I(Ph 8PcH) and [Co I(Ph 8PcH 2)] +, respectively, which react immediately with O 2. The rate-determining step is a proton-coupled electron-transfer reduction of O 2 by Co II(Ph 8Pc) in the Co II(Ph 8Pc)-catalyzed cycle with Me 2Fc, whereas it is changed to the electron-transfer reduction of [Co II(Ph 8PcH)] + by Me 10Fc in the Co I(Ph 8PcH)- catalyzed cycle with Me 10Fc. A single crystal of monoprotonated [Co III(Ph 8Pc)] +, [Co IIICl 2(Ph 8PcH)], produced by the proton-coupled electron-transfer reduction of O 2 by Co II(Ph 8Pc) with HCl, was obtained, and the crystal structure was determined in comparison with that of Co II(Ph 8Pc). © 2012 American Chemical Society.
DOI
10.1021/ja209978q
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자연과학대학 > 화학·나노과학전공 > Journal papers
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