Mechanistic insights into hydride-transfer and electron-transfer reactions by a manganese(IV)-oxo porphyrin complex

Shunichi Fukuzumi, Naofumi Fujioka, Hiroaki Kotani, Kei Ohkubo, Yong Min Lee, Wonwoo Nam

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Abstract

Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogs to a manganese(IV)-oxo porphyrin complex, (TMP)MnIV(O) [TMP = 5,10,15,20-tetrakis(2,4,6-trimethylphenyl) porphyrin], occurs via disproportionation of (TMP)MnIV(O) to [(TMP)MnIII] + and [(TMP)MnV(O)]+ that acts as the actual hydride acceptor. In contrast, electron transfer from ferrocene derivatives to (TMP)MnIV(O) occurs directly to afford ferricenium ions and (TMP)MnIII(OH) products. The disproportionation rate constant of (TMP)MnIV(O) was determined by the dependence of the observed second-order rate constants on concentrations of NADH analogs to be (8.0 ± 0.6) × 106 M-1 s-1 in acetonitrile at 298 K. The disproportionation rate constant of (TMP)Mn IV(O) in hydride-transfer reactions increases linearly with increasing acid concentration, whereas the rate constant of electron transfer from ferrocene to (TMP)MnIV(O) remains constant irrespective of the acid concentration. The rate constants of electron transfer from a series of ferrocene derivatives to (TMP)MnIV(O) were evaluated in light of the Marcus theory of electron transfer to determine the reorganization energy of electron transfer by the (TMP)MnIV(O) complex.

Original languageEnglish
Pages (from-to)17127-17134
Number of pages8
JournalJournal of the American Chemical Society
Volume131
Issue number47
DOIs
StatePublished - 2 Dec 2009

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