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Photocatalytic Oxygenation of Substrates by Dioxygen with Protonated Manganese(III) Corrolazine

Title
Photocatalytic Oxygenation of Substrates by Dioxygen with Protonated Manganese(III) Corrolazine
Authors
Jung J.Neu H.M.Leeladee P.Siegler M.A.Ohkubo K.Goldberg D.P.Fukuzumi S.
Ewha Authors
Shunichi Fukuzumi정지은Kei Okubo
SCOPUS Author ID
Shunichi Fukuzumiscopus; 정지은scopus; Kei Okuboscopus
Issue Date
2016
Journal Title
Inorganic Chemistry
ISSN
0020-1669JCR Link
Citation
vol. 55, no. 7, pp. 3218 - 3228
Publisher
American Chemical Society
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
UV-vis spectral titrations of a manganese(III) corrolazine complex [MnIII(TBP8Cz)] with HOTf in benzonitrile (PhCN) indicate mono- and diprotonation of MnIII(TBP8Cz) to give MnIII(OTf)(TBP8Cz(H)) and [MnIII(OTf)(H2O)(TBP8Cz(H)2)][OTf] with protonation constants of 9.0 × 106 and 4.7 × 103 M-1, respectively. The protonated sites of MnIII(OTf)(TBP8Cz(H)) and [MnIII(OTf)(H2O)(TBP8Cz(H)2)][OTf] were identified by X-ray crystal structures of the mono- and diprotonated complexes. In the presence of HOTf, the monoprotonated manganese(III) corrolazine complex [MnIII(OTf)(TBP8Cz(H))] acts as an efficient photocatalytic catalyst for the oxidation of hexamethylbenzene and thioanisole by O2 to the corresponding alcohol and sulfoxide with 563 and 902 TON, respectively. Femtosecond laser flash photolysis measurements of MnIII(OTf)(TBP8Cz(H)) and [MnIII(OTf)(H2O)(TBP8Cz(H)2)][OTf] in the presence of O2 revealed the formation of a tripquintet excited state, which was rapidly converted to a tripseptet excited state. The tripseptet excited state of MnIII(OTf)(TBP8Cz(H)) reacted with O2 with a diffusion-limited rate constant to produce the putative MnIV(O2 •-)(OTf)(TBP8Cz(H)), whereas the tripseptet excited state of [MnIII(OTf)(H2O)(TBP8Cz(H)2)][OTf] exhibited no reactivity toward O2. In the presence of HOTf, MnV(O)(TBP8Cz) can oxidize not only HMB but also mesitylene to the corresponding alcohols, accompanied by regeneration of MnIII(OTf)(TBP8Cz(H)). This thermal reaction was examined for a kinetic isotope effect, and essentially no KIE (1.1) was observed for the oxidation of mesitylene-d12, suggesting a proton-coupled electron transfer (PCET) mechanism is operative in this case. Thus, the monoprotonated manganese(III) corrolazine complex, MnIII(OTf)(TBP8Cz(H)), acts as an efficient photocatalyst for the oxidation of HMB by O2 to the alcohol. © 2016 American Chemical Society.
DOI
10.1021/acs.inorgchem.5b02019
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자연과학대학 > 화학·나노과학전공 > Journal papers
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