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

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• 作者：Jieun Jung ; Heather M. Neu ; Pannee Leeladee ; Maxime A. Siegler ; Kei Ohkubo ; David P. Goldberg ; Shunichi Fukuzumi
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：April 4, 2016
• 年：2016
• 卷：55
• 期：7
• 页码：3218-3228
• 全文大小：727K
• ISSN：1520-510X

文摘

UV–vis spectral titrations of a manganese(III) corrolazine complex [Mnp>IIIp>(TBP₈Cz)] with HOTf in benzonitrile (PhCN) indicate mono- and diprotonation of Mnp>IIIp>(TBP₈Cz) to give Mnp>IIIp>(OTf)(TBP₈Cz(H)) and [Mnp>IIIp>(OTf)(H₂O)(TBP₈Cz(H)₂)][OTf] with protonation constants of 9.0 × 10p>6p> and 4.7 × 10p>3p> Mp>–1p>, respectively. The protonated sites of Mnp>IIIp>(OTf)(TBP₈Cz(H)) and [Mnp>IIIp>(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 [Mnp>IIIp>(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 Mnp>IIIp>(OTf)(TBP₈Cz(H)) and [Mnp>IIIp>(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 Mnp>IIIp>(OTf)(TBP₈Cz(H)) reacted with O₂ with a diffusion-limited rate constant to produce the putative Mnp>IVp>(O₂p>•–p>)(OTf)(TBP₈Cz(H)), whereas the tripseptet excited state of [Mnp>IIIp>(OTf)(H₂O)(TBP₈Cz(H)₂)][OTf] exhibited no reactivity toward O₂. In the presence of HOTf, Mnp>Vp>(O)(TBP₈Cz) can oxidize not only HMB but also mesitylene to the corresponding alcohols, accompanied by regeneration of Mnp>IIIp>(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, Mnp>IIIp>(OTf)(TBP₈Cz(H)), acts as an efficient photocatalyst for the oxidation of HMB by O₂ to the alcohol.