Mechanism of four-electron reduction of dioxygen to water by ferrocene derivatives in the presence of perchloric acid in benzonitrile, catalyzed by cofacial dicobalt porphyrins
Mechanism of four-electron reduction of dioxygen to water by ferrocene derivatives in the presence of perchloric acid in benzonitrile, catalyzed by cofacial dicobalt porphyrins
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DOI：
10.1021/ja048403c
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发表时间：
2004-08-25
影响因子：
15
通讯作者：
Guilard, R
中科院分区：
文献类型：
--
作者：
Fukuzumi, S;Okamoto, K;Guilard, R
在单钴卟啉[Co（OEP）]的情况下发生分子氧的选择性两电子还原，而在共面双钴卟啉[Co-2（DPX）]的情况下发生分子氧的选择性四电子还原。其他共面双钴卟啉[Co-2（DPA）、Co-2（DPB）和Co-2（DPD）]也催化分子氧的两电子还原，但四电子还原不如Co-2（DPX）的情况有效。的μ-superoxo物种的cofacial二钴卟啉的反应，产生的cofacial二钴（II）卟啉与分子氧的存在下，一个庞大的碱和随后的单电子氧化所产生的μ-peroxo物种碘。由于两个等价的钴核的超超精细结构在室温下观察到的μ-superoxo物种的ESR谱。超超精细耦合常数的μ-superoxo物种的钴-2（DPX）是最大的那些cofacial双钴卟啉。这表明Co-2（DPX）对Fe（C_5H_4Me）（2）四电子还原分子氧的有效催化作用是由于还原氧与Co-2（DPX）的强结合，而Co-2（DPX）的两个钴核之间具有用于氧结合的微小距离。二茂铁衍生物的催化二电子和四电子还原双氧的机制将讨论的基础上详细的动力学研究的整体催化反应，以及在催化循环中的每个氧化还原反应。在Co（OEP）催化的双电子还原反应中，决定转化率的步骤是从二茂铁衍生物到Co（OEP）I的电子转移，而在Co-2（DPX）催化的双氧四电子还原反应中，决定转化率的步骤是从电子转移到过氧物种Co-2（DPX）的O-O键断裂，这取决于二茂铁衍生物的给电子能力.
The selective two-electron reduction of dioxygen occurs in the case of a monocobalt porphyrin [Co(OEP)], whereas the selective four-electron reduction of dioxygen occurs in the case of a cofacial dicobalt porphyrin [Co-2(DPX)]. The other cofacial dicobalt porphyrins [Co-2(DPA), Co-2(DPB), and Co-2(DPD)] also catalyze the two-electron reduction of dioxygen, but the four-electron reduction is not as efficient as in the case of Co-2(DPX). The mu-superoxo species of cofacial dicobalt porphyrins were produced by the reactions of cofacial dicobalt(II) porphyrins with dioxygen in the presence of a bulky base and the subsequent one-electron oxidation of the resulting mu-peroxo species by iodine. The superhyperfine structure due to two equivalent cobalt nuclei was observed at room temperature in the ESR spectra of the mu-superoxo species. The superhyperfine coupling constant of the mu-superoxo species of Co-2(DPX) is the largest among those of cofacial dicobalt porphyrins. This indicates that the efficient catalysis by Co-2(DPX) for the four-electron reduction of dioxygen by Fe(C5H4Me)(2) results from the strong binding of the reduced oxygen with Co-2(DPX) which has a subtle distance between two cobalt nuclei for the oxygen binding. Mechanisms of the catalytic two-electron and four-electron reduction of dioxygen by ferrocene derivatives will be 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 turnover-determining step in the Co(OEP)-catalyzed two-electron reduction of dioxygen is an electron transfer from ferrocene derivatives to Co(OEP)I, whereas the turnover-determining step in the Co-2(DPX)-catalyzed four-electron reduction of dioxygen changes from the electron transfer to the O-O bond cleavage of the peroxo species Of Co-2(DPX), depending on the electron donor ability of ferrocene derivatives.