Hydrogen atom transfer reactions of imido manganese(V) corrole: One reaction with two mechanistic pathways
Hydrogen atom transfer reactions of imido manganese(V) corrole: One reaction with two mechanistic pathways
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DOI：
10.1021/ja073027s
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发表时间：
2007-09-19
影响因子：
15
通讯作者：
Abu-Omar, Mahdi M.
中科院分区：
文献类型：
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作者：
Zdilla, Michael J.;Dexheimer, Jennifer L.;Abu-Omar, Mahdi M.
研究了(Tpfc)MnNTs(tpfc=5，10，15-三五氟苯基)和ts=对甲苯磺酸的氢原子转移(HAT)反应。在22℃时，9，10-二氢菲和1，4-二氢苯通过HAT还原MnNTs的二级速率常数分别为0.16+/-0.03和0.17+/-0.01M-1 S(-1)，产物分别为芳烃TsNH_2和(Tpfc)Mn-III。(Tpfc)MnNTs与二氢菲反应生成(Tpfc)Mn的反应表现出等色散行为，没有观察到9，9‘，10，10’-四氢联菲的生成，这表明中间体菲自由基在第二个快速步骤中反弹，没有积累Mn-IV中间体。亚胺络合物(Tpfc)-(MnNTs)-N-V也从苯酚中提取氢原子。例如，2，6-二叔丁基苯酚在22℃时被氧化成相应的苯氧基，二级速率常数为0.32+/-0.02M-1 S(-1)。亚胺锰(V)的其他产物是TsNH_2和三价锰钴酸。与二氢芳烃反应不同的是，当使用苯酚时，没有观察到等色散行为，EPR光谱证实了(Tpfc)-Mn-IV(NHTS)的形成。各种p-取代的2，6-二叔丁基苯酚的Hammett图显示出对a的V型依赖关系，给电子取代基表现出预期的负p，而吸电子取代基则落在线性拟合线以上(即正p)。类似地，键离解焓(BDE)关联将吸电子取代基置于给电子取代基的明确负斜率之上。由此建立了HAT反应的两种机制，即协同质子-电子转移和质子门控电子转移，其中质子转移之后是电子转移。
Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,15-tris(pentafluorophenyi)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 +/- 0.03 and 0.17 +/- 0.01 M-1 s(-1), respectively, at 22 degrees C. The products are the respective arenes, TsNH2 and (tpfc)Mn-III. Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9', 10,10'-tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a Mn-IV intermediate. The imido complex (tpfc)-(MnNTs)-N-V abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 +/- 0.02 M-1 s(-1) at 22 degrees C. The other products from imido manganese(V) are TsNH2 and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)-Mn-IV(NHTs) is confirmed by EPR spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on a, with electron-donating substituents exhibiting the expected negative p while electron-withdrawing substituents fall above the linear fit (i.e., positive p). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton-electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer.