Hydrogen-Atom Abstraction Reactions by Manganese(V)- and Manganese (IV)-Oxo Porphyrin Complexes in Aqueous Solution
Hydrogen-Atom Abstraction Reactions by Manganese(V)- and Manganese (IV)-Oxo Porphyrin Complexes in Aqueous Solution
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DOI：
10.1002/chem.200901362
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Nam, Wonwoo
中科院分区：
文献类型：
--
作者：
Arunkumar, Chellaiah;Lee, Yong-Min;Nam, Wonwoo
高价锰（IV或V）-氧代卟啉被认为是锰卟啉催化剂氧化有机底物的反应中间体。我们在碱性水溶液中合成了Mn-V-和Mn-IV-氧代卟啉，并研究了它们在烃类C-H键活化中的反应活性。我们现在报道，Mn-V-和Mn-IV-氧代卟啉能够活化烷基芳族化合物的C-H键，其反应性顺序为Mn-V-氧代>Mn-IV-氧代; Mn-V-氧代络合物的反应性比Mn-IV-氧代络合物在氧杂蒽氧化中的反应性大150倍。基于氧杂蒽和二氢蒽氧化反应中反应速率与底物C-H键离解能（BDE）之间良好的线性相关性和高动力学同位素效应（KIE）值，提出了Mn-V-和Mn-IV-氧代卟啉活化烷基芳烃C-H键是通过夺取氢原子进行的。我们已经证明了在碱性水溶液中Mn-IV-oxo卟啉还原成Mn-V-oxo和Mn-III卟啉是不可行的途径，并且Mn-IV-oxo卟啉能够从烷基芳族化合物中夺取氢原子。通过Mn-V-和Mn-IV-氧代物种的烷基芳族化合物的C-H键活化通过单电子过程进行，其中Mn-IV-氧代卟啉形成其在Mn-IV-氧代卟啉的C-H键活化中的产物，随后Mn-IV-氧代卟啉与底物进一步反应，导致Mn-III卟啉络合物的形成。这一结果与Mn-V-氧代卟啉对硫化物的氧化形成鲜明对比。其中通过Mn-V-氧代络合物氧化苯硫醚产生起始Mn-III卟啉和苯硫醚氧化物。这一结果表明，硫化物的氧化由Mn-V-氧物种发生通过一个双电子氧化过程。相反，Mn-IV-氧代卟啉络合物由于在碱性水溶液中的低氧化能力而不能氧化硫化物。
High-valent manganese(IV or V)-oxo porphyrins are considered as reactive intermediates in the oxidation of organic substrates by manganese porphyrin catalysts. We have generated Mn-V- and Mn-IV-oxo porphyrins in basic aqueous solution and investigated their reactivities in C-H bond activation of hydrocarbons. We now report that Mn-V- and Mn-IV-oxo porphyrins are capable of activating C-H bonds of alkylaromatics, with the reactivity order of Mn-V-oxo>Mn-IV-oxo; the reactivity of a Mn-V-oxo complex is 150 times greater than that of a Mn-IV-oxo complex in the oxidation of xanthene. The C-H bond activation of alkylaromatics by the Mn-V- and Mn-IV-oxo porphyrins is proposed to occur through a hydrogen-atom abstraction, based on the observations of a good linear correlation between the reaction rates and the C-H bond dissociation energy (BDE) Of Substrates and high kinetic isotope effect (KIE) values in the oxidation of xanthene and dihydroanthracene (DHA). We have demonstrated that the disproportionation of Mn-IV-oxo porphyrins to Mn-V-oxo and Mn-III porphyrins is not a feasible pathway in basic aqueous solution and that Mn-IV-oxo porphyrins are able to abstract hydrogen atoms from alkylaromatics. The C-H bond activation of alkylaromatics by Mn-V- and Mn-IV-oxo species proceeds through a one-electron process, in which a Mn-IV-oxo porphyrin is formed its a product in the C-H bond activation by a Mn-IV-oxo porphyrin, followed by a further reaction of the Mn-IV-oxo porphyrin with Substrates that results in the formation of a Mn-III porphyrin complex. This result is ill contrast to the oxidation of sulfides by the Mn-V-oxo porphyrin. in which the oxidation of thioanisole by the Mn-V-oxo complex produces the starting Mn-III porphyrin and thioanisole oxide. This result indicates that the oxidation of sulfides by the Mn-V-oxo species occurs by means of a two-electron oxidation process. In contrast, a Mn-IV-oxo porphyrin complex is not capable of oxidizing sulfides due to a low oxidizing power in basic aqueous solution.