Clarification of the oxidation state of cobalt corroles in heterogeneous
Clarification of the oxidation state of cobalt corroles in heterogeneous
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DOI：
10.1021/ic800458s
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发表时间：
2008-08-04
影响因子：
4.6
通讯作者：
Guilard, Roger
中科院分区：
文献类型：
--
作者：
Kadish, Karl M.;Shen, Jing;Guilard, Roger
在非均相和均相体系中，研究了Co（III）催化剂作为高氯酸存在下还原二氧的有效催化剂。所研究的化合物是（5,10,15-三（五氟苯基）corrole）钴（TPFCor）Co,（10-五氟苯基-5,15-基corrole）钴(F(5)PhMeS(2)Cor)Co和（5,10,15-三氟苯基corrole）钴（MeS(3)Cor）Co，它们都在corrole大环的三个介孔位置含有大块取代基。采用循环伏安法和旋转环盘电极伏安法考察了化合物在1.0 M高氯酸存在下吸附在石墨电极表面时的催化活性，并与含10(-2)M HClO4的苯腈中均相催化还原O-2的结果进行了比较。研究了其在非水介质中的氧化还原性能。一个可逆的单电子氧化发生在E-1/2值之间0.42和0.89 V与SCE取决于溶剂和化合物上的氟取代基的数量，这是随后的第二次可逆的单电子萃取在E-1/2 = 0.86至1.18 V在CH2Cl2， THF，或PhCN。在这三种溶剂中，还观察到每种氯的两次还原。观察到氧化或还原的E-1/2与化合物上吸电子氟基团的数目之间存在线性关系，并将取代基效应的大小与含有中位取代C6F5取代基的四苯基卟啉的情况进行了比较。电化学生成的络合物形式可以与Co(I), Co（II）或Co（IV）中心金属离子共存，并且在初始Co（III）络合物的每次氧化或还原中，电子转移的位置通过紫外-可见光谱电化学检查。ESR表征也用于表征单氧化(F(5)PhMeS(2)Cor)Co，其被明确分配为Co（III）自由基阳离子，而不是具有未氧化大环的预期Co（IV）阳离子。
Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the presence of perchloric acid in both heterogeneous and homogeneous systems. The investigated compounds are (5,10,15-tris(pentafluorophenyl)corrole)cobalt (TPFCor)Co, (10-pentafluorophenyl-5,15-dimesitylcorrole)cobalt (F(5)PhMeS(2)Cor)Co, and (5,10,15-trismesitylcorrole) cobalt (MeS(3)Cor)Co, all of which contain bulky substituents at the three meso positions of the corrole macrocycle. Cyclic voltammetry and rotating ring-disk electrode voltammetry were used to examine the catalytic activity of the compounds when adsorbed on the surface of a graphite electrode in the presence of 1.0 M perchloric acid, and this data is compared to results for the homogeneous catalytic reduction of O-2 in benzonitrile containing 10(-2) M HClO4. The corroles were also investigated as to their redox properties in nonaqueous media. A reversible one-electron oxidation occurs at E-1/2 values between 0.42 and 0.89 V versus SCE depending upon the solvent and number of fluorine substituents on the compounds, and this is followed by a second reversible one-electron abstraction at E-1/2 = 0.86 to 1.18 V in CH2Cl2, THF, or PhCN. Two reductions of each corrole are also observed in the three solvents. A linear relationship is observed between E-1/2 for oxidation or reduction and the number of electron-withdrawing fluorine groups on the compounds, and the magnitude of the substituent effect is compared to what is observed in the case of tetraphenylporphyrins containing meso-substituted C6F5 substituents. The electrochemically generated forms of the corrole can exist with Co(I), Co(II), or Co(IV) central metal ions, and the site of the electron-transfer in each oxidation or reduction of the initial Co(III) complex was examined by UV-vis spectroelectrochemistry. ESR characterization was also used to characterize singly oxidized (F(5)PhMeS(2)Cor)Co, which is unambiguously assigned as a Co(III) radical cation rather than the expected Co(IV) corrole with an unoxidized macrocyclic ring.