ELECTROCHEMICAL REACTIVITY OF MANGANESE(II) PORPHYRINS - EFFECTS OF DIOXYGEN, BENZOIC ANHYDRIDE, AND AXIAL LIGANDS
ELECTROCHEMICAL REACTIVITY OF MANGANESE(II) PORPHYRINS - EFFECTS OF DIOXYGEN, BENZOIC ANHYDRIDE, AND AXIAL LIGANDS
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DOI：
10.1021/ic00263a013
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发表时间：
1987-08-12
影响因子：
4.6
通讯作者：
MURRAY, RW
中科院分区：
文献类型：
--
作者：
CREAGER, SE;MURRAY, RW
电化学还原锰（III）卟啉在含氧，非质子介质中的电流对应于通过之间的一个和两个电子每个卟啉，这取决于实验的时间尺度，轴向基地存在，和特定的卟啉。双电子过程对应于涉及中间体Mn（II）-双氧加合物的形成和随后的还原的“ECE”反应序列。第二个电子台阶的形式电势为ca-1.5。0.17对于Mn（TPP）苯甲酸盐，V相对于NaSCE。第二个电子的通道是suppressedby强大的轴向基地和竞争性轴向结合，但促进使用的轴向阴离子，使最负的电位通过的第一个电子，锰（TPP）苯甲酸是一个具体的例子。估计中间化学步骤的总速率常数。在添加的亲电体苯甲酸酐的存在下，并且在较慢的时间尺度上，通过两个以上电子的还原通过假定涉及亲电体对0-0键的异裂解的过程发生，产生甚至更容易还原的高价锰-氧代卟啉。亲电试剂的进攻速率比分子氧的进攻速率慢。
Currents for electrochemical reductions of manganese (III) porphyrins in oxygenated, aprotic media correspond to passage of between one and two electrons per porphyrin, depending on the experimental time scale, the axial base present, andthe particular porphyrin. The two-electron process corresponds to an “ECE” reaction sequence involving formation and subsequent reduction of an intermediate Mn (II)-dioxygen adduct. The formal potential of the second electron step is shown to be ca.-0.17 V vs. NaSCE for Mn (TPP) benzoate. Passage of the second electron is suppressedby strong axial bases andby competitive axial binding but is promoted by use of an axial anion that gives the most negative potential for passage of the first electron, Mn (TPP) benzoate being a specific example. The overall rate constant for the intermediate chemical step is estimated. In the presence of the added electrophile benzoic anhydride, and on a slower time scale, reduction by more than two electrons occurs by a process postulated to involve heterolysis of the 0-0 bond by the electrophile, producing an even more easily reduced, high-valent manganese-oxo porphyrin. The rate of electrophile attack is slower thanthat for dioxygen binding.