A Porphyrin-Doped Polymer Catalyzes Selective, Light-Assisted Water Oxidation in Seawater
A Porphyrin-Doped Polymer Catalyzes Selective, Light-Assisted Water Oxidation in Seawater
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DOI：
10.1002/anie.201107355
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Swiegers, Gerhard F.
中科院分区：
文献类型：
--
作者：
Chen, Jun;Wagner, Pawel;Swiegers, Gerhard F.
在一个经典的实验中，Naruta和同事在1994年证明了二锰配合物1（方案1）在高于1.2 V的电位下促进水氧化催化生成二氧（O2）而相应的未连接的mn -卟啉单体则不具有催化活性随后的研究表明，OÀO键形成导致1生成O2涉及两个短寿命，高价的MnV= O中间体在每个卟啉上的协同相互作用，可能是在二聚体的构象弯曲期间这些中间体的短暂性和短暂的寿命可能使游离单体失去活性。像图1所示的催化作用，包括两个或多个催化基团之间同步的、合作的相互作用，具有重要的基础和实际意义例如，酶被认为采用同步蛋白质运动来协同利用活性中间体，这些中间体通常太短而不能用于其他类型的催化剂。[3-5]这也许可以解释为什么它们可以催化一些在生物学之外无法催化的反应。由此产生的问题是：如何设计简单实用的非生物分子催化剂来同步利用寿命非常短的反应中间体？在之前的报告[6]中，我们描述了一种解决这个问题的方法，该方法涉及在有限的体积内急剧集中相应的单体催化基团。可以想象，这可能会导致一些小但统计上显著比例的单体被偶然地理想地放置，以促进协同催化。如果单体结合的反应中间体寿命太短，不能以任何其他方式隔离和利用，则只能得到协同催化的产物在这里，我们报告了这种“统计接近”方法[6]在mn -卟啉催化的水氧化中的应用。我们发现，通常不具有催化活性的磺化单体mn -卟啉2（方案1），在聚噻吩（PTTh）的薄层中，浓度为[7]，产生了一种显著的光辅助催化剂，在pH7下具有低过电位的水氧化。该催化剂在海水中选择性氧化水，先于氯。mn -卟啉单体2在含有2的乙醇/二氯甲烷（体积比1:1）中进行电化学聚合时，作为阴离子反离子被均匀地掺入一层薄薄的PTTh薄膜中（见支持信息）。将pth -2作为复合薄膜沉积在氧化铟锡（ITO）玻璃或柔性ITO涂层的聚对苯二甲酸乙酯（PET）薄片上。图S1（辅助信息）显示了将PTTh-2涂覆在ITO-PET上得到的柔性电极。紫外/可见测量证实了2在涂层中的掺入。能量色散x射线图显示，2均匀分散在涂层中（图3）。元素分析表明，pth -2内部密度为2,2 （Mn+ S）与噻吩(S)的摩尔比约为1:3。
In a classic experiment, Naruta and co-workers demonstrated in 1994 that the dimanganese complexes 1 (Scheme 1) facilitate water oxidation catalysis yielding dioxygen (O2) at potentials above 1.2 V vs. Ag/AgCl.[1] The corresponding, unconnected Mn-porphyrin monomers were, however, catalytically inactive.[1] Subsequent work suggested that OÀO bond formation leading to O2 generation by 1 involved a concerted interaction between two short-lived, high-valent MnV= O intermediates at each of the porphyrins, presumably during conformational flexing of the dimer.[2] The transience and brief lifetime of these intermediates likely rendered the free monomers inactive. Catalytic actions like those of 1, which encompass a synchronized, cooperative interplay between two or more catalytic groups, are of significant fundamental and practical interest.[3] For example, enzymes are believed to employ synchronous protein motions to cooperatively harness reactive intermediates that are often too short-lived to be utilized in other classes of catalyst.[3–5] This may explain how they can catalyze some reactions that cannot be catalyzed outside of biology. The question that arises is: how can one design simple, practical abiological molecular catalysts to synchronously harness very short-lived reactive intermediates? In a previous report [6] we described an approach to this problem that involved drastically concentrating the corresponding monomeric catalytic groups within a limited volume. This may conceivably cause some small but statistically significant proportion of the monomers to be adventitiously ideally placed to facilitate cooperative catalysis. If the monomer-bound reactive intermediates are too short-lived to be sequestered and exploited in any other way, then only the product deriving from cooperative catalysis should be obtained.[6] Here we report the application of this “statistical proximity” approach [6] to water oxidation catalyzed by Mn-porphyrins. We show that concentration of the sulfonated, monomeric Mn-porphyrin 2 (Scheme 1), which is normally catalytically inactive,[7] within a thin layer of poly (terthiophene)(PTTh) yields a remarkable light-assisted catalyst with a low overpotential for water oxidation at pH7. The catalyst selectively oxidizes water before chloride in seawater.Mn-porphyrin monomer 2 was uniformly incorporated as an anionic counter-ion into a thin PTTh film during the electrochemical polymerization of TTh monomer in ethanol/dichloromethane (1: 1 by volume) containing 2 (see Supporting Information). PTTh-2 was deposited as a composite film onto indium tin oxide (ITO) glass or flexible ITO-coated poly (ethylene terephthalate)(PET) sheet. Figure S1 (Supporting Information) shows the flexible electrode obtained when PTTh-2 was coated on ITO-PET. UV/vis measurements confirmed the incorporation of 2 in the coating. Energydispersive X-ray mapping indicated that 2 was uniformly dispersed in the coating (FigureS3). Elemental analysis indicated a high density of 2 within the PTTh-2, with the mole ratio of 2 (identified by Mn+ S): terthiophene (identified by S) being ca. 1: 3.