Facile synthesis and functionality-dependent electrochemistry of Fe-only hydrogenase mimics.
Facile synthesis and functionality-dependent electrochemistry of Fe-only hydrogenase mimics.
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DOI：
10.1021/ic800676y
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发表时间：
2008-08
影响因子：
4.6
通讯作者：
Gang Si;Wenguang Wang;Hong-Yan Wang;C. Tung;Lizhu Wu
中科院分区：
文献类型：
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作者：
Gang Si;Wenguang Wang;Hong-Yan Wang;C. Tung;Lizhu Wu
一系列氮杂二硫醇盐（adt）桥联的Fe-唯氢酶模型配合物Fe 2（CO）6（mu-adt）C6 H 4 I-4（1），Fe 2（CO）6（mu-adt）C6 H 4 C [三键]CR [R = C6 H 4 NO 2 -4（2），C6 H 4 CHO-4（3），C6 H 4 NH 2 -4（4），C6 H 4 COOH-4（5），C6 H 4 COOCH 2 CH 3 -4（6），C6 H 4 F-4（7），C6 H 5（8），在温和的条件下以高产率合成了C6 H4 OCH 3 -4（9），C6 H4 N（CH 3）2-4（10）]，[Fe 2（CO）5（PPh 3）（mu-adt）C6 H4 I-4（11），和Fe 2（CO）5（PPh 3）（mu-adt）C6 H4 C [三键] CC 6 H4 NO 2 -4（12）。三键的线性几何形状和刚性作为一个有效的桥梁，锚的功能范围从给电子到电子接受，甚至在adt模型配合物的配位基团。2、3和6-12的X射线晶体分析表明，模型配合物保留了Fe 2S 2模型类似物的蝴蝶结构。一个刚性的苯乙炔提供了很好的控制之间的距离的功能团和活性位点的Fe 2S 2模型配合物。在6分子堆积中发现的不寻常的Fe-Fe距离和角度来源于有趣的分子间C-H键。O和C-H S互动。更重要的是，电化学研究表明，所有的配合物都可以催化质子电化学还原为分子氢，但电子转移步骤的还原电位可以显着改变官能度R。2和12中的电还原活性硝基在比[Fe（I）Fe（I）] + e（-）--> [Fe（I）Fe（0）]的还原负得多的电势下显示出增强的电流，这是最容易的并且成为初始步骤。对于络合物3，电子转移步骤的第二还原峰涉及醛官能团的贡献。当引入电还原惰性基团时，首先出现[Fe（I）Fe（I）] + e（-）--> [Fe（I）Fe（0）]的还原过程，并且清楚地观察到来自[Fe（I）Fe（0）] + e（-）--> [Fe（0）Fe（0）]过程的电子转移步骤的第二个还原峰持续4-10。因此，电子和质子吸收的顺序与电还原活性官能团R密切相关。改变功能性R的性质导致电子转移步骤从电还原活性R基团的还原到随后的Fe 2S 2模型络合物的活性位点的变化。因此，尽管乙酸太弱而不能使2-12系列质子化，但可以遵循不同的还原途径，并且电化学催化行为可以在不同的还原水平下发生。
A series of azadithiolate (adt)-bridged Fe-only hydrogenase model complexes, Fe2(CO)6(mu-adt)C6H4I-4 (1), Fe2(CO)6(mu-adt)C6H4C[triple bond]CR [R = C6H4NO2-4 (2), C6H4CHO-4 (3), C6H4NH2-4 (4), C6H4COOH-4 (5), C6H4COOCH2CH3-4 (6), C6H4F-4 (7), C6H5 (8), C6H4OCH3-4 (9), C6H4N(CH3)2-4 (10)], [Fe2(CO)5(PPh3)(mu-adt)C6H4I-4 (11), and Fe2(CO)5(PPh3)(mu-adt)C6H4C[triple bond]CC6H4NO2-4 (12), have been synthesized in high yields under mild conditions. The linear geometry and rigidity of a triple bond act as an effective bridge to anchor a functionality ranging from electron-donating to electron-accepting, even coordinative groups in the adt model complexes. X-ray crystal analysis of 2, 3, and 6-12 reveals that the model complexes retain the butterfly structure of Fe2S2 model analogues. A rigid phenylacetylene offers excellent control over the distance between the functional group and the active site of Fe2S2 model complexes. The unusual Fe-Fe distance and the angles found in the molecular packing of 6 are originated from the intriguing intermolecular C-H...O and C-H...S interactions. More importantly, electrochemical studies reveal that all of the complexes can catalyze electrochemical reduction of protons to molecular hydrogen, but the reduction potential for the electron-transfer step can be remarkably altered by the functionality R. The electroreductively active nitro group in 2 and 12 displays the enhanced current at a potential substantially less negative than the reduction of [Fe(I)Fe(I)] + e(-) --> [Fe(I)Fe(0)], which is most accessible and becomes the initial step. For complex 3, the second reduction peak for the electron-transfer step involves the contribution from the aldehyde functionality. As the electroreductively inactive groups are incorporated, the reduction process of [Fe(I)Fe(I)] + e(-) --> [Fe(I)Fe(0)] appears first and the second reduction peak for the electron-transfer step from the [Fe(I)Fe(0)] + e(-) --> [Fe(0)Fe(0)] process for 4-10 is clearly observed. Therefore, the order of electron and proton uptake is closely related to the electroreductively active functionality, R. Varying the nature of the functionality R leads to the electron-transfer step changes from the reduction of the electroreductively active R group to the active site of Fe2S2 model complexes subsequently. Accordingly, notwithstanding, acetic acid is too weak to protonate the series of 2-12, different reduction pathways can be followed, and the electrochemically catalyzed behavior may occur at different reduction levels.