Nitrogenase-Relevant Reactivity of a Synthetic Iron-Sulfur-Carbon Site.
Nitrogenase-Relevant Reactivity of a Synthetic Iron-Sulfur-Carbon Site.
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DOI：
10.1021/jacs.9b05353
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发表时间：
2019-08
影响因子：
15
通讯作者：
Amy L. Speelman;I. Čorić;Casey Van Stappen;S. DeBeer;B. Mercado;Patrick L. Holland
中科院分区：
文献类型：
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作者：
Amy L. Speelman;I. Čorić;Casey Van Stappen;S. DeBeer;B. Mercado;Patrick L. Holland
仅S和C给体的简单合成化合物提供了类似于氮酶（FeMoco）活性位点的连接环境，从而在自然界中展示了N2结合和还原的合理机制和几何形状。我们最近报道了仅由S和C供体支持的单核铁位点上N2结合的第一个例子。在这项工作中，我们报告了研究该系统中N2结合机制的实验。铁（II）三（硫酸盐）配合物与1等量的KC8的还原导致了一种热不稳定的中间体，Mössbauer， EPR和x射线吸收光谱的组合表明它是一种高自旋（S = 3/2）铁(I)，保持了所有三个硫原子的配位。DFT计算表明，该铁(I)中间体具有伪四面体几何形状，类似于FeMoco静息状态下带铁位点的S3C铁配位环境。在氩气条件下进一步还原到铁(0)氧化水平，导致其中一种硫代给体解离，得到与N2反应的η - 6-芳烃。因此，在该体系中，硫酸盐的损失和N2的结合需要铁(I)水平以上的还原到铁(0)水平。铁(0)-N2络合物的进一步还原得到活性的铁（- 1）物质。用弱酸处理假定的铁(i)配合物，氨和肼的产率很低，这表明这些氮酶产物可以在合成的Fe-S-C位点由N2生成。没有观察到催化N2还原，这是由于支持配体的质子化和配合物通过配体解离的降解。识别该系统中的挑战可以深入了解功能性仿生复合物所需的设计特征。
Simple synthetic compounds with only S and C donors offer a ligation environment similar to the active site of nitrogenase (FeMoco) and thus demonstrate reasonable mechanisms and geometries for N2 binding and reduction in nature. We recently reported the first example of N2 binding at a mononuclear iron site supported by only S and C donors. In this work, we report experiments that examine the mechanism of N2 binding in this system. The reduction of an iron(II) tris(thiolate) complex with 1 equiv of KC8 leads to a thermally unstable intermediate, and a combination of Mössbauer, EPR, and X-ray absorption spectroscopies identifies it as a high-spin (S = 3/2) iron(I) species that maintains coordination of all three sulfur atoms. DFT calculations suggest that this iron(I) intermediate has a pseudotetrahedral geometry that resembles the S3C iron coordination environment of the belt iron sites in the resting state of the FeMoco. Further reduction to the iron(0) oxidation level under argon causes the dissociation of one of the thiolate donors and gives an η6-arene species which reacts with N2. Thus, in this system the loss of thiolate and binding of N2 require reduction beyond the iron(I) level to the iron(0) level. Further reduction of the iron(0)-N2 complex gives a reactive, formally iron(-I) species. Treatment of the putative iron(-I) complex with weak acids gives low yields of ammonia and hydrazine, demonstrating that these nitrogenase products can be generated from N2 at a synthetic Fe-S-C site. Catalytic N2 reduction is not observed, which is attributed to protonation of the supporting ligand and degradation of the complex via ligand dissociation. Identification of the challenges in this system gives insight into the design features needed for functional biomimetic complexes.