Nitrogen Fixation by a Molybdenum Catalyst Mimicking the Function of the Nitrogenase Enzyme: A Critical Evaluation of DFT and Solvent Effects.
Nitrogen Fixation by a Molybdenum Catalyst Mimicking the Function of the Nitrogenase Enzyme: A Critical Evaluation of DFT and Solvent Effects.
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模拟固氮酶功能的钼催化剂固氮：DFT 和溶剂效应的批判性评估。
DOI：
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发表时间：
2007
影响因子：
5.5
通讯作者：
P. Carloni
中科院分区：
文献类型：
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作者：
A. Magistrato;Arturo Robertazzi;P. Carloni
模仿固氮酶的化合物代表了当前哈伯-博世从分子氢和氮工业合成氨的有前途的替代路线。在这项工作中，我们通过 DFT 计算研究了其中一种化合物 Mo(HIPTN3N)（HIPT = 六异丙基三联苯）的完整催化循环。我们的结果表明这些大配体主要对催化剂的结构性质产生空间影响。此外，我们还提供了假定反应中间体的结构和电子表征，以及分子氮 N-N 键断裂的电子机制图。计算的反应自由能和实验的反应自由能之间观察到很大的差异，这表明在目前的情况下，DFT 反应自由能的可预测性是有限的。对特定催化中间体以及质子化剂和还原剂的显式溶剂化的研究揭示了溶剂分子（苯和庚烷）所发挥的关键作用，特别是对于质子化步骤。此外，对几个 DFT 泛函的分析表明，必须仔细选择这些泛函才能重现还原步骤的能量分布。这项研究表明，DFT 计算可能是描述催化循环中间体的结构和电子性质的有力工具，然而，由于系统的复杂性，如果不仔细选择溶剂化模型和交换相关函数，则无法轻松再现反应能量。
Compounds mimicking the enzyme nitrogenase represent promising alternative routes to the current Haber-Bosch industrial synthesis of ammonia from molecular hydrogen and nitrogen. In this work, we investigated the full catalytic cycle of one of such compounds, Mo(HIPTN3N) (with HIPT = hexaisopropylterphenyl), by means of DFT calculations. Our results suggest these large ligands to exert mainly a steric influence on the structural properties of the catalyst. In addition, we provided a structural and electronic characterization of the putative reaction intermediates along with a picture of the electronic mechanism of molecular nitrogen N-N bond breaking. A large discrepancy was observed between calculated and experimental reaction free energies, suggesting that in the present case the predictability of DFT reaction energies is limited. Investigation of explicit solvation of specific catalytic intermediates as well as of the protonation and reducing agents reveal the crucial role played by the solvent molecules (benzene and heptane) particularly for protonation steps. Furthermore, the analysis of several DFT functionals indicates that these have to be carefully chosen in order to reproduce the energetic profile of reduction steps. This study shows how DFT calculations may be a powerful tool to describe structural and electronic properties of the intermediates of the catalytic cycle, yet, due to the complexity of the system, reaction energies cannot be easily reproduced without a careful choice of the solvation model and the exchange-correlation functional.