Vanadium-Catalyzed Dinitrogen Reduction to Ammonia via a [V]=NNH2 Intermediate
Vanadium-Catalyzed Dinitrogen Reduction to Ammonia via a [V]=NNH2 Intermediate
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DOI：
10.1021/jacs.2c08000
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发表时间：
2023-01-03
影响因子：
15
通讯作者：
Hu, Shaowei
中科院分区：
文献类型：
--
作者：
Huang, Wenshuang;Peng, Ling-Ya;Hu, Shaowei
通过过渡金属络合物将N2催化转化为NH3具有极大的兴趣和重要性，但迄今为止仍然是一个挑战。尽管钒在生物固氮中起着重要作用，但能够催化N2转化为NH3的定义明确的钒配合物却很少。特别是，一个V（NxHy）的中间体来自配位N2的质子/电子转移反应仍然未知。本文报道了一种含POCOP（2，6-（tBu 2 PO）2-C6 H3）钳形和芳氧基配体的二氮桥联二钒配合物，它可以作为催化剂用于N2还原为NH3和N2 H4。低温质子化和还原的双氮络合物提供了第一个结构特征的中性金属肼基（2-）物种（[V]= NNH 2），它介导15 N2转化为15 NH3，表明它是一个合理的催化中间体。DFT计算表明，钒酰肼配合物[V]= NNH 2的N-H键离解自由能（BDFEN-H）高达59.1 kcal/mol.钒酰胺络合物（[V]-NH 2）与[Ph 2NH 2][OTf]的质子化导致NH3的释放和三氟甲磺酸钒络合物的形成，其在N2下还原时得到钒二氮络合物。这些转化模拟了钒催化的N2还原循环的最后步骤。实验和理论研究都表明，催化反应可能通过远端途径释放NH3。这些发现提供了前所未有的见解N2还原相关的FeV固氮酶的机制。
The catalytic transformation of N2 to NH3 by transition metal complexes is of great interest and importance but has remained a challenge to date. Despite the essential role of vanadium in biological N2 fixation, well-defined vanadium complexes that can catalyze the conversion of N2 to NH3 are scarce. In particular, a V(NxHy) intermediate derived from proton/electron transfer reactions of coordinated N2 remains unknown. Here, we report a dinitrogen-bridged divanadium complex bearing POCOP (2,6-(tBu2PO)2- C6H3) pincer and aryloxy ligands, which can serve as a catalyst for the reduction of N2 to NH3 and N2H4. Low-temperature protonation and reduction of the dinitrogen complex afforded the first structurally characterized neutral metal hydrazido(2-) species ([V]=NNH2), which mediated 15N2 conversion to 15NH3, indicating that it is a plausible intermediate of the catalysis. DFT calculations showed that the vanadium hydrazido complex [V]=NNH2 possessed a N-H bond dissociation free energy (BDFEN-H) of as high as 59.1 kcal/mol. The protonation of a vanadium amide complex ([V]-NH2) with [Ph2NH2][OTf] resulted in the release of NH3 and the formation of a vanadium triflate complex, which upon reduction under N2 afforded the vanadium dinitrogen complex. These transformations model the final steps of a vanadium-catalyzed N2 reduction cycle. Both experimental and theoretical studies suggest that the catalytic reaction may proceed via a distal pathway to liberate NH3. These findings provide unprecedented insights into the mechanism of N2 reduction related to FeV nitrogenase.