A century after hydrazine was discovered, its synthesis remains a challenge due to its high energy requirement and favourable subsequent conversion. As an alternative to the traditional industrial processes, the direct electrochemical oxidation of ammonia is an ideal reaction for hydrazine synthesis. However, suitable methods still need to be developed. Here we show that ruthenium complexes bearing 2-[5-(pyridin-2-yl)-1H-pyrrol-2-yl]pyridine ligands display high catalytic activity for the direct electrochemical oxidation of ammonia to generate hydrazine in acetonitrile. Our developed CSU-2 complex reached a turnover number for hydrazine formation of 5,735 within 24 h at an applied potential of 1.0 V versus Cp2Fe+/0. The results reveal a bimolecular N‒N coupling mechanism involving RuII–aminyl or RuIII–iminyl intermediates.
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Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2158154 (CSU-1) and 2158155 (CSU-2). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. Source data are provided with this paper. All other data supporting the findings of this study are available within the article and its supplementary information or from the corresponding author upon request.
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We thank G.-L. Liang from Southeast University, Z.-M. Yang from Nankai University and Q.-G. Wang from Tongji University for their encouragement, motivation and very fruitful discussions. We also thank Y.-W. Lin from the University of South China, L. Yu from the High Magnetic Field Laboratory of the Chinese Academy of Sciences for the EPR measurement and discussion and Z.-C. Zhang from Huaiyin Normal University for refinement of single crystal structures. X.-Y.Y. acknowledges the National Natural Science Foundation of China (21571190), the Foundation of Central South University Research Programme of Advanced Interdisciplinary (2023QYJC019) and the Natural Science Foundation of Hunan Province of China (2022JJ30689). G.C. thanks the Postgraduate Scientific Research Innovation Project of Hunan Province (CX20210170).
Y.-X.Y. and G.C. have filed patents based on the work described here (China patent application no. 202111584527.X, international application no. PCT/CN2022/139184, US patent application no. 18272369, European patent application no. 22909854.6, Korean patent application no. 10-2023-7024287, Japanese patent application no. 2023-524432).
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Nature Catalysis thanks Jeffrey W. Bacon, Victor Batista, Ignacio Funes-Ardoiz, Sungho Park and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Figs. 1–82, Tables 1–4 and Note 1.
H2, N2H4 and N2 production in CPC experiments. Electrolytic conditions: 0.01 mM CSU-2 in NH3-saturated MeCN solutions at a constant potential of 0.76 V versus Cp2Fe+/0 at room temperature.
The atomic coordinates of the optimized models of CSU-1, CSU-2 and intermediates.
cif file of CSU-1.
cif file of CSU-2.
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Chen, G., He, P., Liu, C. et al. Direct synthesis of hydrazine by efficient electrochemical ruthenium-catalysed ammonia oxidation. Nat Catal 6, 949–958 (2023). https://doi.org/10.1038/s41929-023-01025-z
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