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Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic

Nature Chemistry volume 5, pages 320–326 (2013)Cite this article

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Abstract

Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber–Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3– and NH2– species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed.

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Figure 1: Hypothetical diiron sites of ammonia production from dinitrogen.
Figure 2: Synthesis of diiron NxHy complexes and their methyl-substituted analogues.
Figure 3: Characterization by 15N NMR spectra.
Figure 4: Oak Ridge thermal ellipsoid plot (ORTEP) diagrams, with the thermal ellipsoids shown at a 50% probability level.
Figure 5: Computed minimum free-energy pathway for the transformation of 3am+ to 4am+.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (nos 21231003, 21174023, 21104008, 21076037, 21028001, 20972022) and the ‘111’ project of the Ministry of Education of China. The authors also thank the Network and Information Center of Dalian University of Technology for providing some of the computational resources.

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  1. Yang Li and Ying Li: These authors contributed equally to this work

Authors and Affiliations

  1. State Key Laboratory of Fine Chemicals, School of Pharmaceutical Science and Technology, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, 2 Linggong Road, Dalian, 116024, China

    Yang Li, Ying Li, Baomin Wang, Yi Luo, Dawei Yang, Peng Tong, Jinfeng Zhao, Lun Luo, Yuhan Zhou, Si Chen, Fang Cheng & Jingping Qu

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Contributions

J.Q. and B.W. supervised the project. J.Q. and Ya.L. conceived and designed the experiments. Ya.L., Yi.L., D.Y. and P.T. performed the experiments. Y.Lu., L.L. and S.C. performed the computational studies. J.Q., Ya.L., B.W. and F.C. co-wrote the paper. J.Z. and Y.Z. analysed the data. All authors discussed the results and commented on the manuscript.

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Correspondence to Jingping Qu.

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Supplementary information

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Supplementary information (PDF 13219 kb)

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Crystallographic data for compound 1 (CIF 34 kb)

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Crystallographic data for compound 2a[PF6] (CIF 20 kb)

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Crystallographic data for compound 3b[BPh4] (CIF 24 kb)

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Crystallographic data for compound 4b[BPh4] (CIF 24 kb)

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Crystallographic data for compound 5[BPh4] (CIF 25 kb)

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Li, Y., Li, Y., Wang, B. et al. Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic. Nature Chem 5, 320–326 (2013). https://doi.org/10.1038/nchem.1594

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