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

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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Authors and Affiliations

Authors

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.

Corresponding author

Correspondence to Jingping Qu.

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The authors declare no competing financial interests.

Supplementary information

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Supplementary information (PDF 13219 kb)

Supplementary information

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 2b (CIF 13 kb)

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Crystallographic data for compound 2b[PF6] (CIF 22 kb)

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Crystallographic data for compound 3a[BAr(F)4] (CIF 39 kb)

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

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Crystallographic data for compound 4a[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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