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Dinitrogen binding and activation at a molybdenum–iron–sulfur cluster

Abstract

The Fe–S clusters of nitrogenases carry out the life-sustaining conversion of N2 to NH3. Although progress continues to be made in modelling the structural features of nitrogenase cofactors, no synthetic Fe–S cluster has been shown to form a well-defined coordination complex with N2. Here we report that embedding an [MoFe3S4] cluster in a protective ligand environment enables N2 binding at Fe. The bridging [MoFe3S4]2(μ-η11-N2) complex thus prepared features a substantially weakened N–N bond despite the relatively high formal oxidation states of the metal centres. Substitution of one of the [MoFe3S4] cubanes with an electropositive Ti metalloradical induces additional charge transfer to the N2 ligand with generation of Fe–N multiple-bond character. Structural and spectroscopic analyses demonstrate that N2 activation is accompanied by shortened Fe–S distances and charge transfer from each Fe site, including those not directly bound to N2. These findings indicate that covalent interactions within the cluster play a critical role in N2 binding and activation.

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Fig. 1: Strategy for binding N2 at a synthetic [MoFe3S4] cluster.
Fig. 2: Synthesis of [MoFe3S4–N2] complexes.
Fig. 3: Characterization of [MoFe3S4–N2] complexes.
Fig. 4: Spectroscopic and structural evidence for increasing cluster covalency in the series 1–3.

Data availability

Crystallographic data for compounds were deposited in the Cambridge Structural Database under deposition numbers 2058639 (1), 2058637 (2), and 2058638 (3). Other data that support the findings of this study can be found in the article and Supplementary Information; alternatively, this information is also available upon request to the corresponding author.

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Acknowledgements

We thank N. B. Thompson for assistance with Mössbauer spectroscopic experiments and P. Müller for assistance with X-ray crystallographic experiments. We acknowledge the MIT Research Support Committee Fund for financial support of this work.

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A.M. performed the experiments. A.M. and D.L.M.S. designed the research, analysed the data, and wrote the manuscript.

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Correspondence to Daniel L. M. Suess.

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Supplementary Information

Supplementary Figs. 1–15, Tables 1–6, discussion.

Crystallographic data 1

CIF file for compound 1

Crystallographic data 2

CIF file for compound 2

Crystallographic data 3

CIF file for compound 3

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McSkimming, A., Suess, D.L.M. Dinitrogen binding and activation at a molybdenum–iron–sulfur cluster. Nat. Chem. 13, 666–670 (2021). https://doi.org/10.1038/s41557-021-00701-6

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