The role of bridging ligands in dinitrogen reduction and functionalization by uranium multimetallic complexes



Cooperativity between metal centres is identified as a crucial step in dinitrogen reduction both for the industrial Haber–Bosch process and for the natural fixation of nitrogen by nitrogenase enzymes, but the mechanism of N2 reduction remains poorly understood. This is in large part because multimetallic complexes that reduce and functionalize dinitrogen in the absence of strong alkali reducing agents are crucial to establish a structure–activity relationship, but remain extremely rare. Recently, we reported a multimetallic nitride-bridged diuranium(iii) complex capable of reducing and functionalizing dinitrogen. Here we show that an analogous complex assembled with an oxo instead of a nitride linker also effects the four-electron reduction of dinitrogen, but the reactivity of the resulting oxo–(N2) complex differs significantly from that of the nitride–(N2). Computational studies show a different bonding scheme for the dinitrogen where the bridging nitride does participate in the binding and consequent activation of N2, while the oxide does not.

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Fig. 1: Dinitrogen reduction and functionalization by a multimetallic uranium nitride.
Fig. 2: Synthesis and reactivity of oxo-bridged diuranium complexes.
Fig. 3: Molecular structure of 2, 3, 4 and 5.
Fig. 4: Magnetic susceptibility.
Fig. 5: Molecular orbitals of the different complexes.

Data availability

All data generated and analysed during this study are included in this Article and its Supplementary Information or are available from the corresponding author upon reasonable request. Atomic coordinates and structure factors for the reported crystal structures have been deposited in the Cambridge Crystallographic Data Centre under accession codes CCDC 1821630 (2), 1821631 (3), 1821633 (4), 1821634 (5) and 1821632 (6).


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The authors acknowledge support from the Swiss National Science Foundation (grant nos. 200021_162430 and 200021_178793) and from the Ecole Polytechnique Fédérale de Lausanne (EPFL). The authors thank E. Solari for carrying out the elemental analyses, L. Y. M. Eymann for synthesis of the IMesN2O adduct and R. Scopelliti for important contributions to the X-ray single-crystal structure analyses.

Author information




M.F. and L.B. carried out the synthetic experiments and analysed the experimental data. J.A. performed preliminary experiments and characterized the U–O–U complexes. F.F.T. carried out the X-ray single-crystal structure analyses. I.Z. measured and analysed the magnetic data. A.F. and C.C. performed the theoretical computations. K.S. contributed to the identification of a new route to oxo complexes. M.M. originated the central idea, coordinated the work and analysed the experimental data. M.M., M.F. and L.B. wrote the manuscript.

Corresponding author

Correspondence to Marinella Mazzanti.

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Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Characterization, Supplementary Computational analysis

Crystallographic data

CIF for compound 2; CCDC reference: 1821630.

Crystallographic data

CIF for compound 3; CCDC reference: 1821631.

Crystallographic data

CIF for compound 4; CCDC reference: 1821633.

Crystallographic data

CIF for compound 5; CCDC reference: 1821634.

Crystallographic data

CIF for compound 6; CCDC reference: 1821632.

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Falcone, M., Barluzzi, L., Andrez, J. et al. The role of bridging ligands in dinitrogen reduction and functionalization by uranium multimetallic complexes. Nature Chem 11, 154–160 (2019).

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