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Uranium azide photolysis results in C–H bond activation and provides evidence for a terminal uranium nitride

Abstract

Uranium nitride [U≡N]x is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U≡N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U–N=N=N) precursor. The transient U≡N fragment is reactive and undergoes insertion into a ligand C–H bond to generate new N–H and N–C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C6F5)3. These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C–H bonds.

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Figure 1: Generation of UIV azide complexes.
Figure 2: Photochemical generation and reactivity of terminal uranium nitride.
Figure 3: UV–visible–NIR absorption spectra in a toluene solution.
Figure 4: DFT calculations on the mechanism for the formation of 5 from 3.
Figure 5: Deconvoluted UV–vis spectrum of (C5Me5)2U[N(SiMe3)2](N3) (3) and calculated (TD-DFT) electronic transitions (vertical red lines).
Figure 6: Analogy between cytochrome P450 and uranium nitride C−H activation.

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Acknowledgements

The authors thank the Los Alamos National Laboratory (LANL) G. T. Seaborg Institute for Transactinium Science for a postdoctoral fellowship to R.K.T., LANL for a Director's postdoctoral fellowship to T.C., and the Division of Chemical Sciences, Office of Basic Energy Science, Heavy Element Chemistry program and the LANL Laboratory Directed Research and Development (LDRD) program for funding. R. M. Chamberlin and D. L. Clark (both LANL) are thanked for helpful discussions.

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Contributions

R.K.T. synthesized and characterized the compounds and wrote the manuscript. B.L.S. collected single-crystal X-ray crystallographic data and solved the structures. T.C. and E.R.B. performed DFT calculations. D.E.M. aided in the analysis and interpretation of UV–vis–NIR spectral data. J.L.K. generated and managed the project and helped write the manuscript.

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Correspondence to Enrique R. Batista or Jaqueline L. Kiplinger.

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The authors declare no competing financial interests.

Supplementary information

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Supplementary information (PDF 1656 kb)

Supplementary information

Crystallographic data for compound 2 (CIF 16 kb)

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Crystallographic data for compound 3 (CIF 28 kb)

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Crystallographic data for compound 4 (CIF 18 kb)

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Crystallographic data for compound 5 (CIF 29 kb)

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Crystallographic data for compound 7 (CIF 25 kb)

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Thomson, R., Cantat, T., Scott, B. et al. Uranium azide photolysis results in C–H bond activation and provides evidence for a terminal uranium nitride. Nature Chem 2, 723–729 (2010). https://doi.org/10.1038/nchem.705

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