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Reduction and selective oxo group silylation of the uranyl dication

Abstract

Uranium occurs in the environment predominantly as the uranyl dication [UO2]2+. Its solubility renders this species a problematic contaminant1,2,3 which is, moreover, chemically extraordinarily robust owing to strongly covalent U–O bonds4. This feature manifests itself in the uranyl dication showing little propensity to partake in the many oxo group functionalizations and redox reactions typically seen with [CrO2]2+, [MoO2]2+ and other transition metal analogues5,6,7,8,9. As a result, only a few examples of [UO2]2+ with functionalized oxo groups are known. Similarly, it is only very recently that the isolation and characterization of the singly reduced, pentavalent uranyl cation [UO2]+ has been reported10,11,12. Here we show that placing the uranyl dication within a rigid and well-defined molecular framework while keeping the environment anaerobic allows simultaneous single-electron reduction and selective covalent bond formation at one of the two uranyl oxo groups. The product of this reaction is a pentavalent and monofunctionalized [O = U ... OR]+ cation that can be isolated in the presence of transition metal cations. This finding demonstrates that under appropriate reaction conditions, the uranyl oxo group will readily undergo radical reactions commonly associated only with transition metal oxo groups. We expect that this work might also prove useful in probing the chemistry of the related but highly radioactive plutonyl and neptunyl analogues found in nuclear waste.

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Figure 1: Reductive silylation of the uranyl dication.
Figure 2: X-ray crystal structures of [UO(OSi(CH3)3)(thf)Fe2I2(L)] and [UO(OSi(CH3)3)(thf)Zn2I2(L)].

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Acknowledgements

We thank the EPSRC (UK), the Royal Society, and the Universities of Edinburgh and Nottingham for support, J. Sanchez-Benitez and P. Anderson of Edinburgh University for help with magnetic susceptibility measurements and chloride analysis respectively, R. Edge and the EPSRC EPR service at the University of Manchester, and D. Leigh for his advice.

Author Contributions D.P. synthesized and characterized the compounds, and solved the crystal structure data. C.W. mounted the crystals, collected the single-crystal X-ray crystallographic data, modelled the disorder components in the structures, and checked the final structure solutions. P.L.A. and J.B.L. generated and managed the project, helped characterize the complexes, analysed the data and wrote the manuscript.

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Correspondence to Polly L. Arnold or Jason B. Love.

Additional information

X-ray crystallographic coordinates for 3 and 5 have been deposited at the Cambridge Crystallographic Database, numbers 649987 and 649988 respectively.

Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Table S1, Supplementary Figures S1-S3 with Legends and additional references. The document describes general experimental procedures, synthetic and characterisation data for compounds 1 to 6, and additional reactivity studies. The Supplementary Figures show FTIR spectroscopic data (1), selected variable temperature magnetic susceptibility data (3), and preliminary EPR data (1) for complexes 1 to 6. Crystallographic details for 3 and 5. (PDF 865 kb)

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Arnold, P., Patel, D., Wilson, C. et al. Reduction and selective oxo group silylation of the uranyl dication. Nature 451, 315–317 (2008). https://doi.org/10.1038/nature06467

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