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Spontaneous reduction and C–H borylation of arenes mediated by uranium(III) disproportionation

Nature Chemistry volume 4, pages 668–674 (2012)Cite this article

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Abstract

Transition-metal–arene complexes such as bis(benzene)chromium Cr(η6-C6H6)2 are historically important to d-orbital bonding theory and have modern importance in organic synthesis, catalysis and organic spintronics. In investigations of f-block chemistry, however, arenes are invariably used as solvents rather than ligands. Here, we show that simple uranium complexes UX3 (X = aryloxide, amide) spontaneously disproportionate, transferring an electron and X-ligand, allowing the resulting UX2 to bind and reduce arenes, forming inverse sandwich molecules [X2U(µ-η6:η6-arene)UX2] and a UX4 by-product. Calculations and kinetic studies suggest a ‘cooperative small-molecule activation’ mechanism involving spontaneous arene reduction as an X-ligand is transferred. These mild reaction conditions allow functionalized arenes such as arylsilanes to be incorporated. The bulky UX3 are also inert to reagents such as boranes that would react with the traditional harsh reaction conditions, allowing the development of a new in situ arene C–H bond functionalization methodology converting C–H to C–B bonds.

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Figure 1: Storage of arene solutions of UX3 (X = aryloxide, amide) results in the spontaneous formation of the inverse sandwich arene complex bound to UX2 moieties by two-electron reductive activation of the arene solvent.
Figure 2
Figure 3: Reactions of UX3 with dihydroanthracene to test for X radicals and reactions that demonstrate that fused arenes such as naphthalene can bind and influence the reaction rate, and reactions with transition metal (η-arene) complexes.
Figure 4: Thermal ellipsoid drawings of the molecular structures of [{X2U}2(µ-arene)] complexes.
Figure 5: Four different calculated mechanisms of formation of [{X2U}2(µ-η6,η6-C6H6)] from UX3 and benzene.
Figure 6: Two different computed mechanisms of borylation of [{(PhO)2U}2(µ-η6,η6-C6H6)].

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Acknowledgements

P.L.A. and S.M.M. thank the Engineering and Physical Sciences Research Council (EPSRC), the University of Edinburgh and EaStCHEM for funding, and E. Colineau and R. Caciuffo of the ITU, Karlsruhe, for the SQUID measurements. L.M. and D.M. thank the European Research Council for financial support for this work (post-doctoral fellowship to D.M.). L.M. thanks the Université Paul Sabatier and CNRS for financial support and is a member of the Institut Universitaire de France. CalMip and CINES are acknowledged for generous provision of computing time.

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Authors and Affiliations

  1. EastCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, The King's Buildings, Edinburgh, EH9 3JJ, UK

    Polly L. Arnold & Stephen M. Mansell

  2. LPCNO, UMR 5215, INSA, Université Paul Sabatier Toulouse III, CNRS, 135, Avenue de Rangueil, Toulouse cedex 4, 31077, France

    Laurent Maron & David McKay

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Contributions

S.M.M. synthesized and characterized the compounds and analysed the data. P.L.A. generated and managed the project, helped analyse the data and wrote the manuscript. D.M. and L.M. carried out and interpreted the computational analyses.

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Correspondence to Polly L. Arnold.

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Crystallographic data for compound 1 (CIF 58 kb)

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Crystallographic data for compound 2 (CIF 28 kb)

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Crystallographic data for compound 9 (CIF 53 kb)

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Crystallographic data for compound 2a (CIF 100 kb)

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Crystallographic data for compound 3 (CIF 31 kb)

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Crystallographic data for compound 7 (CIF 39 kb)

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Crystallographic data for compound 6 (CIF 33 kb)

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Crystallographic data for compound 6a (CIF 37 kb)

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Crystallographic data for compound 6b (CIF 57 kb)

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Crystallographic data for compound 10 (CIF 44 kb)

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Arnold, P., Mansell, S., Maron, L. et al. Spontaneous reduction and C–H borylation of arenes mediated by uranium(III) disproportionation. Nature Chem 4, 668–674 (2012). https://doi.org/10.1038/nchem.1392

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