Author: ["Polly L. Arnold","Stephen M. Mansell","Laurent Maron","David McKay"]
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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. Simple uranium complexes, UX3, are shown to disproportionate in the presence of a reducing agent under mild conditions, cooperatively binding and reducing arenes. This enables arene C–H bond activation and borylation, and the trapping of reactive substituted arenes in inverse sandwich complexes. Cite this article
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 