Abstract
Two-coordinate boron cations (R2B+), referred to as borinium ions, are chemical species in which the boron bears only four valence electrons, and that are isoelectronic with hypothetical carbon dications (R2C2+). Although lone-pair-donating substituents such as amino groups have enabled the isolation of several borinium ions, diarylated and dialkylated borinium derivatives remain entirely unexplored. Here, we present the synthesis, structure and reactivity of the dimesitylborinium ion, which displays unexpectedly high thermal stability. X-ray crystallography and 11B NMR spectroscopy, supported by density functional theory calculations, reveal that the borinium ion adopts a linear two-coordinate structure in both the solid state and in solution. The boron centre is stabilized by pπ bonding from the mesityl groups and is free from coordination by the counterion or solvent molecules. This diarylborinium ion possesses exceptional Lewis acidity, accepting a pair of electrons from CO2 to cause an unusual deoxygenation reaction.
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Acknowledgements
This work was supported by KAKENHI (22750046). The authors thank C.A. Reed for his instruction regarding carboranes synthesis and valuable discussions. RIKEN Integrated Cluster of Clusters (RICC) provided the computer resources for the DFT calculations.
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Y.S. and T.F. conceived and designed the work. Y.S. and N.T. performed the experiments. Y.S., N.T. and T.F. analysed the experimental data. K.M. and M.U. performed the DFT calculations and analysed the computational data. Y.S., M.U. and T.F. co-wrote the paper.
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Crystallographic data for compound 1a (CIF 57 kb)
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Crystallographic data for compound 1b (CIF 18 kb)
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rystallographic data for compound 2a (CIF 49 kb)
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Shoji, Y., Tanaka, N., Mikami, K. et al. A two-coordinate boron cation featuring C–B+–C bonding. Nature Chem 6, 498–503 (2014). https://doi.org/10.1038/nchem.1948
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DOI: https://doi.org/10.1038/nchem.1948
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