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A boron–boron coupling reaction between two ethyl cation analogues

Nature Chemistry volume 5, pages 1029–1034 (2013)Cite this article

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Abstract

The design of larger architectures from smaller molecular building blocks by element–element coupling reactions is one of the key concerns of synthetic chemistry, so a number of strategies were developed for this bottom-up approach. A general scheme is the coupling of two elements with opposing polarity or that of two radicals. Here, we show that a B–B coupling reaction is possible between two boron analogues of the ethyl cation, resulting in the formation of an unprecedented dicationic tetraborane. The bonding properties in the rhomboid B4 core of the product can be described as two B–B units connected by three-centre, two-electron bonds, sharing the short diagonal. Our discovery might lead the way to the long sought-after boron chain polymers with a structure similar to the silicon chains in β-SiB3. Moreover, the reaction is a prime textbook example of the influence of multiple-centre bonding on reactivity.

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Figure 1: Isolobal analogy and reaction sequence leading to 3.
Figure 2: Measured and simulated high-resolution mass spectrometry (HR-ESI+) peaks of 3[HB(C6F5)3]2, showing the absence of monocation 2.
Figure 3: Structure of tetraborane dication 3 in the salt 3[HB(C6F5)3]2, as revealed by single-crystal XRD analysis and calculated charge density of 3.

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Acknowledgements

The authors thank W. Siebert for discussions and the Deutsche Forschungsgemeinschaft (DFG) for continuous financial support.

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Authors and Affiliations

  1. Institute of Inorganic Chemistry, Ruprecht-Karls-University Heidelberg, Im Neuenheimer Feld 270, Heidelberg, 69120, Germany

    Sebastian Litters, Elisabeth Kaifer, Markus Enders & Hans-Jörg Himmel

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  1. Sebastian Litters
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  2. Elisabeth Kaifer
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Contributions

H-J.H. conceived and supervised the study. S.L. performed the syntheses and the computational experiments. E.K. performed the X-ray crystallographic measurements. M.E. performed the DOSY-NMR measurements. S.L. and M.E. analysed the data and co-wrote the paper.

Corresponding author

Correspondence to Hans-Jörg Himmel.

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The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 973 kb)

Supplementary information

Crystallographic data for compound 3[HB(C6F5)3]2. (CIF 69 kb)

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Litters, S., Kaifer, E., Enders, M. et al. A boron–boron coupling reaction between two ethyl cation analogues. Nature Chem 5, 1029–1034 (2013). https://doi.org/10.1038/nchem.1776

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