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Neutral zero-valent s-block complexes with strong multiple bonding

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Abstract

The metals of the s block of the periodic table are well known to be exceptional electron donors, and the vast majority of their molecular complexes therefore contain these metals in their fully oxidized form. Low-valent main-group compounds have recently become desirable synthetic targets owing to their interesting reactivities, sometimes on a par with those of transition-metal complexes. In this work, we used stabilizing cyclic (alkyl)(amino)carbene ligands to isolate and characterize the first neutral compounds that contain a zero-valent s-block metal, beryllium. These brightly coloured complexes display very short beryllium–carbon bond lengths and linear beryllium coordination geometries, indicative of strong multiple Be–C bonding. Structural, spectroscopic and theoretical results show that the complexes adopt a closed-shell singlet configuration with a Be(0) metal centre. The surprising stability of the molecule can be ascribed to an unusually strong three-centre two-electron π bond across the C–Be–C unit.

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Figure 1: Known zero-valent p-block compounds, and synthesis, reactivity and crystal structures of zero-valent beryllium compounds.
Figure 2: Frontier molecular orbitals, NOCVs and electronic structure of 3.

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Acknowledgements

Financial support from the Julius-Maximilians-Universität Würzburg (H.B.) and the Alexander von Humboldt Foundation (postdoctoral fellowship to M.A.) is gratefully acknowledged. We also thank G. Frenking for helpful discussions regarding the computational analysis.

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Authors

Contributions

J.K.S. designed the study under the supervision of H.B., performed all the reactions and collected and analysed the data. J.M. carried out preliminary synthetic work on compound 3. M.A.C. and W.C.E. performed the theoretical calculations. I.K. collected the CV data. K.H. synthesized the starting materials. T.D., T.K. and K.R. collected and refined the crystallographic data. W.C.E., M.A.C., M.A. and R.D.D. wrote the paper. All the authors discussed the results and commented on the manuscript.

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Correspondence to Holger Braunschweig.

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The authors declare no competing financial interests.

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Supplementary information (PDF 7035 kb)

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Crystallographic data for compound 1 (CIF 1577 kb)

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Crystallographic data for compound 2 (CIF 1019 kb)

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Crystallographic data for compound 3 (CIF 512 kb)

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Crystallographic data for compound 4 (CIF 569 kb)

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Arrowsmith, M., Braunschweig, H., Celik, M. et al. Neutral zero-valent s-block complexes with strong multiple bonding. Nature Chem 8, 890–894 (2016). https://doi.org/10.1038/nchem.2542

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