Replying to C. Foroutan-Nejad Nature Communications https://doi.org/10.1038/s41467-021-24238-x (2021)
In our original paper1, we reported synthesis of 1,2,2,3,4,4-hexa-tert-butylbicyclo[1.1.0]tetrasilane (2, Fig. 1). The X-ray crystallography of 2 showed a planar geometry around the bridgehead silicon atom (angle sums except for the inter-bridgehead bond = 359.79°). On the basis of experimental results of X-ray crystallography, electron paramagnetic resonance, magnetic susceptibility, UV/Vis and 29Si NMR spectra, and theoretical calculations including natural bond orbital analysis, we concluded that 2 has a silicon–silicon π single bond between the bridgehead silicon atoms. We have been aware that the HOMO–6 and HOMO–1 represent in-phase and out-of-phase orbital interactions between the linearly arranged two σ(Sibridgehead–Ctert-butyl) orbitals, respectively. We did not discuss them in the original paper because (i) we considered that the σ-type bonding interaction between the bridgehead silicon atoms due to the in-phase interaction (HOMO–6) should be canceled out by the corresponding out-of-phase interaction (HOMO–1) and (ii) we did not find σ-type interaction between the bridgehead silicon atoms within the above-mentioned our theoretical investigation (output threshold > 2.1 kJ mol–1).
Chemical structure of 2.
In their commentary, Dr. Foroutan-Nejad took a different approach to characterize 2. The author analyzed electron density of 2 theoretically and concluded that the silicon–silicon π bond is accompanied by a weak but non-negligible σ bond. We welcome discussion about the unusual bonding situation in the isolable compound 2 from diverse viewpoints to obtain deeper understanding of this chemical bond.
Reference
Kyushin, S. et al. Silicon–silicon π single bond. Nat. Commun. 11, 4009 (2020).
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S.K., S.I. and H.M. discussed the content of this reply and wrote the manuscript. Y.K., K.O., H.I., T.K. and M.H. read and agreed to this reply.
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Kyushin, S., Kurosaki, Y., Otsuka, K. et al. Reply to: “A double bond with weak σ- and strong π-interactions is still a double bond”. Nat Commun 12, 4036 (2021). https://doi.org/10.1038/s41467-021-24239-w
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DOI: https://doi.org/10.1038/s41467-021-24239-w
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