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Dianionic species with a bond consisting of two pentacoordinated silicon atoms

Abstract

Silicon can form bonds to other tetracoordinated silicon atoms and these bonds form the framework of many organosilicon compounds and crystalline silicon. Silicon can also form a pentacoordinated anionic structure—a so-called ‘silicate’. No compounds containing a direct bond between two silicate moieties—‘disilicates’ where two silicate structures are combined in one species—have been reported because of the electronic repulsion between the anionic halves and difficulty preventing the release of anions. Here we report the synthesis of thermally stable and isolable disilicates by the reductive coupling reaction of a silane bearing two electron-withdrawing bidentate ligands. Two pentacoordinated silicons, positively charged despite the formal negative charge, constitute a single σ-bond and bind eight negatively charged atoms. They can be reversibly protonated, cleaving two Si–O bonds, to afford a tetracoordinated disilane. Their unique electronic properties could be promising for the construction of functional materials with silicon wire made up of silicate chains.

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Figure 1: Synthesis and reactivities of disilicates 2a–c.
Figure 2: The solid-state structure of disilicate 2c determined by single-crystal X-ray crystallography.
Figure 3: UV–vis spectra of 2b (solid line, 9.7 × 10−5 mol l−1) and 4 (dashed line, 1.32 × 10−4 mol l−1) in dichloromethane at room temperature.
Figure 4: Calculated molecular orbital diagrams of the frontier orbitals of the dianion part of disilicate 2d at the B3PW91/6-311 + G(2d)[Si]:6-31G(d)[C,H,O,F] level of theory.

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Acknowledgements

This work was partially supported by research grants from Yamada Science Foundation, The Japan Securities Scholarship Foundation, the Global COE program, Scientific Research on Priority Area, Creative Scientific Research, and Next Generation Super Computing Project (Nanoscience Project) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, and Research Fellowship from the Japan Society for the Promotion of Science. We thank Tosoh Finechem, Shin-etsu Chemical, and Central Glass for gifts of alkyllithiums, silicon reagents, and fluorine compounds, respectively.

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N.K. directed the project, performed the X-ray crystallographic analysis and wrote the manuscript with contributions by all authors; H.M. and K.S. conducted and analysed experiments; T.K. directed the project; N.M. and S.N. conducted theoretical calculations. All authors contributed to discussions.

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Correspondence to Naokazu Kano or Takayuki Kawashima.

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The authors declare no competing financial interests.

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Crystallographic data for compound 2c (CIF 26 kb)

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Kano, N., Miyake, H., Sasaki, K. et al. Dianionic species with a bond consisting of two pentacoordinated silicon atoms. Nature Chem 2, 112–116 (2010). https://doi.org/10.1038/nchem.513

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