A new strategy for the highly selective synthesis of tricyclo[2,2,0,0^2,5]hexasilanes R₆Si₆X₂ (R = 2,4,6-Me₃C₆H₂; X = H, Cl) and a bridged tricyclic R₆Si₆ dianion starting from the tetrachlorotrisilane RCl₂SiSi(H)RSiCl₂R (1) was described. Reduction of 1 with lithium naphthalene afforded tricyclohexasilane R₆Si₆H₂ (2), which was halogenated to give the dichloride R₆Si₆Cl₂ (3). Reduction of 3 with four equivalents of potassium graphite in the presence of 18-crown-6 afforded the first R₆Si₆ dianion (5) paired with [K(18-crown-6)]⁺₂counterions. The dianion 5 could act as a two-electron reductant toward transition metal halides and a nucleophile toward chlorosilanes. These reactions allowed the efficient and selective access to three types of silicon cages. The structures of the representative cages were confirmed by X-ray diffraction studies. Density functional theory calculations on 5 indicate that the negative charges are localized mainly on the anionic silicon atoms.

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Yang Li^†, Jianfeng Li^† , Jianying Zhang^†, Haibin Song^†, and Chunming Cui^*. Isolation of R₆Si₆ Dianion: A Bridged Tricyclic Isomer of Dianionic Hexasilabenzene. J. Am. Chem. Soc., Article ASAP DOI: 10.1021/jacs.7b12163.
http://pubs.acs.org/doi/abs/10.1021%2Fjacs.7b12163.