Isolation of R_6Si_6 Dianion: A Bridged Tricyclic Isomer of Dianionic Hexasilabenzene

摘要

A new strategy for the highly selective synthesis of tricyclo[2,2,0,0~(2,5)]hexasilanes R_(6)Si_(6)X_(2) (R = 2,4,6-Me_(3)C_(6)H_(2); X = H, Cl) and a bridged tricyclic R_(6)Si_(6) dianion starting from the tetrachlorotrisilane RCl_(2)SiSi(H)RSiCl_(2)R ( 1 ) was described. Reduction of 1 with lithium naphthalene afforded tricyclohexasilane R_(6)Si_(6)H_(2) ( 2 ), which was halogenated to give the dichloride R_(6)Si_(6)Cl_(2) ( 3 ). Reduction of 3 with four equivalents of potassium graphite in the presence of 18-crown-6 afforded the first R_(6)Si_(6) dianion ( 5 ) paired with [K(18-crown-6)]~(+)_(2) counterions. 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.