Silicon in a Negatively Charged Shell: Anions of Spirosilabifluorene

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• 作者：Alexander V. Zabula ; Andrey Yu. Rogachev ; Ilia A. Guzei ; Robert West
• 刊名：Organometallics
• 出版年：2013
• 出版时间：July 8, 2013
• 年：2013
• 卷：32
• 期：13
• 页码：3760-3768
• 全文大小：476K
• 年卷期：v.32,no.13(July 8, 2013)
• ISSN：1520-6041

文摘

Mono- and dianions of a polycyclic compound with a central sp³-hybridized silicon atom, spirosilabifluorene (C₂₄H₁₆Si, 1), were prepared by reduction with alkali metals. The salts containing 1^{鈥⑩€?/sup> and 12鈥?/sup> anions were isolated and studied by single-crystal X-ray diffraction. The lithium salt of the C₂₄H₁₆Si鈥⑩€?/sup> radical monoanion ([Li(THF)₄+][1鈥⑩€?/sup>], 2) exists as a solvent-separated ion pair in the solid state. Substantially different geometrical parameters were found for each of the fluorene groups within the C₂₄H₁₆Si鈥⑩€?/sup> anion of 2 due to asymmetric charge distribution. The C₂₄H₁₆Si2鈥?/sup> dianion was isolated in the form of its sodium ([{Na(THF)₃+}{Na(THF)+(12鈥?/sup>)], 3) or potassium ([{K(THF)+}₂(12鈥?/sup>)], 4) salt. The environment at the central silicon atom in the dianion is flattened in comparison to the monoanion and neutral compound, with the angle between the two fluorene planes measured at 55掳 in 12鈥?/sup> vs 89掳 in 1鈥⑩€?/sup> and 83掳 in 10. The aggregation of dianions and alkali-metal counterions leads to the formation of dimeric units and 1D polymeric chains in the solid sodium and potassium salts, respectively. The structure of the cesium salt 5, containing both mono- and dianions in the crystal lattice, was also studied by X-ray diffraction. Complexes 2鈥?b>5 were investigated by ESR and variable-temperature multinuclear NMR spectroscopy. Theoretical investigations at the PBE0, MP2, and multireference NEVPT2 levels of theory for the C₂₄H₁₆Sin鈥?/sup> (n = 0鈥?) species revealed the conjugation of two fluorene units over the central silicon atom and a singlet ground state for the dianion.}