Potential Formation of Antiaromatic Silolosiloles (Disilapentalenes) from Their Saturated Diketosilolosilole Precursors via a [1,3]-Si → O Sigmatropic Shift

Antiaromatic pentalenes and heteropentalenes are interesting for organic optoelectronics and semiconductors due to their low HOMO–LUMO gaps. However, disilapentalenes (silolosiloles, here called SSs), carrying two Si=C double bonds, are a rarely explored class of compounds. Herein, we probed the formation of antiaromatic SS compounds 1b–3b, by density functional theory calculations, from their corresponding precursors diketosilolosiloles (DSSs) 1a–3a, through [1,3]-Si → O sigmatropic shifts. The relative Gibbs free energy (ΔG) displays that, among several migrants (H, Me, CF3, CN, NH2, F, Cl, SiH3, SiMe3, and SiF3), the migration of the SiF3 group is exergonic (−7.6 kcal mol–1), which could be further improved (−13.7 kcal mol–1) by introducing CN groups at the β-positions to the ring’s silicon atoms, overcoming an activation barrier of ∼35 kcal mol–1. The frontier orbital energies and natural population analysis charges on the Si and O atoms of the Si–C­(−O) bond in the SS compounds display a good relationship with the ΔG. Further, it is revealed that the SS compounds have smaller HOMO–LUMO gaps and are significantly less antiaromatic than the parent pentalene. The thermally or photoinduced DSS to SS conversion could be attractive for single-molecule conductance “double” switches and logic gates.反芳香性戊搭烯与杂戊搭烯（antiaromatic pentalenes and heteropentalenes）因具有较窄的HOMO–LUMO能隙，在有机光电子学与半导体领域颇具研究价值。然而，带有两条Si=C双键的二硅戊搭烯（silolosiloles，下称SSs）却是一类鲜有探索的化合物。本研究通过密度泛函理论（density functional theory）计算，探究了反芳香性SS类化合物1b~3b由其对应前驱体二酮硅洛硅洛（diketosilolosiloles，下称DSSs）1a~3a经由[1,3]-硅→氧σ迁移重排的生成过程。相对吉布斯自由能（ΔG）结果表明，在诸多迁移基团（H、Me、CF3、CN、NH2、F、Cl、SiH3、SiMe3及SiF3）中，SiF3基团的迁移为放能过程（-7.6 kcal·mol⁻¹）；若在环硅原子的β位引入氰基（CN），可将该过程的自由能变进一步优化至-13.7 kcal·mol⁻¹，且仅需克服约35 kcal·mol⁻¹的活化能垒。SS类化合物中Si–C(−O)键的硅、氧原子的前沿轨道能量与自然布居分析电荷，与ΔG呈现良好的线性相关性。进一步研究显示，相较于母体戊搭烯，SS类化合物的HOMO–LUMO能隙更窄，且反芳香性显著减弱。热或光诱导下DSS向SS的转化，在单分子电导“双”开关与逻辑门领域具备良好的应用前景。