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.