[1,5] Sigmatropic rearrangements in silolides and germolides—a computational investigation

[1,5] Sigmatropic rearrangements of different groups R in anionic sila- and germacyclopentadienes (silolides and germolides) were studied by density functional methods. This investigation was prompted by our recent finding that silylene-substituted 1 H-silolides and 1 H-germolides rearrange to the corresponding 2 H-isomers (Chem. Commun. 2024, 60, 11295). The anionic 2 H-silolides and germolides feature a negatively charged E=C double bond (E = Si, Ge) that is integrated in a cyclopentadienyl system. The aim of this computational study is to enable the use of the full synthetic capacity of these novel compounds by identifying optimal substitution patterns at the siloles and germoles that allow their synthesis. The results of our computational study suggest that electron-withdrawing substituents (either by π-resonance or by negative hyperconjugation) at the carbon atom of the E=C double bond significantly favours the 2 H-tetrolides over the 1 H-isomer. In addition, the computations revealed that migrating electropositive groups R such as silyl, boryl, or silylenyl have small calculated barriers for the [1,5] sigmatropic rearrangement (Δ G ‡ < 50 kJ mol −1 ), which allow the 1 H tetrolide → 2 H tetrolide isomerisation to occur at ambient conditions.