New generation of dialkylsilylenes with stabilities comparable to diaminosilylenes: A theoretical study

A new family of dialkylsilylenes is introduced which enjoys the stabilizing effect of α-cyclopropyl substituents. The singlet and triplet states of acyclic and saturated/unsaturated cyclic dicyclopropylsilylenes are fully optimized using MP2/6-31G(d) and B3LYP/6-31+G(d) levels. Their higher ΔE_S-T values compared to the corresponding analogues which possess isopropyl groups instead of cyclopropyl represents the stabilizing interaction of the occupied Walsh orbital of the cyclopropyls with the vacant p-orbital of the silylene center. Appropriate isodesmic reactions clearly show that the stabilizing effect of this interaction on the singlet state is much more considerable than the corresponding triplet state. Cyclopropyls can serve as good sites for bulky substitution and, hence, provide steric protection for silylene.