Theoretical descriptions on novel heteroatoms analogs of Hammick silylenes using density functional theory

Abstract

In this investigation, we have been compared and contrasted the substituent effects on stability using ΔΕ_s-t (E_t − E_s), frequency, ΔΕ_HOMO-LUMO (E_LUMO − E_HOMO), polarity, polarizability, Mülliken charge distribution and reactivity descriptors of the singlet and triplet Hammick silylenes derived from silapyridine-4-ylidene (1-s, 2x-s, 3x-s and 1-t, 2x-t, 3x-t; x = NH, PH, AsH, O, S, and Se) as well as the synthesized dialkylsilylenes by West (4-s), Denk (5-s), and Kira (6-s). In all cases, singlet (s) silylenes appear as ground states, exhibiting more stability than their corresponding triplet (t) states. All the above s and t silylenes appear as minima on their energy surfaces showing the positive force constant and the positive harmonic vibration frequency. Regardless of how orchestrated substituent groups in either “W” or “chair” position; the most stability is demonstrated by substitution of NH, and O groups in the fused pyrrole ring, while the least stability is considered by Kira's silylene. In contrast to previous report on the N-Heterocyclic Hammick carbenes, silylenes, and germylenes (NHCs, NHSis, and NHGes) that size, type, orientation, and the number of fused rings pronounced effect on stability of the corresponding divalent species, here σ-donor/π-donor groups (such as PH, AsH, S, and Se) similar to σ-acceptor/π-donor groups (such as NH and O) stabilize their corresponding silylenes. Furthermore, the scrutinized singlet silylenes reveal lesser nucleophilicity (N), greater electrophilicity (ω), higher chemical potential (μ), higher global hardness (η), and lower global softness (S) than the analogous triplet silylenes. All singlet and triplet species show the maximum electronic charge (ΔN_max) with positive sign.