Nucleophilicity of cyclic conjugated silylenes using DFT method

Abstract

Assuming aromaticity (cyclic continuous conjugation, planarity, and obeying the Hückel 4n + 2 rule), nucleophilic (N), and electrophilic (ω) characters are anticipated to alternate for σ2 and π2 singlet 3‐, 5‐, 7, and 9‐membered silylenes, 1sσ2 (N?), 2sπ2 (ω?), 3sσ2 (N?), and 4sπ2 (ω?), respectively. Our calculations show silacyclopropenylidene (1sσ2) and silacyclopenta‐2,4‐dienylidene (2sπ2) as N and ω, respectively, for exhibiting all the above criteria, at B3LYP/6‐311++G**, B3LYP/6‐311++G(2df,2p), and M06/6‐311++G** levels of theory. Silacyclohepta‐2,4,6‐trienylidene (3sσ2) meets our prediction of being N, despite deviating from planarity. Contrary to our expectation, silacyclonona‐2,4,6,8‐tetraenylidene (4sπ2) not only does not turn out to be ω but also because of its intrinsic angle strain and boat‐like structure, turns out as the most N among singlet silylenes. In all cases, singlet silylenes appear as ground states, exhibiting more stability than their corresponding triplet states. In contrast to our previous report on the 3‐, 5‐, 7‐, and 9‐membered carbenes (Kassaee, et al, Tetrahedron, 1985), all the above singlet and triplet silylenes appear as minima on their energy surfaces. Besides, no allenic isomer is found as a minimum in the silylene series, and finally, 2sπ2 appears planar while its carbenic analog is nonplanar. Nucleophilicity for singlets increases as a function of the ring size 4s > 3s > 2s > 1s, and it decreases as the aromaticity increases. Our triplet silylenes show higher N than their corresponding singlet structures.

Novel phenolic compounds by DFT: Electronic effects on antioxidant activity of 4‐vinylphenol derivatives

“…The results indicate that in going from 1 NMe2 to 10 CF3 , E HOMO of antioxidants gets more negative (lower). This observation appears consistent with the reported results 59 which show that by increasing the EWGs, the level of E HOMO decreases and ΔE H-L increases (Table 5 and Figure 5 The calculated spin density plots of corresponding radicals of our phenols are depicted (Figure 6). It is obvious that the unpaired electron is delocalized, especially in 1 NMe2 .…”

New monodentate and bidentate silylene ligands byDFT

“…The singlet-triplet energy gap (ΔE s-t , kcal/mol), band gap (ΔH H-L , eV), nucleophilicity (N, eV), chemical potential (μ, eV), and proton affinity (PA, kcal/mol) are calculated for monodentate (1)(2)(3)(4) Rh ). To further investigation on the strength of complexation, the final energy change of complexation (ΔE Com ) is calculated as follows:…”

“…Silylenes have attracted much attention in the past two decades due to their unique structures and reactivities. [1] They mostly prefer singlet ground states [2] and appear as both Lewis acids and Lewis bases because of their empty 3p orbital and a lone pair of 3s orbital, respectively. [3] As a result, they can serve as ancillary ligands in transition metal complexes [4][5][6][7][8] in which there are synergic electron transfers between the low valent silicon atoms and transition metals such as rhodium.…”

“…[29][30][31] The most common type of bidentate silylene is known as interconnected in which two Si atoms are connected directly. [32,33] Following our quest to reach at new silylene ligands, we have investigated eight monodentate (1)(2)(3)(4) Rh , respectively).…”

Cyclonona‐3,5,7‐trienylidene and its Si, Ge, Sn, and Pb analogs versus their α‐halogenated derivatives at B3LYP and MP2 methods

“…As important reactive intermediates in many reactions, attention has been paid to carbenes (R 2 C:), and their heavier metallylene congeners, including silylenes (R 2 Si:), germylenes (R 2 Ge:), stannylenes (R 2 Sn:), and plumbylenes (R 2 Pb:) . Metallylenes are considered monomeric species of the polymetallanes, and the choice of the substituent “R” is of great importance in determining their “stability.” Since metallylenes are M II species (M = Si, Ge, Sn, and Pb), their synthesis is mainly approached by four methods, perhaps the best is reduction of an M IV species (Scheme A), or substitution reactions of M II halides, such as SnCl 2 , with an organometallic species such as RLi or ArLi (Scheme B) …”