A quest for triplet silylenes XHSi3 at ab initio and DFT levels (X=H, F, Cl and Br)

2020

J Chinese Chemical Soc

In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1-4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC 4 H 3 X (1 X ), SiC 4 H 2 X 2 (2 X ), SiC 4 HX 3 (3 X ), and SiC 4 X 4 (4 X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔE s-t , a possible indication of stability), and band gap (ΔE H-L ) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X . Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F . The trend of divalent angle (Â) for each X is 4 X > 1 X > 3 X > 2 X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔE s-t and ΔE H-L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry. K E Y W O R D Sband gap, DFT, halogen, silylene, singlet-triplet energy gap, stability

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Novel halogenated cyclopentasilylene‐2,4‐dienes via DFT

2020

J Chinese Chemical Soc

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Nucleophilicity of cyclic conjugated silylenes using DFT method

J of Physical Organic Chem

Ashenagar

et al. 2019

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.

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A Quest for (sila)0-4cyclopentasilylenes and their Arduengo Analogs by DFT

2020

Silicon