From singlet R 2 Si silylene to triplet R 2 Si═Si ground state by DFT

2022

J Chinese Chemical Soc

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Trapping of CO 2 is probed by a set of three N-heterocyclic vinylidene minima, from the azole family, including imidazole (1), 1,2,4-triazole (2), and tetrazole(3), at M06-2X/6-311++G** level of theory. Exothermic adsorption of CO 2 over 1, 2, and 3 gives the initial CO 2 -complex, 1 a , 2 a , and 3 a , with no transition state (TS). Consequently, carbenic π-additions to CO 2 (within 1 a , 2 a , and 3 a ) may give reactant-like, three-membered cyclic TSs, which lead to the exothermic formation of 1 b > 2 b > 3 b . Alternatively, CO 2 intramolecular reactions within 1 a , 2 a , and 3 a may result in the formation of the product-like, fivemembered cyclic TSs, which lead to the endothermic formation of unstable side products 1 c , 2 c, and 3 c , which revert to 1 a , 2 a , and 3 a , respectively. Hence, this manuscript focuses on the main CO 2 trapped products (1 b , 2 b , and 3 b ), and takes advantage of the immense potential of the NBO and AIM data in elucidating their formation provisional mechanisms. Unprecedentedly, contributions of different donor-acceptor interacting orbitals to the formation of each product are assessed on the basis of their second-order perturbation stabilization energy (E 2 ) values.

CO₂ trapping of selected N‐heterocyclic vinylidenes with an NBO mechanistic scrutiny by DFT

Soroudi

2022

J Chinese Chemical Soc

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New N – heterocyclic mono – and disilavinylidene iron – complexes by density functional theory

Purlak

J of Physical Organic Chem

2020

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Recently, we found less nucleophilicity (N) for normally and abnormally disubstituted Arduengo‐type monosilylenes [R2N4Si:] (1–10) than their corresponding disilavinylidene ligands [R2N4SiSi:] (1′–10′). Considering the importance of silylene–iron complexes, here we compare and contrast thermodynamic properties of their novel [R2N4Si: → Fe(N(SiH3)2)2] (1c–10c) and [R2N4SiSi: → Fe(N(SiH3)2)2] iron complexes (1′c–10′c), for R = H, Me, ethyl, i‐propyl, and t‐butyl, at B3LYP/6‐311++G**+ LANL2DZ level of theory. Isodesmic reactions show higher stability for disilavinylidenes 1′c–10′c compared with their corresponding monosilylene 1c–10c. In all species, the natural bond orbital (NBO) calculations show transfer of charge from the silylene (of the ligand) to iron(II). Multiple Fe–Si bonding character is detected in all complexes (Wiberg bond index > 1). Yet Fe–Si bond distances in 1′c–10′c appear shorter than those in their corresponding 1c–10c. Binding energy (ΔEbin) of [Fe(N(SiH3)2)2] with 1′–10′ appears higher in 1′c–10′c than the corresponding 1c–10c.

The effects of halogen substituents on structure, stability, and electronic properties of bicyclo[1.1.1]pentanylene at density functional theory

Abedini

J of Physical Organic Chem

2021

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In a quest to identify novel bicyclic carbenes, the effects of halogen substituents on the stability and reactivity of singlet (s) and triplet (t) forms of carbenes with one, two, and three carbenic centers (1-15) are compared and contrasted, at B3LYP/6-311++G** level of theory. All carbene scrutinized turn out as minima for showing no negative force constant on their energy surfaces. The highest stability (ΔE s-t ) and band gap (ΔE HOMO-LUMO ) belongs to carbene 11 (37.36 and 133.45 kcal/mol, respectively) with three carbenic centers. Such higher stabilization attributed to three coordinate covalent bonds with their carbenic centers. The nucleophilicity (N) for each series (1-5, 6-10, and 11-15) appears inverse correlation with our results of chemical potential (μ) values. Also, the N of the carbenic center is decreased due to the higher electronegativity of substituted halogens. In addition, the electrostatic potential (ESP) maps qualitatively confirm the relative N for our bicyclic carbenes.The aim of the present work was to assess the effects of halogen substituents on the stability (ΔE s-t ), ΔΕ HOMO-LUMO , N, electrophilicity (ω), and proton affinity (ΔE PA ). Finally, our investigation introduces carbene 1 s with high stability (ΔE s-t = 30.38 kcal/mol), N (3.438 eV), and negative ΔE PA (À244.94 kcal/mol) that can be applied as accumulated multidentate ligands. K E Y W O R D Sband gap, bicyclic carbene, coordinate covalent bond, stability | INTRODUCTIONCarbenes, in a Lewis sense, have two electrons not involved in bonding (singlet (s) or triplet state (t)) and two non-bonding orbitals into which to place those electrons. [1][2][3][4][5][6][7][8][9][10] The electronic structure and stability of a carbene are affected by the mesomeric or inductive effects of substituents attached to the carbenic center. [11][12][13][14][15] Goddard and coworkers have suggested certain simple, empirically corrected computational approaches to estimate s-t gaps, particularly for halo-substituted carbenes. [16][17][18][19] The substituents by changing the orbital hybridizations at the carbenic center affect the energetic separation between the formally non-bonding orbitals. The carbenic center might be expected to reduce its s character in a bonding orbital to electronegative atom (F) and provide a corresponding increase in s character to its other in-plane orbitals. The electronegative effect includes an increase in splitting between the carbon 2s and 2p orbitals as partial positive charge builds up on the