Computational Insight into the Carbenic Character of Nitrilimines from a Reactivity Perspective

Abstract

Nitrilimines (R-CNN-R) can be described through a carbenic valence bond structure, and although intermolecular carbenic reactions from nitrilimines are unknown, intramolecular reaction products from ortho-vinyl MeCOO-CNN-Ph (1) and Ph-CNN-Ph (2) that seem to have followed two typical carbene reaction mechanisms, [1+2] cycloaddition and C-H insertion, have been reported. This study sheds light on whether such reaction mechanisms are tenable, using the electron density and its Laplacian (QTAIM), natural bond orbital (NBO) descriptions, and reaction profiles. It is shown that the reaction in 1 is distinctly different from the [1+2] cycloadditions of ethene with the typical singlet carbene CF(2) and the nitrilimine F-CNN-F with its large carbenic character, and the formal [1+2] cycloaddition product from 1 is in fact not the primary product. Similarly, it is shown that the reaction in 2 is fundamentally different from the C-H insertions of CF(2), F-CNN-F, and even H-CNN-H with its small carbenic character into methane, and again the formal C-H insertion product from 2 is not the primary product. The small model reactions from CF(2), F-CNN-F, and H-CNN-H were analyzed using B3LYP, MP2, and B2PLYP with the aug-cc-pVTZ basis set, whereas the full study was performed with B3LYP/6-31+G(2d,2p), as it was shown to be sufficient.

The Quest for Carbenic Nitrile Imines: Experimental and Computational Characterization of C‐Amino Nitrile Imine

“…This is particularly noticeable by the CNN antisymmetric stretching IR absorption of the nitrile imine moiety appearing over a wide range of frequencies (2000-2250 cm -1 ). [20,29,30] For instance, Bégué and Wentrup have theo-retically investigated different amino-, hydroxy-, and fluorosubstituted nitrile imines (R-CNN-H, H-CNN-R, and R-CNN-R; R = NH 2 , OH, and F) and predicted that some of the studied molecules should exhibit carbenic character. [17] In addition, theoretical studies have indicated that substituents bearing a lone-electron pair should increase the importance of the carbenic resonance structure of nitrile imines.…”

“…[17] In addition, theoretical studies have indicated that substituents bearing a lone-electron pair should increase the importance of the carbenic resonance structure of nitrile imines. [20,29,30] For instance, Bégué and Wentrup have theo-retically investigated different amino-, hydroxy-, and fluorosubstituted nitrile imines (R-CNN-H, H-CNN-R, and R-CNN-R; R = NH 2 , OH, and F) and predicted that some of the studied molecules should exhibit carbenic character. [30] These postulated carbenic nitrile imines were predicted to lack the intense IR absorption in the 2000-2250 cm -1 region that characterizes other nitrile imines.…”

Understanding Reactivity Patterns in Light‐Induced Nitrile Imine Mediated Tetrazole–Ene Cycloadditions

“…Although some computational studies have already been undertaken on nitrile imines, [14] not much attention has been paid to the tetrazole activation step, [15] which in our opinion is crucial to understand their reactivity.H erein, density functional theory (DFT) calculationso ft he three tetrazoles, Tet, Py-Tet and Biph-Tet,w ere carriedo ut. First, an examination of the transitions of the ground state of the selected tetrazoles was carried out.…”

Laplacian of the electron density: a hole–lump interaction as a tool to study stereoelectronic control of chemical reactions

“…In the case of a maximally depleted charge, it is possible to report which sites are able to stabilize an overload uptake of electronic charge and that they are especially reactive toward electron‐rich reactants (nucleophiles) . Additionally, studies dealing with chemical reactivity relationships and QTAIM have shown that the Laplacian can be reliably used to predict reactive sites, such as the positions of sites for electrophilic or nucleophilic attack in aromatic systems, N‐heterocyclic carbenes, α‐ and β‐halonaphthalenes, non‐steroidal anti‐inflammatory drugs, and other chemical systems …”

“…[3,4] Additionally, studies dealing with chemical reactivity relationships and QTAIM have shown that the Laplacian can be reliably used to predict reactive sites, such as the positions of sites for electrophilic or nucleophilic attack in aromatic systems, [5] N-heterocyclic carbenes, [6] αand β-halonaphthalenes, [7] non-steroidal anti-inflammatory drugs, [8] and other chemical systems. [9][10][11] Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products and their structures. In a previous work, we showed that the most important topological feature in the ethene protonation reaction over acidic zeolite is the electron charge density redistribution.…”