Halogen bonds with carbenes acting as Lewis base units: complexes of imidazol-2-ylidene: theoretical analysis and experimental evidence

Abstract

The ωB97XD/aug-cc-pVDZ and ωB97XD/aug-cc-pVTZ calculations were performed on complexes of imidazol-2-ylide that are linked by halogen bonds. This singlet carbene acts as the Lewis base through lone electron pair located...

Halogen Bond to Experimentally Significant N-Heterocyclic Carbenes (I, IMe2, IiPr2, ItBu2, IPh2, IMes2, IDipp2, IAd2; I = Imidazol-2-ylidene)

“…Then, Del Bene et al [94] performed theoretical studies of the halogen bond between ClCCH, ClCN, ClNC, or ClF and some rather exotic small carbenes. Quite recently, Grabowski performed calculations for imidazol-2-ylidene complexes with XCCH, XCN, and X 2 (X = F, Cl, Br, I) [95]. As might be expected, the F molecules did not form a halogen bond to the carbene carbon atom.…”

“…However, the characteristics of the relationship between H C•••X and d C•••X cause that with the decrease in the distance C• • • I, the value of H C•••X decreases rapidly, becoming a significantly negative number, which indicates a significant covalent contribution of the interaction. In extreme cases, an [IR 2 X] + [D] − ionic pair may be formed [95].…”

“…The examples cited [89][90][91][92][93][94][95] clearly show that currently there is practically no theoretical work on halogen bonding involving larger and experimentally significant NHCtype carbenes. In the vast majority of cases, these are derivatives of imidazol-2-ylidene containing large groups at both nitrogens of the heterocycle, e.g., 1-adamantyl (= Ad), 2,6-diisopropylphenyl (= Dipp), mesityl (= Mes), tert-butyl (= t Bu), or iso-propyl (= i Pr).…”

C–H⋯C hydrogen bond and alkali metal C⋯Z⋯C (Z = Li, Na, K) analogues –N-heterocyclic carbenes in coordination spheres of protons and alkali metal cations: crystal structures and theoretical analysis

“…9 One can also mention a recent study on halogen bonds that link imidazol-2-ylidene with XCCH, XCN and X 2 Lewis acid units (X = F, Cl, Br and I); the calculations on these complexes were performed at the ωB97XD/aug-cc-pVDZ and ωB97XD/aug-cc-pVTZ levels. 10 Electrostatic potentials, EPs, were analysed in a later study, 10 and it was found that halogen bonds occur between the positive EP sites, i.e. σ-holes, 11–14 of halogen centres and the negative EP C-centre of imidazol-2-ylidene species.…”

Unveiling the Noncovalent Interaction of Thiazol‐2‐ylidene and Its Derivatives as N‐heterocyclic Carbene with Different Proton Donor Molecules

“…At the outset, the interaction of carbene with transition metal [2,[19][20][21] produced highly valuable complexes in organic, material, and organo-metallic chemistry. [2,3,6] In addition, carbene also engages with other intermolecular interactions such as hydrogen bonds, [16,[22][23][24][25][26] halogen bonds, [26][27][28][29][30][31] beryllium bonds, [8,[32][33][34][35] lithium bonds, [8,29,[36][37][38] triel bonds, [29,[39][40][41][42] magnesium bonds, [34,35,[43][44][45] chalcogen bonds, [46] and aerogen bonds. [47] These interactions occur due to a lone pair of electrons in the carbene carbon atom.…”