Mapping C−H×××M Interactions in Confined Spaces: (a-ICyD Me )Au, Ag, Cu Complexes Reveal "Contra-electrostatic H-bonds" Masquerading as Anagostic Interactions
Résumé
What happens when a C-H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as "contra-electrostatic" H-bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H-bonding with an unusual contra-electrostatic component. While electrostatics is strongly stabilizing component in the conventional C-H … X bonds where X is an electronegative main group element, it is destabilizing in the C-H … M contacts when M is Au(I), Ag(I), or Cu(I) of NHC-M-Cl systems. Such remarkable C-H … M interaction became experimentally accessible within (α-ICyD Me )MCl, NHC-Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C-H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set of d -orbitals. A combination of experimental and computational data demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C-H bond to point toward the metal, and reveals a still attractive "contra-electrostatic" H-bonding interaction.
Domaines
ChimieOrigine | Fichiers produits par l'(les) auteur(s) |
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