Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 27, Issue 31, Pages 8127-8142Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202100263
Keywords
anagostic interactions; C− H metal interactions; coinage metals; confinement; cyclodextrins; hydrogen bonds
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Funding
- National Science Foundation [CHE-1800329]
- Canada's Natural Sciences and Engineering Research Council (NSERC)
- Canada Foundation for Innovation
- Government of Ontario
- Ontario Research Fund - Research Excellence
- University of Toronto
- CSC
- LabEx MiChem part of French state funds [ANR-11-IDEX-0004-02]
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This study explores the interaction between C-H bonds and positively charged metal unpaired electrons, resulting in contra-electrostatic H-bonding. The research demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C-H bond to point towards the metal, revealing an attractive contra-electrostatic H-bonding interaction.
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 (alpha-ICyDMe)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.
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