Mapping C−H•••M interactions in confined spaces: (α-ICyDᴹᵉ)Au, Ag, Cu complexes reveal “contra-electrostatic H-bonds” masquerading as anagostic interactions

28 April 2020, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

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-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.

Keywords

C-H•••Metal interactions
Cyclodextrin
Supramolecular Interactions
Stereoelectronic Effects
Agostic Interactions
Anagostic Interactions
Computational Organic Chemistry
DFT

Supplementary materials

Title
Description
Actions
Title
SI Ag Au Cu cyclodextrins 04 23 2020 ChemRxiv v1
Description
Actions
Title
toc
Description
Actions

Supplementary weblinks

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.