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

preprint
revised on 27.04.2020, 14:43 and posted on 28.04.2020, 10:50 by Gabriel dos Passos Gomes, Guangcan Xu, Xiaolei Zhu, Lise-Marie Chamoreau, Yongmin Zhang, Olivia Bistri Aslanoff, Sylvain Roland, Igor Alabugin, Matthieu Sollogoub

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.

Funding

National Science Foundation (Grant CHE-1800329)

NSF XSEDE (TG-CHE160006)

ANR-11-IDEX-0004-02

History

Email Address of Submitting Author

gabriel.gomes@utoronto.ca

Institution

Florida State University, Sorbonne Université, University of Toronto

Country

USA, France, Canada

ORCID For Submitting Author

0000-0002-8235-5969

Declaration of Conflict of Interest

We declare no conflict of interests.

Version Notes

Version 1: pre-journal submission. Version 2: pre-journal submission, improved Schemes.

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