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ortho–para-Directing Deactivators: Halogens

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Direct π-Activation vs. O-Activation in Halogen-Bonding Catalysis.

Raphaël Robidas¹, Claude Y Legault¹

¹Department of Chemistry, Université de Sherbrooke, Centre in Green Chemistry and Catalysis Sherbrooke, Québec, J1K 2R1, Canada.

Angewandte Chemie (International Ed. in English)

|February 14, 2023

Summary

New computational data reveals that iodine-based halogen bond donors can activate unsaturated carbonyls via π-complexation, not just carbonyl coordination. Solvent polarity may switch this activation mechanism, impacting future catalyst design.

Keywords:

Catalysis Halogen Bonding Iodine Mechanism Molecular Iodine

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Area of Science:

Catalysis
Supramolecular Chemistry
Computational Chemistry

Background:

Halogen bond donors, particularly iodine-based ones, are increasingly vital in catalysis.
Activation of carbonyl groups via coordination is a common mechanism for these donors.

Purpose of the Study:

To investigate alternative activation modes for unsaturated carbonyl substrates using halogen bond donors.
To explore the influence of solvent polarity on the activation mechanism.

Main Methods:

Computational analysis was employed to study the interactions between halogen bond donors and unsaturated carbonyl substrates.
The study focused on evaluating direct π-complexation as an alternative to carbonyl coordination.

Main Results:

Computational data strongly suggests direct π-complexation is an operative activation mode for unsaturated carbonyls.
Solvent polarity appears to influence the preferred activation mode, indicating a potential for mechanistic switching.

Conclusions:

The findings challenge the ubiquitous carbonyl coordination model by introducing π-complexation.
Solvent-dependent mechanistic switching offers new avenues for designing advanced halogen-bond donor catalysts.