Catalytic Activation via π –Backbonding in Halogen Bonds?

09 July 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


The role of halogen bonding (XB) in chemical catalysis has largely involved using XB donors as Lewis acid activators to modulate the reactivity of partner Lewis bases. We explore a more uncommon scenario, where a Lewis base modulates reactivity via a spectator halogen bond interaction. Our computational studies reveal that spectator halogen bonds may play an important role in modulating the rate of SN2 reactions. Most notably, π acceptors such as PF3 significantly decrease the barrier to substitution by decreasing electron density in the very electron-rich transition state. Such π-backbonding represents an example of a heretofor unexplored situation in halogen bonding: the combination of both s-donation and π-backdonation in this “non-covalent” interaction.


halogen bonds
pi bonding
Density Functional Theory calculations

Supplementary materials

Supplementary Information
Additional details regarding computational methods including molecule geometries, energies, NPA analysis, and charge decomposition analysis.


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