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Catalytic Activation via π –Backbonding in Halogen Bonds?
preprintsubmitted on 18.11.2020, 18:01 and posted on 19.11.2020, 12:38 by Andrew Wang, Pierre Kennepohl
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 subsitution 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.
Natural Sciences and Engineering Research Council of Canada (NSERC)
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