Host-Guest Mismatch Enables Selective Hydrogen Atom Transfer

Area of Science:

• Supramolecular Chemistry
• Catalysis
• Organic Chemistry

Background:

• Endogenous host-guest binding is common in catalysis.
• Exogenous binding, where guests bind to host exteriors due to size mismatch, is less explored for reaction control.

Purpose of the Study:

• To investigate exogenous binding between cyclodextrins (CDs) and a polyoxometalate (POM) catalyst.
• To demonstrate control over chemical reaction selectivity using this unexplored binding paradigm.

Main Methods:

• Noncovalent association of decatungstate anion (W10O32^4-) with CDs in aqueous solution.
• Characterization using 1H NMR titration and X-ray crystallography to confirm binding at the CD rim.
• Photoexcitation to initiate hydrogen atom transfer (HAT) reactions.

Main Results:

• W10O32^4- associates exogenously with the narrow rim of CDs due to size mismatch.
• This binding increases local concentration of the catalyst near C6-H bonds.
• Accelerated HAT at C6 positions leads to selective C6 functionalization.

Conclusions:

• Host-guest size mismatch enables selective exogenous binding for catalytic control.
• This strategy provides a general platform for selective ligation of CDs to various molecules.
• The approach facilitates one-step ligations for applications in drug delivery, diagnostics, and synthesis.