Anion-Mediated Allosteric Catalysis of [2 + 2] Photocycloaddition Based on a Flexible Metallo-Amine Cage for High Diastereoselectivity

Anions can exert a notable influence on the solubility and folding
of protein structures, consequently altering their activity and stability
due to the well-known Hofmeister effect. Herein, we report a protein-like
allosteric metal–organic cage (MOC-68) with the solubility
and conformation regulated through anion exchange, leading to conversion
between the relaxed state (R-state) and the tensed state (T-state)
to show distinct host–guest interactions. This conformational
change enables allosteric catalysis of intermolecular [2 + 2] photocycloaddition
of acyclic olefins with greatly enhanced yield and diastereoselectivity.
Kinetic experiments reveal that the T-state of MOC-68 is superior
in catalytic performance for the steric and thermodynamic unfavored syn-HH product, displaying a threefold rate enhancement
over the R-state and totally a sevenfold increase owing to the reaction
acceleration contributed by an enzymatic cage effect. Notably, this
allosteric cage exhibits exceptional stability and recyclability,
maintaining consistent catalytic efficiency and selectivity over five
cycles. This work highlights the potential of structural allostery
in flexible cages to enhance the substrate-binding ability and catalytic
selectivity, providing a way to advance enzyme-mimicking cage catalysis
to regulatable and efficient allosteric catalysis.