Strong halide anion binding within the cavity of a conformation-adaptive phenazine-based Pd₂L₄ cage

Herein, we report a de novo design of a phenazine-based Pd₂L₄ cage receptor capable of binding a series of anions with extremely high affinity. The main core of our molecular design rationale is based on a conformation-adaptive phenazine ligand, which makes the resultant cage highly flexible and readily alters its conformation to fit target anion guests. Consequently, this Pd₂L₄-type cage can efficiently encapsulate a variety of anions, ranging from halides, such as Cl⁻, Br⁻, and I⁻, to BF₄⁻ and NO₃⁻, resulting in a series of anion-encapsulating cages, which were thoroughly characterized by X-ray crystallography. Impressively, the cage exhibited very strong anion-binding affinity, and the binding constant toward chloride in acetonitrile was estimated to exceed 10¹⁴ M⁻¹. Moreover, we successfully demonstrate that the cage could promote the scission of carbon–halogen (C–X) bonds, largely because of its excellent halide sequestration property and the intrinsic photoredox catalytic property of the phenazine moiety.