An Organo‐Palladium Host Built from a Dynamic Macrocyclic Ligand: Adaptive Self‐Assembly, Induced‐Fit Guest Binding, and Catalysis

Abstract

Artificial hosts with rich conformational dynamics are attractive to supramolecular chemists due to their adaptive guest‐binding properties and enzyme‐like catalytic functions. We report here the adaptive self‐assembly and host‐guest catalysis of a new water‐soluble organo‐palladium host (Pd2L2) built from a pyridinium‐bonded macrocyclic ligand (L) and cis‐blocked palladium corners (Pd). While the direct self‐assembly of L with Pd gives rise to a dynamic mixture of products, both neutral polyaromatic hydrocarbons and an anionic polyoxometalate cluster (W10O324−) can template the dominant formation of the Pd2L2 host. Guest‐adaptive conformational changes and induced‐fit cavity deformation of the Pd2L2 host have been clearly observed in the crystal structures. Moreover, the installation of the electron‐rich W10O324− cluster within the cationic redox‐active host (W10O32⊂Pd2L2) facilitates the efficient and selective C−H photooxidation of toluene derivatives to aldehyde products under mild conditions, thus representing an ideal platform for green supramolecular catalysis.

Dynamic Interconversion and Induced-Fit Guest Binding with Two Macrocycle-Based Coordination Cages

“…We have successfully obtained the crystal structures for the host−guest complexes of the dynamic macrocycle ligand in this work, which was not achieved in our previous work. 46 Xray crystallography unambiguously confirmed the structure of both free L and its 1:1 host−guest complexes for G4 ⊂ L and G5 ⊂ L (Figure 1B−D). Single crystals suitable for X-ray diffraction studies were obtained by slowly evaporating the aqueous solution of the sample.…”

“…In the crystal structure of G2 ⊂ Pd 1 L 1 , one anthracene was situated in the optimal position of the cavity, host from the dynamic mixture through induced-fit guest encapsulation. In sharp contrast, the Pd 1 L 1 complex with mmethylphenyl linkers in our previous work 46 does not have an internal cavity for PAH guest encapsulation.…”

“…The DOSY spectrum confirmed the formation of Pd 2 L 2 with a single diffusion band (Figure S33). According to our previous work, there was an equilibrium between Pd 2 L 2 and the other product Pd 1 L 1 in D 2 O.…”

“…Novel and functional macrocyclic hosts with conformational change and cavity tunability have sparked a lot of interest in molecular recognition and supramolecular materials. − They also serve as promising building blocks in the design of coordination supramolecular architectures with rich host–guest chemistry. − Recently, we have reported a flexible organopalladium host built from a dynamic macrocyclic ligand with two m -methylphenyl linkers, which exhibited both induced-fit guest binding and efficient photooxidation catalysis.…”

“…31−41 They also serve as promising building blocks in the design of coordination supramolecular architectures with rich host− guest chemistry. 42−45 Recently, we have reported a flexible organopalladium host built from a dynamic macrocyclic ligand with two m-methylphenyl linkers, 46 which exhibited both induced-fit guest binding and efficient photooxidation catalysis.…”