Triggered Exchange of Anionic for Neutral Guests inside a Cationic Coordination Cage

Abstract

Molecular encapsulation processes under the control of an external trigger play a major role in biological signal transduction processes and enzyme catalysis. Here, we present an artificial mimic of a controllable host system that forms via self-assembly from a simple bis-monodentate ligand and Pd(II) cations. The resulting interpenetrated double cage features three consecutive pockets which initially contain one tetrafluoroborate anion, each. Activation of this host system with two halide anions triggers a conformational change that renders the central pocket susceptible to the uptake of small neutral guest molecules. Thereby, the pentacationic cage expels the central anion and replaces it with a neutral molecule to give a hexacationic species. The cage structures prior and after the halide triggered binding of benzene were examined by X-ray crystallography, ESI MS, and NMR techniques. The kinetics and thermodynamics of the encapsulation of benzene, cyclohexane, and norbornadiene are compared.

Anion Receptor Chemistry

“…Lö ffler et al 66 have recently reported the synthesis of the interpenetrated double palladium cage 136 (Scheme 2). The double cage contains a stack of four palladium ions each bridged by a tetrafluoroborate anion.…”

Light-Induced Charge Separation in Densely Packed Donor–Acceptor Coordination Cages

“…[3] The obtained structure was optimized on ωB97XD/def2-SVP DFT level (charge: +5, multiplicity: singlet, with three BF 4 − inside the three internal pockets, no constraints) using the dispersion-corrected ωB97XD functional implemented in Gaussian '09 [4] and the Ahlrich def2-SVP basis set obtained from the EMSL basis set exchange website https://bse.pnl.gov/bse/portal. [5] Hydrogen atoms are omitted for clarity.…”

Synthesis and Applications of Endohedrally Functionalized Metal‐Ligand Cage Complexes

“…Varying the guest anions can force the double cages into binding less favorable secondary guests. Small halides are favored in the terminal cavities, which forces the central Pd II ions closer to each other, creating a larger internal cavity that is capable of binding neutral species such as benzene or norbornane in an allosteric manner . As well as simple lone pairs, the other obvious small function to internalize is a hydrogen bond donor group such as a urea, alcohol or the like.…”

“… Selective anion recognition in functionalized cage complexes . Adapted with permission from reference 25, copyright 2017 American Chemical Society.…”