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