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.

Despite its cramped interior, a [Pd2L4] coordination cage consisting of bulky adamantyl ligands shows impressive motility and a rich encapsulation chemistry.

Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units were synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UVvis spectroscopy. Reductive quenching of the 3 MLCT excited state of the [Re(phen)(CO)3(py)]+ complex (phen = 1,10-phenanthroline, py = pyridine) by the two pyridylphenols and two reference phenol molecules was investigated by steady-state and time-resolved luminescence spectroscopy, as well as by transient absorption spectroscopy. Stern-Volmer analysis of the luminescence quenching data provides rate constants for the bimolecular excited-state quenching reactions. H/D kinetic isotope effects (KIEs) for the pyridylphenols are on the order of 2.0, and the bimolecular quenching reactions are up to 100 times faster with the pyridylphenols than with the reference phenols. This observation is attributed to the markedly less positive oxidation potentials of the pyridylphenols with respect to the reference phenols (ca. 0.5 V), which in turn is caused by protoncoupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, i. e., the overall photoreaction is clearly a PCET process

A halide-triggered metallosupramolecular host was systematically studied for the uptake of small neutral molecules using NMR and MS experiments. Starting from benzene, cyclic guests were screened with respect to size (ring count), shape (flatness, 3D structure, substitution pattern, flexibility) and hetero atom content (number, position, donor character). 5-Rings and substituted 5/6-rings bind only weakly, while oversized (e.g. naphthalene, adamantane, ferrocene) and linear alkanes do not bind at all. Bridged 6-rings of the norbornane type and in particular DABCO bind strongly, likewise other guests with oppositely arranged hetero atoms. For the DABCO complex, a single crystal X-ray structure was obtained. The contribution of dispersive interactions to binding was derived from electronic structure calculations. Together, experimental and theoretical data deepen the understanding of guest selectivity and encapsulation driving force towards application of the host as a switchable receptor and reaction chamber.

Multiple functionalities of an acridone-based metallosupramolecular assembly: photosensitization of singlet oxygen, allosteric activation as host and encapsulation of the substrate and product of a hetero-Diels-Alder reaction.