Pathway-Dependent Post-assembly Modification of an Anthracene-Edged MII^{II}4L6_4L_6 Tetrahedron

Fe$^{II}$$_4L_6$ tetrahedral cage $\textbf{1}$ undergoes post-assembly modification (PAM) via a Diels-Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage $\textbf{2}$ possesses an enclosed cavity suitable for encapsulation of the fullerene C$_{60}$, whereas original cage $\textbf{1}$ forms a unique covalent adduct through a Diels-Alder cycloaddition of three of its anthracene ligands with C$_{60}$. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C$_{60}$ and TCNE. Modified cage $\textbf{2}$ was also able to bind an anionic guest, [Co(C$_2$B$_9$H$_{11}$)$_2$]$^{-}$, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts.Engineering and Physical Sciences Research Council, University of Cambridge (Herchel Smith Research Fellowship), Corpus Christi College (Cambridge; Fellowship

Guest Encapsulation within Surface-Adsorbed Self-Assembled Cages

Coordination cages encapsulate a wide variety of guests in the solution state. This ability renders them useful for applications such as catalysis and the sequestration of precious materials. A simple and general method for the immobilization of coordination cages on alumina is reported. Cage loadings are quantified via adsorption isotherms and guest displacement assays demonstrate that the adsorbed cages retain the ability to encapsulate and separate guest and non-guest molecules. Finally, a system of two cages, adsorbed on to different regions of alumina, stabilizes and separates a pair of Diels-Alder reagents. The addition of a single competitive guest results in the controlled release of the reagents, thus triggering their reaction. This method of coordination cage immobilization on solid phases is envisaged to be applicable to the extensive library of reported cages, enabling new applications based upon selective solid-phase molecular encapsulation

Subcomponent Exchange Transforms an Fe(II)4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System

Subcomponent exchange transformed new high-spin Fe(II)4L4 cage 1 into previously-reported low-spin Fe(II)4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage's Fe(II) centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin Fe(II)4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system's behavior, fundamentally altering its response to the subsequent signal p-anisidine.This work was funded by the European Research Council (695009) and EPSRC (EP/M01083X/1