Contributed
Coordination cages for the transportation of molecular cargo

Coordination cages can selectively encapsulate guests based on their size and shape,¹ making these structures promising scaffolds for performing size-selective separations.² To successfully address practical separations problems, however, a guest molecule cannot simply be isolated from its environment; the molecular cargo must be removed to a separate physical space.³ We demonstrate that coordination cages transfer reversibly between immiscible water and ethyl acetate layers upon anion exchange (Figure 1).^4,5 This process was monitored by slice-selective ¹H NMR, which indicates no significant degradation of the cages even after crossing the phase boundary many times. Furthermore, we designed a series of systems that achieve sequential phase transfer of individual cage species within a mixture, thereby separating different cages and their respective cargoes.

Figure 1. Cages 1⁸⁺, 2⁸⁺, and 3¹⁶⁺ were observed to transport reversibly between water and ethyl acetate.

1) A. J. McConnell, C. M. Aitchison, A. B. Grommet, J. R. Nitschke J. Am. Chem. Soc., 2017, 139, 6294.

2) A. B. Grommet, J. L. Bolliger, C. Browne, J. R. Nitschke Angew. Chem. Int, Ed., 2015, 54, 15100.

3) A. B. Grommet, J. R. Nitschke J. Am. Chem. Soc., 2017, 139, 2176.

4) A. B. Grommet, J. B. Hoffman, E. G. Percástegui, J. Mosquera, D. J. Howe, J. L. Bolliger, J. R. Nitschke J. Am. Chem. Soc., 2018, 140, 14770.

5) A. J. McConnell, C. J. E. Haynes, A. B. Grommet, C. M. Aitchison, J. Guilleme, S. Mikutis, J. R. Nitschke submitted.