Synthesis of a hierarchical porous organic [4[2+3]+6] ‘cage of cages’

Abstract We report a new two-step, hierarchical synthesis that assembles a trigonal prismatic organic cage into a more symmetrical, higher-order tetrahedral cage, or ‘cage of cages’. Both the pre-formed [2 + 3] trigonal cage building blocks and the resultant [4[2 + 3] + 6] tetrahedral cage molecule are constructed using ether bridges. This affords the [4[2 + 3] + 6]cage molecule excellent hydrolytic stability that is not a feature of more common dynamic cage linkers, such as imines. Despite its relatively high molar mass (3002 g mol − 1 ), this [4[2 + 3] + 6]cage exhibits good solubility and crystallises into a porous superstructure with a surface area of 763 m 2 g − 1 . By contrast, the [2 + 3] prismatic cage building block is not porous. The hierarchical [4[2 + 3] + 6]cage molecule shows high CO 2 uptakes due to its polar skeleton. The preference for the [4[2 + 3] + 6]cage over other possible cage products can be predicted by computational modelling, suggesting a broader design strategy for hierarchical organic cages with synthetically engineered functions.