Computationally guided synthesis of a hierarchical [4[2+3]+6] porous organic ‘cage of cages’
Qiang Zhu, Hang Qu, Gökay Avcı, Roohollah Hafizi, Chengxi Zhao, Graeme M. Day, Kim E. Jelfs, Marc A. Little, Andrew I. Cooper
Abstract
Abstract Here we report a two-step, hierarchical synthesis that assembles a trigonal prismatic organic cage into a more symmetric, higher-order tetrahedral cage, or ‘cage of cages’. Both the preformed [2+3] trigonal prismatic cage building blocks and the resultant tetrahedral [4[2+3]+6]cage molecule are constructed using ether bridges. This strategy 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 (3,001 g mol −1 ), [4[2+3]+6]cage exhibits good solubility and crystallizes into a porous superstructure with a surface area of 1,056 m 2 g −1 . By contrast, the [2+3] building block is not porous. The [4[2+3]+6]cage molecule shows high CO 2 and SF 6 uptakes due to its polar skeleton. The preference for the [4[2+3]+6]cage molecule over other cage products can be predicted by computational modelling, as can its porous crystal packing, suggesting a broader design strategy for the hierarchical assembly of organic cages with synthetically engineered functions.