Enantioseparation in Hierarchically Porous Assemblies of Homochiral Cages

Abstract

Efficient enantioselective separation using porous materials requires tailored and diverse pore environments to interact with chiral substrates; yet, current cage materials usually feature uniform pores. Herein, we report two porous assemblies, <b>PCC-60</b> and <b>PCC-67</b>, using isostructural octahedral cages with intrinsic microporous cavities of 1.5 nm. The <b>PCC-67</b> adopts a densely packed mode, while the <b>PCC-60</b> is a hierarchically porous assembly featuring interconnected 2.4 nm mesopores. Compared with <b>PCC-67</b>, the <b>PCC-60</b> demonstrates excellent enantioselectivity and recyclability in separating racemic diols and amides. This solid adsorbent <b>PCC-60</b> is further utilized as a chiral stationary phase for high-performance liquid chromatography (HPLC), enabling the complete separation of six valuable pharmaceutical intermediates. According to quantitative dynamic experiments, the hierarchical pores facilitate the mass transfer within the superstructure, shortening the equilibrium time for adsorbing chiral substrates. Notably, this hierarchically porous material <b>PCC-60</b> indicates remarkably higher enantiomeric excess (ee) values in separating racemates than <b>PCC-67</b> with uniform microporous cavities. Control experiments confirm that the presence of mesopores enables the <b>PCC-60</b> to separate bulky substrates. These results uncover the traditionally underestimated role of hierarchical porosity in porous-superstructure-based enantioseparation.