Enhancing the Chemical Stability of P 12 L 24 Cage: Transformation of the Chemically Labile Imine Cage into a Robust Carbamate Cage

Herein, we report enhancement in chemical stability of the imine-based porphyrinic cage P L by converting it into a robust carbamate porphyrinic cage, c-P L , through a two-step post-synthetic modification process. First, the imine bonds in P L were reduced to form an amine-based cage, r-P L , followed by carbamation using N,N'-carbonyldiimidazole (CDI) to yield c-P L . The resulting carbamate cage exhibits high stability under acidic and basic conditions (pH 1-13) and in the presence of moisture. H NMR, DOSY NMR, and DFT calculations revealed that reducing the imine bonds to amine increases the framework's flexibility, causing partial structural collapse, whereas the carbamate formation restores structural rigidity. The insertion of a 4.0 nm molecular ruler into the cavity of zinc-metallated c-P L via metal-ligand coordination further confirmed restoration of the cavity size and geometry of the original cage. This enhancement of chemical stability through carbamate formation can pave the way to a wide range of potential applications for the gigantic porphyrinic cage.