Enhancing the Chemical Stability of P₁₂L₂₄ Cage: Transformation of the Chemically Labile Imine Cage into a Robust...

Herein, we report enhancement in chemical stability of the imine-based porphyrinic cage P₁₂L₂₄ by converting it into a robust carbamate porphyrinic cage, c-P₁₂L₂₄, through a two-step post-synthetic modification process. First, the imine bonds in P₁₂L₂₄ were reduced to form an amine-based cage, r-P₁₂L₂₄, followed by carbamation using N,N'-carbonyldiimidazole (CDI) to yield c-P₁₂L₂₄. The resulting carbamate cage exhibits high stability under acidic and basic conditions (pH 1-13) and in the presence of moisture. ¹H 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-P₁₂L₂₄ 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.