A nitrogen-rich ionic metal-organic vessel: Temperature triggered improved CO2 separation and hydrogen-bond mediated cycloaddition with pore-space-partition induced size-selective Friedel-Crafts alkylation

Abstract

Herein, we built a two-fold interpenetrated, robust pillar-bilayered framework from anionic [Cd3(µ2-OH)(COO)6] unit and –NH2 hooked nitrogen-rich struts. The activated MOF shows temperature variable CO2 adsorption with minimum uptake loss during multiple cycle and under humid environment. Interestingly, CO2/N2 selectivity displays notable enhancement upon rise in temperature, reaching a value of 490 at 313 K that outperforms some best-performing adsorbents. The MOF catalyses solvent-free and mild-condition CO2 cycloaddition with wide substrate scope, good recyclability and high turnover number. Opposed to common Lewis acid-mediated reaction, pendent –NH2 sites activate the epoxide via H-bonding interaction, as validated from performance comparison of an un-functionalized MOF, and guest-mediated concomitant fluorescence articulation. These hydrogen-bond-donating (HBD) sites further benefit effective Friedel−Crafts (FC) alkylation of indole with β-nitrostyrene, where product is additionally characterized by single-crystal X-ray diffraction. The reaction includes twenty electronically assorted substrates and transpires with high catalyst reusability. The key role of HBD moiety in directing C-C coupling is detailed from correlating the performance of two isostructural MOFs without –NH2 site, judicious choice of the substrates, and fluorescence modification derived framework-electrophile interaction. Importantly, pore-space-partitioning by flanked pyridyl linker induces size-selectivity via restricting the channel diffusion of sterically encumbered indole.