Largely Entangled Diamondoid Framework with High-Density Urea and Divergent Metal Nodes for Selective Scavenging of CO2 and Molecular Dimension-Mediated Size-Exclusive H‑Bond Donor Catalysis

• Published in: Inorganic chemistry 2023-01, Vol.62 (2), p.871-884
• Main Authors: Singh, Manpreet, Neogi, Subhadip
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c03684

Pore environment modulation with high-density polarizing groups in metal–organic frameworks (MOFs) can effectively accomplish selective and multicyclic carbon dioxide (CO2) adsorption, whereas the incorporation of task-specific organic sites inside these porous vessels promise to evade self-quenching, solubility, and recyclability issues in hydrogen-bond donating (HBD) catalysis. However, concurrent amalgamation of both these attributes over a single platform is rare but extremely demanding in view of sustainable applications. We designed a robust diamondoid framework CSMCRI-17 (CSMCRI = Central Salt and Marine Chemicals Research Institute) from the mixed-ligand assembly of azo group-containing dicarboxylate ligand, urea-functionalized pyridyl linker, and Zn­(II) nodes with specific divergent coordination. Seven-fold interpenetration to the microporous structure largely augments N-rich functionality that facilitates high CO2 uptake in the activated form (17a) with good CO2 selectivity over N2 and CH4 that outperform many reported materials. The framework displays very strong CO2 affinity and no reduction in adsorption capacity over multiple uptake–release cycles. Benefitting from the pore–wall decoration with urea functionality from the pillaring strut, 17a further demonstrates hydrogen-bond-mediated Friedel–Crafts alkylation of indole with β-nitrostyrene under mild conditions, with multicyclic usability and excellent reactivity toward wide ranges of substituted nucleophiles and electrophiles. Interestingly, interpenetration-generated optimum-sized pores induce poor conversion to sterically encumbered substrate via molecular dimension-mediated size selectivity that is alternatively ascribed from additional control experiments and support the occurrence of HBD reaction within the MOF cavity. The catalytic path is detailed in light of the change of emission intensity of the framework by the electrophile as well as the judicious choice of the substrate, which authenticates the prime role of urea moiety-governed two-point hydrogen bonding.