Topologically Driven Pore/Surface Engineering in a Recyclable Microporous Metal–Organic Vessel Decorated with Hydrogen-Bond Acceptors for Solvent-Free Heterogeneous Catalysis

Abstract

The use of metal–organic frameworks (MOFs) comprising custom-designed linkers/ligands as efficient and recyclable heterogeneous catalysts is on the rise. However, the topologically driven bifunctional porous MOFs for showcasing a synergistic effect of two distinct activation pathways of substrates (e.g., involving hydrogen bonding and a Lewis acid) in multicomponent organic transformations are very challenging. In particular, the novelty of such studies lies in the proper pore and/or surface engineering in MOFs for bringing the substrates in close proximity to understand the mechanistic aspects at the molecular level. This work represents the topological design, solid-state structural characterization, and catalytic behavior of an oxadiazole tetracarboxylate-based microporous three-dimensional (3D) metal–organic framework (MOF), {[Zn2(oxdia)­(4,4′-bpy)2]·8.5H2O} n (1), where the tetrapodal (4-connected) 5,5′-(1,3,4-oxadiazole-2,5-diyl)­diisophthalate (oxdia4–), the tetrahedral metal vertex (Zn­(II)), and a 2-connected pillar linker 4,4′-bipyridine (4,4′-bpy) are unique in their roles for the formation, stability, and function. As a proof of concept, the efficient utilization of both the oxadiazole moiety with an ability to provide H-bond acceptors and the coordinatively unsaturated Zn­(II) centers in 1 is demonstrated for the catalytic process of the one-pot multicomponent Biginelli reaction under mild conditions and without a solvent. The key steps of substrate binding with the oxadiazole moiety are ascertained by a fluorescence experiment, demonstrating a decrease or increase in the emission intensity upon interaction with the substrates. Furthermore, the inherent polarizability of the oxadiazole moiety is exploited for CO2 capture and its size-selective chemical fixation to cyclic carbonates at room temperature and under solvent-free conditions. For both catalytic processes, the chemical stability, structural integrity, heterogeneity, versatility in terms of substrate scope, and mechanistic insights are discussed. Interestingly, the first catalytic process occurs on the surface, while the second reaction occurs inside the pore. This study opens new ways to catalyze different organic transformation reactions by utilizing this docking strategy to bring the multiple components close together by a microporous MOF.

Exploiting a Multi-Responsive Oxadiazole Moiety in One Three-Dimensional Metal–Organic Framework for Remedies to Three Environmental Issues

“…The weight loss in the TGA profile of 1 below 100 °C corresponds to the loss of the lattice solvent molecules: calc. 5.6 wt %, found 6.4 wt % (four water molecules). An additional weight loss between 100 and 150 °C (calc.…”

“…For instance, the frameworks are largely exploited for the sorption and separation of gases and solvent vapors owing to their exceptionally high porosity and large surface areas . Additionally, incorporating molecular recognition sites on the organic building units (struts) or engineering the functionalities through postsynthesis of MOFs contributes highly in this direction. − Pollutant gases, such as flue gas, which are emanated from the basic combustion reactions, contain small toxic molecules, like carbon monoxide (CO), carbon dioxide (CO 2 ), methane (CH 4 ), sulfur oxides (SO x ), nitrogen oxides (NO x ), and other particulates. The anthropogenic CO 2 emissions into the environment have raised a red alert, causing an imbalance of the ecosystem and adverse climate changes.…”

Multifunctional Eu3+‐coordination polymer for highly selective recognition of Fe3+ and MnO4− ions in water and efficient catalytic fixation of carbon dioxide

“…The literature reports show that the heterogeneous CPs catalysts have incomparable advantages in terms of high catalytic activity, high recyclability, and convenient recovery, for instance, {[Cu 2 (4‐TPOM)(3,7‐DBTDC) 2 ]·4H 2 O·3DMF} n [ 62 ] and {[Zn 2 (oxdia)(4,4′‐bpy) 2 ]·8.5H 2 O} n . [ 64 ] These CPs catalysts are constructed through transition‐metal ions. However, the catalytic performance of Ln‐based CPs is less reported.…”

“…[41][42][43][44][45][46][47] These chemicals have been widely applied as aprotic polar solvents, lithium batteries, and chemical intermediates for the synthesis of chemicals. [48][49][50] So far, various homogeneous (such as phosponium salts [51,52] and ionic liquids [53,54] ) and heterogeneous catalysts (such as metal oxides, [55,56] covalent organic frameworks [COFs], [57,58] and CPs [45][46][47][59][60][61][62][63][64] ) have been explored for the cycloaddition of CO 2 with epoxides. Among these, CPs with high-density coordinationunsaturated metal sites are conducive to the fixation of CO 2 , which has attracted extensive attention.…”

Hydroxyl-Imidazolium Ionic Liquid-Functionalized MIL-101(Cr): A Bifunctional and Highly Efficient Catalyst for the Conversion of CO2 to Styrene Carbonate

“…Mesoporous materials, including zeolites, porous carbon materials, and metal organic frameworks (MOFs), play an important role in gas separation, drug delivery, encapsulation, and heterogeneous catalysis due to their porous structure. The unique nature of MOFs makes them attractive for catalysis since they have adjustable porosity, unsaturated metal sites, high surface area, and capability to incorporate functional groups. − In the past decade, MOFs have been widely applied as heterogeneous catalysts for carbon dioxide (CO 2 ) conversion. − …”