Mixed-Linker Isoreticular Zn(II) Metal–Organic Frameworks as Brønsted Acid–Base Bifunctional Catalysts for Knoevenagel Condensation Reactions

Abstract

Multicomponent metal–organic frameworks (MOFs) have received an increasing amount of attention due to their potential to produce new topologies, pore metrics, and functionalities compared to MOFs with a single metal cluster and one organic linker. Herein, five isoreticular Zn MOFs were obtained by mixing two types of linear ditopic linkers in a one-pot solvothermal synthesis. Interestingly, in the resulting Zn MOFs a six-connected cyclic trinuclear Zn­(II) cluster and an eight-connected linear trinuclear Zn­(II) cluster coexist, leading to an uncommon (6,8)-connected network. Catalytic activities toward the solvent-free Knoevenagel reactions were observed for all of these MOFs. Further experimental and computational studies suggest that they are Brønsted acid–base bifunctional catalysts. Through chemical modifications of dicarboxylate ligands, including their aromatic backbones and substituents, we have successfully implemented reticular chemistry for the modulations of pore sizes, surface areas, and catalytic performances in a series of four-component isoreticular MOFs.

Bifunctional {Pb10K2}–Organic Framework for High Catalytic Activity in Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation

“…On account of the structural feature of NUC-45a and reported MOF-based catalysts, − a plausible mechanism for the Knoevenagel reaction is shown in Figure . First, the reaction is initiated by the weak contact of the carbonyl oxygen of the aldehyde group and the exposed metal sites of NUC-45a , making the carbon atom of the aldehyde group become the positive carbon center.…”

Nanocage-Based Tb3+-Organic Framework for Efficiently Catalyzing the Cycloaddition Reaction of CO2 with Epoxides and Knoevenagel Condensation

“…Based on the structural characteristics and components of NUC-58a as well as documented related catalysis, − the reaction mechanism of Knoevenagel condensation in the presence of NUC-58a is speculated as Figure b. First, the active sites of Tb 3+ and μ 3 –OH ions contact with the oxygen atoms of aldehyde groups by Van der waals’ force or hydrogen bonds to weaken the CO bonds.…”

Robust acid–base Ln-MOFs: searching for efficient catalysts in cycloaddition of CO2 with epoxides and cascade deacetalization–Knoevenagel reactions

“…Currently, Ln-MOFs as Lewis acids have been applied for a number of organic transformations, including cycloaddition of CO 2 , Knoevenagel condensation, and Heck reactions. [4][5][6] Carbon dioxide (CO 2 ), as the primary greenhouse gas, is also a nontoxic, economic, and renewable C1 building block. CO 2 capture and conversion into value-added chemicals are attractive in terms of green chemistry.…”

“…28,29 Meanwhile, the lanthanide ions embedded in Ln-MOFs have proven to be valuable Lewis acid sites for a number of organic reactions, as mentioned before. [4][5][6] Bearing these considerations in mind, one would expect a Ln-MOF incorporating triphenylamine group to be an acid-base bifunctional catalyst for both cycloaddition of epoxides with CO 2 and one-pot deacetalization-Knoevenagel reaction.…”

“…Currently, Ln-MOFs as Lewis acids have been applied for a number of organic transformations, including cycloaddition of CO 2 , Knoevenagel condensation, and Heck reactions. 4–6…”