A Zinc(II) Porous Metal–Organic Framework and Its Morphologically Controlled Catalytic Properties in the Knoevenagel Condensation Reaction

Abstract

A new metal–organic framework (MOF), {Zn(oba)(3‐bpdh)0.5}∝⋅2 H2O (1 Zn; oba=4,4′‐oxybis(benzoic acid), 3‐bpdh=N,N′‐bis(1‐pyridine‐3‐yl‐ethylidene)hydrazine), was successfully assembled in a solvothermal system. The Zn2+ ion center located in a five‐coordinate environment combined with oba to produce a layer‐like structure, which is again linked with 3‐bpdh to yield a 3D channel framework. MOF 1 Zn microcrystals with different morphologies were synthesized through coordination modulation and solvent‐dependent methods. The effects of the concentration of the modulator, the reaction temperature, and the volume ratio of mixed solvents have been investigated. Furthermore, the catalytic performance in Knoevenagel condensation was studied for different morphologies of 1 Zn microcrystals; this revealed that the MOF microcrystals exhibited excellent and morphology‐dependent catalytic properties.

Synthesis and Structure of Three New Alkaline Earth Metal–Organic Frameworks with High Thermal Stability as Catalysts for Knoevenagel Condensation

“…Regarding MOFs containing carboxylate ligands, the M n + -O 2– Lewis acid–base can catalyze the Knoevenagel condensation . For instance, the catalytic activity of [Zn­(ADA)­(L)]·2H 2 O (ADA = 1,3-adamantanediacetic acid and L = 4-pyridylcarboxaldehydeisonicotinoylhydrazone) and [Zn 2 (oba) 4 ­(3-bpdh) 2 ]·4H 2 O (oba = 4,4′-oxybis­(benzoic acid) and 3-bpdh = N , N ′-bis­(1 pyridine-3-yl-ethylidene)-hydrazine) have been associated with the M n + -O 2– Lewis acid–base pair which can catalyze Knoevenagel condensation.…”

“…Concerning M-HBDC (M = Mg, Ca, Sr) MOFs reported here, the polarized M n+ −O 2− bonds in the structures endow the MOFs with cooperative Lewis acid−base sites which can synergistically catalyze the reaction. On the basis of the reported mechanism for Knoevenagel condensation, 40 the alkaline earth ions impart the acidic sites and interact with the CO group of benzaldehyde which improves the electrophilicity of the carbon of CO group. Also, the basic sites of the MOFs which are associated with the O atoms of BDC-OH can interact with the methylene group of ethyl cyanoacetate and facilitate its reaction with benzaldehyde.…”

Picolinohydrazide-Based Covalent Organic Polymer for Metal-Free Catalysis and Removal of Heavy Metals from Wastewater

“…COP retains its catalytic activity and frameworks up to 4 cycles (Figures d and S19). A summary of different catalysts used in Knoevenagel condensation is shown in Table S1. − …”

Ligand geometry controlling Zn-MOF partial structures for their catalytic performance in Knoevenagel condensation

“…The catalytic activity of all the Zn-MOFs may be related to the size, dispersion and accessible surface areas of the catalyst. 36 For contrast, we studied the Knoevenagel condensation reaction with n -heptanal, keeping other conditions unchanged. The results are shown in the ESI (Fig.…”

“… 39 In our study, the three Zn-MOFs seemed to prefer the acid-catalyzed mechanism since they did not have a strong basic group, such as the amino group; although the ligand contains two N atoms, these two N atoms already have three bonds, the electron cloud is dispersed, and the –NO 2 and –COOH groups on the organic carboxylic acid ligands also weaken the basicity. Based on other studies, 36,40,41 we proposed a possible bifunctional acid–base catalytic mechanism. The Zn( ii ) in the Zn-MOF has empty atomic orbitals, which can be used as the Lewis acid sites.…”