Amino functionalized Zn/Cd-metal-organic frameworks for selective CO2 adsorption and Knoevenagel condensation reactions

Coordination Polymers from an Amino-Functionalized Terphenyl-Tetracarboxylate Linker: Structural Multiplicity and Catalytic Properties

An amino-functionalized terphenyl-tetracarboxylic acid, 2'-amino-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4tpta), was used as an adaptable linker to synthesize, under hydrothermal conditions, eight coordination polymers (CPs). The obtained products were formulated as [Co(μ6-H2tpta)]n (1), [Co(μ3-H2tpta)(2,2'-bipy)]n (2), [M3(μ6-Htpta)2(2,2'-bipy)2]n (M = Mn (3), Cd (4)), [Ni2(μ4-tpta)(phen)2(H2O)4]n (5), [Zn2(μ6-tpta)(phen)2]n (6), {[Zn2(μ6-tpta)(μ-4,4'-bipy)]·H2O}n (7), and [Zn2(μ6-tpta)(μ-H2biim)(H2O)2]n (8), wherein 2,2'-bipyridine (2,2'-bipy), 4,4'-bipyridine (4,4'-bipy), 1,10-phenanthroline (phen), or 2,2'-biimidazole (H2biim) are present as additional stabilizing ligands. The structural types of 1-8 vary from one-dimensional (1D) (2, 5) and two-dimensional (2D) (3, 4, 6) CPs to three-dimensional (3D) metal-organic frameworks (MOFs) (1, 7, and 8) with a diversity of topologies. The products 1-8 were investigated as catalysts in the Knoevenagel condensation involving aldehydes and active methylene derivatives (malononitrile, ethyl cyanoacetate, or tert-butyl cyanoacetate), leading to high condensation product yields (up to 99%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were investigated. This work broadens the application of H4tpta as a versatile tetracarboxylate linker for the generation of diverse CPs/MOFs.

Catalytic Oxidation of Benzoins by Hydrogen Peroxide on Nanosized HKUST-1: Influence of Substituents on the Reaction Rates and DFT Modeling of the Reaction Path

In this research, the oxidation of a series of benzoins, R-C(=O)-CH(OH)-R, where R = phenyl, 4-methoxyphenyl, 4-bromophenyl, and 2-naphthyl, by hydrogen peroxide in the presence of nanostructured HKUST-1 (suspension in acetonitrile/water mixture) was studied. The respective benzoic acids were the only products of the reactions. The initial average reaction rates were experimentally determined at different concentrations of benzoin, H₂O₂ and an effective concentration of HKUST-1. The sorption of the isotherms of benzoin, dimethoxybenzoin and benzoic acid on HKUST-1, as well as their sorption kinetic curves, were measured. The increase in H₂O₂ concentration expectedly led to an acceleration of the reaction. The dependencies of the benzoin oxidation rates on the concentrations of both benzoin and HKUST-1 passed through the maxima. This finding could be explained by a counterplay between the increasing reaction rate and increasing benzoin sorption on the catalyst with the increase in the concentration. The electronic effect of the substituent in benzoin had a significant influence on the reaction rate, while no relation between the size of the substrate molecule and the rate of its oxidation was found. It was confirmed by DFT modeling that the reaction could pass through the Baeyer-Villiger mechanism, involving an attack by the HOO^- anion on the C atom of the activated C=O group.

Coordination Polymers Constructed from an Adaptable Pyridine-Dicarboxylic Acid Linker: Assembly, Diversity of Structures, and Catalysis

4,4'-(Pyridine-3,5-diyl)dibenzoic acid (H₂pdba) was explored as an adaptable linker for assembling a diversity of new manganese(II), cobalt(II/III), nickel(II), and copper(II) coordination polymers (CPs): [Mn(μ₄-pdba)(H₂O)]_n (1), {[M(μ₃-pdba)(phen)]·2H₂O}_n (M = Co (2), Ni (3)), {[Cu₂(μ₃-pdba)₂(bipy)]·2H₂O}_n (4), {[Co(μ₃-pdba)(bipy)]·2H₂O}_n (5), [Co₂(μ₃-pdba)(μ-Hbiim)₂(Hbiim)]_n (6), and [M(μ₄-pdba)(py)]_n (M = Co (7), Ni (8)). The CPs were hydrothermally synthesized using metal(II) chloride precursors, H₂pdba, and different coligands functioning as crystallization mediators (phen: 1,10-phenanthroline; bipy: 2,2'-bipyridine, H₂biim: 2,2'-biimidazole; py: pyridine). Structural networks of 1-8 range from two-dimensional (2D) metal-organic layers (1-3, 5-8) to three-dimensional (3D) metal-organic framework (MOF) (4) and disclose several types of topologies: sql (in 1), hcb (in 2, 3, 5), tfk (in 4), 3,5L66 (in 6), and SP 2-periodic net (6,3)Ia (in 7, 8). Apart from the characterization by standard methods, catalytic potential of the obtained CPs was also screened in the Knoevenagel condensation of benzaldehyde with propanedinitrile to give 2-benzylidenemalononitrile (model reaction). Several reaction parameters were optimized, and the substrate scope was explored, revealing the best catalytic performance for a 3D MOF 4. This catalyst is recyclable and can lead to substituted dinitrile products in up to 99% product yields. The present study widens the use of H₂pdba as a still poorly studied linker toward designing novel functional coordination polymers.

Three Si-substituted polyoxovanadates as efficient catalysts for Knoevenagel condensation and selective oxidation of styrene to benzaldehyde

Three new Si-substituted polyoxovanadates (POVs), [Cd₂(dien)₂][Cd(dien)][Cd(Hdien)₂][V₁₅Si₆O₄₆(OH)₂(H₂O)]·7H₂O (1), [Co(enMe)₂]₃[Co₂(enMe)₂(H₂O)₂][V₁₆Si₄O₄₄(OH)₂(H₂O)]·6H₂O (2), and [Co(teta)]₄[V₁₆Si₄O₄₂(OH)₄(H₂O)]·10H₂O (3) (dien = diethylenetriamine; enMe = 1,2-diaminopropane; teta = triethylenetetramine) were synthesized by the hydrothermal method and characterized. Structural analysis sheds light on the fact that the {V₁₅Si₆O₄₈}/{V₁₆Si₄O₄₆} clusters of compounds 1-3 were formed by replacing {VO₅} square pyramids in the classical {V₁₈O₄₂} cluster with {Si₂O₇} units. Compound 1 is a 2D bilayer structure formed by the [V₁₅Si₆O₄₆(OH)₂(H₂O)]^10- cluster and two types of bridging Cd complexes containing binuclear groups [Cd₂(dien)₂]⁴⁺. Compound 2 is a 3D framework constructed from the [V₁₆Si₄O₄₄(OH)₂(H₂O)]^10- cluster and two types of Co complex fragments including binuclear [Co₂(enMe)₂(H₂O)₂]⁴⁺. In compound 3, the [V₁₆Si₄O₄₂(OH)₄(H₂O)]^8- cluster is connected with bridging [Co(teta)]²⁺ to expand into a 2D network. Compounds 1 and 3 represent the first 2D assemblies based on a vanadosilicate cluster. 1-3 served as heterogeneous catalysts and exhibited highly efficient catalytic activities for the Knoevenagel condensation under mild ambient conditions with low catalyst loading, featuring the open Lewis base {V₁₅Si₆O₄₈}/{V₁₆Si₄O₄₆} sites and Lewis acid Cd²⁺/Co²⁺ sites. The conversion of benzaldehyde was up to 99.3% in 80 min at room temperature using 1 as a heterogeneous catalyst with only 0.37% catalyst loading. Moreover, compounds 1-3 as catalysts for selective oxidation of styrene to benzaldehyde exhibited excellent catalytic performance, high selectivity and could be readily recycled. Most strikingly, compound 1 showed excellent catalytic performance with 97.6% conversion of styrene and 100% selectivity of benzaldehyde in 15 min. In addition, the catalytic activity of catalyst 1 was well maintained after five cycling reactions.

A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

Amorphous zirconium metal-organic frameworks assembled from mixed porphyrins as solvent-free catalysts for Knoevenagel condensation

Three mixed porphyrins, icpp (1–3) were synthesized via the reactions of 4-formylbenzoic acid and 4-imidazolecarboxaldehyde in different proportions, and then five amorphous or crystalline Zr-MOFs—SPUZ (1–5) were obtained from icpp...

Nanochannel {InZn}-Organic Framework with a High Catalytic Performance on CO2 Chemical Fixation and Deacetalization-Knoevenagel Condensation

The rare combination of In^III 5p and Zn^II 3d in the presence of a structure-oriented TDP^6- ligand led to a robust hybrid material of {(Me₂NH₂)[InZn(TDP)(OH₂)]·4DMF·4H₂O}_n (NUC-42) with the interlaced hierarchical nanochannels (hexagonal and cylindrical) shaped by six rows of undocumented [InZn(CO₂)₆(OH₂)] clusters, which represented the first 5p-3d nanochannel-based heterometallic metal-organic framework. With respect to the multifarious symbiotic Lewis acid-base and Brønsted acid sites in the high porous framework, the catalytic performance of activated NUC-42a upon CO₂ cycloaddition with styrene oxide was evaluated under solvent-free conditions with 1 atm of CO₂ pressure, which exhibited that the reaction could be well completed at ambient temperature within 48 h or at 60 °C within 4 h with high yield and selectivity. Moreover, because of the acidic function of metal sites and a central free pyridine in the TDP^6- ligand, deacetalization-Knoevenagel condensation of acetals and malononitrile could be efficiently facilitated by an activated sample of NUC-42a under lukewarm conditions.

Two new calix[4]resorcinarene-based coordination cages adjusted by metal ions for the Knoevenagel condensation reaction

Two new calix[4]resorcinarene-based coordination cages, namely, [Zn4(TPC4R)(PDC)4]·2DMF·6H2O (1-Zn) and [In11(TPC4R)2(PDC)16(μ2-OH)2(H2O)2]·[(CH3)2NH2]·8DMF·20H2O·EtOH (2-In), have been synthesized via solvothermal reactions (TPC4R = tetra(2-(4H-pyrazol-3-yl)pyridine)calix[4]resorcinarene, H2PDC = 3,5-pyridinedicarboxylic acid, DMF = N,N'-dimethylformamide). By carefully tuning different metal ions, two structurally different cages 1-Zn and 2-In were achieved. The former shows a bowl-shaped structure, while the latter features a dumbbell-like structure. After activation, they exhibited unsaturated Zn(ii) or In(iii) Lewis acid sites and the free nitrogen Lewis base sites of the PDC2-. Therefore, they were employed as catalysts for the Knoevenagel condensation reaction in the absence of a solvent. Particularly, 1-Zn featured high structural stability and enhanced the catalytic activity.

The crystal structure of 2,5-bis(3,5-dimethylphenyl)thiazolo[5,4-d]thiazole, C20H18N2S2

C20H18N2S2, monoclinic, P21/n (no. 14), a = 7.92140(10) Å, b = 6.08080(10) Å, c = 17.8091(3) Å, β = 90.592(2)°, V = 857.79(2) Å3, Z = 4, R gt(F) = 0.0382, wR ref(F 2) = 0.1051, T = 149.99(10) K.

CCDC no.: 2085420

Catalytic C-H Bond Activation and Knoevenagel Condensation Using Pyridine-2,3-Dicarboxylate-Based Metal-Organic Frameworks

Three 1D coordination polymers (CPs) [M(pdca)(H2O)2] n (M = Zn, Cd, and Co; 1-3), and a 3D coordination framework {[(CH3)2NH2][CuK(2,3-pdca)(pa)(NO3)2]} n (4) (2,3-pdca = pyridine-2,3-dicarboxylate and pa = picolinic acid), have been synthesized adopting a solvothermal reaction strategy. The CPs have been thoroughly characterized using various spectral techniques, that is, elemental analyses, FT-IR, TGA, DSC, UV/vis, and luminescence. Structural information on 1-4 was obtained by PXRD and X-ray single-crystal analyses, whereas morphological insights were attained through FESEM, AFM, EDX, HRTEM, and BET surface area analyses. Roughness parameters were calculated from AFM analysis, whereas dimensions of small domains and interplanar spacing were defined with the aid of HRTEM. CPs 1-3 are 1D isostructural networks, whereas 4 is a 3D framework. Moreover, 1-4 display moderate luminescence at rt. In addition, 1-4 have been applied as economic and efficient porous catalysts for the Knoevenagel condensation reaction and C-H bond activation under mild conditions with good yields (95-98 and 97-99%), respectively. Notably, 1-3 can be reused up to seven cycles, whereas 4 can be reused up to five catalytic cycles with retained catalytic efficiency. Relative catalytic efficacy toward the Knoevenagel condensation reaction follows in the order 2 > 1 > 3 > 4, whereas 2 > 4 > 1 > 3 for C-H activation. The present result demonstrates synthetic, structural, optical, morphological, and catalytic aspects of 1-4.

Three Resorcin[4]arene-Based Two-Dimensional Zn(II) Supramolecular Isomers Synthesized via a Structure-Directing Strategy for Knoevenagel Condensation

Herein, in the presence of three structure-directing agents (SDAs), a family of imidazole-functionalized resorcin[4]arene-based coordination polymers (CPs), [Zn(TIC4R)(HCOO)]·HCOO·0.5DMF·1.5H₂O (1), [Zn(TIC4R)(CN)]·HCOO·DMF·2.5H₂O (2), and [Zn(TIC4R)(H₂O)]·2HCOO·2H₂O (3), were assembled under solvothermal conditions [TIC4R = tetra(imidazole) resorcin[4]arene]. 1 exhibits a double-layer structure with rectangle windows, and 2 and 3 display monolayer structures. The layers of CPs 2 and 3 are slides with different offsets along the a-axis. In addition, three CPs were used as catalysts to catalyze Knoevenagel condensations. Strikingly, all CPs exhibit remarkable catalytic performance for several substrates. To the best of our knowledge, this is the first time that a small organic acid as SDA was used in the syntheses of resorcin[4]arene-based supramolecular isomers.

Devising Mixed-Ligand Based Robust Cd(II)-Framework From Bi-Functional Ligand for Fast Responsive Luminescent Detection of Fe3+ and Cr(VI) Oxo-Anions in Water With High Selectivity and Recyclability

Environmental issue related applications have globally surfaced as hottest areas of research, wherein luminescent metal-organic frameworks (LMOFs) with functionalized pores put unique signature in real-time monitoring of multiple classes of toxic compounds, and overcome many of the challenges of conventional materials. We report a two-fold interpenetrated, mixed-ligand Cd(II)-organic framework (CSMCRI-11) [Cd_1.5(L)₂(bpy)(NO₃)]·DMF·2H₂O (CSMCRI = Central Salt and Marine Chemical Research Institute, HL = 4- (1H-imidazol-1-yl)benzoic acid, bpy = 4,4'-bipyridine) that exemplifies bipillar-layer structure with two different Cd(II) nodes, and displays notable robustness in diverse organic solvents and water. Intense luminescence signature of the activated MOF (11a) is harnessed in extremely selective and fast responsive sensing of Fe³⁺ ions in aqueous phase with notable quenching constant (1.91 × 10⁴ M^-1) and impressive 166 ppb limit of detection (LOD). The framework further serves as a highly discriminative and quick responsive scaffold for turn-off detection of two noxious oxo-anions (Cr₂O₇ ^2- and CrO₄ ^2-) in water, where individual quenching constants (CrO₄ ^2-: 1.46 × 10⁴ M^-1; Cr₂O₇ ^2-: 2.18 × 10⁴ M^-1) and LOD values (CrO₄ ^2-: 179 ppb; Cr₂O₇ ^2-: 114 ppb) rank among best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress the outstanding reusability of the MOF towards detection of all these aqueous pollutants, besides their vivid monitoring by colorimetric changes under UV-light. Mechanism of selective quenching is comprehensively investigated in light of absorption of the excitation/emission energy of the host framework by individual studied analyte.

Cobalt-Based Metal-Organic Frameworks for Adsorption of CO2 and C2 Hydrocarbons: Effect of Auxiliary Ligands with Different Functional Groups

Recently, metal-organic frameworks (MOFs) have been investigated as potential materials for CO₂ capture and light hydrocarbon storage/separation due to their high porosity, large surface area, and tunable skeleton structures. In this work, the six cobalt-based MOFs 1-6 were successfully synthesized under solvothermal conditions by a mixed-ligand strategy. 1 and 2 have the same framework structure with a topology of {4²·5}₂{4⁴·5¹⁰·6⁷·7⁶·8}, while the structures of the 3-6 frameworks are the same with a topology of {4²·5}₂{4⁴·5¹⁰·6⁹·7⁴·8}. The adsorption properties of these MOFs for CO₂ and C₂ hydrocarbons were then investigated, and the effect of the functional groups was discussed. The results revealed that the introduction of amino and bromo groups could effectively strengthen the adsorption performance.

Metal–organic architectures designed from a triphenyl-pentacarboxylate linker: hydrothermal assembly, structural multiplicity, and catalytic Knoevenagel condensation

Eight new metal(ii) coordination compounds driven by a triphenyl-pentacarboxylate linker were hydrothermally assembled and fully characterized. Their structural features and catalytic behavior were investigated.

Size and function influence study on enhanced catalytic performance of a cooperative MOF for mild, green and fast C-C bond formation

Tuning of pore function and size (surface area) are two key factors that play important roles in the performance of metal-organic-frameworks (MOFs) as catalysts. The catalytic performance of two bulk and nanosized MOFs with different functional groups such as a Brønsted base and Lewis acid was studied in line with the sustainable development of catalysts and green chemistry principles. Bifunctional imine decorated TMU-33, ([Cd3(BDC)3(OPP)(DMF)2]·2DMA)n (TMU-33), (OPP: N,N'-(oxybis(4,1-phenylene))bis(1-(pyridin-4yl)methanimine)), with an adjustable structure and amine functionalized TMU-40, [Zn(BDC)(L*)]·DMF, (L*: N1,N2-bis(pyridin-4-ylmethylene)ethane-1,2-diamine), were evaluated in the C-C bond forming reaction under mild and green conditions. The results show that the nanosized samples of bifunctional TMU-33 which simultaneously have an imine and open metal site exhibit higher performance as Knoevenagel catalysts. Furthermore, among the nanosized samples, the nanoplate TMU-33 with more access to open metal sites shows the highest catalytic activity without any side product in water, at room temperature for 5 min, which confirms that the Lewis acid is the effective catalyst for this reaction. The catalyst could be reused for at least three cycles without any significant loss of its activity. The performance of the structure indicates that the tuning of functionality of MOFs can be a very promising route for the extension of green catalysts.

Metal–organic frameworks for the energy-related conversion of CO2 into cyclic carbonates

MOFs are promising heterogeneous catalysts for chemical fixation of CO₂ and epoxides into cyclic carbonates.

A new type IV DES: a competent green catalyst and solvent for the synthesis of α,β-unsaturated diketones and dicyano compounds by Knoevenagel condensation reaction

Preparation, characterisation and application of novel type IV DESs from CeCl₃·7H₂O and HBDs (urea, ethylene glycol, glycerol and lactic acid).

A series of host–guest coordination polymers containing viologens: syntheses, crystal structures, thermo/photochromism and factors influencing their thermo/photochromic behaviors

Some viologen-containing compounds displaying thermo/photochromic behaviors which can be used as inkless print media and anti-counterfeiting materials have been reported.