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ChemInform Abstract: Hydrogen-Bonding 2D Metal-Organic Solids as Highly Robust and Efficient Heterogeneous Green Catalysts for Biginelli Reaction.
Abstract
Two new Zn(II) and Cd(II) MOFs have been synthesized. These MOFs have been applied as heterogeneous catalysts for the green synthesis of a variety of dihydropyrimidinone derivatives through the Biginelli reaction and the desired products were obtained in high yields with short reaction time under mild solvent- free conditions. Moreover, the MOF catalysts may be readily recovered after the reaction and reused for many cycles.
... [132][133][134][135] Recently, IRMOF-3 and Cd-based MCCs were successfully employed in the synthesis of DHPMs with good yields. [136,137] Though considerable catalytic protocols for the Biginelli reaction have been explored, there exist some problems including low yield, amenable reaction conditions, isolated issues and tedious workup procedure, which remains a formidable challenge. More importantly, the DHPMs with the sensitive groups were found in the moderate yield (62-65%). ...
... At the same time, the cobalt ions and phenyl sulfonate one were usually employed in the organic chemistry. [117,136,[141][142][143][144][145][146][147], [148][149][150][151][152][153][154] Therefore, we would like to explore and study this kind of catalysts for the synthesis of DHPMs. Herein, we wish to report the cobalt-based MCCs containing (E)-1,2-di (pyridin-4-yl) ethene and phenyl sulfonate ligand as catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones through one-pot solvent-free Biginelli reaction. ...
Three new metal coordination complexes, namely, [Co (DPE)(H2O)4](DPE)(BS)2 (1), [Co (DPE)2(H2O)4](ABS)2 (2), [Co (DPE)(H2O)4](MBS)2(CH3OH)2 (3) [DPE = (E)‐1,2‐di (pyridin‐4‐yl) ethene, BS = phenyl sulfonic acid, ABS = p‐aminobenzene sulfonic acid, MBS = p‐methylbenzene sulfonic acid] were obtained under hydrothermal conditions. Complexes 1‐3 were structurally characterized by X‐ray single‐crystal diffraction, powder X‐ray diffraction and IR. Complexes 1 and 3 exhibit a one‐dimensional chain structure, and complex 2 does a zero‐dimensional one. These three complexes further generate a three‐dimensional supramolecular architecture via strong hydrogen bonding interactions and packing interactions. These three metal coordination complexes show high catalytic performance for green synthesis of a variety of 3,4‐dihydropyrimidin‐2(1H)‐ones through the Biginelli reactions, which show several advantages such as excellent yields, short reaction times, eco‐friendly synthesis conditions, and simple isolated workup procedure. Interestingly, the order of catalytic activities for these catalysts is the following: 3>1>2, which can be ascribed to the acidities and hydrophobic interactions of phenyl sulfonate groups. Three new metal coordination complexes containing phenyl sulfonate were obtained under hydrothermal conditions, which show high catalytic performance for green synthesis of a variety of 3,4‐dihydropyrimidin‐2(1H)‐ones through the Biginelli reactions, and show several advantages such as excellent yields, short reaction times, eco‐friendly synthesis conditions, and simple isolated workup procedure.
... These products are mainly known for their pharmacological activities [14,15]. This scaffold gives variety of biological activities such as anti-cancer, anti-inflammatory, anti-tubercular, anti-diabetic, anti-malarial and anti-microbial [16][17][18][19][20]. The synthesis of 3,4-dihydropyrimidine-2(1H)one/thiones has been traditionally done in the presence of Brønsted or Lewis acid catalysts [21], such as para-toluene sulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, ZrCl 4 , TiCl 3 ,CoCl 2 ·6H 2 O, FeCl 3 ·6H 2 O [22], and some heterogeneous catalytic systems like silica-supported materials, immobilized magnetic nanoparticles and carbon-based materials [23][24][25][26][27] [31][32][33][34][35][36][37][38][39]. ...
Polymer supported ferric chloride catalyst is prepared and characterized by IR, SEM, TEM, EDS, TGA, ICP-MS and XRD. The heterogenized Lewis acid catalyst was found to efficiently promote three component Biginelli reaction, where the 3,4-dihydropyrimidine-2(1H)-ones/thiones were efficiently synthesized from urea/thiourea. The catalyst was found to be quite robust for this reaction with very less leaching of metal was observed, and hence can be efficiently recycled. The catalyst was found to be effective for multiple uses, establishing its reusability in this important reaction.
Graphical Abstract
... Later, other studies on MOF catalyzed A 3 coupling reactions were also reported by Jayaramulu et al., 17 20 Li et al. have reported the use of two isostructural Zn 21 and Cd 21 MOFs prepared with the ligands 1,2-bis(4-pyridyl)ethylene and 1,3-benzenedisulfonic acid, for the synthesis of dihydropyrimidinone derivatives through the Biginelli three-component coupling reaction (Scheme 14.13). 21 One year later, the same group also reported the use of these two MOFs as catalysts for the three component coupling reaction of aldehydes, malononitrile, and thiophenols leading to the one-pot synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines (Scheme 14.14). 22 Although this is only the beginning, we are witnessing an increasing interest in developing new catalytic applications of MOFs, focused on the synthesis of high added value products and designing new, more efficient, one-pot synthesis procedures. ...
Catalysis has always been part of the development of mankind; from the fermentation of alcoholic drinks, through the development of fertilisers in the agricultural revolution and production of bulk chemicals in the 20th Century. Today, society demands improved production routes with greater product output and energy efficiency; the ultimate goal to achieving this would be having all catalytic reactions in concert, effectively functioning like a biological cell.
Metal organic frameworks (MOFs) are a relatively new type of hybrid material. Their crystalline porous structure, built up from organic and inorganic building blocks, presents a vast array of composition, porosity and functionality offering enormous potential in catalytic systems.
This book examines the latest research and discovery in the use of MOFs in catalysis, highlighting the extent to which these materials have been embraced by the community. Beyond presenting a digest of recent research by major players in the field, the book presents the strategies behind recent developments, providing a lasting reference for seasoned researchers and newcomers to the field.
... Bose et al., 28 synthesized tetrahydropyrimidinone using grindstone technique and found the yield to be 95%, with melting point 236-238°C. While Sun et al., 57 also reported the melting point of the compound to lie between 236-238°C. Ushati Das et al., 58 also synthesized Ethyl 4-(4-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine -5carboxylate monohydrate using 4-Hydroxy benzaldehyde, ethyl acetoacetate, urea and p-TSA in mortar and pestel (yield 95%, m.p. 509-511 K). ...
The objective of present research work is to provide green technique for synthesis of 4-(4-Hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylic acid ethyl ester. Pyrimidine derivatives are well known in the pharmaceutical industry and exhibit to possess a broad spectrum of biological activities which makes their wider application as a key building block for pharmaceutical agents. Highly efficient and simple methods complying with principle of Green chemistry have been described in this manuscript for the synthesis with competent yields. As part of current studies, we here in report economical practical techniques like-microwave synthesis, mortal-pastel method (mechanochemistry) and by application of green solvents for the synthesis. On completion of reaction the products were characterized by Infra Red Spectroscopy, Nuclear Magnetic Resonance Spectroscopy and Mass Spectra. The specified methods for synthesis are more convenient and reactions can be carried out in higher yield (80-96%), shorter reaction time (3-30 min) and milder conditions, without generation of pollution and safer to analyst.
... 4,5 Several alkaloids isolated from marine sources whose molecular structures contain the dihydropyrimidinone unit also exhibit interesting biological activities. 1 The Biginelli reaction involves a three-component, one-pot condensation of benzaldehyde, β-keto ester, and urea under strongly acidic conditions. 1 However, some methods often require harsh conditions, long reaction times, expensive catalysts, and volatile organic solvent. [5][6][7][8][9][10][11][12][13] The search for new, efficient, and green catalysts is still being actively pursued. ...
... In show the merit of the present study, the results of using complex 1 for the synthesis of product 5a by reacting benzaldehyde, ethyl acetoacetate, and urea with other homogeneous and heterogeneous catalysts were compared (Table 4, entries [3][4][5][6][7][8][9][10][11][12][13][14]. According to the obtained results [7,9,13,24,27,[31][32][33][53][54][55] our catalyst shows better catalytic activity with a shorter reaction time using solvent-free conditions with good recyclability. Apparently, the long fluoroalkyl chain in the sulfonate must be responsible for the hydrophobicity and increasing the catalytic activity. ...
An air‐stable complex of zirconium (IV)‐salophen perfluorooctanesulfonate (1) was successfully synthesized by reacting Zr (salphen)Cl2 and C8F17SO3Ag. Complex 1 was characterized and studied by different techniques (NMR, IR, HRMS, TG‐DSC, conductivity and acidity measurements), and was found to be air‐stable, water tolerant, thermally stable and strongly Lewis‐acidic. Complex 1 exhibited high catalytic efficiency for the synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones/thiones via the Biginelli reaction of aldehydes, 1,3‐dicarbonyl compounds and urea/thiourea under solvent‐free conditions. Furthermore, complex 1 could be reused 5 times with minimal changes in catalytic efficiency. Compared with previously reported methods, the important features of this protocol are the solvent‐free conditions, the short reaction times, the wide substrate compatibility, the high efficiency and the good reusability. An air‐stable zirconium (IV)‐salophen perfluorooctanesulfonate complex was successfully synthesized, and showed high catalytic activity for the synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones/thiones via Biginelli reaction of aldehydes, 1,3‐dicarbonyl compounds and urea/thiourea. Compared to the reported methods, the main advantage of this protocol is (i) solvent‐free conditions, (ii) short reaction time, (iii) high efficiency, (iv) wide substrate scope and (v) good reusability.
... 33 The original advantages of heterogeneous catalysts over homogeneous catalysts are their great surface area, which provides the needful active sites to fulfill the reaction and recyclability, and other advantages are easily in investigation, segregation and its thermal consistency. 34 MOFs have been used as solid catalysts in Suzuki, 35 alkene epoxidation, 36 Biginelli, 37 aldol, 38 aza Michael, 39 Sonogashira, 40 and Friedel-Crafts alkylation and acylation. 41 Recently, we reported diverse synthetic methods for the preparation of multiple biologically interesting products using nanocatalysts. ...
Curcumin, a category of phenolic compound derivatives from the base of Curcuma longa (Zingiberaceae), represent a variety of beneficial effects on health and on events that succor in hampering certain diseases. The present research explains an efficient procedure for the synthesis of pyrano[2,3-d] pyrimidine-2,4(3H)-diones in high yields and short response times via a three-ingredient reaction of curcumin, aromatic aldehydes and 1,3-dimethylbarbituric acid in the presence of NiCo2O4@OCMC@Zn(BDC) nanocomposite. The catalyst was determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared, (FT-IR) X-ray powder diffraction (XRD) and Brunauer–Emmett–Teller (BET). Moreover, the NiCo2O4@OCMC@Zn(BDC) catalyst can be recovered and reused several times without significant loss of its activity.
... Surprisingly, the application of cadmium is also used, i.e. for oxidation of primary and secondary alcohols 65 and for the synthesis of a variety of dihydropyrimidinone derivatives through the Biginelli reaction. 66 In the first case, the green label is assigned due to the possible seven-time reuse of the catalyst without significant loss of performance, as well as the manner of catalyst preparation by thermal decomposition and calcinations. The other case is favored by its stability under the reaction conditions, short reaction time with high yields of the desired products simultaneously, and organic solvent less reaction. ...
Catalysis is very important process in industry and laboratory practice, especially from the point of green chemistry principles. However, eco-friendly character of heterogeneous catalysts, containing transition metal components has not been evaluated, yet. Therefore, we perform a comprehensive assessment of 18 heterogeneous metal catalysts (Pd, Pt, V, Co, Ni, Mo, Ru, Mn, Au, Cu, Cd, Zr, Fe, Rh, Ir, Sn, Zn, Ag) using multicriteria decision analysis approach. The ranking of alternatives according to relevant criteria like toxicity of pure metals and metal salts towards fish and Daphnia magna, algae/plants, metal toxicity towards rats via ingestion, carcinogenicity, the endangerment degree of metals, boiling point and energy for atom detachment, estimated as metal-metal bond strength in diatomic transition metal units, classification of elemental impurities according to International Conference on Harmonization (ICH) and their degree of importance is presented. Life cycle assessment (LCA) related parameters of metals have been also included. The assessment showed ruthenium, iron and molybdenum as the most favourable alternatives, in contrary to nickel, cobalt and rhodium. Results of environmental evaluation strictly depend on chosen scenario of assessment, in terms of toxicity, endangered elements or LCA. Sensitivity analyses towards variations in input data and applied weights, prove that results are reliable. Multicriteria decision analysis can be successfully applied in metal catalysts evaluation for particular case studies of different reactions.
... [11,12] Aw ide diversity of coordinationp olymers crystallize with al ayered (2D) structured ue to the planar geometryo ft he building units.T his is the case, for instance, in transition metal (T) tetracyanometallates, T[M(CN) 4 ]w ith M = Ni, Pd, Pt. [8,13] From organic buildingb locks, al arge family of 2D metal-organic frameworksc an also be obtained. [14,15] Such diversity of 2D materials widens thep erspectives of novel applications based on their exceptional physical and functional properties. ...
1‐methyl‐2‐pyrrolidone (1m2p) is a solvent with proven abilities for 2D‐solid exfoliation due to its extremely high surface tension. In principle, such a feature could be used also to induce the selective breaking of certain bonds in solids to obtain new materials. Such a hypothesis is demonstrated in this study for transition metal nitroprussides, where 2D solids are obtained from 3D frameworks by selective rupture of axial bonds. This contribution discusses the mechanism involved in such molecular manufacture. The crystal structure for the formed 2D solids was solved and refined from XRD powder patterns recorded using synchrotron radiation. Mössbauer, IR and Raman spectra provided fine details on the electronic structure of the resulting new series of layered materials. The experimental information was complemented with calculations for the molecule configuration in its non‐activated and activated forms. In the obtained 2D solids, neighboring layers of about 1 nm of thickness remain separated by activated 1m2p molecules. The interaction between neighboring layers is of a physical nature, without the presence of a chemical bond between them, as corresponds to a 2D material.
... 14 Numerous methods have been used to control the shape and the size of MOF crystals, such as hydrothermal/solvothermal treatment, 15 ultrasonic synthesis, 16 microwave heating 17 and reverse microemulsion. 18 MOFs have been used as solid catalysts for some organic reactions as biodiesel production, 19 cyanosilylation of aldehydes, 20 synthesis of coumarins, 21 catalytic degradation of o/m/p-nitrophenol, 22 synthesis of indolizines through aldehyde-amine-alkyne couplings, 23 synthesis of 1,5-benzodiazepine, 24 Biginelli reaction, 25 oxidation, 26 aza-Michael condensation 27 and so on. However, due to the low thermal stability and processability of MOFs, the practical applications of them are limited. ...
Monometallic and bimetallic MOF/MCM-41 composites (Cu, Ag and Cu-Ag) were synthesized via a solvothermal method. The synthesized composites were characterized by XRD, FTIR, SEM, EDX and BET surface area measurements. The acidity was determined through two techniques; potentiometric titration with n-butyl amine for determining the strength and the total number of acid sites and FTIR spectra of chemisorbed pyridine on the surface of MOFs for determining the type of acid sites (Brønsted and/or Lewis). All the prepared MOFs showed Lewis-acid sites and the higher acidity was observed for the bimetallic Cu-Ag MOF/MCM-41 composite. The catalytic activity was examined on the synthesis of 1-amidoalkyl-2-naphthol via the reaction of benzaldehyde, 2-naphthol and benzamide. The best yield (92.86%) was obtained in the least time (10 min) with a molar ratio 1.2 : 1.2 : 1.7 of benzaldehyde : β-naphthol : benzamide and 0.1 g bimetallic Cu-Ag MOF/MCM-41 composite under solvent-free conditions at 130 °C. Reuse of the catalysts showed that they could be used at least four times without any reduction in the catalytic activity.
... The MOFs which are synthesized by self-assembly of metal ions or clusters with polytopic organic linkers 5 have attracted much attention in heterogeneous catalysis due to their intriguing features such as extraordinarily large surface area, well-dened pore structure, easily tailorable chemistry, and high acid-base catalytic activities. 6 Because of their high intrinsic metal loading, they have been intensively studied as catalysts in various reactions such as aldol condensation, 7 Suzuki coupling, 8 Friedel-Cras reactions, 9 Biginelli reaction, 10 Claisen-Schmidt condensation, 11 Beckmann rearrangement, 12 Sonogashira reaction, 13 polymerization 14 etc. In recent years there has been remarkable growth in the synthesis of MOFs, largely due to their potential applications in gas storage, separations, catalysis, nonlinear optics, magnetic and electronic materials, and so on. ...
A sulfonic acid functionalized metal-organic framework (S-IRMOF-3) has been synthesized by dropwise addition of chlorosulfonic acid (0.5 mL) in IRMOF-3 (1 g) containing 20 mL of CHCl3 at 0 °C under simple stirring. The catalyst was applied in Knoevenagel condensation of various aromatic and hetero-aromatic aldehydes forming acrylonitrile derivatives. The catalyst was characterized thoroughly by using FT-IR, XRD, 13C MAS NMR, SEM, EDX, elemental mapping, TEM, BET, NH3-TPD and TGA/DTA techniques. The presence of characteristic bands at 1694 cm-1, 1254-769 cm-1 and 1033 cm-1 in the FT-IR spectrum, 2θ ≃ 6.7° and 9.8° in the XRD pattern and δ = 31.79, 39.55, 129.61, 131.46 (4C, CH), 133.54, 140.07 (2C), 167.71, 171.47 ppm (2C, 2C[double bond, length as m-dash]O) in the solid state 13C MAS NMR spectrum confirmed the successful formation of catalyst. This new eco-friendly approach resulted in a significant improvement in the synthetic efficiency (90-96% yield), high product purity, and minimizing the production of chemical wastes without using highly toxic reagents for the synthesis of acrylonitriles with selectivity for (Z)-isomer. Steric interactions seem to have an influence on the control of the Z-configurational isomers. By performing DFT calculations, it was found that the (Z)-isomer 3a is stabilized by 1.64 kcal mol-1 more than the (E)-isomer. The catalyst could be reused for five consecutive cycles without substantial loss in catalytic activity.
... The reusability of the recovered catalyst was found for five consecutive cycles with insignificant loss in activity. 184 The MOFs hybrid catalysts were succeeded for the Biginelli reaction with advantageous improvements over classical conditions. ...
The Biginelli product, dihydropyrimidinone (DHPM) core and its derivatives are of immense biological importance. There are several methods reported as the modification in original Biginelli reaction. Among that many involves the uses of different catalysts. The advancements that have been consistently done in Biginelli reaction, intended to improve product yields, to provide less hazardous reaction conditions and easy isolation of products from reaction medium. Recently, solid phase synthetic protocol has attracted research community towards itself for better yields, less hectic steps for product purification, recyclability of solid support which forms a special economic approach for Biginelli reaction. The present review highlights the role of polymer supported catalysts in Biginelli reaction. Catalysts are loaded on organic and inorganic polymer supports. Few of schemes involve magnetically recoverable catalysts where work up provides green approach relative to traditional methods. Some of research groups used polymer–catalyst nanocomposites and polymer supported ionic liquids as catalyst. Solvent free, ultrasound assisted, microwave assisted Biginelli reactions with polymer supported catalysts are also reported.
... MOF-based structures demonstrate various advantages such as high surface area, adjustable pore size and the simplicity of processing, tunability and use of stable alternative materials. Recently,MOFs were used as solid catalysts in some organic reactions such as Friedel-Crafts acylation, [32] Knoevenagel condensation, [33] Paal-Knorr, [34] Biginelli, [35] and also in the synthesis of cyclic carbonates, [36] pyrroles, [37] 2-amino-6-(alkylthio)pyridine-3,5-dicarbonitriles [38] and dihydro-2-oxypyrrole. [39] Herein, in continuation of the progress of the synthetic approach for the preparation of various heterocyclic compounds with biological activities, we wish to report the synthesis pyrimidine derivatives using a metal-organic framework NiCo 2 O 4 @Ni(BDC) as a novel, efficient and green heterogeneous catalyst (Scheme 1). [40][41][42][43][44][45] Moreover, we successfully evaluated the antibacterial and antifungal activities of the synthesized pyrimidine derivatives via disk diffusion method. ...
In this research, an efficient and simple method has been reported for the preparation of spiro[indene[1,2‐d]pyrimidine‐one derivatives through the multi‐component reactions of cyclic ketones, urea/thiourea/guanidine and 1,3‐indandion in the presence of NiCo2O4@Ni(BDC) (terephthalic acid) nanocatalyst. In this method, the products were obtained in short reaction times and excellent yields. The prepared metal‐organic frameworks have been fully analyzed by fourier transform infrared spectrophotometry (FT‐IR), field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), thermogravimetric analysis (TGA),vibrating sample magnetometry (VSM), transmission electron microscopy (TEM), N2 adsorption‐desorption by Brunauer–Emmett‐Teller (BET) and X‐ray diffraction (XRD)analysis. In addition, all of the synthesized pyrimidines screened against different pathogenic bacteria including Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa and also their antifungal activity were investigated against Candida albicans. In this study, some spiro[indene[1,2‐d]pyrimidine‐ones were synthesized in excellent yields and short reaction times by a one‐pot multi‐component cyclocondensation of cyclic ketones, urea/thiourea/guanidine and 1,3‐indandion using NiCo2O4@Ni(BDC) nanocatalyst as an effective and robust catalyst. The present protocol offers the advantages including short reaction times, excellent yields and recoverability of the catalyst. The prepared metal‐organic frameworks have been fully analyzed by FT‐IR, FE‐SEM (field emission scanning electron microscopy), EDX (energy‐dispersive X‐ray spectroscopy), TGA (thermogravimetric analysis), VSM (vibrating sample magnetometry), TEM, BET and XRD analysis. Furthermore, all compounds were subsequently evaluated for their antimicrobial activities.
... The century-old Biginelli reaction, which involves the one-pot condensation of an aldehyde, βketoester and urea or thiourea gives straightforward access to functionalized 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) with a diverse range of biological properties [21][22][23][24][25][26], and is considered to be one of the most useful MCR [27][28][29][30][31]. Since the discovery of this reaction, a number of improved catalytic systems have been developed, such as Brønsted acids [32][33][34][35][36][37][38] or bases [39,40], metal Lewis acids [41][42][43][44][45][46][47][48][49][50], organocatalysts [51][52][53][54][55][56][57][58], and heterogeneous catalysts [59][60][61][62][63][64][65][66][67][68][69][70][71]. However, to the best of our knowledge, there have been only a few reports on the Biginelli reaction starting directly from alcohols [72][73][74][75]. ...
Efficient, eco-friendly and sustainable access to 3,4-dihydropyrimidin-2(1H)-ones directly from alcohols under microwave and solvent-free conditions has been reported. The practical protocol involves heteropolyanion-based catalyzed oxidation of alcohols to aldehydes with NaNO3 as the oxidant followed by cyclocondensation with dicarbonyl compounds and urea or thiourea in a two-step, one-pot manner. Compatibility with different functional groups, good to excellent yields and reusable catalysts are the main highlights. The utilization of alcohols instead of aldehydes is a valid and green alternative to the classical Biginelli reaction.
... So far, only a few examples of MOFs containing coordinatively unsaturated metal ions for heterogeneous catalysis have been investigated in comparison with a large numbers of being discovered MOFs. Moreover, most works focused on organic transformations such as Knoevenagel condensation, cyanosilylation, oxidation, aldol condensation, Michael condensation, Friedel-Crafts alkylation, and Biginelli reaction [18][19][20][21][22][23][24][25][26][27][28][29]. Indeed, reports on heterogeneous N-arylation of imidazole using Cu-MOF catalysts are very limited in the literature [12]. ...
N-arylation of imidazole was accomplished with a two-dimensional (2D) [Cu(ima)(2)](n) metal-organic framework in methanol at room temperature. A variety of N-arylimidazoles were isolated in good yields after a short reaction time. Moreover, the robust MOF may be readily recovered after the reaction and reused for many cycles without loss of catalytic activity.
... Although, catalysis is a developing application of MOFs, several MOFs have been employed as solid catalysts or catalyst supports for a variety of organic transformations. These include Knoevenagel condensation, [41][42][43][44] aldol condensation 45,46 oxidation reactions, 47-52 epoxide formation, [53][54][55][56] hydrogenation, 57-60 Suzuki coupling, 35,61,62 ketalization reactions, 63 ring-opening, 64-67 alkylation of amines, 68 cyclopropanation reactions, 69,70 Henry reactions, 71 Friedel-Crafts reactions, 72-75 cyanosilylation, 76-79 cyclization reactions, 80,81 Friedlander reaction, 82,83 acetalization, 84,85 hydroformylation, 86 Biginelli reaction, 87 Claisen-Schmidt condensation, 88 Beckmann rearrangement, 89 Sonogashira reaction, 90 and polymerization. 91 3 ] (H 2 bdc = benzene-1,4-dicarboxylic acid) for Friedel-Crafts benzylation of toluene with benzyl bromide as a heterogeneous acid catalyst. ...
Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.
Aiming at environmentally benign catalyses with less energy consumption, reduction in chemical usage and minimization of wastes, metal-organic frameworks (MOFs) combining basic functionality enriched pores and unsaturated metal centers (UMCs) is most promising. Alternatively, astute tuning of channel dimension in these materials can benefit much anticipated size-exclusive catalysis, whereas fabrication of flexible MOF-composite is imperative considering facile applicability over real-life platforms. The pillar-bilayered and hydrolytically robust MOF, built from tri-carboxylate ligand, linear linker and solvent-bound [Cd3(COO)6] secondary building unit exhibits N-functionality enriched porous channels and activation-driven generation of open metal sites. Benefiting from unique bifunctional character, the MOF acts as excellent solvent-free catalyst toward one-pot Biginelli reaction and deacetalization–Knoevenagel condensation under mild condition. Both the reactions transpire with broad substrate scope, high recyclability and superior activity to contemporary materials, wherein single-crystal X-ray diffraction is first time applied as product characterization tool. Judiciously designed control experiments validate individual catalytic routes, thereby substantiating the importance of contrasting pore-functionalities at the interface of structure–property synergism. To the best of three-component coupling and acid-base tandem catalysis, substrates with incompatible molecular dimension to that of the twofold interpenetration generated optimized pores exhibit insignificant conversion and demonstrate unprecedented pore-fitting-actuated size selectivity. In view of practically advanced and eco-friendly substrate design, reconfigurable MOF–cotton fiber composite is fabricated via in situ growth, which delivered excellent yields for both these reactions with comparable reusability to that of pristine framework, delineating a paradigm shift to smart, futuristic and green strategy in synergistic catalysis.
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.
The development of a novel heterogeneous catalyst for effectively catalyzing target reactions with specific selectivity is an intriguing issue. Considering that the metal-organic frameworks (MOFs) exhibited excellent prospect in catalytic chemistry, a novel MOF [Ni3(OABDC)2(bipy)3 (H2O)6]n(CH3OH)n(H2O)4.5n (1) was synthesized in this study using the hydrothermal method with the coordination of 3, 5-dicarboxyphenoxyacetic acid (H3OABDC) and 4, 4′-bipy ligand with nickel(II) nitrate. The structure of MOF 1 was characterized by single-crystal diffractions. In the crystal of MOF 1, the H3OABDC connected the metal nodes to form 2D wavy layer structure while the 4, 4′-bipy connected the wavy layers to form a 3D porous framework through double helix coordination. Their diameters of the porous are about 15.914 Å×15.289 Å and 16.030 Å×15.289 Å, respectively. Interestingly, MOF 1 presented efficiency and selective catalytic performance for oxidizing cyclohexene into cyclohexenone using oxygen in the air under heterogeneous conditions. The average conversion rate of cyclohexene is 84.2%, and the catalytic selectivity for oxidation product cyclohexenone is 72.7%.
Synthesis of heterocyclic compounds is an important issue in organic chemistry. A large variety of natural products such as hormones, vitamins, and even antibiotics essential for living bear heterocyclic skeletons. Heterocyclic compounds find immense industrial applications in food, dyes, perfumery and cosmetics, and especially in pharmaceutical formulations. This chapter is aimed to offer an update of the catalytic applications of porous materials covering zeolites, silicates and metallosilicates, carbons in their different forms, and metal–organic frameworks (MOFs) involved in the catalytic synthesis of bioactive heterocycles or intermediates of those. The most recent achievements concerning the mechanistic insights of some condensation reactions useful in the synthesis of biologically active heterocycles or related compounds are also commented. Moreover, novel families of advanced functional nanostructured materials with improved physicochemical properties and enhanced catalytic performances, particularly in the synthesis of biologically relevant heterocycles, as well as the used synthetic strategies are also summarized. Such is the case of new and exciting highly porous carbon-based catalysts from emerging precursors such as MOFs and covalent organic frameworks including also CNTs and graphene. This overview also includes a few examples on the application of a novel type of atomically metal-dispersed carbon catalysts on fine chemical synthesis as a new challenge in heterogeneous catalysis and, particularly, for the synthesis of biologically valuable heterocyclic compounds through cascade reactions.
Electrospray ionization (ESI) combined with ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques is used to examine the Biginelli reaction in an ensemble of ions generated from droplets. We find evidence for rapid dihydropyrimidinone formation from condensation of ethyl acetoacetate, benzaldehyde, and urea on the very short timescales associated with the electrospray process (~10 µs to ~1.0 ms). Control bulk-solution reactions show no product formation even after several days. This implies that the in-droplet reaction rate is enhanced by an astonishing factor. Examination of the reaction conditions and characterization of the intermediates en route to product shows evidence for variations in the reaction mechanism. IMS separation shows that the Knoevenagel condensation intermediate from benzaldehyde and ethyl acetoacetate exists as both the cis- and trans-isomer, in a ~5 to 1 ratio. We suggest that the dramatic acceleration arises because of increased reagent confinement as electrosprayed droplets shrink. The ability of IMS-MS to resolve intermediates (including isomers) provides a new means of understanding reaction pathways.
A straightforward and efficient methodology for the one-pot multicomponent synthesis of 1,4-dihydropyridine has been developed using MIL-101-SO3H Metal-Organic Framework as a solid Brønsted acid. The presence of the uniformly distributed Brønsted acidic sulfonic acid sites throughout the framework and high stability bestow excellent reactivity of the catalyst towards the synthesis of 1,4-dihydropyridine under simple reaction conditions using renewable ethanol as a solvent. The present methodology tolerates various functional groups and allows the synthesis of 1,4-dihydropyridine derivatives in good to excellent yield through Hantzsch reaction. The developed methodology proceeds under a mild condition, avoid corrosive reagents and special reaction conditions, also amenable to gram scale synthesis. Sustainable nature of the catalyst was proved by the easy recovery and reused for several times without loss in activity and which was confirmed from the FTIR, PXRD and SEM analyses of the reused catalyst.
NiII immobilized on aminated Fe3O4@TiO2 yolk-shell NPs functionalized by (3-glycidyloxypropyl)trimethoxysilane (Fe3O4@TiO2 YS-GLYMO-UNNiII) was prepared as a stable, highly efficient, and reusable magnetic nanostructured catalyst for the C-P cross coupling reaction. A variety of spectroscopic and microscopic techniques such as fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), EDS-map, thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), inductively coupled plasma atomic emission spectroscopy (ICP-OES) and CHNS analysis were used to characterize the synthesized nanostructured catalyst. The characterizations determined that the nanostructured catalyst is superparamagnetic in nature, structured as core-shell and its average particle size is 30-32 nm. The catalytic activity of this new magnetic nanostructured catalyst (Fe3O4@TiO2 YS-GLYMO-UNNiII) was examined in the C-P cross coupling reaction of aryl halides/ arylboronic acids/ styrene/ phenylacetylene with diethylphosphite/ triethylphosphite in the presence of WERSA so that arylphosphonates/ vinylphosphonate/ alkynylphosphonate could be prepared in a short period of time. In all the cases, the nanostructured catalyst could be easily recovered magnetically for at least seven runs and a simple work-up procedure was used to isolate the obtained products. The present methodology proved to be quite suitable for scale-up and commercialization.
The anchorage of a supported copper Schiff base complex on SBA-15 materials provides highly efficient heterogeneous catalysts towards the solvent-free synthesis of dihydropyrimidinones derivatives via the Biginelli condensation reaction. The novel nanocatalysts exhibited a highly ordered mesostructure with a surface area of 346 m2g−1 and an average pore diameter of 8.6 nm. Additionally, the supported copper nanocatalysts were reused at least ten times, remaining almost unchanged from the initial activity. Both the mesoporous scaffold and the tridentate Schiff base ligand contributed to the stabilization of copper species.
Two new coordination polymers, namely [Co(pip)(H2O)2]n (H2pip = 6-(3-pyridyl)isophthalic acid) (1) and [Co(pip)(bidmb)0.5]n (bidmb = 1,4-bis(1-imidazoly)-2,5-dimethylbenzene) (2), have been prepared under solvothermal conditions, and characterized by single-crystal X-ray diffraction, PXRD, elemental analyses, IR and TGA. Structure analysis reveals that complex 1 presented one dimensional (1D) ladder-like chain structures, which are further linked into a 3D supramolecular structure through hydrogen-bonds. Then, under the same synthetic conditions, complex 2 was obtained with a 3D “layer-pillar” structure when adding bidmb as the auxiliary pillar ligand. TGA and PXRD results reveal that both 1 and 2 possess relative high hydrothermal stability. In addition, the catalytic applications of obtained complexes were also investigated. It shows that 1 displayed superior catalytic behavior in both cycloaddition of carbon dioxide with epoxide and hydrogenation of 4-nitrophenol (4-NP) process, and could be reused for more than five times without obvious fading in activity. Excellent stability and recyclability make this new catalyst also attractive for other applications.
The present article describes an efficient one-pot method for the preparation of spiro[diindeno[1,2-b:2′,1′-e]pyridine-11,3′-indoline]-trione derivatives from a three-component condensation reaction of 1,3-indandione, aromatic amines and isatins in the presence of a zinc terephthalate metal-organic framework Zn (BDC) MOF as the catalyst under solvent-free conditions. High yields, short reaction times, simple workup and environmentally benign procedure are advantages of this protocol. The Zn (BDC) MOF catalyst can be recovered and reused several times without loss of activity. The catalyst was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infra red, X-ray powder diffraction and thermal gravimetric analysis.
In this research, Zn3(BTC)2 as a novel, metal–organic framework, biodegradable, and reusable heterogeneous nanoporous catalyst according to the aims of green chemistry was synthesized and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and FT-IR analysis. Then, Zn3(BTC)2 as a novel and full-fledged catalyst was used for the synthesis of β-azido alcohols and β-thiocyanohydrins from the regioselective conversation of some epoxides by sodium azide (NaN3) and thiocyanate (SCN) anion in aqueous. The some advantages of this method are as follows: work-up procedure, excellent regioselectivity, an environmentally benign, mild reaction conditions, and recyclability of the catalyst without loosing its activity.
Graphical Abstract
We report the synthesis of Zn3(BTC)2 as metal–organic framework, biodegradable, and reusable heterogeneous nanoporous catalyst for the synthesis of β-azido alcohols and β-thiocyano hydrins. Zn3(BTC)2 showed excellent activity for ring opening of epoxides in water.
Zn3(BTC)2 metal-organic frameworks as recyclable and heterogeneous catalysts were effectively used to catalyze the synthesis of benzimidazole derivatives from o-phenylendiamine and aldehydes in ethanol. This method provides 2-aryl-1H-benzimidazoles in good to excellent yields with little catalyst loading. The catalyst was characterized using different techniques such as X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy.
Metal-organic frameworks (MOFs) are crystalline solids formed by inorganic clusters or metal ions (generally transition metal) linked by bi- or multifunctional organic ligands. Exploiting the advantages of the MOFs including large surface area, high metal content, and flexibility in designing the active sites, would be an innovative idea to make novel catalysts. This review gives a useful overview on the catalytic applications of MOFs regarding their structural developments toward catalyst fabrication. The catalytic applications cited in this review include the condensation of organic reaction of two or more components involved in a verity of reactions. More specifically, the review has explored the catalytic applications of MOFs in C-C and C-X (S, N, O) bond formation reactions leading to the formation of a more complicated compounds. The emphasis has been made on discussing the stability of the MOFs, their reusability and in providing a comparison of the performance of MOFs with respect to other homogeneous and heterogeneous catalysts.
Gold nanoparticle catalysts have attracted much attention due to their catalytic efficiency under mild conditions. We report here the synthesis of a series of shapes of gold nanocrystals by simple reduction of HAuCl 4 ⋅3H 2 O and application them as the catalysts for multicomponent Biginelli reaction. Amongst these, unsupported gold nanorods show the best catalytic activity. Its efficiency allows one‐pot synthesis of 3,4‐dihydropyrimidin‐2(1 H )‐ones to proceed in high yield under mild conditions.
Two mono nuclear coordination complexes, namely, [Co(4,5-Imdc)2 (H2O)2] (1) and [Cd(4,5-Imdc)2(H2O)3]·H2O (2) were constructed using Co(II) and Cd(II) metal salts with 4,5-Imidazoledicarboxylic acid (4,5-Imdc) as organic ligand. Both 1, 2 were structurally characterized by single crystal XRD and the results reveal that 1 belongs to P21/n space group with unit cell parameters [a = 5.0514(3) Å, b = 22.5786(9) Å, c = 6.5377(3) Å, β = 111.5°] whereas, 2 belongs to P21/c space group with unit cell parameters [a = 6.9116(1) Å, b = 17.4579(2) Å, c = 13.8941(2) Å, β = 97.7°]. While Co(II) in 1 exhibited a six coordination geometry with 4,5-Imdc and water molecules, Cd(II) ion in 2 showed a seven coordination with the same ligand and solvent. In both 1 and 2, the hydrogen bond interactions with mononuclear unit generated 3D-supramolecular structures. Both complexes exhibit solid state fluorescent emission at room temperature. The efficacy of both the complexes as heterogeneous catalysts was examined in the green synthesis of six pyrano[2,3,c]pyrazole derivatives with ethanol as solvent via one-pot reaction between four components, a mixture of aromatic aldehyde, malononitrile, hydrazine hydrate and dimethyl acetylenedicarboxylate. Both 1 and 2 have produced pyrano [2,3,c]pyrazoles in impressive yields (92–98%) at room temperature in short interval of times (<20 min), with no need for any chromatographic separations. With good stability, ease of preparation and recovery plus reusability up to six cycles, both 1 and 2 prove to be excellent environmental friendly catalysts for the value-added organic transformations using green principles.
A series of isomorphic 3D layered rare earth hydroxide (LREH) frameworks RE3(OH)7(1,5-NDS) (RE = Y (1), Gd (2), Er (3), Yb (4); 1,5-NDS = 1,5-naphthalenedisulfonate) has been synthesized under hydrothermal conditions. The crystal structures, thermal stabilities, photoluminescence, and magnetic properties of these compounds have been investigated. The results demonstrate that the compounds are highly stable even at 351 °C and emit strong purple fluorescence, whose colour can be tuned by the coordinated rare earth ions. Their magnetic susceptibilities have also been measured, leading the compounds to be promising multifunctional materials.
A new alkaline metal-organic framework, [Mg3(NDC)3(DMF)4].H2O (1) is synthesized solvothermally by using 2,6-naphthalenedicarboxylic acid (NDC) as ligand and dimethylformamide (DMF) and water as mixed solvent. Single crystal X-ray studies shows that 1 crystallizes in the space group C2/c with parameters a = 13.4191(2), b = 18.0669(2), c = 20.9746(3) Å, β = 99.66(0)o. The central metal atom Mg(II) adopts a six coordinated octahedral geometry with carboxylate oxygen atoms and DMF molecules. Due to the involvement of oxygen atoms in bridging and chelation binding, a trinuclear secondary building unit is built up, which further connects to other six NDC ligands and finally leading to a three dimensional network. The thermal and luminescent analysis revealed that the compound is thermally stable with violet emission. The creation of coordinatively unsaturated Mg(II) centers, acting as Lewis-acidic sites upon activation, are explored to use 1 as heterogeneous catalyst in value-added organic conversions. MOF showed a superb catalytic performance in the synthesis of eight 4H-pyran derivatives via one-pot three-component reaction between aromatic aldehydes, malononitrile, and cyanoacetamide at room temperature. All the reactions worked exceptionally well with excellent yields (91-96%), in short reaction times (< 40 min). Green solvent (ethanol) and easy separation, reusability and robust structure of catalyst are the attractions of the protocol and making [Mg3(NDC)3(DMF)4].H2O an ideal catalyst for wide-ranging organic transformations.
A novel polyethylene-supported Fe/ionic liquid complex (PEt@Fe/IL) is prepared, characterized and its catalytic performance is investigated in the synthesis of 3,4-dihydropyrimidinones. The chemical properties and thermal stability of the PEt@Fe/IL material were studied by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermal gravimetric analysis (TGA) and energy dispersive X-ray (EDAX) analysis. The morphology of the material was obtained using scanning electron microscopy (SEM). The PEt@Fe/IL material was then successfully applied in the Biginelli condensation of aldehydes, urea and alkylacetoacetates to prepare a set of different 3,4-dihydropyrimidinone derivatives in high to excellent yields. The PEt@Fe/IL was recovered and reused several times without significant decrease in efficiency. The other advantages of this novel catalytic system include excellent yield, short reaction time and solvent-free conditions.
Three new metal coordination complexes, namely [Co(BPY)2(H2O)2](BPY)(BS)2(H2O)4 (1), [Co(BPY)2(H2O)4](ABS)2(H2O)2 (2) and [Co(BPY)(H2O)4](MBS)2 (3) (BPY = 4,4′-bipyridine, BS = phenylsulfonic acid, ABS = p-aminobenzenesulfonic acid, MBS = p-methylbenzenesulfonic acid), were obtained under hydrothermal conditions. Complexes 1, 2, 3 were structurally characterized using single-crystal X-ray diffraction and infrared spectroscopy. All of them display low-dimensional motifs: complex 1 displays a two-dimensional structure; and complexes 2 and 3 exhibit a one-dimensional tape structure. Through strong intermolecular hydrogen bonding interactions and weak packing interactions, all of them further stack to generate a three-dimensional supramolecular architecture. Catalysts 1, 2, 3 were involved in the green synthesis of a variety of 3,4-dihydropyrimidin-2(1H)-ones under solvent-free conditions through Biginelli reactions. The corresponding catalytic product was obtained in quantitative yields (99%) under eco-friendly synthesis conditions for the variety of reactions. Catalysts 1, 2, 3 exhibit excellent efficiency for the desired product, and their catalytic performance shows the following order: 2 > 1 ≈ 3, which can be ascribed to the hydrophobic interactions of different phenylsulfonate groups. The catalytic performance for the Biginelli reaction is not only dependent on the selected solvents, but also inversely proportional to the polarities of the solvents.
A highly porous metal–organic framework Cu3 BTC2 (copper(II)-benzene-1,3,5-tricarboxylate) that known as MOF-199 was synthesized, and characterized by common methods including, FT-IR, XRD, EDX, SEM and then used as an efficient and recyclable catalyst for the direct synthesis of symmetric organic disulfides. A variety of symmetric diaryl disulfides with high chemoselectivity can be obtained by domino reaction of aryl halides (and tosylates) and potassium 5-methyl-1,3,4-oxadiazole-2- thiolate, as the base and sulfur-transfer reagent, in the presence of MOF-199.
Graphical Abstract
Three new metal coordination complexes, namely, [Co(BPO)2(H2O)4](BS)2(H2O)2 (1), [Co(BPO)2(H2O)4](ABS)2(H2O)2 (2), [Co(BPO)2(H2O)4](MBS)2(H2O)2 (3) [BPO = 2,5-di(pyridin-4-yl)−1,3,4-oxadiazole, BS = benzenesulphonate, ABS = 4-aminobenzenesulphonate, MBS = 4-methylbenzenesulphonate] were obtained under hydrothermal conditions. Complexes 1-3 were structurally characterized by single-crystal X-ray diffraction, powder X-ray diffraction,, IR and thermogravimetric analyses (TGA). All of them display a zero-dimensional motif, in which strong intermolecular hydrogen bonding interactions (O-H···O/N) and packing interactions (C-H···π and π···π) make them achieve a three-dimensional supramolecular architecture. The primary catalytic results of these three complexes show that high efficiency for the green synthesis of a variety of 3,4-dihydropyrimidin-2(1 H)-ones was observed under solvent free conditions through Biginelli reactions. The present catalytic protocols exhibit advantages such as excellent yield, easy isolation, eco-friendly conditions, and short reaction time.
A novel copper–ethylenediamine tetracarboxylate modified core–shell magnetic catalyst is introduced. The prepared catalyst was fully characterized by various spectroscopic analyses such as XRD, SEM, FT-IR, EDX, ICP, and CHNOS. After characterization, its activity was evaluated as a supported transition metal catalyst in the multi-component Biginelli reaction. The novel catalyst acts as an efficient heterogenized catalyst for synthesis of 3,4-dihydropyrimidin-2(1H)-one/thione derivatives in solvent-free conditions. A wide range of biologically active dihydropyrimidin-2(1H)-one/thiones were synthesized in the presence of the novel catalyst in 10–15 minutes with high yields (85–98% isolated yields). In addition, the reusability of the catalyst was tested by an external magnet. The investigation showed that no notable reduction of yields was observed after reusing over ten runs, proving its stability during recycling processes. More importantly, very small amounts (0.35 mol%) of the novel catalyst were required to result in the maximum turnover frequency of the Biginelli reaction obtained to date (TOF about 1000–1680 h−1 and total TOF over 14000 h−1).
In this paper, we adopt a facile method to prepare a type of porous silica nanoparticles (n-SiO2) from tetraethyl orthosilicate as the source of silica. Then, dendritic polymer supported on nanosilica with surface amino groups was fabricated. Finally, H3PW12O40 nanoparticles (PWAn) were synthesized by the treatment of H3PW12O40 powder with n-Octane as solvent by a solvothermal method and then immobilized onto the dendrimer polymer functionalized nanosilica. The synthesized nanostructures were characterized by fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), N2 adsorption–desorption isotherm analysis, UV–Vis and elemental analysis. The morphology of the catalyst was characterized using transmission electron microscopes (TEM). The acidity of the catalyst was determined by FTIR pyridine adsorption spectroscopy. Then, this catalytic system was used as an efficient catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones via multi-component and one-pot reactions of various aldehydes, phthalic anhydride, hydrazinium hydroxide, and dimedone under thermal solvent-free conditions or ultrasound irradiation at room temperature. Also, the catalyst can be easily recovered and reused for six consecutive reaction cycles without significant loss of activity.
Biginelli reaction is one of the most remarkable examples of MCRs discovered in 1893 and proof of its importance is the high number of articles reported in the last decade covering this field. This strategy allows the synthesis of important building blocks and versatile synthons such as 3,4-dihydropyrimidin-2-(1H)-one derivatives (DHPMs), which are present motives in organic synthesis owing their biological and pharmacological properties. In this chapter we will cover only some aspects overlooked in the incredible revision performed by Suresh and Sandhu, and reported since 2006. Chiral Lewis and Brønsted acid catalyzed examples, Brønsted base-catalyzed ones, organocatalytic enantioselective Biginelli works or important targets will be disclosed in this interesting chapter.
Organoboron reagents, especially boronic acids and boronates, have been widely explored as suitable and powerful reagents for the formation of new C–C bonds in organic synthesis, medicinal chemistry and material science. Since these species have been the center of numerous studies giving rise to a complete area of investigation, we give a brief overview of the interesting chemistry developed with organoboron compounds related with their crucial participation in multicomponent processes. Herein, we will cover examples where the boron atom remains in the final structure of the product and other cases in which the boron atom is released through the course of the process.
Three new metal coordination polymers, namely, [Co(DPP)2(H2O)2]·(BS)2·2H2O (), [Co(DPP)2(H2O)2]·(ABS)2·2H2O () and [Co(DPP)2(MBS)2] () [DPP = 1,3-di(pyridin-4-yl)propane, BS = phenyl sulfonic acid, ABS = p-aminobenzene sulfonic acid, MBS = p-methylbenzene sulfonic acid] were obtained under hydrothermal conditions. Complexes were structurally characterized using X-ray single-crystal diffraction, XRD and IR spectroscopy. Both complexes and display a 1D tape structure. Meanwhile, complex exhibits a 2D layer and further stacks via C-Hπ interactions to generate a three-dimensional supramolecular architecture. These three metal coordination polymers have been applied as catalysts for the green synthesis of a variety of 3,4-dihydropyrimidin-2(1H)-ones under solvent-free conditions through the Biginelli reaction. Interestingly, the catalysis products have been obtained in high yields under eco-friendly synthesis conditions.
Two novel coordination polymers (CPs) have been synthesized, characterized and successfully applied as robust heterogeneous catalysts for the Biginelli multicomponent reaction to obtain 3,4-dihydropyrimidin-2(1H)-one or thione (DHPMs) derivatives. The reaction was initially developed using both CPs and the Zn-based material showed much better catalytic activity. After the reaction optimization under batch conditions, a continuous flow protocol was developed and applied with impressive results. Four bioactive DHPMs were successfully synthesized with high yields. The mechanism of the transformation was also investigated by electrospray (tandem) mass spectrometry (ESI-MS(/MS)) analyses. Online monitoring of the reaction indicated under the developed conditions that the iminium mechanism is preferred over the enamine- and Knoevenagel-based mechanisms. Nine DHPMs had their antitumoral activities evaluated against MCF-7 (human breast cancer cells), A549 (human alveolar basal epithelial cells) and Caco-2 (human epithelial colorectal cells) cancer cell lineages. Fibroblasts (healthy cells) were not affected by the tested DHPMs showing an excellent selectivity for tumour cells. Three DHPMs returned impressive results, being capable of inhibiting tumour cell proliferation in 72 h.
Two new Cu(I) compounds, namely [Cu2(bds)(bpy)2]·2H2O (1) and [Cu4(bds)2(azpy)4]·6H2O (3) (where bds = benzene-1,3-disulfonate, bpy = 4,4′-bipyridine and azpy = 4,4′-azopyridine), and four Ag(I) compounds, namely [Ag2(bds)(bpy)2]·2H2O (2), [Ag2(bds)(azpy)2]·4H2O (4), [Ag(bds)1/2(bpe)]·3H2O (5), and [Ag4(bds)2(tmdp)4]·9H2O (6) (where bpe = 1,2-di(4-pyridyl)ethylene and tmdp = 4,4′-trimethylenedipyridine), have been synthesized, and their structures were determined and characterized by elemental analysis, IR, UV-vis and thermal studies. The structure of the compounds changed from 1D (1 and 2) to 2D (3–5) and interpenetrated 3D (6). In the case of 5, a solid-state [2 + 2] photochemical cycloaddition reaction has been performed. Compound 2 exhibits a reversible anion exchange for perchlorate and permanganate, whereas the other compounds (1, 3–6) exhibit an irreversible anion exchange behaviour for perchlorate. Catalytic studies on 2 indicate Lewis acidity.
A new highly efficient and reusable Cu-MOF has been developed for the regioselective synthesis of 1,2,3-triazoles via the 1,3-dipolar cycloaddition of organic azides to terminal alkynes under solvent-free conditions. This protocol has the advantages of excellent product yields and a low catalyst loading. Moreover, the catalyst may be recovered and reused efficiently up to 5 cycles without major loss of reactivity.
A novel iron-containing Schiff base and ionic liquid based bifunctional periodic mesoporous organosilica (Fe@SBIL-BPMO) was prepared, characterized, and its catalytic application was developed. The SBIL-BPMO was first prepared by the grafting of 3-aminopropyltrimethoxysilane on an ionic-liquid-based PMO followed by treatment with 2-hydroxybenzaldehyde in toluene at reflux. This material was then reacted with Fe(NO3)3⋅9 H2O to afford the Fe@BPMO-SBIL nanocatalyst. The catalyst was characterized by thermogravimetric analysis, nitrogen sorption experiments, diffuse reflectance FTIR spectroscopy, low-angle powder XRD, and TEM. The Fe@SBIL-BPMO catalyst was successfully applied in the one-pot synthesis of 3,4-dihydropyrimidinone/thione derivatives under solvent-free reactions. The stability, reactivity, and reusability of the catalyst under the reaction conditions have also been investigated.
An efficient and green route for the synthesis of dihydropyrimidinones via microwave-assisted Biginelli reaction catalyzed by 3 mol% of heteropolyanion-based ionic liquids under solvent-free conditions has been reported. The practical reaction was found to be compatible with different structurally diverse substrates. Good to excellent yields, short reaction times, and operational simplicity are the main highlights of this protocol. Moreover, the heteropolyanion-based ionic liquids were easily reusable for this Biginelli reaction.
A new highly efficient and reusable Cu(I)-MOF has been developed for the synthesis of propargylamine compounds via the three-component reaction of secondary amines, alkynes, and aromatic aldehydes under solvent-free conditions. The desired propargylamines were obtained in good to excellent yields with a low catalyst loading. The catalyst may be recovered and reused for up to 5 cycles without major loss of activity. This protocol has the advantages of excellent yields, low catalyst loading, and catalyst recyclability.
The preparation, characterization and catalytic application of a novel copper-loaded ionic liquid-based periodic mesoporous organosilica (Cu@PMO-IL) are described. The mesoporous structure of the Cu@PMO-IL material is characterized by transmission electron microscopy (TEM) and nitrogen adsorption desorption analysis. The thermal stability of the material is also determined by thermal gravimetric analysis (TGA). The presence of copper species in the material framework is confirmed by X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA). The catalytic application of Cu@PMO-IL nanocatalyst is then investigated in the Biginelli condensation of different aldehydes with urea and alkylacetoacetates under solvent-free conditions and at moderate temperature. Moreover, the stability, reactivity and reusability of the catalyst are improved under applied reaction conditions.
Three-component condensation of an aliphatic aldehyde, 1,3-dicarbonyl compound and urea proceeds efficiently in absolute ethanol under refluxing temperature using zinc methanesulfonate as a catalyst to afford corresponding 3,4-dihydropyrimidinone. The catalyst can be reused for several times without distinct decrease in reaction yields. The procedure is very useful for the synthesis of dihydropyrimidinones with a wide range of aliphatic aldehydes.
4-Aryl-3, 4-dihydropyrimidinones were synthesized using microwave-assisted, solvent-free protocol of the Biginelli reaction. The simple method provides the title compounds in 78%-95% yields by the reaction of aromatic aldehydes with ethyl acetoacetate and urea/thiourea in the presence of a catalytic amount of conc. HCl. Lewis acids, such as ZnCl2, SnCl2, FeCl3·6H2O, and CuCl2·2H2O, were also found to be efficient catalysts for the synthesis of dihydropyrimidinones.
An efficient and practical procedure for the synthesis of dihydropyrimidinones from aldehydes, 1,3-dicarbonyl compounds and urea under solvent-free reaction condition using zinc triflate as a catalyst is described. In comparison with the classical Biginelli reaction, the yields for this new procedure increased from 20%—50% to 75%— 98% while the reaction time was significantly shortened from 18 h to 20 min.
This book aims to introduce the reader to the design, development, and evaluation processes of new Green Chemistry methodologies. A comprehensive introductory text, it takes a broad view of the subject and integrates a wide variety of topics. Topics covered include: alternative feedstocks, environmentally benign synthetic methodologies, designing safer chemical products, new reaction conditions, alternative solvents and catalyst development, and the use of biosynthesis and biomimetic principles. The reader is introduced to the new evaluation process that encompasses the health and environmental impact of a synthetic pathway from choice of starting materials through to target molecule. Throughout the text, comparisons and contrasts with classical methodologies are offered as illustrative examples. This accessible text is aimed at all those involved with the design, manufacture, use and disposal of chemicals and their products - especially synthetic chemicals at the graduate and professional level, process development chemists and environmental scientists. From reviews of the hardback: ‘An excellent introduction into the fast growing field and the fascinating science of green chemistry.... Should be consulted by anyone who wants to know about environmentally benign chemistry and, especially, by scientists who contemplate adopting its principles in their own research or teaching efforts.’ Science
Marine natural products possessing guanidine functionalities
display a considerable array of biological activity and not surprisingly
have attracted considerable synthetic interest. This review discusses the
isolation of several guanidine containing metabolites, primarily from the
sponge Ptilocaulis spiculifer, but also from other marine
organisms. It also explores the synthetic methodologies adopted for their
preparation and speculates on the structural similarity of the metabolite
ptilomycalin A to abiotic guanidine based anionic receptor molecules.
Five new isostructural two-dimensional lanthanide-based coordination polymers with the formula Ln2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (Ln=Tb, 1; Gd, 2; Eu, 3; La, 4; Nd, 5; F4BDC2−=2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate ligands; DEF=N,N′-diethylformamide), have been synthesized by reaction of Ln(NO3)3 and F4BDC in a DEF/EtOH solvent mixture. The compounds were characterized by single-crystal and powder X-ray diffraction. In all cases, the metal ion is coordinated by nine oxygen atoms from two bidentate μ2-F4BDC2− ligands, two bridging μ2-F4BDC2− ligands, one μ3-F4BDC2− ligand, one DEF molecule and one EtOH molecule forming a tri-capped trigonal prism. The Ln(1) metal ion is linked to an adjacent Ln(1) metal ion through the oxygen atoms of two bridging μ2-F4BDC2− ligands and two μ3-F4BDC2− bridging ligands to form a Ln2O18 dimer. The Ln2O18 polyhedra building units are linked to each other through four F4BDC2− ligands to form 2D sheets that are held together by hydrogen bonding to form a 3D framework. Compounds 1–5 were further characterized using thermogravimetric analysis and infrared spectroscopy. Studies of the photoluminescence properties of compounds 1 and 3, as well as the catalytic activity of compounds 3–5 in the Biginelli reaction, are presented.
Based on 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis-(methylenephosphonic acid) (dotpH8), compounds [Ln(dotpH7)(H2O)2]Cl2·xH2O (1·Ln) (Ln=La, Nd, Sm, Eu, Gd, Tb) and [Ln(dotpH7)(H2O)2](ClO4)2·xH2O (2·Ln) (Ln=Nd, Sm, Eu, Gd, Tb) are synthesized in aqueous solutions at low pH. Compounds within each kind are isostructural. Both show chain structures where the neighboring {LnO8} polyhedra are doubly bridged by {CPO3} tetrahedra through corner-sharing. The packing of chains, however, are different in the two cases. In 1·Ln, each chain is surrounded by six equivalent chains, with the Cl− counterions and the lattice water molecules locating between the chains. In 2·Ln, neighboring chains are connected via strong hydrogen bond interactions to form a supramolecular layer in the ab plane. The ClO4- counterions fill in the inter-layer spaces. The catalytic and luminescent properties are investigated.
The synthesis, structural characterization, thermal stability, guest desorption-sorption, luminescence, and catalytic properties of a series of lanthanide oxalatophosphites,were studied. The redhydration pattern at 150°C shows that the sample compound remains crystalline after loss of lattice water and the integrity of the framework is not affected by the water release. The layered cerium phosphite reported different coordination modes of the phosphate groups in the cerium compound. The emission spectrum of the lanthanide oxalatophosphites are found to excite at 392 nm, exhibiting the characteristic bands of metal ions in the visible regions. The results also indicate that the lanthanide triflates can efficiently catalyze the Biginelli reaction under mild conditions and the structure of lanthanide oxalatophosphites allow incorporation of second type of lanthanide ions.
The cyclocondensation of suitable CH‐acidic carbonyl compounds, aldehydes, and urea‐type blocks under acidic conditions provides multifunctionalized derivatives. The discovery of this three‐component condensation process was made by Biginelli in 1893, therefore this reaction is called the “Biginelli reaction,” “Biginelli condensation,” or the “Biginelli dihydropyrimidine synthesis.” While the early examples of this cyclocondensation process typically involved a beta‐ketoester, aromatic aldehyde, and urea, the scope has now been extended considerably by variation of three building blocks, allowing access to a large number of multifunctionalized pyridmidine derivatives. The importance of multicomponent reactions in combinatorial chemistry has generated a renewed interest in the Biginelli reaction and the number of patents and publications on this subject is growing.
In this chapter, all three‐component condensations involving suitable CH‐acidic carbonyl compounds, aldehydes, and urea‐type building blocks following the Biginelli concept are covered. Therefore, reactions involving 1,3‐diketones or nitroacetone as building blocks leading to dihydropyrimides that follow the discussed substitution pattern are included in contrast to earlier articles. Patents are only cited if they contain information not otherwise available.
Metal-organic frameworks (MOFs) are constructed by linking organic bridging ligands with metal-connecting points to form infinite network structures. Fine tuning the porosities of and functionalities within MOFs through judicious choices of bridging ligands and metal centers has allowed their use as efficient heterogeneous catalysts. This chapter reviews recent developments in designing porous MOFs for a variety of catalytic reactions. Following a brief introduction to MOFs and a comparison between porous MOFs and zeolites, we categorize catalytically active achiral MOFs based on the types of catalytic sites and organic transformations. The unsaturated metal-connecting points in MOFs can act as catalytic sites, so can the functional groups that are built into the framework of a porous MOF. Noble metal nanoparticles can also be entrapped inside porous MOFs for catalytic reactions. Furthermore, the channels of porous MOFs have been used as reaction hosts for photochemical and polymerization reactions. We also summarize the latest results of heterogeneous asymmetric catalysis using homochiral MOFs. Three distinct strategies have been utilized to develop homochiral MOFs for catalyzing enantioselective reactions, namely the synthesis of homochiral MOFs from achiral building blocks by seeding or by statistically manipulating the crystal growth, directing achiral ligands to form homochiral MOFs in chiral environments, and incorporating chiral linker ligands with functionalized groups. The applications of homochiral MOFs in several heterogeneous asymmetric catalytic reactions are also discussed. The ability to synthesize value-added chiral molecules using homochiral MOF catalysts differentiates them from traditional zeolite catalysis, and we believe that in the future many more homochiral MOFs will be designed for catalyzing numerous asymmetric organic transformations.
Chiral metal-organic frameworks with a three-dimensional network structure and wide-open pores (>30 Å) were obtained by using chiral trifunctional linkers and multinuclear zinc clusters. The linkers, H(3) ChirBTB-n, consist of a 4,4',4''-benzene-1,3,5-triyltribenzoate (BTB) backbone decorated with chiral oxazolidinone substituents. The size and polarity of these substituents determines the network topology formed under solvothermal synthesis conditions. The resulting chiral MOFs adsorb even large molecules from solution. Moreover, they are highly active Lewis acid catalysts in the Mukaiyama aldol reaction. Due to their chiral functionalization, they show significant levels of enantioselectivity, thereby proving the validity of the modular design concept employed.
Metal-organic frameworks (MOFs), also known as coordination polymers, have emerged as a new class of crystalline porous materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers. MOFs have tunable pores and functionalities, and usually exhibit very high surface areas. The potential applications of porous MOFs cover a broad range of fields and most of their applications are related to pore sizes, shapes and structures/environments. In this feature article, we provide an overview of the recent developments of porous MOFs as platforms in the functional applications of sorption and separation, heterogeneous catalysis, as supports/host matrices for metal nanoparticles, and as templates/nanoreactors for new material preparation.
A novel 3D porous metal-organic framework containing 1D nanoscale opening channels was constructed from two kinds of pyridine carboxylates and copper(II) nodes with reachable copper sites located in the channel walls, which can be subsequently used to prompt the Henry reaction of benzaldehydes and nitroalkanes with remarkable catalytic activity compared with homogeneous copper cations.
The research done on metal organic frameworks (MOFs) and how one can engineer metal organic frameworks to build catalysts in which the active sites could be the metals at the nodes of the framework was studied. The possibility to generate the metal component of the MOF with a large variety of transition metals could be largely exploited for Lewis acid catalysis, provided that the metal is able to accept electrons from the reactant. In addition, the organic component of the MOF can support acid, base, or acid-base pairs that will allow one to perform cascade reactions. MOFs offer great promise as enantioselective catalysts. Asymmetric syntheses are routinely practiced in the synthesis of drugs, and these reactions are almost completely performed using expensive homogeneous catalysts. By using chiral ligands, a vast number of new MOFs would be available to be tested in this field. MOFs, if properly engineered, can complement the inorganic molecular sieves, as catalysts in the field of chemicals and fine chemicals production.
A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).
This tutorial review presents recent developments of homochiral metal-organic frameworks (MOFs) in enantioselective catalysis. Following a brief introduction of the basic concepts and potential virtues of MOFs in catalysis, we summarize three distinct strategies that have been utilized to synthesize homochiral MOFs. Framework stability and accessibility of the open channels to reagents are then addressed. We finally survey recent successful examples of catalytically active homochiral MOFs based on three approaches, namely, homochiral MOFs with achiral catalytic sites, incorporation of asymmetric catalysts directly into the framework, and post-synthetic modification of homochiral MOFs. Although still in their infancy, homochiral MOFs have clearly demonstrated their utility in heterogeneous asymmetric catalysis, and a bright future is foreseen for the development of practically useful homochiral MOFs in the production of optically pure organic molecules.
A porous homochiral MOF was constructed from a serine derivate ligand bridged and chelated copper atom subunit, which can expand one chiral center into multitopic homochiral centers to systematically tune the heterogeneous catalytic properties.
Four isostructural organically templated lanthanide oxalatophosphates, (H(4)APPIP)[Ln(3)(C(2)O(4))(5.5)(H(2)PO(4))(2)].5H(2)O (Ln = Er-Lu and APPIP = 1,4-bis(3-aminopropyl)piperazine), have been synthesized under hydrothermal conditions and characterized by single-crystal and powder X-ray diffraction. Their structures contain LnO(8) trigonal dodecahedra linked by three bis-bidentate oxalates to form layers in the (102) plane, which are connected by dihydrogen phosphate and bis-monodentate oxalate ligands to form a 3D framework. The charge-compensating tetraprotonated 1,4-bis(3-aminopropyl)piperazinium cations and lattice water molecules are located in the 12-membered ring straight channels. They are the first examples of organically templated lanthanide oxalatophosphates. The thermal stability, guest desorption-sorption properties, variable-temperature in situ powder X-ray diffraction, magnetic susceptibility, and photoluminescence spectrum of the Er compound and catalytic activity of the Yb compound for the Biginelli reaction have also been studied.
In 1893, the synthesis of functionalized 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) via three-component condensation reaction of an aromatic aldehyde, urea and ethyl acetoacetate was reported for the first time by P. Biginelli. In the past decades, such Biginelli-type dihydropyrimidones have received a considerable amount of attention due to the interesting pharmacological properties associated with this heterocyclic scaffold. In this review, we highlight recent developments in this area, with a focus on the DHPMs recently developed as calcium channel modulators, alpha(1a) adrenoceptor-selective antagonists and compounds that target the mitotic machinery.
For Abstract see ChemInform Abstract in Full Text.
For Abstract see ChemInform Abstract in Full Text.
For Abstract see ChemInform Abstract in Full Text.
Reactions of 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid) [notpH6, C9H18N3(PO 3H2)3] with different lanthanide salts result in four types of Ln-notp compounds: [Ln{C9H20N 3(PO3H)2(PO3)}(NO 3)(H2O)].4H2O (1), [Ln = Eu (1Eu), Gd (1Gd), Tb (1Tb)], [Ln{C9H20N3(PO3H) 2(PO3)}(H2O)]C1-3H20 (2) [Ln = Eu (2 Eu), Gd (2 Gd), Tb (2Tb)], [Ln{C9H20N3(PO 3H)2(PO3)](H2O)]C1O 4-8H3O, (3) [Ln = Eu (3 Eu), Gd (3Gd)], and [Ln(C 9H20N3(PO3H)2(PO 3))(H2O)]C1O4.3H2O (4), [Ln = Gd (4Gd), Tb (4Tb)]. Compounds within each type are isostructural. In compounds 1, dimers of (Ln2(notpH4)2(NO3) 2(H2O)2) are found, in which the two lanthanide atoms are connected by two pairs of O-P-O and one pair of μ-O bridges. The NO3 ion serves as a bidentate terminal ligand. Compounds 2 contain similar dimeric units of {Ln2(notpH4)2(H 2O)3} that are further connected by a pair of O-P-O bridges into an alternating chain. The Cr ions are involved in the interchain hydrogen-bonding networks. A similar chain structure is also found in compounds 3; in this case, however, the chains are linked by C1O4 counterions through hydrogen-bonding interactions, forming an undulating layer in the (Oil) plane. These layers are fused through hydrogen-bonding interactions, leading to a three-dimensional supra-molecular network with large channels in the [100] direction. Compounds 4 show an interesting brick-wall-like layer structure in which the neighboring lanthanide atoms are connected by a pair of O-P-O bridges. The C1O4 counterions and the lattice water molecules are between the layers. In all compounds the triazamacrocyclic nitrogen atoms are not coordinated to the LnIII ions. The anions and the pH are believed to play key roles in directing the formation of a particular structure. The fluorescence spectroscopic properties of the Eu and Tb compounds, magnetic properties of the Gd compounds, and the catalytic properties of 4Gd were also studied.
Zinc bromide catalyzes the three component condensation reaction of an aldehyde, urea, and beta-ketoester or beta-diketone under solvent-free conditions to afford the corresponding dihydropyrimidinones (DHPMs) with moderate to high yields in short reaction time. The present method is very effective for the Biginelli condensation of aliphatic aldehydes.
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