Synthesis of chiral Cu(II) complexes from pro-chiral Schiff base ligand and investigation of their catalytic activity in the asymmetric synthesis of 1,2,3-triazoles

A pro-chiral Schiff base ligand (HL) was synthesized by the reaction of 2-amino-2-ethyl-1,3-propanediol and pyridine-2-carbaldehyde in methanol. The reaction of HL with CuCl2·2H2O and CuBr2 in methanol gave neutral mononuclear Cu(II) complexes with general formula of [Cu(HL)Cl2] (1) and [Cu(HL)Br2] (2), respectively. By slow evaporation of the methanolic solutions of 1 and 2, their enantiomers were isolated in crystalline format. The formation of pure chiral crystals in the racemic mixture was amply authenticated by single crystal X-ray analysis, which indicated that S-[Cu(HL)Cl2], R-[Cu(HL)Cl2], and S-[Cu(HL)Br2] are crystallized in chiral P212121 space group of orthorhombic system. Preferential crystallization was used to isolate the R and S enantiomers as single crystals and the isolated compounds were also studied by CD analysis. Structural studies indicated that the origin of the chirality in these compounds is related to the coordination mode of the employed pro-chiral ligand (HL) because one of its carbon atoms has been converted to a chiral center in the synthesized complexes. Subsequently, these complexes were used in click synthesis of a β-hydroxy-1,2,3-triazole and the results of catalytic studies indicated that 1 and 2 can act as enantioselective catalysts for the asymmetric synthesis of β-hydroxy-1,2,3-triazole product under mild condition. This study illustrates the significant capacity of the use of pro-chiral ligands in preparing chiral catalysts based on complexes which can also be considered as an effective approach to cheap chiral catalysts from achiral reagents.

Green Approach Toward Triazole Forming Reactions for Developing Anticancer Drugs

Compounds containing triazole have many significant applications in the dye and ink industry, corrosion inhibitors, polymers, and pharmaceutical industries. These compounds possess many antimicrobial, antioxidant, anticancer, antiviral, anti-HIV, antitubercular, and anticancer activities. Several synthetic methods have been reported for reducing time, minimizing synthetic steps, and utilizing less hazardous and toxic solvents and reagents to improve the yield of triazoles and their analogues synthesis. Among the improvement in methods, green approaches towards triazole forming biologically active compounds, especially anticancer compounds, would be very important for pharmaceutical industries as well as global research community. In this article, we have reviewed the last five years of green chemistry approaches on click reaction between alkyl azide and alkynes to install 1,2,3-triazole moiety in natural products and synthetic drug-like molecules, such as in colchicine, flavanone cardanol, bisphosphonates, thiabendazoles, piperazine, prostanoid, flavonoid, quinoxalines, C-azanucleoside, dibenzylamine, and aryl-azotriazole. The cytotoxicity of triazole hybrid analogues was evaluated against a panel of cancer cell lines, including multidrug-resistant cell lines.

NiFe2O4@SiO2-Cu as a novel and efficient magnetically recoverable nanocatalyst for regioselective synthesis of β-thiol-1,2,3-triazoles under benign conditions

A green, mild and eco-friendly approach for the three component one-pot regioselective synthesis of 1,2,3-triazoles from thiiranes has been introduced in the presence of NiFe2O4@SiO2-Cu as a new and recoverable nanocatalyst. First, the NiFe2O4 nanoparticles have been produced through a solid-state reaction of hydrated nickel sulfate, hydrated iron(iii) nitrate, NaOH and NaCl salts, and then calcined at 700 °C. Next, in order to protect the ferrite particles from oxidation and aggregation, the NiFe2O4 was core-shelled using tetraethyl orthosilicate (TEOS) and converted to NiFe2O4@SiO2. Finally, the novel NiFe2O4@SiO2-Cu nanocomposite was successfully prepared by adding copper(ii) chloride solution and solid potassium borohydride. The catalyst has been characterized by FT-IR, SEM, EDX, VSM, ICP-OES, TEM and XRD techniques. The 1,3-dipolar cyclization of 1,2,3-triazoles was performed successfully in water at room temperature in high yields. The recoverability and reusability of the heterogeneous NiFe2O4@SiO2-Cu have also been investigated using VSM, SEM and FT-IR analyses. The catalyst was used four times in consecutive runs without considerable loss of activity. The presented procedure provides significant benefits such as using water as a green solvent, absence of hazardous organic solvents, high yields, benign conditions and recyclability of the magnetic catalyst.

An Overview on the Performance of 1,2,3-Triazole Derivatives as Corrosion Inhibitors for Metal Surfaces

This review accounts for the most recent and significant research results from the literature on the design and synthesis of 1,2,3-triazole compounds and their usefulness as molecular well-defined corrosion inhibitors for steels, copper, iron, aluminum, and their alloys in several aggressive media. Of particular interest are the 1,4-disubstituted 1,2,3-triazole derivatives prepared in a regioselective manner under copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reactions. They are easily and straightforwardly prepared compounds, non-toxic, environmentally friendly, and stable products to the hydrolysis under acidic conditions. Moreover, they have shown a good efficiency as corrosion inhibitors for metals and their alloys in different acidic media. The inhibition efficiencies (IEs) are evaluated from electrochemical impedance spectroscopy (EIS) parameters with different concentrations and environmental conditions. Mechanistic aspects of the 1,2,3-triazoles mediated corrosion inhibition in metals and metal alloy materials are also overviewed.

Preparation, characterization and application of MgFe2O4/Cu nanocomposite as a new magnetic catalyst for one-pot regioselective synthesis of β-thiol-1,4-disubstituted-1,2,3-triazoles

Magnesium ferrite magnetic nanoparticles were synthesized by a solid-state reaction of magnesium nitrate, hydrated iron(iii) nitrate, NaOH and NaCl salts and then calcined at high temperatures. In order to prevent oxidation and aggregation of magnesium ferrite particles, and also for preparing a new catalyst of supported copper on the magnetic surface, the MgFe2O4 was covered by copper nanoparticles in alkaline medium. Magnetic nanoparticles of MgFe2O4/Cu were successfully obtained. The structure of the synthesized magnetic nanoparticles was identified using XRD, TEM, EDS, FT-IR, FESEM and VSM techniques. The prepared catalyst was used in the three component one-pot regioselective synthesis of 1,2,3-triazoles in water. The various thiiranes bearing alkyl, allyl and aryl groups with terminal alkynes, and sodium azide in the presence of the MgFe2O4/Cu nanocatalyst were converted to the corresponding β-thiolo/benzyl-1,2,3-triazoles as new triazole derivatives. The effects of different factors such as time, temperature, solvent, and catalyst amount were investigated, and performing the reaction using 0.02 g of catalyst in water at 60 °C was chosen as the optimum conditions. The recovered catalyst was used several times without any significant change in catalytic activity or magnetic property.

Cu(II)-Hydrazide Coordination Compound Supported on Silica Gel as an Efficient and Recyclable Heterogeneous Catalyst for Green Click Synthesis of β-Hydroxy-1,2,3-triazoles in Water

A hydrazone ligand, (E)-6-(2-((2-hydroxynaphthalen-1-yl)methylene)hydrazinyl)nicotinohydrazide (H₂L), was synthesized and characterized by spectroscopic methods. The reaction of H₂L with CuCl₂·2H₂O in methanol gave Cu(II) coordination compound, [Cu(HL')(Cl)]·CH₃OH (1), which was characterized by elemental analysis and spectroscopic methods (Fourier transform infrared (FT-IR) and UV-vis). The structure of 1 was also determined by single-crystal X-ray analysis. Structural studies confirmed the formation of esteric group during the synthesis of 1. Compound 1 was immobilized on 3-aminopropyltriethoxysilane (APTS)-functionalized silica gel through the amidification reaction and the obtained heterogeneous coordination compound was utilized as a catalyst for the three-component azide-epoxide-alkyne cycloaddition reaction in water as a green solvent. The structural properties of the heterogeneous catalyst were characterized by a combination of FT-IR, UV-vis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) analyses. The effect of the amount of catalyst and temperature on the cycloaddition reaction was studied, and the obtained 1,2,3-triazoles were characterized by spectroscopic studies and single-crystal X-ray analysis. The catalytic investigations revealed that this catalytic system has high activity in the synthesis of β-hydroxy-1,2,3-triazoles. It was also found that the aromatic and aliphatic substituents on the alkyne and epoxide together with the reaction temperature have considerable effects on the activity and regioselectivity of this catalytic system.

Synthesis, characterization and in vitro anticancer activity of thiabendazole-derived 1,2,3-triazole derivatives

Thiabendazolium salts with 1,2,3-triazole motifs were synthesized and characterized; they exhibit good cytotoxic activity.

Highly Stable Copper(I)-Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water

Environmentally friendly metal-organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two Cu^I -based MOFs, namely, [Cu₄ Cl₄ L]⋅CH₃ OH⋅1.5 H₂ O (1-Cl) and [Cu₄ Br₄ L]⋅DMF⋅0.5 H₂ O (1-Br), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X^- (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br, as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active Cu^I sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.

CoFe2O4/Cu(OH)2 magnetic nanocomposite: an efficient and reusable heterogeneous catalyst for one-pot synthesis of β-hydroxy-1,4-disubstituted-1,2,3-triazoles from epoxides

A magnetically separable CoFe₂O₄/Cu(OH)₂ nanocomposite was prepared and characterized by various techniques such as FESEM, EDS, TEM, XRD, VSM and FT-IR. This novel composite was used as a heterogeneous catalyst for the regioselective synthesis of β-hydroxy-1,4-disubstituted-1,2,3-triazoles from sodium azide, terminal alkynes and structurally different epoxides in water at 60 °C. The formation of the product proceeds in one pot through a mechanism that involves an in situ generated organic azide intermediate, followed by rapid ring closure with the alkyne component. The simple procedure, short reaction times, perfect regioselectivity, high product yields, and use of a benign solvent and nontoxic catalyst are among the considerable advantages of this protocol. Furthermore, the catalyst was easily separated using an external magnet and reused several times without any significant loss of catalytic activity or magnetic properties.

Magnetically separable CoFe₂O₄/Cu(OH)₂ nanocomposite was prepared and used as a novel heterogeneous catalyst for synthesis of β-hydroxy-1,4-disubstituted-1,2,3-triazoles from epoxides.

The effect of the orientation of the Jahn–Teller distortion on the magnetic interactions of trinuclear mixed-valence Mn(ii)/Mn(iii) complexes

The effect of the orientation of the Jahn–Teller distortion on the magnetic interactions in two new mixed-valence trinuclear Mn(iii)–Mn(ii)–Mn(iii) complexes has been investigated.

Preparing Mn(iii) salen-type Schiff base complexes using 1,3-oxazines obtained by Mannich condensation: towards removing ortho-hydroxyaldehydes

Synthesis of Mn(iii)-salen type Schiff base complexes from 1,3-oxazines obtained from Mannich condensation. This method eliminates the restrictions on the use ofortho-hydroxyaldehydes.