Azide–Alkyne Cycloaddition Catalyzed by Copper(I) Coordination Polymers in PPM Levels Using Deep Eutectic Solvents as Reusable Reaction Media: A Waste-Minimized Sustainable Approach

Abstract

Two air-stable copper­(I)–halide coordination polymers 1 and 2 with NNS and NNO ligand frameworks were synthesized and successfully utilized as efficient catalysts in an important organic reaction, namely, copper-catalyzed azide–alkyne cycloaddition, which is generally conducted in a mixture of water and organic solvents. The azide–alkyne “click” reaction was successfully conducted in pure water at r.t. under aerobic conditions. Other green solvents, including ethanol and glycerol, were also effectively used. Finally, deep eutectic solvents as green and sustainable reaction media were successfully utilized. In deep eutectic solvents, complete conversion with excellent isolated yield was achieved in a short period of time (1 h) with low catalyst loading (1 mol %) at r.t. Full conversion could also be achieved within 24 h with ppm-level (50 ppm) catalyst loading at 70 °C. Optimized reaction conditions were used for the syntheses of a large number of 1,4-disubstituted 1,2,3-triazoles with various functionalities. Triazole products were easily isolated by simple filtration. The reaction media, such as water and deep eutectic solvents, were recovered and recycled in three consecutive runs. The limited waste production is reflected in a very low E-factor (0.3–2.8). Finally, the CHEM21 green metrics toolkit was employed to evaluate the sustainability credentials of different optimized protocols in various green solvents such as water, ethanol, glycerol, and deep eutectic solvents.

Copper(i)-catalyzed click chemistry in deep eutectic solvent for the syntheses of β-d-glucopyranosyltriazoles

“…[108][109][110] Recently, our group reported an air-stable and well-dened copper(I)-chloride coordination polymer with NNS ligand framework for sustainable synthesis of various triazoles in green solvents. 84 However, coordination of that NNS ligand with CuI resulted in insoluble solid and we could not reveal its identity. Similar tridentate NNO ligand system 111,112 might also be effective to develop copper(I) catalyst with high efficiency.…”

“…Very recently, we reported CuAAC reaction in presence of copper( i ) coordination polymer as effective catalyst in DES as sustainable solvent. 84 The selection of sustainable solvents in “click chemistry” for the syntheses of glucopyranosyltriazoles is equally important. The catalytic protocols for the syntheses of 1,4-disubstituted 1,2,3-triazoles linked with glycoconjugates mostly used environmentally hazardous solvents like dichloromethane (DCM), toluene, dimethylformamide (DMF) and acetonitrile.…”

Green synthesis of 1,4-disubstituted 1,2,3-triazoles: a sustainable approach

“…In a study conducted by Bagh and group, the azide-alkyne cycloaddition was catalyzed by two air-stable copper(I)-halide coordination polymers featuring NNS and NNO ligand frameworks using DES as a green and sustainable reaction media as illustrated in Table 2, entry (22). 90 DES enabled complete conversion with excellent yield with low catalytic loading (1 mol%) at rt. The synthesis of diverse N-(substituted phenyl)-2-(4-((dibenzylamino)methyl)-1H-1,2,3triazol-1-yl)acetamide through a green chemistry approach utilizing water and eco-friendly catalysts, as demonstrated in Table 2, entry (23) by Gondaliya et al 91 The optimization of the reaction towards greener practice involved the use of choline azide and ecologically suitable solvent systems at rt.…”

Selective aerobic oxidation of biomass model compound veratryl alcohol catalyzed by air-stable copper(ii) complexes in water

“…94 Earlier various catalytic transformations were also evaluated by using this toolkit. [117][118][119][120][121][122][123][124][125][126] Methods A, C and D gave full conversion, quantitative yield and complete selectivity (reflected by green flags). Although the starting material veratryl alcohol was completely consumed in method B, the yield (as well as selectivity) of the desired product veratraldehyde was much lower due to formation of over-oxidized product.…”