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

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.