Mechanistic Insight into the Light-Triggered CuAAC Reaction: Does Any of the Photocatalyst Go?

Abstract

The attainment of transition-metal catalysis and photoredox catalysis has represented a great challenge over the last years. Herein, we have been able to merge both catalytic processes into what we have called "the light-triggered CuAAC reaction". Particularly, the CuAAC reaction reveals opposite outcomes depending on the nature of the photocatalyst (eosin Y disodium salt and riboflavin tetraacetate) and additives (DABCO, Et 3 N, and NaN 3 ) employed. To get a better insight into the operating processes, steady-state, time-resolved emission, and laser flash photolysis experiments have been performed to determine reactivity and kinetic data. These results, in agreement with thermodynamic estimations based on reported data, support the proposed mechanisms. While for eosin Y (EY), Cu(II) was reduced by its triplet excited state; for riboflavin tetraacetate (RFTA), mainly triplet excited RFTA state photoreductions by electron donors as additives are mandatory, affording RFTA •− (from DABCO and NaN 3 ) or RFTAH • (from Et 3 N). Subsequently, these species are responsible for the reduction of Cu(II). For both photocatalysts, photogenerated Cu(I) finally renders 1,2,3-triazole as the final product. The determined kinetic rate constants allowed postulating plausible mechanisms in both cases, bringing to light the importance of kinetic studies to achieve a strong understanding of photoredox processes.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

“…Recent mechanistic studies on photoinduced CuAAC (Cu-catalyzed azide–alkyne cycloaddition) reaction triggered by EY also strongly support the oxidative quenching cycle. 84 …”

“…Recent mechanistic studies on photoinduced CuAAC (Cu-catalyzed azide-alkyne cycloaddition) reaction triggered by EY also strongly support the oxidative quenching cycle. 84 In the EY/Cu dual catalysis, both Cu I /L and 3 EY* can react with molecular oxygen (E 1/2 (O 2 /O 2 c − ) ¼ −0.87 V vs. SCE). The continuous regeneration of the Cu I /L activator by EY provides high oxygen tolerance (Fig.…”

New Acetamidine Cu(II) Schiff base complex supported on magnetic nanoparticles pectin for the synthesis of triazoles using click chemistry

“…In the synthesis of 1,2,3-triazole derivatives, copper plays a prominent role in the formation of these compounds. On the premise of the work of Sharpless and Medal, special copper resources inclusive of Cu (I) 35 – 40 , MNP@PIL-Cu 41 , Cu-complicated 42 , Cu NPs 43 , and HMS-DP-Cu(II) 44 had been tested. Moreover, in current years, as a way to synthesize triazoles, many other strategies had been counseled 45 – 47 .…”

Pyrazine Based Type‐I Sensitizing Assemblies for Photoreduction of Cu(II) in ‘One‐Pot Three‐Component’ CuAAC Reaction Under Aerial Conditions

“…Very recently, 'light-triggered' click reaction has been reported in which photoredox systems based on commercially available dyes (eosin Y, fluorescein, methylene blue, rose bengal, riboflavin tetraacetate and perylene) under inert/aerial conditions work efficiently to induce photoreduction of Cu(II) ions (Figure 1B). [17,18] Though the 'reductant free' strategy is efficient but it does not work well in case of 'one-pot three-component' approach using benzyl bromide, sodium azide and phenylacetylene as reactants. In the reported strategy, the photoreduction of Cu(II) is initiated in the triplet state of the dye and since sodium azide is triplet state quencher, this 'one-pot threecomponent' strategy does not work under the reaction conditions.…”