Organic/Inorganic Heterogeneous Silica‐Based Photoredox Catalyst for Aza‐Henry Reactions

Abstract

The transformation of light into chemical energy is a leitmotiv in the development of sustainable and environmentally concerned chemical processes. Chemists invented original concepts to address this purpose, like photoredox catalysis, which became a wonderful tool to transform simple organic compounds into high‐value products. Nevertheless, the most relevant transition metal based photocatalysts suffer from major disadvantages like toxicity, cost, and poor recyclability potential. To circumvent this, we propose a new generation of heterogeneous photoredox catalysts resulting from the combination of porous silica materials and Rose Bengal. They promote carbon–carbon bond formations under visible‐light in environmentally benign solvent using air as the only stoichiometric redox partner. The pure covalent photocatalytic system provides a robust and recyclable system for greener catalysis. This report would be of broad significance because it addresses important sustainability issues: recycling, non‐toxic metal‐free photocatalysts, and less‐waste‐producing chemical process.

Photoredox Catalysis Using Heterogenized Iridium Complexes**

“…A few examples exist using derivatives of tris(2,2'‐bipyridine)‐ruthenium coordination complexes immobilized onto silica, [9] glass wool, [10] or polymer [11] supports. Other unique examples have also been tested such as Rose Bengal [12] dye or perylene diimide (PDI) [13] molecules immobilized on silica, and porphyrins immobilized onto cotton threads [14] . Heterogenized iridium photoredox catalysts are even less explored, with only a few examples existing where polypyridyl‐based iridium complexes have been incorporated into polymer supports; [15] note that in polymer supports, iridium leaching can be an issue leading to catalyst instability [15b] .…”

Triplet Photosensitizers Showing Strong Absorption of Visible Light and Long-Lived Triplet Excited States and Application in Photocatalysis: A Mini Review

“…There was no significant decrease in yields after three recycles (82%, 76%, and 69%, respectively). These results indicated that the organic photocatalysts showing a strong visible-light-harvesting ability are versatile, and they can outcompete the conventional Ru­(byp) 3 X 2 photocatalyst, even if immobilized for a heterogeneous catalysis …”

Heterogeneous photoredox catalysis using fluorescein polymer brush functionalized glass beads

“…As such, cost effectiveness can be improved with the recycling of transition metal catalysts. Various heterogeneous photocatalytic systems have been described-from nanoparticles [35][36][37][38] to polymer gels/networks [39][40][41][42][43][44] to metal oxides. 45 Each of these approaches introduces its own challenges: nanoparticles require separation steps and catalyst is lost during the separation process, 46 photocatalyst-functionalized polymer gels (and networks) may require multiple cleaning steps, and metal oxides can introduce toxic heavy metal contaminants.…”