Optically Controlled Recovery and Recycling of Homogeneous Organocatalysts Enabled by Photoswitches

• Published in: Angewandte Chemie International Edition 2023-03, Vol.62 (13), p.e202300723-n/a
• Main Authors: Qiu, Qianfeng, Sun, Zhenhuan, Joubran, Danielle, Li, Xiang, Wan, Joshua, Schmidt‐Rohr, Klaus, Han, Grace G. D.
• Format: Article
• Language: English
• Subjects: Catalysts; Design for recycling; Environmental impact; Homogeneous Catalyst; Photoswitches; Recovery; Recycling; Solubility; Solubility Change
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202300723

We address a critical challenge of recovering and recycling homogeneous organocatalysts by designing photoswitchable catalyst structures that display a reversible solubility change in response to light. Initially insoluble catalysts are UV‐switched to a soluble isomeric state, which catalyzes the reaction, then back‐isomerizes to the insoluble state upon completion of the reaction to be filtered and recycled. The molecular design principles that allow for the drastic solubility change over 10 times between the isomeric states, 87 % recovery by the light‐induced precipitation, and multiple rounds of catalyst recycling are revealed. This proof of concept will open up opportunities to develop highly recyclable homogeneous catalysts that are important for the synthesis of critical compounds in various industries, which is anticipated to significantly reduce environmental impact and costs. Photoswitchable organocatalysts have been generated that undergo reversible dissolution and precipitation upon photo‐irradiation. The insoluble solid‐state catalysts are photo‐switched to form soluble isomers that activate and complete two types of base‐catalyzed reactions. Irradiation with visible light promotes the precipitation of the catalyst with a recovery rate of 87 %, which can be reused in multiple rounds of subsequent reactions.