Mechanism-based screening accelerates photocatalysis research

Screening strategies to discover new catalysts or types of reactions typically count hits by the number of new products that turn up in crude reaction mixtures. Frank Glorius and colleagues of the University of Münster have decided to try a different approach: They only screen molecules for their ability to take part in a single step of a reaction. If an interaction occurs, the molecule is considered a hit. What’s more, each molecule tested is taken as a representative of an entire class of molecules, which greatly expands the scope of the screen. Once a target molecule is acquired, the researchers flip the screen to use the molecule with various catalysts to identify the optimal catalyst for the job at hand (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201600995). The Münster team tested this approach by looking at excited-state catalyst quenching by an organic reactant, which is the key step common to all photocatalytic reactions. If an interaction occurs, which the researchers determine via spectroscopy, a reactive radical species forms that is capable of following different downstream reaction pathways to form various products. The team’s screen of 100 compounds identified benzotriazoles and phenols as two new molecule classes that interact with iridium catalysts in denitrogenation and bromination reactions, respectively.