The last two decades have witnessed the development of numerous synthetic methods that utilize sensitized or direct photochemistry to facilitate organic reactions under milder conditions, typically at room temperature. These methods also open new reaction pathways that are impossible with thermal chemistry. We will focus on organic reactions that can only be performed photochemically, yielding higher energy products than the starting materials and enabling reactions with better predictability and overall efficiency.
The first class of reactions we discuss involves redox-neutral reactions that require light energy input. The ideal atom economy of these reactions and their excellent energy efficiency make these transformations ideal candidates for preparing chemicals on a larger scale. Cross-coupling reactions are among the most important organic synthesis reactions in both industry and academia. We will examine how photochemistry can enhance the performance of this class of reactions. The new concept of adaptive dynamic homogeneous catalysis (AD-HoC) utilizes light to control the redox state of catalytically active species, enabling the rapid and predictable cross-coupling of all classes of nucleophiles with halogenated (hetero)arenes and vinyl halides. Alternatively, reaction conditions for on-water photochemistry facilitate the formation of electron-donor-acceptor complexes and their activation for cross-coupling.
The examples illustrate the opportunities that arise from combining catalysis with photochemistry. Current challenges include our limited mechanistic understanding of many processes, which necessitates more detailed photophysical investigations. The future for improved catalysis is bright!
Bio:
Prof. Burkhard König is a full professor at the Department of Chemistry, University of Regensburg, Germany. His main research areas are physical-organic chemistry, supramolecular chemistry, photocatalysis, and catalytic conversion of renewable resources. He is an elected member of the German Academy of Sciences, Leopoldina, Halle and of the Bavarian Academy of Sciences, Munich.