Design of Organic Radical Cations as Potent Hydrogen-Atom Transfer Catalysts for C-H Functionalization

Hydrogen-atom transfer (HAT) catalysis offers an atom- and step-economical approach to the direct functionalization of aliphatic C-H bonds. While the structure of HAT catalysts largely affects the reactivity and selectivity in the step where the C-H bond is cleaved, the choice of viable catalysts for HAT from strong C-H bonds is limited. The recent development of organic HAT catalysts based on the flexibly modifiable molecular platform has enabled fine-tuning of the steric and electronic properties of these catalysts, thus greatly expanding their structural diversity. This review focuses on the design of HAT catalysts with cationic moieties as common structural motifs and their application to the selective manipulation of the C-H bonds of challenging substrates, including unactivated hydrocarbons. Hydrogen-atom transfer (HAT) catalysis enables the direct functionalization of C-H bonds in aliphatic compounds with high atom and step economy. This review highlights recently developed HAT catalysts with cationic moieties as common structural motifs, and describes the importance of catalyst design for controlling the reactivity and selectivity in the HAT process.image