Hydrogen Atom Transfer Promoted by Carbon-Centered Biradicals via Energy Transfer Catalysis

Abstract

In the past decade, visible-light-mediated photocatalysis has emerged as an applicable strategy for the generation of diverse radical species via single electron transfer (SET) and energy transfer (EnT) processes. Within this context, visible-light-mediated hydrogen atom transfer (HAT) has attracted major interest due to its mild and environmentally benign conditions applied in the selective activation of C–H bonds. Strategies employing C- and heteroatom-centered radical species to selectively activate C–H bonds have become versatile tools due to their mildness and good functional group compatibility for synthesizing value-added products. In this regard, a review on C-centered radical-promoted HAT processes was reported by Gevorgyan’s group ( Chem. Sci. 2020, 11, 12974, DOI: 10.1039/d0sc04881j), and a review on visible-light-promoted remote C–H functionalization via 1,5-HAT was recently reported by Zhu’s group ( Chem. Soc. Rev. 2021, 50, 7359, DOI: 10.1039/d0cs00774a). Compared to N- and O-centered radical-promoted HAT processes, C(sp³)-centered radical-promoted HAT is more challenging and less explored due to the small differences in C–H bond dissociation energies. Additionally, in the realm of C-centered radical-promoted HAT, the generation of C-centered radicals has mostly involved SET processes, while the EnT-mediated C-centered radical-promoted HAT process has been less discussed because of the considerable scarcity of related reports.