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Carbon radical generation by irreversible metal-to-ligand charge transfer

Metal-to-ligand charge transfer (MLCT) is a fundamental photoinduced process that underpins a broad range of energy- or electron-transfer events1,2. In the absence of productive substrate engagement, the MLCT excited state typically relaxes to the ground state via photophysical deactivation, reflecting its largely reversible character3,4. Here we report a class of isolable copper–heteroaryl sulfone complexes that, upon visible light irradiation, undergo an irreversible MLCT-driven fragmentation through C–S bond cleavage within the coordinated sulfone ligand, generating carbon-centered radicals. Spectroscopic and computational studies support the formation of MLCT-derived excited states and a low-barrier pathway for C–S bond cleavage. This reactivity is largely independent of the reduction potentials of the corresponding free sulfones, enabling the generation of fluoroalkyl and non-fluorinated tertiary, secondary, and primary (even methyl) alkyl radicals. We demonstrate the utility of this platform in copper-catalyzed C–H fluoroalkylation of arenes and terminal alkynes. Leveraging these MLCT-generated trifluoromethyl radicals to initiate halogen-atom transfer (XAT) from perfluorocyclobutyl iodide (I-FCB), we also achieve radical perfluorocyclobutylation–iodination of alkenes, addressing a longstanding challenge in the incorporation of perfluorocyclobutyl motifs.

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