Summary
A Nature study reports copper–heteroaryl sulfone complexes that use visible light to generate carbon-centred radicals through C–S bond cleavage. The researchers demonstrate the chemistry in fluoroalkylation reactions and in a method for adding perfluorocyclobutyl and iodine groups to alkenes.
A study published in Nature reports that isolable copper–heteroaryl sulfone complexes can use visible light to produce carbon-centred radicals. The complexes do this through an irreversible metal-to-ligand charge-transfer process that breaks a carbon–sulfur (C–S) bond in the coordinated sulfone. The researchers used spectroscopic and computational studies to support their explanation of how the reaction proceeds.
The work demonstrates the approach in copper-catalysed fluoroalkylation of arenes and terminal alkynes, and in a reaction that adds perfluorocyclobutyl and iodine groups to alkenes. The paper was published on 4 November 2026; Nature describes the online article as peer-reviewed and accepted, with a final version to follow.
How light triggers bond cleavage
Metal-to-ligand charge transfer, or MLCT, occurs when light moves an electron from a metal-centred state to one associated with a ligand. In many systems, the excited state relaxes back to its ground state without producing a lasting chemical change. The researchers report a different outcome for their copper complexes: excitation leads to fragmentation of the sulfone ligand and formation of carbon radicals.
A carbon-centred radical is a reactive species with an unpaired electron on a carbon atom. Such intermediates are useful in synthesis because they can form new bonds with other molecules. In this system, the C–S bond cleavage converts the ligand into a source of those reactive carbon fragments. The authors’ spectroscopy and calculations support the formation of MLCT-derived excited states and a low-barrier route to bond cleavage.
The reported radical generation is largely independent of the reduction potentials of the corresponding free sulfones. That result matters for the design of the method: the reaction is enabled by the sulfone’s coordination to copper and the resulting light-driven process, rather than being governed mainly by how readily the unbound sulfone accepts an electron. The platform is reported to generate fluoroalkyl radicals as well as non-fluorinated tertiary, secondary and primary alkyl radicals, including methyl radicals.
Demonstrated reactions
The researchers applied the chemistry to copper-catalysed C–H fluoroalkylation, which replaces a carbon–hydrogen bond with a bond to a fluoroalkyl group. They report examples involving both arenes—molecules containing an aromatic ring—and terminal alkynes, compounds with a carbon–carbon triple bond at the end of the molecule.
The study also uses light-generated trifluoromethyl radicals to initiate halogen-atom transfer from perfluorocyclobutyl iodide, abbreviated I-FCB. The authors report that this enables radical perfluorocyclobutylation–iodination of alkenes, combining the addition of a perfluorocyclobutyl group with iodine incorporation. They describe introducing this motif into molecules as a longstanding synthetic challenge.
Together, the results show how an excited-state process in a copper complex can be directed toward bond cleavage and used to access several classes of carbon radicals. The demonstrated reactions make the approach a synthetic method for building carbon–carbon and carbon–halogen connections, rather than simply a study of light absorption or excited-state behaviour.