Copper–sulfone complexes release carbon radicals under visible light via irreversible MLCT
Chemists at the Shanghai Institute of Organic Chemistry isolated copper–heteroaryl sulfone complexes that cleave a C–S bond under visible light, producing alkyl radicals.
Researchers from the Shanghai Institute of Organic Chemistry (Chinese Academy of Sciences) and ShanghaiTech University, with Xiao-Song Xue and Jinbo Hu as corresponding authors, report a class of isolable copper–heteroaryl sulfone complexes. According to the material from static-content.springer.com, under visible light these complexes undergo irreversible fragmentation driven by metal-to-ligand charge transfer (MLCT). A C–S bond within the coordinated sulfone ligand breaks and carbon-centered radicals form static-content.springer.com
static-content.springer.comstatic-content.springer.comOpen source ↗. The work was published in Nature.
MLCT is a fundamental photoinduced process underlying a broad range of energy- and electron-transfer events. Without productive substrate engagement, the MLCT excited state usually relaxes to the ground state through photophysical deactivation, so the process is largely reversible. In the new complexes the excited state instead leads to bond cleavage.
Mechanism and scope of radicals
The authors report that spectroscopic and computational studies support the formation of MLCT-derived excited states and a low-barrier pathway for C–S bond cleavage. The source data include DFT excitation-energy calculations for a copper complex designated Cu-2. The reactivity is largely independent of the reduction potentials of the corresponding free sulfones. This allows the generation of fluoroalkyl radicals and of non-fluorinated tertiary, secondary and primary alkyl radicals, including methyl.
Synthetic applications
The authors demonstrate the platform in copper-catalyzed C–H fluoroalkylation of arenes and terminal alkynes static-content.springer.com
static-content.springer.comstatic-content.springer.comOpen source ↗. In a second application, trifluoromethyl radicals generated through MLCT initiate halogen-atom transfer (XAT) from perfluorocyclobutyl iodide (I-FCB). This gives radical perfluorocyclobutylation–iodination of alkenes, which the authors describe as addressing a longstanding challenge in introducing perfluorocyclobutyl motifs.
This is a laboratory study of molecular complexes and model reactions. The available material does not give yields, the number of substrates or the reaction conditions.
