Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox‐Active Ligands

• Published in: Chemistry : a European journal 2017-10, Vol.23 (60), p.15030-15034
• Main Authors: Jacquet, Jérémy, Cheaib, Khaled, Ren, Yufeng, Vezin, Hervé, Orio, Maylis, Blanchard, Sébastien, Fensterbank, Louis, Desage‐El Murr, Marine
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; CF3. radicals; Chemical reactions; Chemical Sciences; Chemistry; Coordination chemistry; Coordination compounds; Copper compounds; Cross coupling; Electron transfer; Ligands; Nickel; Oxidation; Reactivity; redox-active ligand; single electron transfer; Valence
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201704049

Nickel complexes have gained sustained attention as efficient catalysts in cross‐coupling reactions and co‐catalysts in dual systems due to their ability to react with radical species. Central to this reactivity is nickel's propensity to shuttle through several accessible redox states from Ni0 to NiIV. Here, we report the catalytic generation of trifluoromethyl radicals from a nickel complex bearing redox‐active iminosemiquinone ligands. This unprecedented reactivity is enabled through ligand‐based oxidation performing electron transfer to an electrophilic CF3+ source while the nickel oxidation state is preserved. Additionally, extension of this reactivity to a copper complex bearing a single redox equivalent is reported, thus providing a unified reactivity scheme. These results open new pathways in radical chemistry with redox‐active ligands. Electro[Ni]c: Electronic transfer from a nickel complex bearing redox‐active ligands to form radical species is studied. Combined UV/Vis and DFT experiments suggest that the redox‐active ligands in the complex sustain this reactivity, and have a greater influence than the metal‐based reactivity. This reactivity can be extended to a complex bearing a single “redox‐equivalent”.