Photogeneration of Cobalt-Stabilized Aminium Radical

Transition metal-stabilized radical systems have been of interest in the field of redox chemistry. However, ligand-centered radicals still remain difficult to access and control photochemically in first-row transition-metal complexes. Here we report a cobalt complex based on a dimethylamino-functionalized ImP (bis(imidazolylidene)phenyl) ligand scaffold that undergoes a clean and reversible photooxidation to generate a [Co(ImPNMe2)]2+ featuring a ligand centered aminium radical upon exposure to mild UV irradiation or chemical oxidation. The unpaired electron of the aminium nitrogen is delocalized along the phenyl-Co-phenyl axis, enabling direct characterization by NMR spectroscopy in addition to UV-Vis, SEC-UV-Vis, XAS and EPR spectroscopy. Formation of the radical is accompanied by the emergence of two intense absorption bands, allowing convenient spectroscopic monitoring of the photo-redox process. Together, these results establish a rare example of a light-induced ligand-centered radical in a cobalt complex and highlight its potential for photo-induced reactivity.