Photochemical iron-catalyzed decarboxylative azidation via the merger of ligand-to-metal charge transfer and radical ligand transfer catalysis

Ligand-to-metal charge transfer (LMCT) using stoichiometric copper salts has recently been shown to permit decarboxylative C-N bond formation via an LMCT/radical-polar crossover (RPC) mechanism; however, this method is unable to function catalytically and cannot successfully engage unactivated alkyl carboxylic acids, presenting challenges to the general applicability of this approach. Leveraging the concepts of LMCT and radical-ligand-transfer (RLT), we herein report the first photochemical, iron-catalyzed direct decarboxyla-tive azidation. Simply irradiating an inexpensive iron nitrate catalyst in the presence of azidotrimethylsilane allows for a diverse array of carboxylic acids to be converted to corresponding organic azides directly with broad functional group tolerance and mild conditions. Intriguingly, no additional external oxidant is required for this reac-tion to proceed, simplifying the reaction protocol. Finally, mecha-nistic studies are consistent with a radical mechanism and suggest that the nitrate counteranion serves as an internal oxidant for turnover of the iron catalyst.