Iron-Catalyzed Intermolecular C-H Amination Assisted by an Isolated Iron-Imido Radical Intermediate

Here we report the use of a base metal complex [(^tBu pyrpyrr₂ )Fe(OEt₂ )] (1-OEt₂ ) (^tBu pyrpyrr₂ ^2- =3,5-tBu₂ -bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of C_sp3 -H bonds of 9,10-dihydroanthracene (2 a) using 2,4,6-trimethyl phenyl azide (3 a) as the nitrene source. The reaction is complete within one hour at 80 °C using as low as 2 mol % 1-OEt₂ with control in selectivity for single C-H amination versus double C-H amination. Catalytic C-H amination reactions can be extended to other substrates such as cyclohexadiene and xanthene derivatives and can tolerate a variety of aryl azides having methyl groups in both ortho positions. Under stoichiometric conditions the imido radical species [(^tBu pyrpyrr₂ )Fe{=N(2,6-Me₂ -4-tBu-C₆ H₂ )] (1-imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 Fe^IV complex. Complex 1-imido reacts with 2 a to produce the ferrous aniline adduct [(^tBu pyrpyrr₂ )Fe{NH(2,6-Me₂ -4-tBu-C₆ H₂ )(C₁₄ H₁₁ )}] (1-aniline) in 45 % yield. Lastly, it was found that complexes 1-imido and 1-aniline are both competent intermediates in catalytic intermolecular C-H amination.