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

Abstract

AbstractHere we report the use of a base metal complex [(tBupyrpyrr2)Fe(OEt2)] (1‐OEt2) (tBupyrpyrr22−=3,5‐tBu2‐bis(pyrrolyl)pyridine) as a catalyst for intermolecular amination of Csp3−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 [(tBupyrpyrr2)Fe{=N(2,6‐Me2‐4‐tBu‐C6H2)] (1‐imido) can be isolated in 56 % yield, and spectroscopic, magnetometric, and computational studies confirmed it to be an S = 1 FeIV complex. Complex 1‐imido reacts with 2 a to produce the ferrous aniline adduct [(tBupyrpyrr2)Fe{NH(2,6‐Me2‐4‐tBu‐C6H2)(C14H11)}] (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.