Iron‐Catalyzed Intermolecular C−H Amination Assisted by an Isolated Iron‐Imido Radical Intermediate
Ethan Zars, Lisa Pick, Abinash Swain, Mrinal Bhunia, Patrick J. Carroll, Dominik Munz, Karsten Meyer, Daniel J. Mindiola
Abstract
Abstract Here we report the use of a base metal complex [( t Bu pyrpyrr 2 )Fe(OEt 2 )] ( 1 ‐OEt 2 ) ( t Bu pyrpyrr 2 2− =3,5‐ t Bu 2 ‐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 ‐OEt 2 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 [( t Bu pyrpyrr 2 )Fe{=N(2,6‐Me 2 ‐4‐ t Bu‐C 6 H 2 )] ( 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 [( t Bu pyrpyrr 2 )Fe{NH(2,6‐Me 2 ‐4‐ t Bu‐C 6 H 2 )(C 14 H 11 )}] ( 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.