Nitrene Insertion into Aromatic and Benzylic C−H Bonds Catalyzed by Copper Complexes of Fluorinated Bis‐ and Tris(pyrazolyl)borates

Abstract

AbstractFluorinated bis‐ and tris(pyrazolyl)boratocopper complexes catalyze the nitrene insertion to C−H bonds of aromatic hydrocarbons efficiently producing amination products in good to excellent yields at room temperature. Imidoiodanes, PhI=NTs (Ts=p‐toluenesulfonyl) and PhI=NNs (Ns=p‐nitrophenylsulfonyl) serve as the nitrene source. The bis(pyrazolyl)borate catalyst [H2B(3,5‐(CF3)2Pz)2]Cu(NCMe) with PhI=NNs produced the arene C−H functionalized product of mesitylene in 87 % yield with only trace amounts of benzylic C−H insertion. The use of [H2B(3,5‐(CF3)2‐4‐(NO2)Pz)2]Cu(NCMe) that has an even weakly donating pyrazolate generated the arene C−H insertion product exclusively. The tris(pyrazolyl)borate complex [HB(3,5‐(CF3)2Pz)3]Cu(NCMe), in contrast, generated the benzylic amination product from mesitylene and PhI=NNs in 82 % yield with only very minor amounts of arene C−H functionalization. DFT calculations suggest that Cu‐nitrene moiety generated from [HB(3,5‐(CF3)2Pz)3]Cu(NCMe) and PhI=NNs activates the benzylic C−H bond of mesitylene via a hydrogen atom abstraction (HAA) followed by a radical rebound (RR) pathway, whereas the functionalization of sp2 C−H bonds of mesitylene by [H2B(3,5‐(CF3)2Pz)2]Cu(NNs) ensues possibly via a nitrene addition to the arene core.