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

摘要

Fluorinated 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)(2)Pz)(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)(2)Pz)(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)(2)Pz)(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 sp(2) C-H bonds of mesitylene by [H2B(3,5-(CF3)(2)Pz)(2)]Cu(NNs) ensues possibly via a nitrene addition to the arene core.