C–N Bond Formation at Discrete CuIII–Aryl Complexes

Copper(III) aryl species are widely proposed as intermediates in Cu-catalyzed C–C and C-heteroatom bond formation reactions. Despite their wide utility, mechanistic aspects of C-heteroatom formation at CuIII centers as well as factors that lead to byproducts, e.g., Ar–H, Ar–Ar, remain elusive due to the rarity of discrete CuIII–Ar complexes. Herein, we report the synthesis and reactivity of a series of CuII and CuIII aryl complexes that closely mimic the intermediates in Cu-catalyzed C–N coupling reactions. Copper(II) aryl complexes [TBA][LCuII–ArR] were synthesized via the treatment of CuII with a range of aryl donors, such as ZnAr2R, TMS–ArR, and ArR–Bpin. Oxidation of [TBA][LCuII–ArR] produces formal copper(III) aryl complexes LCuIII–ArR. Treatment of copper(III) aryl complexes with neutral nitrogen nucleophiles produces the C–N coupling product in up to 64% yield, along with commonly observed byproducts, such as Ar–H and Ar–Ar. Hammett analysis of the C–N bond formation performed with various N-nucleophiles shows a ρ value of −1.66, consistent with the electrophilic character of LCuIII–ArR. We propose mechanisms for common side reactions in Cu-catalyzed coupling reactions that lead to the formation of Ar–Ar and Ar–H.