C-N Bond Formation at Discrete Cu III -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 Cu III centers as well as factors that lead to byproducts, e.g. , Ar-H, Ar-Ar, remain elusive due to the rarity of discrete Cu III -Ar complexes. Herein, we report the synthesis and reactivity of a series of Cu II and Cu III aryl complexes that closely mimic the intermediates in Cu-catalyzed C-N coupling reactions. Copper(II) aryl complexes [TBA][ L Cu II -Ar R ] were synthesized via the treatment of Cu II with a range of aryl donors, such as ZnAr 2 R , TMS-Ar R , and Ar R -Bpin. Oxidation of [TBA][ L Cu II -Ar R ] produces formal copper(III) aryl complexes L Cu III -Ar R . 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 L Cu III -Ar R . We propose mechanisms for common side reactions in Cu-catalyzed coupling reactions that lead to the formation of Ar-Ar and Ar-H.