Crystal Structure and Bioinspired Reactivity of an Ambient-Stable Mononuclear Copper(III)-Azide Complex

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The synthesis, stabilization, and structural characterization of high-valent copper complexes are critical for understanding biological and chemical oxidation processes and for developing new catalytic transformations. Herein, we report the ambient generation of a novel terminal mononuclear CuIII–N3 complex supported by a dicarboxamide ligand, H2L (H2L = N,N′-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide). The electronic and structural features of the terminal azide ligand play a crucial role in controlling the stability and reactivity of the CuIII-complex. The high-valent complex [(L)CuIII(N3)] (2) was prepared from Bu4N[(L)CuII(N3)] (1) through a one-electron oxidation process. Both complexes 1 and 2 were characterized by X-ray crystallography and UV–vis, 1H/13C NMR, FT-IR, and EPR spectroscopies, and ESI-MS. The single-crystal X-ray structure of 2─a rare example of a crystallographically characterized mononuclear CuIII–N3 complex─revealed shortened Cu–N bond distances (Cu–Navg. = 1.878(2) vs 1.972(1) Å). Fascinatingly, 2 performed direct azidation of very strong C–H bonds in hydrocarbons (e.g.; cyclohexane). We found that complex 2 drives hydrocarbon azidation via hydrogen atom abstraction or basicity-driven PCET and a subsequent radical-capture mechanism. 2 also exhibited aldehyde deformylation, and phenol and phosphine oxidation reactions. Our results found a very interesting new class of metal oxidant with diverse bioinspired reactivity profile.