Crystal Structure and Bioinspired Reactivity of an Ambient-Stable Mononuclear Copper(III)-Azide Complex
Alok Panigrahi1, Chinmay Parida1, Prasenjit Mondal1
1Department of Chemistry, Indian Institute of Technology Tirupati (IIT Tirupati), Tirupati517619, India.
Abstract:
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.
Related Concept Videos
Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
Formation of Complex Ions
Complexation Equilibria: Factors Influencing Stability of Complexes
Coordination Number and Geometry
Valence Bond Theory


