Terminal Cyanate in Stabilizing Mononuclear Cu(III) Complex: Room Temperature Preparation, Characterization, and...

Great efforts have been made to generate new types of late transition metal oxidants by tuning terminal ligands. These metal oxidants play a key role to activate and functionalize C─H bond via proton coupled electron transfer (PCET) mechanism. Herein, we have developed a unique oxidant, high valent metal-cyanate, under ambient conditions. The high valent complex [(L)Cu^III(NCO)] (2, H₂L ═ N,N'-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide) was prepared from [(L)Cu^II(NCO)]Bu₄N (1) by one electron oxidation and both complexes were characterized by x-ray crystallography and UV-vis, ¹H/¹³C NMR, Raman, FT-IR and EPR spectroscopies, and ESI-MS. 2 reacted with C─H and O─H bond via hydrogen atom transfer mechanism, as evidenced by kinetic data, product analysis and computational findings, and reaction rates are comparable to some reported reactive metal oxidants. Fascinatingly, 2 performed direct C─N bond formation by activating C─H bond and cyanate group transfer reactions. We observed solvent dependent reactions of 2. Our results found a new class of metal oxidant for strong C─H bond functionalization. We believe that high valent metal-cyanates could open new avenues for very interesting coordination and bioinspired oxidation chemistry due to electronic, resonating, and ambidentate properties of terminal cyanate ligand with potential two different proton accepting sites (N and O).