Nonspectator Behavior of N‑Heterocyclic Carbenes Directly Observed in High-Valent Copper Systems

N-Heterocyclic carbenes (NHCs) have become highly popular ligands in modern copper chemistry, leading to the widespread application of Cu–NHCs in photoluminescent materials, catalysis, and biomedicine. In sharp contrast to copper­(I) and copper­(II) NHC complexes, examples of copper­(III) NHCs are exceedingly rare. Synthetic methods for these complexes remain largely unexplored, and their reactivity is poorly understood. Additionally, although NHCs are typically considered spectator ligands, a longstanding debate persists regarding their potential nonspectator behavior at Cu­(III), which is crucial for elucidating the true role of NHCs and for the rational design of Cu­(III)/NHC systems. In this work, we present a rarely reported Cu­(III) NHC system costabilized by CF3 donors. By exploring synthetic strategies, photo- and thermo-induced reactivity studies, as well as experimental and computational investigations, this study enables, for the first time, the direct observation of NHC-involved reactivity at Cu­(III), along with relevant mechanistic insights.