Enhanced Catalytic Activities of Palladium Complexes with Nitron-Based <i>N</i> -Heterocyclic Carbene Ligands

A series of palladium complexes supported by tert-butylamine-functionalized amido-NHC ligands were synthesized and systematically evaluated with respect to their structure, electronic properties, and catalytic performance. Single-crystal X-ray diffraction confirmed distorted square-planar geometries, with greater distortion observed in Nitron-based and polydentate systems, as quantified by τ4 and τ4′ indices. Computational studies revealed that deprotonated Nitron-based ligands exhibit strong σ-donation and HOMOs delocalized over the ligand, enhancing electron density at the Pd center. These features translated into superior reactivity in Sonogashira, Suzuki–Miyaura, and Mizoroki–Heck coupling reactions, particularly for unreactive aryl chlorides. DFT calculations further confirmed that oxidative addition barriers are lowest for deprotonated Nitron-based ligands, supporting their role in promoting challenging bond activations. These results highlight the utility of anionic NHC ligands as a robust platform for designing next-generation Pd catalysts for demanding cross-coupling transformations.