Unraveling the Enhanced Reactivity of Abnormal N‐Heterocyclic Carbene Palladium Complexes over Their Normal Analogs: Insights from Density Functional Theory Studies

Abnormal N‐heterocyclic carbenes ( a NHCs) have recently attracted significant attention as ligands in transition‐metal catalysis due to their stronger σ‐donating ability compared to normal NHCs ( n NHCs). In this study, we employ density functional theory to explore the bonding characteristics and electronic properties of palladium complexes containing both n NHC and a NHC ligands. The analysis focuses on the nature of the PdC carbene interaction, evaluating bond strength, charge distribution, and orbital contributions. Frontier orbital analysis reveals that the highest occupied molecular orbital in a NHCs corresponds to a destabilized σ ‐lone pair on the carbene carbon, which enhances their donor capacity relative to n NHCs. Natural bond orbital (NBO) and bond dissociation energy calculations confirm that a NHC ligands transfer electron density more effectively, resulting in shorter and stronger PdC bonds. At the same time, reduced π‐backbonding is observed in a NHC complexes, consistent with their weaker π ‐acceptor character. Quantum theory of atoms in molecules and energy decomposition analysis further demonstrate that the PdC carbene bonds possess mixed ionic–covalent character, with electrostatics dominating the interaction. Collectively, these results explain the greater reactivity and catalytic efficiency of a NHCPd complexes and provide guiding principles for the design of next‐generation carbene ligands in organometallic catalysis.