A Comparative DFT Study of Pd- and Ni-Based Catalysts in the Narasaka-Heck/C(sp³)-H Activation Reaction

Density functional theory (DFT) calculations were performed to investigate the mechanistic features of metal-catalyzed C(sp³)-H activation in the Narasaka-Heck cascade reaction, with a particular focus on comparative trends between palladium- and nickel-based catalyst systems. Using the experimentally reported Pd-PCy₃ complex as a benchmark, two nickel catalysts supported by distinct ligand frameworks (NHC_F and ADAP) were examined to assess how metal identity and ligand environment jointly influence the catalytic pathway. The computational results confirm that the concerted metalation-deprotonation (CMD) step constitutes the rate-determining process for all systems considered. Compared with palladium, nickel catalysts exhibit systematically lower CMD activation barriers across a range of solvent environments. This behavior is traced to enhanced electronic softness, more delocalized charge redistribution, and reduced structural rigidity in the nickel systems, which collectively facilitate geometric reorganization along the reaction coordinate. In contrast, the Pd-PCy₃ catalyst relies on strongly polarized metal-substrate interactions that correlate with higher energetic penalties upon distortion. Further analysis reveals that key elementary steps, including CMD and reductive elimination, proceed through weakly coordinated and transient intermediates rather than idealized closed-shell geometries. Under these conditions, ligand flexibility and metal-ligand bonding lability emerge as decisive factors governing the relative accessibility of the catalytic steps. Overall, this study highlights relative mechanistic trends and electronic structure effects that rationalize the observed differences between palladium and nickel catalysts, providing design-oriented insights for the development of experimentally relevant nickel-based alternatives.