Distinguishing the Internal/External Base-Assisted Deprotonation Mechanisms in Aromatic C–H Activation with the Pd(II)/LA Catalyst

Base-assisted deprotonation was well acknowledged in versatile transition metal ion-catalyzed C–H activation mechanisms. However, the pathway of deprotonation, that is, internal or external base-assisted deprotonation, remains elusive, which puzzles the mechanism-based catalyst design. Herein, using heterobimetallic Pd(II)/LA (LA: Lewis acid) complexes having bridged internal bases as the platform, stoichiometrically and catalytically aromatic C–H activations were investigated in the absence/presence of different external bases. The results unambiguously supported that Pd(II)-catalyzed aromatic C–H activation proceeded by internal, rather than external, base-assisted deprotonation, and the reasonably strong basicity of the internal base is crucial for its assisting deprotonation in C–H activation. The present studies have provided a better understanding of transition metal ion-catalyzed C–H activation mechanisms.