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.