Mechanistic Insights into Regioselective Functionalization of Metallofullerene La@C ₈₂ under Synergistic External and Built-in Electric Fields

Controllable regioselective functionalization of endohedral metallofullerenes (EMFs), exemplified by La@C₈₂, remains elusive owing to the high similarity among surface sites and pronounced metal-cage charge transfer. Here, we propose an external-electric-field-assisted strategy for the Diels-Alder cycloaddition on La@C₈₂, enabling highly active, regioselective, and tunable derivatization. Density functional theory calculations reveal that the applied field not only modulates intrinsic La-cage interactions and even drives La migration, but also, in synergy with the built-in field, tailors intermolecular charge transfer at transition states and reshapes reaction barriers. By establishing a quantitative field-strength-barrier relationship, this work introduces a target-oriented paradigm for EMF functionalization beyond the reach of conventional chemistry.