Mechanism of F ⁺ Salts Catalyzed Aziridine Synthesis: F‐Halogen Bonding Catalysis or F‐Cation Transfer Catalysis? ^†

Comprehensive Summary Whether the fluorine atom (F) can engage in a halogen bond (XB) has remained a subject of ongoing debate. The discovery of N ‐fluoropyridinium triflate as a unique "F‐cation organocatalyst" for aziridine synthesis has generally been considered the first instance of F‐halogen bonding catalysis. Nevertheless, the mechanistic details of this reaction have remained elusive, and compelling evidence supporting the F‐halogen bond catalysis has been lacking. In this study, we present an in‐depth computational investigation of the mechanism of this reaction to gain insights into the intriguing role of the F‐cation organocatalyst. Our results, however, are inconsistent with the previous prevalent F‐halogen bonding catalysis mechanism but instead, bring to light a new fluorine cation transfer mechanism. This novel mechanism is supported by control experiments and can explain the observed cis ‐ trans selectivity.