outlines the unexpected energy profile of the reaction. In summary, when 1 and 2 combine, a new Fhalogen bond adduct complex CP1 is formed, which subsequently undergoes outer-sphere single-electron transfer (OSET), affording a N-fluoropyridinium radical ([N-FluoroPy]  ) and a N-arylimine radical cation (2 ,+ ) with the barrier for single-electron transfer from 2 to 1 estimated, by Marcus theory 41 , to be 14.3 kcal mol -1 . Subsequent F atom transfer between [N-FluoroPy]  and 2 ,+ generates fluorinated N-arylimine Int-1 in a process that is exergonic by 10.5 kcal mol -1 . A sequential single-electron and F-atom transfer is kinetically more favorable than a one-step concert electrophilic fluorine transfer via TS-1 (40.1 kcal mol -1 , Figure in SI). Furthermore, a spin density distribution study on 2 ,+ (see Figure in SI) confirmed the single electron is mostly localised on the nitrogen atom, with little delocalisation on the electron-rich aromatic ring or methoxy group; this results in efficient F atom transfer from 1 to the N-atom of the imine rather than fluorination of the aromatic ring of 2. Transferring a fluorine cation from the Nfluoropyridinium salt to the imine moiety of 2 lowers its LUMO energy and enhances C=N electrophilicity; this facilitates nucleophilic attack by ethyl diazoacetate (3) on Int-1 via TS-2-cis, which generates, ultimately, diazonium β-aminoester Int-2. Of note, this process exhibits a substantially reduced Gibbs free energy barrier of 19.4 kcal mol -1 , a value 26.3 kcal mol -1 lower than that of the uncatalyzed process. Subsequent cyclization of Int-2 via TS-3 has a free energy barrier of 7.2 kcal mol -1 relative to Int-2 and affords N-fluorinated racemic cis-aziridine Int-3.