Discovery of iron-oxo-catalyzed oxidation of fluorophenyl systems to carbonyls or epoxides: reactive intermediates determined mechanism.

CONTEXT

Carbonyl and epoxide compounds play crucial roles in organic synthesis, and the utilization of metal catalysis offers distinct advantages. However, the catalysis of their synthesis by high-valent iron-oxo remains a challenge. In this study, we investigated iron-oxo-catalyzed phenyl systems in detail. Our results show that the carbon atoms on the aromatic ring are positively charged by replacing a hydrogen atom with a fluorine atom, which leads to different catalytic mechanisms. Specifically, the cationic intermediate formed via a double-electron transfer in the low-spin (LS) state of a non-fluorinated benzene ring transforms into a radical intermediate via single-electron transfer when fluorine substitution occurs. Further computational investigations revealed that different intermediates in LS drive the formation of different products. The carbocation intermediate strongly favors the generation of carbonyl compounds through the migration of the ipso - hydrogen (known as the "NIH shift"). In contrast, the radical intermediate exhibits kinetic advantages in this pathway, leading to the formation of epoxides. This research provides theoretical support and facilitates the exploration of innovative pathways for carbonyl and epoxide synthesis.

METHODS

Computing was performed via Gaussian 09 software. Geometric optimization, transition state search, and intrinsic reaction coordinate (IRC) analysis were conducted via the hybrid functional B3LYP and the 6-311G(d,p) basis set. Single-point energy calculations were performed via a higher-level basis set, def2-TZVP. Multiwfn 8.0 and VMD 1.9.1 software are utilized for spin density and molecular frontier orbital analysis, as well as for graphically representing key intermediates.