Year: 2026
Type: preprint
Abstract: Manganese porphyrins have been widely employed as catalysts for nitrogen-group transfer (NGT) and oxygen-atom transfer (OAT) reactions with olefins and C–H bonds. These transformations are typically proposed to proceed via high-valent manganese nitrenoid and oxo intermediates, respectively. While porphyrin redox non-innocence — in which electron transfer from the ligand to the metal delocalizes high-valent states across the metal and the ancillary ligand — is well established. The potential role of porphyrin chemical non-innocence — in which an atom or group inserts into the M–pyrrolide bond — is much less appreciated. Here, we demonstrate that treatment of Mn(tpp)Cl with iminoiodinanes (PhI═NR, R = Ts (tosyl) and Ns (nosyl)) affords the corresponding tucked-in Mn porphyrins in which the iminoiodinane-derived nitrene fragment has inserted into one of the Mn–N bonds. Nitrene insertion into the Mn–N bond was characterized by NMR, UV-vis, and high-frequency and -field EPR (HFEPR) spectroscopies, as well as single-crystal X-ray diffraction. Nitrene insertion into the Mn–N bond is reversible under both thermal and photochemical conditions; untucking in the presence of styrene affords the corresponding aziridine, demonstrating that the tucked-in porphyrin can function as a latent nitrene equivalent. In situ UV-vis spectroscopy and kinetics experiments of Mn(tpp)Cl-catalyzed styrene aziridination demonstrate that, despite the chemical viability of nitrene insertion / de-insertion reactions, the formation of tuck-in porphyrins is slow relative to olefin aziridination. These results demonstrate that reversible formation of nitrene tuck-in porphyrins is chemically accessible and represents a latent source of electrophilic nitrene equivalents and that in the context of Mncatalyzed aziridination, these elementary steps are slow relative to catalysis.
Source: ChemRxiv
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220941986