Fe‐Based Complexes as Styrene Aziridination Catalysts: Ligand Substitution Tunes Catalyst Activity

Abstract

As part of our effort to improve our understanding of aziridination mechanism, we used tetra substitution of a diphenol ligand to modify the redox properties of corresponding Fe complexes. This allowed us to confirm that aziridination catalysis by Fe‐based complexes is governed by electron affinity of the active species and further show that it correlates with the FeIII/FeII redox potential.

Fe-Catalyzed Aziridination Is Governed by the Electron Affinity of the Active Imido-Iron Species

“…57,65 Their recent DFT analysis 45 of the reaction profile revealed a two-step mechanism, where the initial formation of the C -N bond is rate determining as we found. 42,46 To further analyze their behavior we computed the charges developing in the first transition state TS1 and found that a small charge transfer (ca 0.2 e -) occurs from decene to the imido nitrogen (Table S10). Consistently, these catalysts have small EAs (Table S6) and they operate in significantly harsher conditions (substrate used as solvent, long time and temperatures in the range 80 -90 °C) than our standard ones.…”

“…38 A few limited mechanistic studies of iron-based catalytic aziridination systems have been reported in the past decade but a rationalization of their activities is still lacking, owing to the widely different if not opposite behaviors reported. [39][40][41][42][43][44][45][46] Using a similar dipyrromethene ligand ( DCP L Ad )Fe (DCP = 2,6-dichlorophenyl, Ar = p-tBu-Ph),…”

Imidazoline synthesis: mechanistic investigations show that Fe catalysts promote a new multicomponent redox reaction

“…In addition, this Fe V catalyst is acidic enough for acetonitrile to bind it, whereas it cannot bind the Fe IV catalyst. 26,27 Consequently, the acetonitrile molecule attacking the benzyl cation comes from Fe coordination sphere, whereas that attacking the benzyl radical comes from the solvent. Noteworthy, in both cases, all these events occur within or close to the Fe coordination sphere.…”

“…These studies eventually revealed that Fe-catalyzed aziridination is governed by the electron affinity of the Fe-imide active species. 28 This conclusion was based on the study of mononuclear (1a) and dinuclear (1b) Fe complexes of aminophenol ligands 26,27 (Figure 1) and mononuclear complexes of nitrogen ligands. Please do not adjust margins Please do not adjust margins Scheme 2.…”

“…Imidazoline synthesis through aziridine opening. 14 We recently developed integrated experimental 25-28 and theoretical [26][27][28][29] studies of styrene aziridination through Fe-catalyzed nitrene transfer (Scheme 2a). These studies eventually revealed that Fe-catalyzed aziridination is governed by the electron affinity of the Fe-imide active species.…”