A Diiron(III,IV) Imido Species Very Active in Nitrene‐Transfer Reactions

Abstract

Metal-catalyzed nitrene transfer reactions arouse intense interest as clean and efficient procedures for amine synthesis. Efficient Rh-and Ru-based catalysts exist but Fe alternatives are actively pursued. However, reactive iron imido species can be very short-lived and getting evidence of their occurrence in efficient nitrene-transfer reactions is an important challenge. We recently reported that a diiron(III,II) complex is a very efficient nitrene-transfer catalyst to various substrates. We describe herein how, by combining desorption electrospray ionization mass spectrometry, quantitative chemical quench experiments, and DFT calculations, we obtained conclusive evidence for the occurrence of an {Fe III Fe IV = NTosyl} intermediate that is very active in H-abstraction and nitrene-transfer reactions. DFT calculations revealed a strong radical character of the tosyl nitrogen atom in very low-lying electronic configurations of the Fe IV ion which are likely to confer its high reactivity.

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

“…This observation is consistent with our previous findings using mono-and dinuclear aminophenolate iron complexes. 69,70 Aiming at evidencing the trend linking aziridination yields (Y) and EA of the active species we have plotted them against each other (Figure 5). It is worth noting that all catalytic aziridination experiments were conducted along the same protocol and that EA of all active species were calculated in the same manner (see Table S13).…”

“…The monotonous character of the observed trend supports that no steric hindrance plays a significant role in the reaction in spite of notable differences in accessibility between the mono iron aminophenolate complexes where the ligands are tetradentate, the pentadentate ligands of this work and the dinuclear complex. 69,70 The absence of steric influence is probably due to the fact that the charge transfer occurring in the rate determining step does not require a close contact of the two reactants. S10 for electron affinities and aziridination yields values.…”

Highly sialylated recombinant human erythropoietin production in large‐scale perfusion bioreactor utilizing CHO‐gmt4 (JW152) with restored GnT I function

“…Both the NAr and PhINAr moieties of complex A could be involved in the nitrogen group transfer/insertion reactions. In the literature, nonheme FeNAr11a or FeNTs11c, 16a,c intermediates, Mn‐PhINTs intermediates17 bearing porphyrin or salen ligands, and [Mn(corrole)(NSO 2 Ar)(PhINSO 2 Ar)] intermediates have been proposed to be the active species that undergo nitrene/imide transfer or insertion reactions.…”

Experiments and DFT Computations Combine to Decipher Fe-Catalyzed Amidine Synthesis through Nitrene Transfer and Nitrile Insertion

“…29 Through ElectroSpray Ionization-Mass Spectrometry two active species were evidenced and are hereafter designated [1.Fe IV (NTs)] 2+ and [1.Fe V (NTs)] 2+ . 30,31 DFT analyses of their electronic structure showed, in both cases, significant charge transfer from both ligands NTs and 1 to the high-valent Fe generating actual configurations involving ligand radicals such as [1.Fe III ( • NTs)] 2+ and [1.Fe IV ( • NTs)] 2+ , respectively. This complex is indeed an efficient catalyst for aziridination of styrenes (yields ca 80 %) and other olefins.…”

“…Our earlier studies of nitrene transfer catalyzed by 1.Fe II (NCMe) 2+ revealed that its ferric site (Scheme 2a) did not change redox state during catalysis which involved activation of the Fe II site formally to Fe IV and Fe V . 30,31 This incited us to develop simpler monoiron catalysts with similar environments (Scheme 2b). We observed that the monoiron catalyst [2.Fe II (NCMe) 2 ] (Scheme 2b) exhibited a mechanistically similar reactivity for styrene aziridination albeit with more modest conversions.…”