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.

Going beyond electrospray: mass spectrometric studies of chemical reactions in and on liquids

“…Similar to this Rh chemistry, Gouré et al also detected a short-lived diiron( iii / iv ) imido intermediate that was active for nitrene transfer and amine synthesis. 33 Again, abstraction of a hydrogen atom from solvent competed with productive nitrene transfer.…”

“…The very short timescales of DESI makes it ideal to study highly reactive intermediates that are prepared “on-the-fly” during the ionization process, or sampled from a surface. 29,33,37 Furthermore, catalyst activation mechanisms can be specifically targeted. 27,35 Perhaps even more important than the timescale of DESI is the simplicity of the technique.…”

Nitrene Insertion into CC and CH Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] For certain metals,nitrene-like activity is inferred by the products derived from inter-a nd intramolecular insertions into CÀH bonds, [20][21][22][23][24][25][26][27] aziridinations, [28][29][30][31] and related reactions. [32][33][34][35][36][37][38][39][40] In many instances,i mide radical character is inferred from the reactivity and supported by calculations, [41,42] and the chemistry can be related to biological transformations such as the oxygenations by cytochrome P450. [43][44][45][46][47][48][49] During the course of examining chromium and iron complexes chelated by adiamide diimine tetradentate ligand, unusual azide-dependent reactivity featuring CÀCa nd CÀH bond activations was discovered in conjunction with redox non-innocence (RNI).…”

Multistage Reactive Transmission-Mode Desorption Electrospray Ionization Mass Spectrometry

“…In addition, ion signals suggesting formation of reactive oxygen species [57] or other unwanted byproducts were not observed (Supplementary Figure S10 + was observed at m/z 270.008 (Figure 3a) with intensity of~4% relative to [4a + H] + at m/z 267.993. Assuming that the concentration of DCIP in the secondary microdroplets is low compared with L-AA, the observed reaction time in microdroplets (t) for TM 1 -DESI (t TM ) and DESI (t DESI ) can be approximated using pseudo-first-order kinetics [58] (see SI) Table S1), which suggests that t TM and t DESI have the same order of magnitude of less than 1 ms (t DESI was experimentally estimated by Latour and coworkers [59,60]). These results agree with previous studies proposing that TM-DESI and DESI have relatively similar desorption/ ionization mechanisms [34], calculations showing that [t ESI / t TM ]>40 at various emitter-inlet distances and concentrations (Supplementary Table S1), and calculations showing that microdroplets of TM 2 -DESI travel at twice the velocity of droplets generated with DESI; see Electronic Supplementary Information for the calculations) [45].…”