Catalytic Nitrene Transfer by an Fe^IV‐Imido Complex Generated by a Comproportionation Process

Abstract

Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV‐visible, Mössbauer), ESI‐MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two‐electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV‐visible, EPR, Hyscore and Mössbauer), ESI‐MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor.

Cationic Divalent Metal Sites (M = Mn, Fe, Co) Operating as Both Nitrene-Transfer Agents and Lewis Acids toward Mediating the Synthesis of Three- and Five-MemberedN-Heterocycles

“…The negative ρ P and ρ + slope values are indicative of an electrophilic oxidant operating and a small positive charge evolving at the benzylic carbon en route to the transition state. The ρ + values are particularly close to those reported by Latour and co-workers (ρ + = −0.38, −0.42) for styrene aziridinations (PhINTs) in MeCN mediated by catalysts [L NO2 Fe II (NCMe) 2 ] (L NO2 is a tripodal ligand with an axial N amine residue along with two 2,4-NO 2 -substituted phenolate arms and a pyridine moiety) and [( Me,Me TC H )­Fe II (NCMe) 2 ]­(PF 6 ) 2 ( Me,Me TC H is a tetracarbene macrocycle) . Other more prominent ρ + slope values for similar aziridinations mediated by cationic Fe­(II) catalysts have been reported by Che (ρ + = −0.72), Jensen (ρ + = −0.58, −0.61), and Latour (ρ + = −0.71, −0.83, −0.94). , …”

Cyclic iron tetra N-heterocyclic carbenes: synthesis, properties, reactivity, and catalysis

“…103 Just recently, complexes 1 and 2 have been tested in aziridination. 71 In this case, (p-toluenesulfonyliminoiodo) benzene (PhI = NTs) as nitrene source and styrene as substrate have been used and both complexes achieved around 75% yield at r.t., indicating that both reactions involve the same active species. Furthermore, 1 and 2 have been tested in the sulfimidation of thioanisole (B98% yield) and the amination of ethylbenzene (B22% yield) and cyclohexane (B15% yield).…”