Nitrene Photochemistry of Manganese N‐Haloamides**

Abstract

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis.

Characterization and Reactivity of an Incredibly Reactive Intermediate in the Protonation Reaction of Dioxo-Manganese(V) Porphyrin with Acid

“…The optimized structures were not largely changed by the functional, except the Mn–OH 2 distance in 3 . The calculated Mn–OH 2 distances (2.50–2.76 Å) in 3 using these three functionals are longer than those (2.1–2.3 Å) reported in X-ray crystal studies of Mn­(III) porphyrins. − The Mn–OH 2 distance using ωB97xD is close to that using the BP86 functional but ∼0.2 Å shorter than that using the B3LYP, probably because of the dispersion effect. The calculated MnO bond length becomes shorter in the order of 1 , 2 , and 3 in the calculations using all of these three functionals because of the trans influence of the axial ligand.…”

Terminal Copper Nitrenoid Formation and Reactivity Induced by Absorption to an Antenna Ligand

“…Interesting methods to generate nitrenoids under mild conditions are based on photofragmentation or photoredox processes using visible light. [13][14][15][16] Iridium or ruthenium photocatalysts are often used in photoredox catalysis, [17] but their high cost makes this approach less attractive for largescale applications.…”

Chiral Iron Porphyrins Catalyze Enantioselective Intramolecular C(sp3)−H Bond Amination Upon Visible‐Light Irradiation

“…Very recently, photochemical reactions were introduced to open new approaches in CÀ H amination reactions via nitrene intermediates. [32][33][34][35][36][37][38] Herein, we describe a panel of chiral porphyrin ligands and their iron complexes that serve as effective catalysts for asymmetric C(sp 3 )À H amination reactions to generate chiral indolines (29 examples) and benzofused cyclic sulfonamides (17 examples) in yields of up to 99 % and good to excellent enantioselectivities (up to 93 % ee) under photochemical conditions. Mechanistic experimental studies and DFT calculations suggest that the reactive Fe(NSO 2 Ar) (iron-arylsulfonyl imido/nitrene) intermediate generated in situ under photochemical conditions is responsible for the amination of C(sp 3 )À H bonds.…”

“…In 2020, Chattopadhyay and co‐workers [31] reported a chiral iron porphyrin complex catalyzed intramolecular C(sp 3 )−H amination of 1,2,3,4‐tetrazoles to afford azaindolines in moderate enantiomeric ratios of up to 73 : 27 er. Very recently, photochemical reactions were introduced to open new approaches in C−H amination reactions via nitrene intermediates [32–38] . Herein, we describe a panel of chiral porphyrin ligands and their iron complexes that serve as effective catalysts for asymmetric C(sp 3 )−H amination reactions to generate chiral indolines (29 examples) and benzofused cyclic sulfonamides (17 examples) in yields of up to 99 % and good to excellent enantioselectivities (up to 93 % ee ) under photochemical conditions.…”