A combined experimental and theoretical study on the reactivity of nitrenes and nitrene radical anions

Abstract

Nitrene transfer reactions represent one of the key reactions to rapidly construct new carbon-nitrogen bonds and typically require transition metal catalysts to control the reactivity of the pivotal nitrene intermediate. Herein, we report on the application of iminoiodinanes in amination reactions under visible light photochemical conditions. While a triplet nitrene can be accessed under catalyst-free conditions, the use of a suitable photosensitizer allows the access of a nitrene radical anion. Computational and mechanistic studies rationalize the access and reactivity of triplet nitrene and nitrene radical anion and allow the direct comparison of both amination reagents. We conclude with applications of both reagents in organic synthesis and showcase their reactivity in the reaction with olefins, which underline their markedly distinct reactivity. Both reagents can be accessed under mild reaction conditions at room temperature without the necessity to exclude moisture or air, which renders these metal-free, photochemical amination reactions highly practical.

Photochemical Nitrene Transfer Reactions of Iminoiodinanes with Sulfides

“…In the course of our studies on photochemical carbene and nitrene transfer reactions, [8,9] we observed an unexpected sulfilimination reaction of methyl phenyl sulfide 9 a with iminoiodinane 4 a in high yield under irradiation with blue LEDs (470 nm) without the exclusion of moisture or air. This reaction outcome is surprising as the photolysis of iminoiodinanes should access a triplet nitrene intermediate, while a singlet nitrene would be required to conduct sulfilimination reactions.…”

“…Analysis of the electron distribution of 4 a* already points at a significant distortion of electron density upon photoexcitation, which leads to a high electron density at the iodine atom. [8] This observation can now help to account for the differences in reactivity of iminoiodinane 4 a in the ground vs. excited state. We hypothesize that upon photoexcitation at 470 nm iodinane 4 a liberates a singlet nitrene INT1 S .…”

“…In addition, the use of visible light instead of UV‐light is highly desirable to reduce unwanted side reactions and to achieve more sustainable reaction conditions. In this context, our group recently uncovered the visible light, photochemical or photocatalytic reaction of iminoiodinanes [8] . Depending on the reaction conditions, either a triplet nitrene or nitrene radical anion intermediates can be accessed, which undergo efficient C−H amination or aziridination reactions with olefins.…”

“…In this context, our group recently uncovered the visible light, photochemical or photocatalytic reaction of iminoiodinanes. [8] Depending on the reaction conditions, either a triplet nitrene or nitrene radical anion intermediates can be accessed, which undergo efficient CÀ H amination or aziridination reactions with olefins.…”

General and Practical Metal-Free Aziridination and Cyclopropanation of XH2 (X = N, C) with Alkenes by Thianthrenation

“…6,10,14,15 Aziridinations of alkenes require the use of suitable and activated nitrene precursors, such as iminoiodinanes and azides in the presence of a transition-metal (Cu, Rh, Co, Fe, Pd, Au). 9,12,[16][17][18][19] These methods are limited to the use of hazardous and explosive carbene and nitrene precursors as well as additional steps for diazo synthesis and transition-metal residue removal. These limitations stimulated the development of more efficient and sustainable alternatives to access cyclopropanes and aziridines from free XH2 (X = C, N).…”