Karthik Gadde

An Fe^IV imide of a tetracarbene macrocycle active in nitrene transfer reactions can be generated from phenyltosyliodinane (PhI=NTs) either from the FeII precursor by oxidative addition (right) or from the FeIII precursor by a comproportionation reaction (left) (AN=acetonitrile, bold horizontal bars=macrocycle).

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 Fe^II and Fe^III 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 Fe^IV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the Fe^II precursor was expected by a two-electron oxidative addition, its formation from an Fe^III 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 Fe^III precursor, an Fe^III tosyliodinane adduct was formed and decomposed into an Fe^V tosylimido species which generated the catalytically active Fe^IV tosylimide through a comproportionation process with the Fe^III precursor.

Synthesis
DOI: 10.1055/a-1932-6937

Visible light photocatalysis has established itself as a promising sustainable and powerful strategy to access reactive intermediates, i.e. radicals and radical ions, under mild reaction conditions using visible light irradiation. This field enables the development of formerly challenging or even previously inaccessible organic transformations. In this tutorial review, an overview of the essential concepts and techniques of visible-light-mediated chemical processes and the most common types of photochemical activation of organic molecules, i.e. photoredox catalysis and photosensitization, are discussed. Selected photocatalytic alkene functionalization reactions are included as examples to illustrate the basic concepts and techniques with particular attention given to the understanding of their reaction mechanisms.1 Introduction2 Photocatalysts3 Photophysical and Electrochemical Properties3.1 Excited-State Energy3.2 Ground-State Redox Potentials3.3 Excited-State Redox Potentials3.4 Local Absorbance Maximum for Lowest Energy Absorption3.5 Excited-State Lifetime3.6 [Ru(bpy)3]2+ as a Case Study3.7 Basic Laws and Equations of Photochemistry and Photocatalysis3.8 Common Terminology in Photochemistry and Photocatalysis4 Activation Modes in Photocatalysis4.1 Photoinduced Electron Transfer4.2 Photoinduced Energy Transfer5 Conclusions and Outlook
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