In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

Publisher Summary This chapter discusses chemical oxidations, oxidations on acidic surfaces, and photoionizations. The formation of cation radicals in solution is also discussed. The chapter outlines the experimental techniques that have been used to study cation radicals and the type of information that can be obtained about their behavior. Examples of such investigations are provided. A large number of electrochemical techniques is available for producing and studying cation radicals (or other electrogenerated). Their instrumentation, techniques, and theory are described. The electrochemical techniques can be separated into two classes: the microelectrode or voltammetric techniques and the bulk electrolysis or coulometric techniques. Detailed descriptions of physical properties of cation radicals are presented in the chapter. Cation radicals react with a variety of nucleophiles. Substitution often occurs, but there are many examples in which electron transfer occurs either entirely or in part.

Formation, Properties and Reactions of Cation Radicals in Solution

Photoredox chemistry with organic or transition metal agents has been reviewed in earlier years, but such is the pace of progress that we will overlap very little with earlier comprehensive reviews. This review first presents an overview of the area of research and then examines recent examples of C–C, C–N, C–O and C–S bond formations via radical intermediates with transition metal and organic radical promoters. Recent successes with Birch reductions are also included. The transition metal chemistry will be restricted to photocatalysts based on the most widely used metals, Ru and Ir, but includes coupling chemistries that take advantage of low-valent nickel, or occasionally copper, complexes to process the radicals that are formed. Our focus is on developments in the past 10 years (2011–2021). This period has also seen great advances in the chemistry of organic photoredox reagents and the review covers this area. The review is intended to present highlights and is not comprehensive.

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Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents.

https://iopscience.iop.org/article/10.1070/RCR4795/pdf

Organofluorine chemistry: promising growth areas and challenges

Electrochemical fluorination (ECF) refers to the introduction of fluorine-containing moieties into organic molecules under electrochemical conditions The primary objective of this review is to provide the reader with the highlights of electron-induced radical fluorinations in the past decade, comprising fluorination, difluoromethylation, trifluoromethylation and perfluoroalkylation Some representative mechanisms are outlined for researchers to gain insight in the basic principles behind this technology

Recent advances in electrochemically driven radical fluorination and fluoroalkylation

A new method of introducing fluorine into the aromatic ring

On the basis of half-wave potential values E1/2 it was shown that perfluoroalkyl halides have pronounced oxidative properties in comparison with unfluorinated analogs. Tertiary perfluoroalkyl iodides, having a higher oxidation potential than iodine, react with I− by a scheme including one-electron transfer.

Oxidative properties of perfluoroalkyl halides

The conjugated nitrofluorination of olefins was studied. This reaction provides a convenient method for the synthesis of various β-fluoro nitro compounds.

Aliphatic fluoro nitro compounds

Reduction potential and relative electron affinity as reactivity indexes perfluoroalkyl halides

The semiempirical quantum chemical MNDO and AMI methods were used to determine the equilibrium geometries and electron properties of molecules of perfluoroalkyl halides (RFX): CF3X, CF3CF2X, (CF3)2CFX, (CF3)3CX for X=Cl, Br, and I. It was determined that the effective charge on the Cl atom in RFCl is negative, positive on the I atom in RFI, and depends on RF for the Br atom in RFBr. The CF3 group can act as either an electron acceptor or donor in various perfluoroalkyl halides. The strongest Cα−I bond in the perfluoroalkyl halides occurs with a tertiary RF group.

Electron structure and reactivity of organofluorine compounds. 3. Mndo and ami calculations of the ground state of perfluoroalkyl chlorides, bromides, and iodides

I. N. Rozhkov

Papers

A new method of introducing fluorine into the aromatic ring

Oxidative properties of perfluoroalkyl halides

Aliphatic fluoro nitro compounds

Reduction potential and relative electron affinity as reactivity indexes perfluoroalkyl halides

Electron structure and reactivity of organofluorine compounds. 3. Mndo and ami calculations of the ground state of perfluoroalkyl chlorides, bromides, and iodides