Signaling Recognition Events with Fluorescent Sensors and Switches.

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

Graphitic carbon nitride, g-C3N4, can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.

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Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

The interaction between an electronically excited photocatalyst and an organic molecule can result in the genertion of a diverse array of reactive intermediates that can be manipulated in a variety of ways to result in synthetically useful bond constructions. This Review summarizes dual-catalyst strategies that have been applied to synthetic photochemistry. Mechanistically distinct modes of photocatalysis are discussed, including photoinduced electron transfer, hydrogen atom transfer, and energy transfer. We focus upon the cooperative interactions of photocatalysts with redox mediators, Lewis and Bronsted acids, organocatalysts, enzymes, and transition metal complexes.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00018

Dual Catalysis Strategies in Photochemical Synthesis

4.2. Solid-Supported Electrolytes 2280 4.3. Solid-Supported Mediators 2282 4.4. Supported Substrate-Product Capture 2283 4.5. A Unique Electrolyte/Solvent System 2285 5. Reaction Conditions 2285 5.1. Supercritical Fluids 2285 5.1.1. Electrochemical Properties of scCO2 2285 5.1.2. Electroreductive Carboxylation in scCO2 2286 5.1.3. Electrochemical Polymerization in scCO2 2286 5.2. The Cation-Pool Method 2286 5.2.1. Generation of N-Acyliminium Ion Pools 2286 5.2.2. Generation of Alkoxycarbenium Ion Pools 2287 5.2.3. Generation of Diarylcarbenium Ion Pools 2288 5.2.4. Generation of Other Cation Pools 2289 6. Electrochemical Devices 2289 6.1. Electrode Materials 2289 6.2. Ultrasound and Centrifugal Fields 2290 6.3. Electrochemical Microflow Systems 2290 7. Combinatorial Electrochemical Synthesis 2292 7.1. Parallel Electrolysis Using a Macrosystem 2292 7.2. Parallel Electrolysis Using a Microsystem 2293 7.3. Serial Electrolysis Using a Microsystem 2294 8. Conclusions 2294 9. Acknowledgments 2294 10. References 2294

Modern Strategies in Electroorganic Synthesis

Dichlorocarbene generated from chloroform and aqueous sodium hydroxide using chiral tertiary amines as a catalyst adds enantioselectively to olefins to give chiral dichlorocyclopropane derivatives. Optical rotations of the products strongly depend on the structure of catalysts employed.

Enantioselective addition of dichlorocarbene to olefins by use of chiral tertiary amines

The photoreaction of a styrene/4-tributylstannylmethyl styrene (4:1) copolymer with di- and tetra-cyanoaromatic compounds in benzene-acetonitrile (1:1) gave polymers having cyanoaromatic functions in the side chain. These polymers were soluble in benzene and served as effective and recoverable sensitizers for three different types of photoinduced electron-transfer mediated organic photoreactions.

Synthesis and properties of polymer-supported cyanoaromatic compounds

The Carbon Dioxide-Catalyzed Ester Exchange Reaction

Photo-induced redox reactions of di-μ-oxo-binuclear manganese complex [Mn2IV,IIIO2(bpy)4]3+(ClO4)3[1] were studied in the presence of organic compounds. Irradiation of a CH3CN-1.0 M H2SO4(3:1) solution of [1] in the presence of anthracene gave anthraquinone with the reduction of [1]. On the other hand, similar irradiation of [1] in the presence of 9,10-dicyanoanthracene promoted the photochemical oxidation of water.

Yoshio Otsuji

Papers

Enantioselective addition of dichlorocarbene to olefins by use of chiral tertiary amines

Synthesis and properties of polymer-supported cyanoaromatic compounds

The Carbon Dioxide-Catalyzed Ester Exchange Reaction

PHOTO-INDUCED ELECTRON-TRANSFER REACTIONS OF DI-μ-OXO-BINUCLEAR MANGANESE COMPLEXES

Synthesis of Medium-Ring Ketolactams from Bicyclic Pyrroles