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

Green Chemistry is a relatively new emerging field that strives to work at the molecular level to achieve sustainability. The field has received widespread interest in the past decade due to its ability to harness chemical innovation to meet environmental and economic goals simultaneously. Green Chemistry has a framework of a cohesive set of Twelve Principles, which have been systematically surveyed in this critical review. This article covers the concepts of design and the scientific philosophy of Green Chemistry with a set of illustrative examples. Future trends in Green Chemistry are discussed with the challenge of using the Principles as a cohesive design system (93 references).

Green Chemistry: Principles and Practice

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Direct C-H transformation via iron catalysis.

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.

Asymmetric multicomponent reactions (amcrs): the new frontier

Iron-catalyzed cross-coupling reactions have, over the past years, developed to maturity and today are an integral part of the organic chemist's toolkit. They benefit from low costs, operational simplicity, and high reactivity and thus constitute the "green" sister of the palladium and nickel establishment. This timely Review traces back major achievements, discusses their mechanistic background, and highlights numerous applications to molecular synthesis.Iron-catalyzed carbon-carbon bond-forming reactions have matured to an indispensable class of reactions in organic synthesis. The advent of economically and ecologically attractive iron catalysts in the past years has stepped up the competition with the established palladium and nickel catalyst systems that have dominated the field for more than 30 years, but suffer from high costs, toxicity, and sometimes low reactivity. Iron-catalyzed protocols do not merely benefit from economic advantages but entertain a rich manifold of reactivity patterns and tolerate various functional groups. The past years have witnessed a rapid development with ever-more-efficient protocols for the cross-coupling between alkyl, alkenyl, alkynyl, aryl, and acyl moieties becoming available to organic chemists. This Review intends to shed light onto the versatility that iron-catalyzed cross-coupling reactions offer, summarize major achievements, and clear the way for further use of such superior methodologies in the synthesis of fine chemicals, bioactive molecules, and materials.

Coming of Age: Sustainable Iron‐Catalyzed Cross‐Coupling Reactions

Reductive cross-electrophile coupling reactions have recently been developed to a versatile and sustainable synthetic tool for selective C-C bond formation. The employment of cheap and abundant electrophiles avoids the pre-formation and handling of organometallic reagents. In situ reductive coupling is effected in the presence of a transition-metal catalyst (Ni, Co, Pd, Fe) and a suitable metallic reductant (Mn, Zn, Mg). This Concept article assesses the current state of the art and summarizes recent protocols with various combinations of alkyl, alkenyl, allyl, and aryl reagents and highlights key mechanistic studies.

Reductive cross-coupling reactions between two electrophiles.

ConspectusPhotoredox catalysis has emerged as a powerful tool for the utilization of visible light to drive chemical reactions between organic molecules that exhibit two rather ubiquitous properties: colorlessness and redox-activity. The photocatalyst, however, requires significant absorption in the visible spectrum and reversible redox activity. This very general framework has led to the development of several new modes of reactivity based on electron and energy transfer steps between photoexcited catalyst states and various organic molecules. In the past years, major effort has been devoted to photoredox-catalytic aromatic substitutions involving an initial reductive activation of various aryl electrophiles by the photocatalyst, which opens a new entry into selective arene functionalizations within organic synthesis endeavors. This, however, has led to a unilateral emphasis of synthetic developments including catalyst modifications, substrate scope studies, and combinations with other chemical processes...

Mechanistic Perspectives on Organic Photoredox Catalysis for Aromatic Substitutions

Our recent development of a proline-derived bimetallic catalyst has led to a number of efficient, catalytic, enantioselective transformations. Herein, we report a practical and general alkynylation of aromatic and α,β-unsaturated aldehydes using our zinc catalyst system.

Axel Jacobi von Wangelin

Papers

Coming of Age: Sustainable Iron‐Catalyzed Cross‐Coupling Reactions

Reductive cross-coupling reactions between two electrophiles.

Mechanistic Perspectives on Organic Photoredox Catalysis for Aromatic Substitutions

Dinuclear Zn-catalyzed asymmetric alkynylation of unsaturated aldehydes.

Domino iron catalysis: direct aryl-alkyl cross-coupling.