Iron Catalysis in Organic Synthesis

The coupling of aryl or vinyl halides with terminal acetylenes catalysed by palladium and other transition metals, commonly termed as Sonogashira cross-coupling reaction, is one of the most important and widely used sp2–sp carbon–carbon bond formation reactions in organic synthesis, frequently employed in the synthesis of natural products, biologically active molecules, heterocycles, molecular electronics, dendrimers and conjugated polymers or nanostructures. This critical review focuses on developments in the Sonogashira reaction achieved in recent years concerning catalysts, reaction conditions and substrates (352 references).

Recent advances in Sonogashira reactions

Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

Over the past 40 years, transition metal catalysis has enabled bond formation between aryl and olefinic (sp(2)) carbons in a selective and predictable manner with high functional group tolerance. Couplings involving alkyl (sp(3)) carbons have proven more challenging. Here, we demonstrate that the synergistic combination of photoredox catalysis and nickel catalysis provides an alternative cross-coupling paradigm, in which simple and readily available organic molecules can be systematically used as coupling partners. By using this photoredox-metal catalysis approach, we have achieved a direct decarboxylative sp(3)-sp(2) cross-coupling of amino acids, as well as α-O- or phenyl-substituted carboxylic acids, with aryl halides. Moreover, this mode of catalysis can be applied to direct cross-coupling of C(sp³)-H in dimethylaniline with aryl halides via C-H functionalization.

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Merging photoredox with nickel catalysis: Coupling of α-carboxyl sp3-carbons with aryl halides

Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.

http://science.sciencemag.org/content/sci/341/6143/1229712.full.pdf

Applications of acceptorless dehydrogenation and related transformations in chemical synthesis.

At present, alcohols are considered sustainable starting materials that can be used in organic synthesis for various organic transformations and the preparation of commodity chemicals. Acceptorless dehydrogenation (AD) and borrowing hydrogen (BH) are two important methods for activating alcohols for alkenylation and alkylation. These approaches are sustainable because their process liberates water and in some cases (i.e., AD) molecular hydrogen as clean byproducts. Moreover, this area of research has attracted significant attention in the catalysis community, and various transition metals have been used to explore the same. Herein, in this review, we focus on the development of Ru-based catalyst systems for C-alkylation/alkenylation reactions via the AD or BH approach. This review also features a comparative study of the various Ru-catalysts used to optimize the reaction conditions. Furthermore, we extensively cover the outcomes of the mechanistic studies to describe the reaction pathways.

Progressive study on ruthenium catalysis for de(hydrogenative) alkylation and alkenylation using alcohols as a sustainable source.

Herein, we describe the application of SNS-based ruthenium pincer catalyst for Guerbet condensation reaction of primary alcohols to prepare β-alkylated dimer alcohols in good yields. Moreover, the scope of these complexes to convert ethanol to butanol was also investigated. Furthermore, the work was extended toward the C-alkylation of secondary alcohols with primary alcohols to give α-alkylated ketones. Several control experiments were also conducted that shows the involvement of “borrowing hydrogen” in the protocol.

Acridine-Based SNS–Ruthenium Pincer Complex-Catalyzed Borrowing Hydrogen-Mediated C–C Alkylation Reaction: Application to the Guerbet Reaction

It is crucial to use an excess of the secondary alcohols to achieve the high yields of the esters.

Ruthenium Pincer-Catalyzed Cross-Dehydrogenative Coupling of Primary Alcohols with Secondary Alcohols under Neutral Conditions.

Schiff bases derived from substituted benzaldehydes are effective ligands for palladium(0) in the Suzuki–Miyaura coupling of phenylboronic acid with aryl, benzyl and allyl bromides under mild conditions.

Dipankar Srimani

Papers

Progressive study on ruthenium catalysis for de(hydrogenative) alkylation and alkenylation using alcohols as a sustainable source.

Acridine-Based SNS–Ruthenium Pincer Complex-Catalyzed Borrowing Hydrogen-Mediated C–C Alkylation Reaction: Application to the Guerbet Reaction

Ruthenium Pincer-Catalyzed Cross-Dehydrogenative Coupling of Primary Alcohols with Secondary Alcohols under Neutral Conditions.

Benzaldimines as Ligands for Palladium in Suzuki—Miyaura Reactions.

Iron Pincer Complex Catalyzed, Environmentally Benign, E-Selective Semi-Hydrogenation of Alkynes.