A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.

Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.






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Figure 1


Ruthenium polypyridyl complexes: versatile visible light photocatalysts.

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Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

23 Stereocontrol of Lactide ROP 6164 231 Isotactic Polylactides 6164 232 Syndiotactic Polylactides 6166 233 Heterotactic Polylactides 6166 3 Anionic Polymerization 6166 4 Nucleophilic Polymerization 6168 41 Mechanistic Considerations 6168 42 Catalysts 6169 421 Enzymes 6169 422 Organocatalysts 6169 43 Stereocontrol of Lactide ROP 6170 44 Depolymerization 6170 5 Cationic Polymerization 6170 6 Conclusion and Perspectives 6171 7 Acknowledgments 6173 8 References and Notes 6173

Controlled ring-opening polymerization of lactide and glycolide.

4.4. Pd on Modified Silica 159 4.5. Pd on Clay and Other Inorganic Materials 159 5. Stille, Fukuyama, and Negishi Reactions 159 5.1. Stille Reactions 159 5.1.1. Pd on Carbon (Pd/C) 159 5.1.2. Palladium on KF/Al2O3 159 5.1.3. Pd on Modified Silica (SiO2/TEG/Pd) 159 5.2. Fukuyama Reactions 159 5.2.1. Pd on Carbon (Pd/C) 159 5.2.2. Pd(OH)2 on Carbon (Perlman’s Catalyst) 160 5.3. Pd/C-Catalyzed Negishi Reactions 160 6. Ullmann-Type Coupling Reactions 161 6.1. Pd/C-Catalyzed Aryl−Aryl Coupling 161 6.2. Pd/C-Catalyzed Homocoupling of Vinyl Halides 162

https://www.chem.ccu.edu.tw/~joyce/referance/ericyang/Chem.%20Rev/Chem.%20Rev.%202007,%20107,%20133-173.pdf

Carbon-Carbon Coupling Reactions Catalyzed by Heterogeneous Palladium Catalysts

In the last few years, visible-light initiated organic transformations have attracted increasing attention. The development of visible-light-promoted photocatalytic reactions, which enable rapid and efficient synthesis of fine chemicals, is highly desirable from the viewpoint of cost, safety, availability, and environmental friendliness. In this Minireview, recent advances made in this fast developing area of research are discussed.

Visible-light photoredox catalysis.

A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

Bowl-shaped π-conjugated compounds are important not only as model compounds of fullerenes but also as possible synthetic intermediates for artificially designed fullerene derivatives, such as hetero-fullerenes ([ 1 ][1]). Most of the attention has been focused on the compounds derived from C 5v

http://science.sciencemag.org/content/sci/301/5641/1878.full.pdf

A Synthesis of Sumanene, a Fullerene Fragment

Dialkyl arylphosphonates are prepared by the palladium-catalyzed reaction of aryl bromides with dialkyl phosphite in the presence of triethylamine The similar treatment of vinyl bromides gives dialkyl vinylphosphonates stereoselectively

Palladium-catalyzed New Carbon-Phosphorus Bond Formation

A novel synthesis of dialkyl arenephosphonates

The structure of sumanene in a solid state was elucidated. The silyl-substituted sumanene was stereoselectively synthesized through generation of the benzylic anions of sumanene.

Structural elucidation of sumanene and generation of its benzylic anions.

Pd/C was found to catalyze the Suzuki−Miyaura coupling reaction of halophenols in aqueous media. When halophenols were treated with ArB(OH)2 and a catalytic amount of 10% Pd/C (0.3 mol % Pd) in aqueous K2CO3 solution, the corresponding hydroxybiaryls were obtained in a high yield or quantitatively. The palladium catalyst was easily recovered and reused.

Toshikazu Hirao

Papers

A Synthesis of Sumanene, a Fullerene Fragment

Palladium-catalyzed New Carbon-Phosphorus Bond Formation

A novel synthesis of dialkyl arenephosphonates

Structural elucidation of sumanene and generation of its benzylic anions.

Pd/C as a reusable catalyst for the coupling reaction of halophenols and arylboronic acids in aqueous media.