Electrochemical deoxygenative homo-couplings of aromatic aldehydes

An electrochemical deoxygenative homo-coupling of aromatic aldehydes is achieved to selectively access bibenzyl and stilbene derivatives. The protocol allows the homo-coupling of aldehydes to occur after single-electron-reduction at the cathode. Taking advantage of the oxophilicity of triphenylphosphine, the electrochemical deoxygenation proceeds smoothly to give reductive homo-coupling products.

Hydrodeoxygenative Coupling and Transformation of Aldehydes at a N2-Derived Tetranuclear Titanium Imide/Hydride Framework

Carbon-carbon bond formation via coupling of two organic components is among the most important chemical transformations in organic synthesis. Herein, we report an unprecedented hydrodeoxygenative coupling of aromatic aldehydes to form bibenzyls by a N₂-derived tetranuclear titanium imide/hydride complex [(Cp'Ti)₄(μ₃-NH)₂(μ-H)₄] (1; Cp' = C₅Me₄SiMe₃). Further reactions with the corresponding aldehydes under air afford hydrobenzamides together with a titanium oxo complex. Both hydride and imide ligands play an important role for the reductive coupling, hydrogenation processes, as well as the functionalization of the N₂-derived imide units without the need of sacrificial reagents. These results demonstrate that the tetranuclear titanium imide/hydride framework is not only applicable for N₂ activation and functionalization but also providing a new platform for the C-C bond formation using carbonyl compounds.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO₂ hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Perylene-Grafted Silicas: Mechanistic Study and Applications in Heterogeneous Photoredox Catalysis

A mechanistic study is herein presented for the use of heterogeneous photocatalysts based on perylene moieties. First, the successful immobilization of perylene diimides (PDI) on silica matrices is demonstrated, including their full characterization by means of electronic microscopy, surface area measurements, powder XRD, thermogravimetric analysis, and FTIR, ²⁹ Si and ¹³ C solid-state NMR, fluorescence, and diffuse reflectance spectroscopies. Then, the photoredox activity of the material was tested by using two model reactions, alkene oxidation and 4-nitrobenzylbromide reduction, and mechanistic studies were performed. The mechanistic insights into their photoredox activity show they have promising dual photocatalytic activity for both organic oxidations and reductions.

A green road map for heterogeneous photocatalysis

In the new millennium the well-established paradigms of organic photochemistry have come alive as the basis for a wide range of synthetic methodologies that take advantage of the enhanced redox properties of excited states. While many strategies have been developed using rare, expensive and non-reusable catalysts, the road forward should include catalysts based on more abundant elements and reusable materials. This green road leads to the exploration of heterogeneous systems that can be eventually adapted for flow photocatalysis, and also adopted for the solution of environmental problems such as water treatment and fuel generation using solar radiation. If heterogeneous photocatalysis can play a role in supplying solutions to drug synthesis, energy and potable water supplies, then photochemistry will have an unprecedented societal impact.

Photocatalyzed Transformation of Free Carbohydrates

In the growing context of sustainable chemistry, one of the challenges of organic chemists is to develop efficient and environmentally friendly methods for the synthesis of high-added-value products. Heterogeneous photocatalytic transformations have brought revolution in this regard, as they take advantage of an unlimited source of energy (solar light) or artificial UV light to onset organic chemical modifications. The abundance of free carbohydrates as chemical platform feedstock offers a great opportunity to obtain a variety of industrial interest compounds from biomass. Due to their chirality and polyfunctionality, the conversion of sugars generally requires multi-step protocols with protection/deprotection steps and hazardous chemical needs. In this context, several selective and eco-friendly methodologies are currently under development. This review presents a state of art of the recent accomplishments concerning the use of photocatalysts for the transformation and valorization of free carbohydrates. It discusses the approaches leading to the selective oxidation of free sugars, their degradation into organic chemicals, or their use for hydrogen production.

Glass wool: a novel support for heterogeneous catalysis

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material - glass wool - can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp3-Csp3 couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.

Light-activated Ullmann homocoupling of aryl halides catalyzed using gold nanoparticle-functionalized potassium niobium oxides

Lamellar, or layered, potassium niobium oxide perovskites are a class of underdeveloped semiconductors in organic photocatalysis that offer the inherent advantages of larger particle size and ease of recoverability as compared to traditional semiconductor materials.

A practical protocol for the synthesis of bibenzyls via C(sp3)–H activation of methyl arenes under metal-free conditions

A variety of bibenzyl derivatives have been synthesized with excellent atom economy via C(sp³)–H–C(sp³)–H coupling of readily available methyl arenes using K₂S₂O₈ under metal-free and environmentally benign conditions.

Cosolvent-Promoted O-Benzylation with Silver(I) Oxide: Synthesis of 1'-Benzylated Sucrose Derivatives, Mechanistic Studies, and Scope Investigation

A cosolvent-promoted O-benzylation strategy with Ag2O was developed. The cosolvent consisting of CH2Cl2 and n-hexane can not only improve the reaction solubility for carbohydrates but also increase the benzylation efficiency. The formation of byproducts is greatly inhibited in the developed method. This method is simple, mild, and highly effective, and numerous 1'-benzylated sucrose derivatives were prepared including a photoreactive (trifluoromethyl)phenyldiazirine-based sucrose. The mechanisms of benzylation with primary and secondary benzyl bromides were also elaborated. Furthermore, the application scope with alcohols, glucose, and ribose derivatives was investigated.

Gold nanoparticles supported on layered TiO2–RGO hybrid as an enhanced and recyclable catalyst for microwave-assisted hydration reaction

A novel composite (Au–SO₄²⁻/TiO₂–RGO) is synthesized and serves as an enhanced catalyst for alkyne hydration.