Synthesis of Azoxy Compounds: from Copper Compounds to Mesoporous Silica-Encaged Ultrasmall Copper Catalysts

Azoxy compounds have aroused extensive attention due to their unique biological activities, but the chemical synthesis of these compounds often suffers from limitations due to their requirement for stoichiometric oxidants, high costs, and restricted substrate range. Herein, a series of azoxy compounds were constructed via facile coupling reactions by using cost-effective N-methoxyformamide and nitroso compounds over Cu-based catalysts, affording high product yields with excellent tolerance of functional groups. Significantly, the mesoporous silica nanosphere-encapsulated ultrasmall Cu (Cu@MSN) catalyst was developed via a one-pot synthetic method and first used for the synthesis of azoxy compounds. As compared with copper salt catalysts, the Cu@MSN catalyst exhibited remarkably enhanced catalytic activity and superior recycling stability. Such a Cu@MSN catalyst overcame the inherent drawbacks of low activity, fast deactivation, and difficult recycling of traditional metal salt catalysts in organic reactions. This work provides a green and efficient method for the construction of azoxy compounds and also creates new prospects for the application of nanoporous materials confined metal catalysts in organic synthesis.

Low-Valent Tungsten-Catalyzed Controllable Oxidative Dehydrogenative Coupling of Anilines

Herein, we have developed an efficient tungsten-catalyzed homogeneous system for oxidative dehydrogenative coupling of anilines to selectively produce various azoaromatics and azoxyaromatics as well as 2-substituted indolone N-oxides by simply regulating the reaction solvent with peroxide as a terminal oxidant under additive-free conditions. These findings provide an experimental framework for exploring tungsten catalysis in organic synthesis and offer an efficient and convenient tactic for the selective oxidation of anilines.

An intriguing tetranuclear Rh-based polyoxometalate for the reduction of nitroarene and oxidation of aniline

An organic-inorganic hybrid polyoxometalate Na₅H_5.68 [Na_0.17Rh_0.83^III(C₆H₈N₂)₂Cl₂]₂(C₈H₈N₂)₂[As₄W₄₀O₁₄₀Rh₄^IV(C₆H₄N₂S)₂]·nH₂O (1) containing 5.66 Rh atoms is prepared; to our knowledge, it owns the largest number of Rh atoms in the Rh-POM family. Compound 1 demonstrates good catalytic performance in the reduction of nitrobenzene to aniline and the oxidation of aniline to azobenzene under mild conditions. Moreover, catalyst 1 exhibits high activity, excellent stability and recyclability.

Zr(OH)4 Catalyzed Controllable Selective Oxidation of Anilines to Azoxybenzenes, Azobenzenes and Nitrosobenzenes

The selective oxidation of aniline to metastable and valuable azoxybenzene, azobenzene or nitrosobenzene has important practical significance in organic synthesis. However, uncontrollable selectivity and laborious synthesis of the expensive required catalysts severely hinder the uptake of these reactions in industrial settings. Herein, we have pioneered the discovery of Zr(OH) 4 as an efficient heterogeneous catalyst capable of the selective oxidation of aniline, using either peroxide or O 2 as oxidant, to selectively obtain various azoxybenzenes, symmetric/unsymmetric azobenzenes, as well as nitrosobenzenes, by simply regulating the reaction solvent, without the need for additives. Mechanistic experiments and DFT calculations demonstrate that the activation of H 2 O 2 and O 2 is primarily achieved by the bridging hydroxyl and terminal hydroxyl groups of Zr(OH) 4 respectively. The present work provides an economical and environmentally friendly strategy for the selective oxidation of aniline in industrial applications.

N–C bond formation between two anilines coordinated to a ruthenium center in cis-form affording a 3,5-cyclohexadiene-1,2-diimine moiety

Four-electron oxidation of two anilines coordinated to a ruthenium(ii) center in a cis-form affords N1-phenylcyclohexa-3,5-diene-1,2-diimine through an N–C bond formation with N–H and C–H bond activation.

Synthesis of sub-nanometric Cu2O catalysts for Pd-free C–C coupling reactions

The current template route provides Cu₂O nanocrystals with various shapes and depends on the homologues of glucose. These morphology-controlled Cu₂O nanocrystals show high activity for the external base-free Ullmann homocoupling of aryl halides.

SBA-15 Anchored Metal Containing Catalysts in the Oxidative Desulfurization Process

Recalcitrant sulfur compounds are common impurities in crude oil. During combustion they produce SOx derivatives that are able to affect the atmospheric ozone layer, increasing the formation of acid rains, and reducing the life of the engine due to corrosion. In the last twenty years, many efforts have been devoted to develop conventional hydrodesulfurization (HDS) procedures, as well as alternative methods, such as selective adsorption, bio-desulfurization, oxidative desulfurization (ODS) under extractive conditions (ECODS), and others. Among them, the oxidative procedures have been usually accomplished by the use of toxic stoichiometric oxidants, namely potassium permanganate, sodium bromate and carboxylic and sulfonic peracids. As an alternative, increasing interest is devoted to selective and economical procedures based upon catalytic methods. Heterogeneous catalysis is of relevance in industrial ODS processes, since it reduces the leaching of active species and favors the recovery and reuse of the catalyst for successive transformations. The heterogenization of different types of high-valent metal transition-based organometallic complexes, able to promote the activation of stoichiometric benign oxidants like peroxides, can be achieved using various solid supports. Many successful cases have been frequently associated with the use of mesoporous silicas that have the advantage of easy surface modification by reaction with organosilanes, facilitating the immobilization of homogeneous catalysts. In this manuscript the application of SBA-15 as efficient support for different active metal species, able to promote the catalytic ODS of either model or real fuels is reviewed, highlighting its beneficial properties such as high surface area, narrow pore size distribution and tunable pore diameter dimensions. Related to this topic, the most relevant advances recently published, will be discussed and critically described.

Oxidative coupling of anilines to azobenzenes using heterogeneous manganese oxide catalysts

Cryptomelane-type manganese oxide shows high efficiency for the NN formation reaction in the oxidative coupling of anilines to azobenzenes. The difference of the Hammett constants (Δσ) of two substituted groups determines the selectivity to unsymmetric azobenzenes in cross-coupling reactions, which are favored at Δσ < 0.32.

TiO2 microspheres supported polyoxometalate-based ionic liquids induced catalytic oxidative deep-desulfurization

A series of TiO₂ microspheres supported [SiW₁₂O₄₀]⁴⁻-based ionic liquids were successfully prepared and used as catalysts in oxidative desulfurization system. DBT was oxidized to DBT sulfone (DBTO₂) efficiently with the help of the catalyst and H₂O₂.