Magnetically Separable CuFe2O4Nanoparticles Catalyzed Ligand-Free CS Coupling in Water: Access to (E)- and (Z)-Styrenyl-, Heteroaryl and Sterically Hindered Aryl Sulfides

Copper nanoparticles catalyzed carbon–heteroatom bond formation and synthesis of related heterocycles by greener procedures

A variety of procedures for the carbon–nitrogen, carbon–oxygen, carbon–sulfur and carbon–selenium bond formation using copper nanoparticles in greener conditions have been highlighted. The synthesis of several heterocyclic compounds of biological importance has also been reported using these protocols.

Regioselective direct sulfenylation of glycals using arylsulfonyl chlorides in the presence of triphenylphosphine: access to C2-thioaryl glycosides

Cheap and easily available arylsulfonyl chlorides as a sulfur source reductively couple with glycals in the presence of triphenylphosphine to afford C2-thioaryl glycosides.

Magnetic Nanoparticle-Containing Supports as Carriers of Immobilized Enzymes: Key Factors Influencing the Biocatalyst Performance

In this short review (Perspective), we identify key features of the performance of biocatalysts developed by the immobilization of enzymes on the supports containing magnetic nanoparticles (NPs), analyzing the scientific literature for the last five years. A clear advantage of magnetic supports is their easy separation due to the magnetic attraction between magnetic NPs and an external magnetic field, facilitating the biocatalyst reuse. This allows for savings of materials and energy in the biocatalytic process. Commonly, magnetic NPs are isolated from enzymes either by polymers, silica, or some other protective layer. However, in those cases when iron oxide NPs are in close proximity to the enzyme, the biocatalyst may display a fascinating behavior, allowing for synergy of the performance due to the enzyme-like properties shown in iron oxides. Another important parameter which is discussed in this review is the magnetic support porosity, especially in hierarchical porous supports. In the case of comparatively large pores, which can freely accommodate enzyme molecules without jeopardizing their conformation, the enzyme surface ordering may create an optimal crowding on the support, enhancing the biocatalytic performance. Other factors such as surface-modifying agents or special enzyme reactor designs can be also influential in the performance of magnetic NP based immobilized enzymes.

Chitosan as capping agent in a robust one-pot procedure for a magnetic catalyst synthesis

Here, we report a one-pot solvothermal method for the development of magnetically recoverable catalysts with Ru or Ag nanoparticles (NPs) capped by chitosan (CS), a derivative of natural chitin. The formation of iron oxide NPs was carried out in situ in the presence of CS and iron acetylacetonate in boiling triethyleneglycol (TEG) due to CS solubilization in warm TEG. Coordination with Ru or Ag species and the NP formation take place in the same reaction solution, eliminating intermediate steps. In optimal conditions the method developed allows stabilization of 2.2 nm monodisperse Ru NPs (containing both Ru⁰ and Ru⁴⁺ species) that are evenly distributed through the catalyst, while for Ag NPs, this stabilizing medium is inferior, leading to exceptionally large Ag nanocrystals. Catalytic testing of CS-Ru magnetically recoverable catalysts in the reduction of 4-nitrophenol to 4-aminophenol with excess NaBH₄ revealed that the catalyst with 2.2 nm Ru NPs exhibits the highest catalytic activity compared to samples with larger Ru NPs (2.9-3.2 nm). Moreover, this catalyst displayed extraordinary shelf-life in the aqueous solution (up to ten months) and excellent reusability in ten consecutive reactions with easy magnetic separation at each step which were assigned to its conformational rigidity at a constant pH. These characteristics as well as favorable environmental factors of the catalyst fabrication, make it promising for nitroarene reduction.

Pd Catalyst Based on Hyperbranched Polypyridylphenylene Formed In Situ on Magnetic Silica Allows for Excellent Performance in Suzuki-Miyaura Reaction

Here, for the first time, we developed a catalytic composite by forming a thin layer of a cross-linked hyperbranched pyridylphenylene polymer (PPP) on the surface of mesoporous magnetic silica (Fe₃O₄-SiO₂, MS) followed by complexation with Pd species. The interaction of Pd acetate (PdAc) with pyridine units of the polymer results in the formation of Pd²⁺ complexes which are evenly distributed through the PPP layer. The MS-PPP-PdAc catalyst was tested in the Suzuki-Miyaura cross-coupling reaction with four different para-Br-substituted arenes, demonstrating enhanced catalytic properties for substrates containing electron withdrawing groups, and especially, for 4-bromobenzaldehyde. In this case, 100% selectivity and conversion were achieved with TOF of >23 000 h^-1 at a very low Pd loading (0.032 mol %), a remarkable performance in this reaction. We believe these exceptional catalytic properties are due to the hyperbranched polymer architecture, which allows excellent stabilization of catalytic species as well as a favorable space for reacting molecules. Additionally, the magnetic character of the support allows for easy magnetic separation during the catalyst synthesis, purification, and reuse, resulting in energy and materials savings. These factors and excellent reusability of MS-PPP-PdAc in five consecutive uses make this catalyst promising for a variety of catalytic reactions.

Facile Synthesis of Magnetically Recoverable Pd and Ru Catalysts for 4-Nitrophenol Reduction: Identifying Key Factors

This paper reports the development of robust Pd- and Ru-containing magnetically recoverable catalysts in a one-pot procedure using commercially available, branched polyethyleneimine (PEI) as capping and reducing agent. For both catalytic metals, ∼3 nm nanoparticles (NPs) are stabilized in the PEI shell of magnetite NPs, whose aggregation allows for prompt magnetic separation. The catalyst properties were studied in a model reaction of 4-nitrophenol hydrogenation to 4-aminophenol with NaBH4. A similar catalytic NP size allowed us to decouple the NP size impact on the catalytic performance from other parameters and to follow the influence of the catalytic metal type and amount as well as the PEI amount on the catalytic activity. The best catalytic performances, the 1.2 min-1 rate constant and the 433.2 min-1 turnover frequency, are obtained for the Ru-containing catalyst. This is discussed in terms of stability of Ru hydride facilitating the surface-hydrogen transfer and the presence of Ru4+ species on the Ru NP surface facilitating the nitro group adsorption, both leading to an increased catalyst efficiency. High catalytic activity as well as the high stability of the catalyst performance in five consecutive catalytic cycles after magnetic separation makes this catalyst promising for nitroarene hydrogenation reactions.

Immobilized glucose oxidase on magnetic silica and alumina: Beyond magnetic separation

Here we report immobilization of glucose oxidase (GOx) on magnetic silica (Fe₃O₄-SiO₂) and alumina (Fe₃O₄-Al₂O₃) functionalized with amino groups using glutaraldehyde as a linker. Magnetic support based biocatalysts demonstrate high catalytic activity in d-glucose oxidation to D-gluconic acid at pH 5-7.5 and temperature of 30-50 °C with the best activities of 95% and 91% for magnetic silica and alumina, respectively. A comparison of magnetic and non-magnetic alumina and silica shows a significant enhancement of the relative catalytic activity for magnetic supports, while the silica based biocatalysts show a higher activity than the biocatalysts based on alumina. A noticeably higher activity of GOx immobilized on magnetic supports is explained by synergy of the GOx inherent activity and enzyme-like activity of iron oxide nanoparticles, while the enhancement with silica based catalysts is most likely due to a larger pore size and stronger Brønsted acid sites. Excellent relative activity of Fe₃O₄-SiO₂-GOx (95% of native GOx) in a tolerant pH and temperature range as well as high stability in a repeated use (6% relative activity loss after five catalytic cycles) makes this catalyst promising for practical applications.

Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2-Propanol

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag⁰ NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp² carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Enhancing the Catalytic Activity of Zn-Containing Magnetic Oxides in a Methanol Synthesis: Identifying the Key Factors

A new family of Ni-, Co-, and Cr-doped Zn-containing magnetic oxide nanoparticles (NPs) stabilized by polyphenylquinoxaline (PPQ) and hyperbranched pyridylphenylene polymer (PPP) has been developed. These NPs have been synthesized by thermal decomposition of Zn and doping metal acetylacetonates in the reaction solution of preformed magnetite NPs, resulting in single-crystal NPs with spinel structure. For the PPQ-capped NPs, it was demonstrated that all three types of metal species (Fe, Zn, and a doping metal) reside within the same NPs, the surface of which is enriched with Zn and a doping metal, while the deeper layers are enriched with Fe. The Cr-doped NPs at the high Cr loading are an exception due to favored deposition of Cr on magnetite located in the NP depth. The PPP-capped NPs exhibit similar morphology and crystallinity; however, the detailed study of the NP composition was barred due to the high PPP amount retained on the NP surface. The catalyst testing in syngas conversion to methanol demonstrated outstanding catalytic properties of doped Zn-containing magnetic oxides, whose activities are dependent on the doping metal content and on the stabilizing polymer. The PPP stabilization allows for better access to the catalytic species due to the open and rigid polymer architecture and most likely optimized distribution of doping species. Repeat experiments carried out after magnetic separation of catalysts from the reaction mixture showed excellent catalyst stability even after five consecutive catalytic runs.

A novel metal-free method for the selenocyanation of aromatic ketones to afford α-carbonyl selenocyanates

A rapid access to α-carbonyl selenocyanates has been developed through the direct selenocyanation of aromatic ketones.

Ru-Containing Magnetically Recoverable Catalysts: A Sustainable Pathway from Cellulose to Ethylene and Propylene Glycols

Biomass processing to value-added chemicals and biofuels received considerable attention due to the renewable nature of the precursors. Here, we report the development of Ru-containing magnetically recoverable catalysts for cellulose hydrogenolysis to low alcohols, ethylene glycol (EG) and propylene glycol (PG). The catalysts are synthesized by incorporation of magnetite nanoparticles (NPs) in mesoporous silica pores followed by formation of 2 nm Ru NPs. The latter are obtained by thermal decomposition of ruthenium acetylacetonate in the pores. The catalysts showed excellent activities and selectivities at 100% cellulose conversion, exceeding those for the commercial Ru/C. High selectivities as well as activities are attributed to the influence of Fe3O4 on the Ru(0)/Ru(4+) NPs. A facile synthetic protocol, easy magnetic separation, and stability of the catalyst performance after magnetic recovery make these catalysts promising for industrial applications.

The Application of Copper/Iron Cocatalysis in Cross-Coupling Reactions

For conventional cross-couplings in organic chemistry, precious metal (such as Pd or Rh) complexes have been the preferable choices as catalysts. However, their high cost, toxicity, and potential contamination of products limit their massive applications on some occasions, particularly in the pharmaceutical industry, where close monitoring of the metal contamination of products is required. Therefore, the use of metals that are less expensive and less toxic than Pd or Rh can be greatly advantageous and earth abundant metal (such Fe or Cu) catalysts have shown promise for replacing the precious metals. Interestingly, a certain copper catalyst combined with an iron catalyst displays higher catalytic efficiency than itself in various coupling reactions. Notably, ligand-free conditions make such protocols more useful and practical in many cases. In this account, we summarize the recent progress made in this increasingly attractive topic by describing successful examples, including our own work in the literature, regarding effective copper/iron cocatalysis. In addition, a few examples involving a magnetic and readily recyclable CuFe2 O4 nanoparticle cocatalyst are also included.

Exploiting amphiphilicity: facile metal free access to thianthrenes and related sulphur heterocycles

Benzodithioloimines are reacted with arynes or alkynes substituted with electron-withdrawing groups to afford the corresponding thianthrene or benzo[b][1,4]dithiine derivatives. The transformation takes place under mild reaction conditions without any transition metal. Furthermore, the reaction mode could be expanded to 2-thiocyanatopyrroles yielding pyrrolothiazoles.

Zinc-Containing Magnetic Oxides Stabilized by a Polymer: One Phase or Two?

Here we developed a new family of Zn-containing magnetic oxides of different structures by thermal decomposition of Zn(acac)2 in the reaction solution of preformed magnetite nanoparticles (NPs) stabilized by polyphenylquinoxaline. Upon an increase of the Zn(acac)2 loading from 0.15 to 0.40 mmol (vs 1 mmol of Fe(acac)3), the Zn content increases, and the Zn-containing magnetic oxide NPs preserve a spinel structure of magnetite and an initial, predominantly multicore NP morphology. X-ray photoelectron spectroscopy (XPS) of these samples revealed that the surface of iron oxide NPs is enriched with Zn, although Zn species were also found deep under the iron oxide NP surface. For all the samples, XPS also demonstrates the atom ratio of Fe(3+)/Fe(2+) = 2:1, perfectly matching Fe3O4, but not ZnFe2O4, where Fe(2+) ions are replaced with Zn(2+). The combination of XPS with other physicochemical methods allowed us to propose that ZnO forms an ultrathin amorphous layer on the surface of iron oxide NPs and also diffuses inside the magnetite crystals. At higher Zn(acac)2 loading, cubic ZnO nanocrystals coexist with magnetite NPs, indicating a homogeneous nucleation of the former. The catalytic testing in syngas conversion to methanol demonstrated outstanding catalytic properties of Zn-containing magnetic oxides, whose activities are dependent on the Zn loading. Repeat experiments carried out with the best catalyst after magnetic separation showed remarkable catalyst stability even after five consecutive catalytic runs.

Tandem approach for the synthesis of 3-sulfenylimidazo[1,5-a]pyridines from dithioesters

Iodine-mediated synthesis of 3-sulfenylimidazo[1,5-a]pyridines via C–H functionalization has been achieved using dithioesters, 2-methylaminopyridines and sulfonyl hydrazides.

Role of TBATB in nano indium oxide catalyzed C-S bond formation

Nano sized indium oxide is found to be an efficient catalyst for the conversion of thiols to sulfides using Na2CO3 as base and TBATB as reagent in DMSO at 110 °C. Here in situ generation of bromo intermediate by TBATB takes place through indium surface. A variety of aryl sulfides can be synthesized in excellent yields from less reactive chlorides, boronic acids and thiols.

An efficient three-component synthesis of coumarin-3-carbamides by use of Ni–NiO nanoparticles as magnetically separable catalyst

An efficient and ecofriendly synthesis of coumarin-3-carbamides has been developed by a three-component reaction of 2-hydroxybenzaldehydes, aliphatic amines (p-/s-) and diethyl malonate using Ni–NiO nanoparticles as catalyst.

Design of ruthenium/iron oxide nanoparticle mixtures for hydrogenation of nitrobenzene

Magnetically recoverable catalysts containing Ru/RuO₂ and iron oxide nanoparticles show remarkable activity and selectivity in nitrobenzene-to-aniline hydrogenation.

Iodine-catalyzed regioselective thiolation of imidazo[1,2-a]pyridines using sulfonyl hydrazides as a thiol surrogate

Iodine-catalyzed regioselective sulfenylation of imidazo[1,2-a]pyridines via C(sp²)–H bond functionalization has been achieved using sulfonyl hydrazides as a thiol surrogate.

Magnetically separable CuFe2O4 nanoparticles as a recoverable catalyst for the addition reaction of C(sp3)–H bond of azaarenes to aldehydes

A green and efficient method for CuFe₂O₄-catalyzed C(sp³)–H functionalization of 2-alkyl azaarenes has been developed. The catalyst can be magnetically recycled and reused for eight times without significant decrease in catalytic activity.

Fabrication of magnetically recoverable catalysts based on mixtures of Pd and iron oxide nanoparticles for hydrogenation of alkyne alcohols

We report a novel method for development of magnetically recoverable catalysts prepared by thermal decomposition of palladium acetylacetonate in the presence of iron oxide nanoparticles (NPs). Depending on conditions, the reaction results either in a dispersed mixture of Pd and iron oxide NPs or in their aggregates. It was demonstrated that the Pd loading, reaction temperature, solvent, and iron oxide NP size and composition are crucial to control the reaction product including the degree of aggregation of Pd and iron oxide NPs, and the catalyst properties. The aggregation controlled by polarization and magnetic forces allows faster magnetic separation, yet the aggregate sizes do not exceed a few hundred nanometers, making them suitable for various catalytic applications. These NP mixtures were studied in a selective hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol, demonstrating clear differences in catalytic behavior depending on the catalyst structure. In addition, one of the catalysts was also tested in hydrogenation of 3-methyl-1-pentyn-3-ol and 3-methyl-1-nonyn-3-ol, indicating some specificity of the catalyst toward different alkyne alcohols.