Solventless and Metal‐Free Synthesis of High‐Molecular‐Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines

The solventless reaction of diisopropylaminoborane with n‐butylamine, at room temperature, leads to a mixture of B_(sp2)H‐, B_(sp3)H₂‐, and B_(sp3)H₃‐containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high‐mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal‐free access to high‐molecular‐mass polyaminoboranes in good to high yields under mild reaction conditions.     

A Highly Efficient Friedel–Crafts Reaction of 3‐Hydroxyoxindoles and Aromatic Compounds to 3,3‐Diaryl and 3‐Alkyl‐3‐aryloxindoles Catalyzed by Hg(ClO4)2⋅3 H2O

We report a highly efficient Friedel–Crafts reaction of 3‐alkyl or 3‐aryl 3‐hydroxyoxindoles with a variety of aromatic and heteroaromatic compounds to unsymmetrical 3,3‐diaryloxindoles or 3‐alkyl‐3‐aryloxindoles, which are interesting medicinal targets and useful building blocks for the synthesis of natural products. Hg(ClO₄)₂ ? 3 H₂O was identified as a powerful catalyst for this reaction, and is significantly more efficient than other screened metal perchlorate hydrates and Brønsted acids such as HOTf and HClO₄. The high catalytic property of Hg(ClO₄)₂ ? 3 H₂O originates from the unprecedented dual activation effects of aromatic mercuration, which could generate a strong protic acid to facilitate the generation of a carbocation at the C3‐position of oxindoles and simultaneously form the more reactive nucleophilic reaction partner.     

Novel type of SO3H–functionalized nano‐titanium dioxide as a highly efficient and recyclable heterogeneous nanocatalyst for the synthesis of tetrahydrobenzo[b]pyrans

n ‐Butylsulfonated nano‐titania (n‐TiO₂‐NH‐(CH₂)₄‐SO₃H) as a highly efficient and reusable nanocatalyst was prepared by grafting 2,4‐toluene diisocyanate as a bi‐functional covalent linker onto a nano‐titania support, followed by reduction and then ring opening‐reaction of the synthesized amine with 1,4‐butanesultone. Fourier transform infrared spectroscopy, X‐ray diffraction, field‐emission scanning electron microscopy and thermogravimetric analysis were used to characterize the catalyst. The catalytic activity of n‐TiO₂‐NH‐(CH₂)₄‐SO₃H was evaluated in the synthesis of tetrahydrobenzo[b ]pyrans, which affords high yields. Statistical experimental design was applied as an efficient and powerful method to achieve the optimal conditions for this catalytic reaction leading to high yield. Moreover, the catalyst was recovered and reused at least six times without a significant decrease in catalytic activity.     

Reaction of o‐Carboryne with Furans: Facile Synthesis of Carborane‐ Fused Oxanorbornenes and Their Derivatives

o‐Carboryne (1,2‐dehydro‐o‐carborane) is a very useful synthon for the synthesis of a variety of carborane‐functionalized molecules. Diels‐Alder reaction of o‐carboryne with furans gave a series of carborane‐fused oxanorbornenes in moderate to high yields using 1‐OTf‐1,2‐C₂B₁₀H₁₁ as carboryne precursor. The resultant cycloadducts can undergo hydrogenation, cyclic oxidation, bromination, [4 + 2]/[2 + 2] cycloaddition and nucleophilic ring opening reaction to afford a variety of highly functionalized carboranes that may find applications as useful basic units in medicine and materials science.     

Silver,iron, and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 MNPs catalyzed one‐pot five‐component reactions for the synthesis of tetrahydropyridines by tandem condensation of amines,aldehydes, and methyl acetoacetate

In this study, Ag, Ni²⁺, and Fe²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ nanoparticles (γ‐Fe₂O₃@HAp‐Ag, γ‐Fe₂O₃@HAp‐Ni²⁺, and γ‐Fe₂O₃@HAp‐Fe²⁺) as a new and reusable Lewis acid magnetic nanocatalyst was successfully synthesized and reported for an atom economic, extremely facile, and environmentally benign procedure for the synthesis of highly functionalized tetrahydropyridines derivatives 4a‐t is described by one‐pot five‐component reaction of 2 equiv of aldehydes 1 , 2 equiv of amines 2 , and 1 equiv of methyl acetoacetate 3 in EtOH at room temperature in good to high yields and short reaction time. The presented methodology offers several advantages such as easy work‐up procedure, reusability of the magnetic nanocatalyst, operational simplicity, green synthesis avoiding toxic reagents and solvent, mild reaction conditions, and no tedious column chromatographic separation.     

ZrOCl2·8H2O as an efficient and recyclable catalyst for the one‐pot multicomponent synthesis of novel [1,3]oxazino[5,6‐c]quinolin‐5‐one derivatives

A simple, efficient and eco‐friendly procedure has been developed using ZrOCl₂·8H₂O as catalyst for the synthesis of novel [1,3]oxazino[5,6‐c]quinolin‐5‐one derivatives in aqueous ethanol at room temperature. The present methodology offers several advantages such as operational simplicity, use of ZrOCl₂·8H₂O as a green, non‐toxic, inexpensive and reusable catalyst, reusability of reaction media, high yields, mild and environmentally benign reaction conditions.     

SiO2 Nanoparticle‐catalyzed Facile and Efficient One‐pot Synthesis of N‐alkyl‐2,5‐bis[(E)‐2‐phenylvinyl]‐1,3‐dioxol‐4‐amine Under Solvent‐free Conditions

1,3‐Dioxole‐4‐amine derivatives have been prepared efficiently in one‐pot reaction using nanosized SiO₂ as a heterogeneous catalyst. The present method does not involve any hazardous organic solvents or catalysts. The high surface‐to‐volume ratio of SiO₂ nanoparticle has promising features for the reaction response such as the short reaction time, good to excellent yields, easy of operation and work‐up procedure, and purification of products by non‐chromatographic methods.     

Effect of Calcination Temperature and Pretreatment with Reaction Gas on Properties of Co/γ‐Al2O3 Catalysts for Partial Oxidation of Methane

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ‐Al₂O₃ catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N₂ adsorption, X‐ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature‐programmed reduction (H₂‐TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction‐atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl₂O₄‐like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α‐Al₂O₃ occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α‐Al₂O₃ surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.     

Defect Engineering of MoS2 and Its Impacts on Electrocatalytic and Photocatalytic Behavior in Hydrogen Evolution Reactions

Molybdenum disulfide (MoS₂) has been regarded as a favorable photocatalytic co‐catalyst and efficient hydrogen evolution reaction (HER) electrocatalyst alternative to expensive noble‐metals catalysts, owing to earth‐abundance, proper band gap, high surface area, and fast electron transfer ability. In order to achieve a higher catalytic efficiency, defects strategies such as phase engineering and vacancy introduction are considered as promising methods for natural 2H‐MoS₂ to increase its active sites and promote electron transfer rate. In this study, we report a new two‐step defect engineering process to generate vacancies‐rich hybrid‐phase MoS₂ and to introduce Ru particles at the same time, which includes hydrothermal reaction and a subsequent hydrogen reduction. Compositional and structural properties of the synthesized defects‐rich MoS₂ are investigated by XRD, XPS, XAFS and Raman measurements, and the electrochemical hydrogen evolution reaction performance, as well as photocatalytic hydrogen evolution performance in the ammonia borane dehydrogenation are evaluated. Both catalytic activities are boosted with the increase of defects concentrations in MoS₂, which ascertains that the defects engineering is a promising route to promote catalytic performance of MoS₂.     

Synthesis and characterization of polyvinylpyrrolidone immobilized on magnetic nanoparticles modified by ionic liquid as a novel and recyclable catalyst for the three‐component synthesis of amidoalkyl naphthols

In this study, an efficient and green procedure is explained for the preparation of 1‐amidoalkyl‐2‐naphthols applying one‐pot condensation reaction of 2‐naphthol, amide and aromatic nanoparticles (Fe₃O₄@SiO₂@IL‐PVP) as a novel solid acid catalyst under solvent‐free conditions. The remarkable features of this method are short reaction time, high conversions, and high yield of product, easy workup procedures and solvent‐free conditions. The Fe₃O₄@SiO₂@IL‐PVP catalyst was characterized via Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction patterns (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), and energy‐dispersive X‐ray spectroscopy (EDS). Also, nanocatalysts could be easily recovered by a simple magnet and reused for the next reactions without significant loss of its catalytic activity.     

Controlled Synthesis of a Vacancy‐Defect Single‐Atom Catalyst for Boosting CO2 Electroreduction

The reaction of precursors containing both nitrogen and oxygen atoms with Ni^II under 500 °C can generate a N/O mixing coordinated Ni‐N₃O single‐atom catalyst (SAC) in which the oxygen atom can be gradually removed under high temperature due to the weaker Ni?O interaction, resulting in a vacancy‐defect Ni‐N₃‐V SAC at Ni site under 800 °C. For the reaction of Ni^II with the precursor simply containing nitrogen atoms, only a no‐vacancy‐defect Ni‐N₄ SAC was obtained. Experimental and DFT calculations reveal that the presence of a vacancy‐defect in Ni‐N₃‐V SAC can dramatically boost the electrocatalytic activity for CO₂ reduction, with extremely high CO₂ reduction current density of 65 mA cm^?2 and high Faradaic efficiency over 90 % at ?0.9 V vs. RHE, as well as a record high turnover frequency of 1.35×10⁵ h^?1, much higher than those of Ni‐N₄ SAC, and being one of the best reported electrocatalysts for CO₂‐to‐CO conversion to date.     

Catalytic Disproportionation of the Superoxide Intermediate from Electrochemical O2 Reduction in Nonaqueous Electrolytes

Tris(pentafluorophenyl)borane (TPFPB) was found to be an efficient catalyst for rapid superoxide (O₂^?) disproportionation. The kinetics for the catalytic disproportionation reaction is much faster than the reaction between O₂^? and propylene carbonate. Therefore, the negative impact of the reaction between the electrolyte and O₂^? produced by the O₂ reduction is minimized. The cathodic current for O₂ reduction can be doubled in the presence of TPFPB. The high reduction current resulted from the pseudo two‐electron O₂‐reduction reaction due to the replenishment of O₂ at the electrode surface. This discovery could lead to a new avenue for the development of high‐capacity, high‐rate, rechargeable Li–air batteries.     

Green and rapid synthesis of dihydropyrimido [4,5‐b]quinolinetrione derivatives using CoFe2O4@PPA as high efficient solid acidic catalyst under ultrasonic irradiation

A new high efficient and green protocol for the preparation of dihydropyrimido[4,5‐b]quinolinetrione derivatives using magnetically solid acid catalyst was presented. High performance solid acid catalyst was prepared through a three‐step reaction. Firstly, CoFe₂O₄ nano particles were synthesized using co‐precipitation method. In second step, CoFe₂O₄ nano particles were coated with SiO₂ shell through treatment with tetraethyl orthosilicate (CoFe₂O₄@SiO₂). Finaly, CoFe₂O₄@SiO₂ was modified with polyphosphoric acid (CoFe₂O₄@SiO₂/PPA) in a simple manner. Green reusable catalyst was characterized in details using FTIR, VSM, TEM, FESEM, EDX and used as catalyst for the synthesis of dihydropyrimido[4,5‐b]quinolinetrione derivatives. Reaction was performed under ultrasonic irradiation as green, effective and mild conditions and products were achieved in high to excellent yields. Green and eco‐friendly conditions, short reaction times with high yield of products in addition to easy workup are some merits of presented method.     

Simple and Highly Efficient Catalytic Thiocyanation of Aromatic Compounds in Aqueous Media

Two simple, mild, and efficient procedures for the thiocyanation of N‐heterocycles, substituted anilines (electron‐rich and electron‐deficient), and N‐substituted aromatic amines at room temperature are reported (Table 3). The first uses H₂O₂ as pollution‐free oxidant and the second H₅IO₆; both with the reagent potassium thiocyanate in H₂O as solvent. These procedures provided the target thiocyanates after a short reaction time in good to excellent yields and high regioselectivity.     

Synthesis of azide end‐functionalized isotactic polypropylene building block and renewed modular synthesis of diblock copolymers of isotactic polypropylene and poly(ε‐caprolactone)

This article details a synthesis of azide end‐functionalized isotactic polypropylene (i‐PP), a unique polymeric building block that can engage in Huisgen's 1,3‐dipolar cycloaddition of azide and alkyne (click reaction) to construct well‐defined i‐PP‐based polymer architecture. Controlled, consecutive chain transfer reaction to 1,2‐bis(4‐vinylphenyl)ethane and hydrogen in metallocene‐mediated propylene polymerization catalyzed by rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ZrCl₂/MAO resulted in styryl‐terminated i‐PP (i‐PP‐t‐St) of controlled molecular weight. Following a regioselective hydrochlorination reaction, the terminal styryl groups were quantatively transformed to 1‐chloroethylbenzene groups, which was further reacted with NaN₃ to give i‐PP terminated with an azide group (i‐PP‐t‐N₃). Structural monitoring of the polymers through the whole transformation process using ¹H NMR and FTIR as well as GPC and DSC reveals a clean and clear formation of i‐PP‐t‐N₃ (M_n in between 10,000 and 40,000 g/mol). This clickable i‐PP building block was applied to a renewed, modular synthesis of amphiphilic i‐PP‐b‐PCL (poly(ε‐caprolactone)) diblock copolymers. Composition‐diversified, structure‐well defined diblock copolymers were obtained in high yields, confirming both the high end group selectivity as well as high reactivity of azide the clickable moiety in the i‐PP building block and the effectiveness of azide‐alkyne click reaction in constructing new i‐PP architecture. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Applications of iron and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 as a nanomagnetic catalyst for the chemoselective oxidation of sulfides to sulfoxides under solvent‐free conditions

In the present study, Fe²⁺ and Ni²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ (γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺) with a high surface area has been synthesized and characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and scanning electron microscope (SEM) techniques. Then, γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺ were used as a new and magnetically recoverable nano catalyst for the selective oxidation of sulfides to sulfoxides with 33% aqueous H₂O₂ (0.5 mL) as an oxidant at room temperature in good to excellent yields and short reaction time. Nontoxicity of reagent, mild reaction condition, inexpensive and high catalytic activity, simple experimental procedure, short period of conversion and excellent yields, and ease of recovery from the reaction mixture using an external magnet are the advantages of the present method.     

Improved and Efficient Synthesis of Chromeno[4,3‐d]pyrazolo [3,4‐b]pyridin‐6(3H)‐ones and Their Fluorescence Properties

A series of chromeno[4,3‐d]pyrazolo[3,4‐b]pyridin‐6(3H)‐one derivatives was easily and efficiently synthesized by the reaction of 2H‐chromen‐2‐ones with pyrazol‐5‐amines catalyzed by CuCl₂?2H₂O in ethanol. This protocol has the advantages of mild reaction conditions, easy work‐up, and high yields. These compounds were showed to have high fluorescence quantum yields, which mentioned their value as luminescence or fluorescence probe.     

Catalytic application of sulfonic acid‐functionalized titana‐coated magnetic nanoparticles for the preparation of 1,8‐dioxodecahydroacridines and 2,4,6‐triarylpyridines via anomeric‐based oxidation

We have developed green, efficient and powerful protocols for the preparation of 2,4,6‐triarylpyridines and 1,8‐dioxodecahydroacridines in the presence of Fe₃O₄@TiO₂@O₂PO₂(CH₂)₂NHSO₃H as a sulfonic acid‐functionalized titana‐coated magnetic nanoparticle catalyst under mild and solvent‐free reaction conditions. These protocols furnished the desired products in short reaction times with good to high yields (20–40 min and 80–86% in the case of 2,4,6‐triarylpyridines; 15–90 min and 80–93% in the case of 1,8‐dioxodecahydroacridines). The final step of the mechanistic route in the synthesis of 2,4,6‐triarylpyridines proceeds via an anomeric‐based oxidation. Also, the nanomagnetic core–shell catalyst can be recycled and reused in both cases of the scrutinized one‐pot multicomponent reactions with high turnover number and turnover frequency.     

Fe3O4@ZrO2/SO42‐: A recyclable magnetic heterogeneous nanocatalyst for synthesis of β‐amino carbonyl derivatives and synthesis of benzylamino coumarin derivatives through Mannich reaction

In the present work, we developed an effective protocol for the synthesis of β‐amino carbonyl compounds and synthesis of benzylamino coumarin derivatives through Mannich type reaction in high yields. Fe₃O₄@ZrO₂/SO₄^2‐ was employed as an effective heterogeneous nanocatalyst for the Mannich reaction. This research consists of two sections. In first section, β‐amino carbonyl derivatives were synthesized under solvent‐free condition. In the other section, benzylamino coumarin compounds were synthesized at room temperature. The present approach offers several advantages such as short reaction times, low cost, easy work‐up, mild reaction conditions, high yields and ease of recovery and reusability of the catalyst without significant loss of activity.     

The Origin of the Selectivity and Activity of Ruthenium‐Cluster Catalysts for Fuel‐Cell Feed‐Gas Purification: A Gas‐Phase Approach

Gas‐phase ruthenium clusters Ru_n⁺ (n=2–6) are employed as model systems to discover the origin of the outstanding performance of supported sub‐nanometer ruthenium particles in the catalytic CO methanation reaction with relevance to the hydrogen feed‐gas purification for advanced fuel‐cell applications. Using ion‐trap mass spectrometry in conjunction with first‐principles density functional theory calculations three fundamental properties of these clusters are identified which determine the selectivity and catalytic activity: high reactivity toward CO in contrast to inertness in the reaction with CO₂; promotion of cooperatively enhanced H₂ coadsorption and dissociation on pre‐formed ruthenium carbonyl clusters, that is, no CO poisoning occurs; and the presence of Ru‐atom sites with a low number of metal–metal bonds, which are particularly active for H₂ coadsorption and activation. Furthermore, comprehensive theoretical investigations provide mechanistic insight into the CO methanation reaction and discover a reaction route involving the formation of a formyl‐type intermediate.