Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

Preparation and surface characterization of Pt–Au/C cathode catalysts with ceria modification for oxygen reduction reaction

Alloy catalysts of Pt₅₀Au₅₀/Ce_xC with various Ce additions (x) were prepared for the oxygen reduction reaction (ORR). The characterization of the alloy structures, surface species, and electro-catalytic activities of prepared alloy catalysts were performed by XRD, temperature-programmed reduction (TPR), and rotating disc electrode (RDE) technique, respectively. The ORR activity of Pt₅₀Au₅₀/C alloy catalyst with a promotion of 15% CeO₂ was enhanced significantly in comparison to the commercial Pt/C catalyst within the mixed kinetic-diffusion control region. The addition of CeO₂ decreased the particle sizes, increased the dispersion and enhanced the surface segregation of Pt which resulting in an alloy surface with a moderate oxophilicity on alloy catalysts.     

Recent advances in oxidative C–C coupling reaction of amides with carbon nucleophiles

The C–C coupling reaction of N-electron withdrawing group (EWG) protected amides with coupling partners is one of the most important methods for C–C bond formation at the α-position of amides to directly give α-substituted amides. Of the four reactions, namely, the reaction via the generation of carbanion with an electrophile, that via the generation of carbon radical with a radical donor, that via the generation of iminium ion species with a nucleophile (oxidative coupling reaction), and that using a transition metal carbenoid, the oxidative coupling reaction presents a challenge although the reaction products are very useful for the transformation of a wide range of nitrogen-containing derivatives. In this review, recent developments in the oxidative coupling reaction of N-EWG protected amides with nucleophiles are summarized with focus on the reaction using a transition metal, the transition-metal-free reaction, the enantioselective reaction using a chiral catalysts, and the organocatalyzed oxidative coupling reaction.     

Platinum–titanium intermetallic nanoparticle catalysts for oxygen reduction reaction with enhanced activity and durability

A facile method to prepare Pt–Ti intermetallic nanoparticles supported on carbon was developed. Starting from a commercial Pt/C catalyst, TiO₂ layers were formed on the Pt/C then thermal annealing under a reducing condition successfully produced intermetallic Pt–Ti nanoparticles with an average size of 4.2 nm. The intermetallic Pt–Ti/C showed enhanced activity and durability for oxygen reduction reaction due to the change in electronic structure and less aggregation.     

Pt–Fe cathode catalysts to improve the oxygen reduction reaction and methanol tolerance in direct methanol fuel cells

High surface area carbon-supported Pt and bimetallic Pt–Fe catalysts are investigated for the oxygen electro-reduction reaction (ORR) in low-temperature direct methanol fuel cells (60 °C). The electrocatalysts are prepared using a combination of colloidal and incipient wetness methods allowing the synthesis of carbon-supported bimetallic nanoparticles with a particle size of about 2–3 nm. These materials are studied in terms of structure, morphology and composition using X-ray diffraction, X-ray fluorescence and transmission electron microscopy techniques. The electrocatalytic behaviour of these catalysts for ORR is investigated by employing the rotating disc technique. An enhancement of the ORR is observed with the bimetallic Pt–Fe catalyst in the oxygen-saturated electrolyte solution, with and without methanol. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Titanium hydride—a stable support for Pt catalysts in oxygen reduction reaction

A new class of conductive and dimensionally stable surface-modified TiH₂ particles prepared by ultra-sonication method is proposed as a non-carbon support for Pt catalysts. Thermal analysis results indicated good thermal stability of these materials at high temperatures in oxygen atmosphere. TiH₂ particles are discovered to be stable at potentials higher than 1.5 V in O₂-saturated H₂SO₄ solution. It is also found that the surface-modified TiH₂ exhibits a modest electrocatalytic activity toward oxygen reduction reaction. Accelerated durability measurements show that Pt catalysts supported on sonicated TiH₂ exhibited superior stability than standard Vulcan XC-72 carbon. High corrosion resistance and thermal stability render better chemical stability and structural integrity to surface-modified TiH₂ particles at elevated temperatures.     

Recent advances in the application of nanoparticles in the selective reduction of carbon–carbon double bonds

Herein, we present recent advances in the application of metal nanoparticles in the selective hydrogenation of C–C double bonds. The review focuses on reduction methods of alkenes, arenes, and aromatic heterocycles, which were classified according to transition metals used as catalysts. The majority of described systems concern direct hydrogenation, which is of particular importance to industrial processes. Nonetheless, interesting transfer hydrogenation protocols were also developed, which may be incredibly convenient for laboratory purposes. Some of the methods are distinguished with excellent chemoselectivity making them the perfect tool for the synthesis of compounds containing reducible functional groups. Apart from noble metals, the application of earth-abundant ones as catalysts was a subject of studies, and the related methods were highlighted.     

Metal-organic-framework-derived formation of Co–N-doped carbon materials for efficient oxygen reduction reaction

Non-precious metal nitrogen-doped carbonaceous materials have attracted tremendous attention in the field of electrochemical energy storage and conversion. Herein, we report the designed synthesis of a novel series of Co-N-C nanocomposites and their evaluation of electrochemical properties. Novel yolkshell structured Co nanoparticles@polymer materials are fabricated from the facile coating polymer strategy on the surface of ZIF-67. After calcination in nitrogen atmosphere, the Co–N–C nanocomposites in which cobalt metal nanoparticles are embedded in the highly porous and graphitic carbon matrix are successfully achieved. The cobalt nanoparticles containing cobalt metal crystallites with an oxidized shell and/or smaller(or amorphous) cobalt-oxide deposits appear on the surface of graphitic carbons. The prepared Co–N–C nanoparticles showed favorable electrocatalytic activity for oxygen reduction reactions,which is attributed to its high graphitic degree, large surface area and the large amount existence of Co–N active sites.     

Effect of de-alloying of Pt–Ni bimetallic nanoparticles on the oxygen reduction reaction

Carbon-supported Pt–Ni alloy nanoparticles with various compositions were prepared by a borohydride reduction method in anhydrous ethanol solvent. Here, we surveyed effect of thermally induced de-alloying on activity of the oxygen reduction reaction (ORR). Especially, changes in surface and bulk structures were investigated through electrochemical and spectroscopic measurements. The activity of as-prepared Pt–Ni alloy nanoparticles showed a monotonous dependence on Pt content. However, heat-treatment induced the phase separation between Pt and NiO and the resultant enhancement in ORR activity without significant increase in surface Pt concentration.     

Recent developments of heterogeneous solid catalysts for liquid-phase Friedel–Crafts type benzylation reaction

Liquid-phase Friedel–Crafts type benzylation of aromatics has been effected traditionally with catalysis by homogeneous protonic acid or Lewis acid. However, heterogeneous catalysts have the advantages, compared to their homogeneous counterparts, of facile recovering and recycling. This short article describes the recent advances in the liquid-phase Friedel–Crafts type benzylation by benzyl chloride of aromatics over redox metal: gallium (Ga), indium (In) and thallium (Tl) containing novel heterogeneous solid catalysts. Unlike conventional acidic catalyst, the benzylation activity of the Ga-, In- or Tl-based solids does not depend solely on their acidic properties, even present; these solids in their non-acidic or basic form also shows high benzylation activity. The catalytic activity order of Ga, In and Tl containing solid catalysts supported on chemically similar inert catalyst carrier is as follows: thallium/support > indium/support > gallium/support, which is quite similar to their redox potential values indicating the role of redox function in the benzylation process. A plausible reaction mechanism for the benzylation reaction over these catalysts is proposed. These heterogeneous solids are highly efficient for the Friedel–Crafts type benzylation, even in the presence of moisture, than the conventional strongly acidic solid acid catalysts.Dedicated to Dr.Vasanth R. Choudhary, National Chemical Laboratory, Pune, India     

Promotion of lanthanum-supported cobalt-based catalysts for the Fischer–Tropsch reaction

This paper focuses on the effect of the La/Co ratio on the structure of alumina cobalt supported catalysts for Fischer–Tropsch synthesis. Catalysts are prepared by wetness impregnation of alumina followed by calcination in air. The catalysts contain 10 wt% of cobalt and between 0 and 20 wt% of La (0, 5, 10, 15, 20). The catalysts were activated by reduction in hydrogen at 673 K and the catalytic performance was evaluated in a fixed bed reactor at 20 bar and 493 K. A wide range of techniques (BET, XRD, TPR, and XPS) were used for catalyst characterization at each preparation step and showed strong impact of the La/Co ratio on the structure, reducibility of supported cobalt phases. It was shown that 10 wt% of lanthanum allows reducing cobalt aluminate and improving catalytic performances.     

Effect of supports on activity and stability of Pt–Pd catalysts for oxygen reduction reaction in proton exchange membrane fuel cells

The platinum–palladium alloy (Pt–Pd) catalysts were prepared on various supports including Vulcan XC72, Hicon Black (HB), multiwalled carbon nanotubes (MWCNTs), and titanium dioxide (TiO₂) by a combined approach of impregnation and seeding using NaBH₄ reduction at low temperature. Their oxygen reduction reaction (ORR) activities in single proton exchange membrane fuel cell (PEMFC) under a H₂/O₂ environment and their stability in an acid electrolyte (0.5 M H₂SO₄) were tested and compared with the Vulcan XC72-supported Pt (Pt/C) catalysts. The presence of the Pd metal as well as different types of supports affected the ORR activity in H₂/O₂ environment and stability in the acid electrolyte. Overall, the HB-supported Pt–Pd (Pt–Pd/HB) catalysts provided the highest current density at 0.6 V under a H₂/O₂ environment, while the MWCNT-supported Pt–Pd (Pt–Pd/MWCNT) catalyst provided the best stability in an acid electrolyte.     

Utility of oxidation–reduction reaction for the spectrophotometric determination of amlodipine besylate

A simple, rapid, accurate, precise and sensitive spectrophotometric method for the determination of amlodipine besylate (ADB) in bulk sample and in dosage forms is described. The method is based on oxidation of the drug by potassium permanganate in acidic medium and determine the unreacted oxidant by measuring the decrease in absorbance for five different dyes; methylene blue (MB), acid blue 74 (AB), acid red 73 (AR), amaranth dye (AM) and acid orange 7 (AO) at a suitable λ_max 663, 609, 511, 520, and 484 nm, respectively. Regression analysis of Beer's law plots showed good correlation in the concentration ranges 1.0–24, 0.9–22, 1.2–26, 0.9–12.8 and 1.0–14 μg ml^?1, respectively. The apparent molar absorptivity, Sandell sensitivity, detection and quantitation limits were calculated. For more accurate results, Ringbom optimum concentration ranges were 1.2–22.4, 1.1–20, 1.4–24.5, 1.0–12.3 and 1.3–13.2 μg ml^?1, respectively. Statistical treatment of the results reflects that the proposed procedures are precise, accurate and easily applicable for the determination of amlodipine besylate in pure form and in pharmaceutical preparations.     

Recent advances of intermolecular Diels–Alder reaction in bio-inspired synthesis of natural products

The Diels–Alder(D–A)reaction is one of the most powerful reactions in organic synthesis.The intermolecular D–A reaction attracts much less attentions than its intramolecular counterpart in natural product synthesis,possibly due to the issues of reactivity and selectivity.In the past decade,the intermolecular D–A reaction has been increasingly utilized in the total synthesis of structurally complex natural products.In this article,we present a few examples for the elegant applications of the intermolecular D–A reaction that are inspired by biosynthetic hypotheses of the target natural products.These examples demonstrate that D–A reaction is not only useful for preparing building blocks but also powerful for coupling structurally complicated and sterically demanding segments in a highly chemo-and stereo-controlled fashion,which may inspire further developments of intermolecular D–A reaction from both strategy and methodology perspectives.     

“Confinement effects for nano-electrocatalysts for oxygen reduction reaction”

Oxygen reduction reaction (ORR) is one of the most technologically relevant reactions. It occurs at the interface of the electrocatalyst and electrolyte, where oxygen reacts with protons and electrons to produce water. Because the electrocatalyst is dispersed on a high surface area support, morphological confinement becomes critical, as it dictates proton and oxygen transport. Furthermore, confinement is induced by ionomer, ionic liquids (ILs), or molecular additives, and their impact on electrocatalyst reactivity and transport properties is currently not well understood. We present an overview of electrostatics and mass transport–induced confinement and zoom in into ILs and molecular additives and try to unravel how local confinement induced by them impacts ORR.     

Recent advances in reaction of organolanthanides containing the N−H bonds with unsaturated organic small molecules

This article is intended to provide an overview on recent progress in the reaction chemistry of organolanthanide complexes with the nitrogen–hydrogen bonds toward a series of unsaturated organic small molecules. The synthesis, stoichiometric and catalytic reactions of these complexes are described.     

Effect of acid treatment of Corich core–Ptrich shell/C electrocatalyst on oxygen reduction reaction

Co_{rich core}–Pt_{rich shell}/C prepared by thermal decomposition and chemical reduction methods were treated by 20% H₂SO₄ aqueous solution and used as the electrocatalysts for the oxygen reduction reaction (ORR). The particle size range of Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1) on carbon powder support decreased from 3–8 to 1–6 nm when the time for the electrocatalysts immersed and treated with 20% H₂SO₄ aqueous solution increased from 0 to 4 h. Using Co_{rich core}–Pt_{rich shell} (molar ratio of 0.92:1)/C treated with 20% H₂SO₄ from 0 to 4 h as the working electrode, the open circuit potential of ORR in 0.5 M HClO₄ aqueous solution increased from 0.9995 to 1.0155 V, and the current density, mass activity, and specific activity at the overpotential of 0.1 V increased from 0.619 mA cm^?2, 6.184 A g^?1, and 18.614 μA cm^?2 to 0.912 mA cm^?2, 15.544 A g^?1, and 23.413 μA cm^?2, respectively.     

Fe–N/C nanofiber electrocatalysts with improved activity and stability for oxygen reduction in alkaline and acid solutions

Fe–N/C nanofiber (Fe–N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO₃)₃) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH?=?13) and 0.5 M H₂SO₄ (pH?=?0) electrolyte solutions. Higher treatment temperature and NH₃ atmosphere were preferred by the Fe–N/CNF catalysts, and especially the concentration of Fe(NO₃)₃ solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe–N/CNFs prepared using 0.5 wt% Fe(NO₃)₃ solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H₂SO₄ solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe–N/CNF catalysts.