(Z)-Selective Partial Hydrogenation of Internal Alkynes by Using Palladium Nanoparticles Supported on Nitrogen-Doped Carbon Nanofiber

Recent Developments in Carbon-Based Nanocomposites for Fuel Cell Applications: A Review

Carbon-based nanocomposites have developed as the most promising and emerging materials in nanoscience and technology during the last several years. They are microscopic materials that range in size from 1 to 100 nanometers. They may be distinguished from bulk materials by their size, shape, increased surface-to-volume ratio, and unique physical and chemical characteristics. Carbon nanocomposite matrixes are often created by combining more than two distinct solid phase types. The nanocomposites that were constructed exhibit unique properties, such as significantly enhanced toughness, mechanical strength, and thermal/electrochemical conductivity. As a result of these advantages, nanocomposites have been used in a variety of applications, including catalysts, electrochemical sensors, biosensors, and energy storage devices, among others. This study focuses on the usage of several forms of carbon nanomaterials, such as carbon aerogels, carbon nanofibers, graphene, carbon nanotubes, and fullerenes, in the development of hydrogen fuel cells. These fuel cells have been successfully employed in numerous commercial sectors in recent years, notably in the car industry, due to their cost-effectiveness, eco-friendliness, and long-cyclic durability. Further; we discuss the principles, reaction mechanisms, and cyclic stability of the fuel cells and also new strategies and future challenges related to the development of viable fuel cells.

Synthesis of alkynamides through reaction of alkyl- or aryl-substituted alkynylaluminums with isocyanates

An efficient and facile method for the preparation of alkynamides through Et₃N-catalyzed alumination of alkyl- or aryl-substituted terminal alkynes with AlMe₃ and sequential nucleophilic addition of in situ generated alkynylaluminums to isocyanates is described. This method has the merits of using readily available isocyanates and monosubstituted alkynes, easy access to organoaluminums, short reaction times, and high efficiency. A gram-scale synthesis of the desired alkynamide and its application to the formation of α-methylene-β-lactams demonstrates the synthetic utility of this method.

Click Nucleophilic Conjugate Additions to Activated Alkynes: Exploring Thiol-yne, Amino-yne, and Hydroxyl-yne Reactions from (Bio)Organic to Polymer Chemistry

The 1,4-conjugate addition reaction between activated alkynes or acetylenic Michael acceptors and nucleophiles (i.e., the nucleophilic Michael reaction) is a historically useful organic transformation. Despite its general utility, the efficiency and outcomes can vary widely and are often closely dependent upon specific reaction conditions. Nevertheless, with improvements in reaction design, including catalyst development and an expansion of the substrate scope to feature more electrophilic alkynes, many examples now present with features that are congruent with Click chemistry. Although several nucleophilic species can participate in these conjugate additions, ubiquitous nucleophiles such as thiols, amines, and alcohols are commonly employed and, consequently, among the most well developed. For many years, these conjugate additions were largely relegated to organic chemistry, but in the last few decades their use has expanded into other spheres such as bioorganic chemistry and polymer chemistry. Within these fields, they have been particularly useful for bioconjugation reactions and step-growth polymerizations, respectively, due to their excellent efficiency, orthogonality, and ambient reactivity. The reaction is expected to feature in increasingly divergent application settings as it continues to emerge as a Click reaction.

Aqueous phase semihydrogenation of alkynes over Ni–Fe bimetallic catalysts

Bimetallic Ni–Fe catalysts (Ni/Fe, 1 : 1, 1 : 3, and 3 : 1) are synthesized and explored for their catalytic activity in semihydrogenation of internal alkynes using H₂ gas in water–ethanol solution.

Indium- and zinc-catalyzed enantioselective amide propargylation of aldehydes with stannylated allenyl amides

The catalytic enantioselective propargylation of aldehydes with newly prepared stannyl allenyl amides is described. The reaction has been accomplished by using catalytic amounts of indium chloride, zinc chloride, and a chiral BINOL derivative, affording amide-functionalized homopropargyl alcohols in excellent yields and enantioselectivities.

Palladium-Catalyzed Three-Component Reaction: A Novel Method for the Synthesis of N-Acyl Propiolamides

Palladium-catalyzed three-component reactions between terminal alkynes, isonitriles, and sodium carboxylates have been developed. This novel and operationally simple methodology provides an alternative for the synthesis of N-acyl propiolamide derivatives under mild conditions using isonitriles as the amine source and sodium carboxylates as the oxygen and acyl source.

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

The catalytic partial hydrogenation of substituted alkynes to alkenes is a process of high importance in the manufacture of several market chemicals. The present paper shortly reviews the heterogeneous catalytic systems engineered for this reaction under continuous flow and in the liquid phase. The main contributions appeared in the literature from 1997 up to August 2016 are discussed in terms of reactor design. A comparison with batch and industrial processes is provided whenever possible.

Preparation of Partially Poisoned Alkanethiolate-Capped Platinum Nanoparticles for Hydrogenation of Activated Terminal Alkynes

Stable and isolable alkanethiolate-stabilized Pt nanoparticles (PtNP) were synthesized using the two-phase thiosulfate method with sodium S-alkylthiosulfate as ligand precursor. The mechanistic formation of octanethiolate-capped PtNP (Pt-SC₈) from both sodium S-octylthiosulfate and 1-octanethiol ligands was investigated by using ¹H NMR and UV-vis spectroscopies, which revealed the formation of different Pt complexes as the reaction intermediates. The synthesis using S-octylthiosulfate ligand precursor produced Pt-SC₈ in higher yields than that using 1-octanethiol ligand. The obtained nanoparticles were characterized by ¹H NMR, UV-vis spectroscopy, infrared spectroscopy (IR), thermogravimetric analysis, and transmission electron microscopy (TEM). The results obtained from ¹H NMR, IR, and UV-vis spectroscopy were consistent with the formation of stable and pure alkanethiolate-capped PtNP. TEM images of PtNP confirmed their small average core size (∼1.5 nm) and high monodispersity. The partially poisoned PtNP with thiolate monolayer ligands were further investigated for the hydrogenation of various alkynes to understand the organic ligands-induced geometric and electronic surface properties of colloidal Pt nanoparticle catalysts. The high catalytic activity of activated terminal alkynes, but the significantly low activity of internal alkynes and unactivated terminal alkynes, were observed under the mild reaction conditions (room temperature and atmospheric pressure). These results indicated that the presence of alkanethiolate ligands could decrease the coordination activity of PtNP surface especially for the bulkier and unactivated substrates.

Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1-0.5MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.

Palladium-Catalyzed Oxidative N-Dealkylation/Carbonylation of Tertiary Amines with Alkynes to α,β-Alkynylamides

The first highly effective Pd/C-catalyzed oxidative N-dealkylation/carbonylation of various aliphatic as well as cyclic tertiary amines with alkynes has been described. The selective sp(3) C-N bond activation of tertiary amines at the less steric side using O2 as a sole oxidant and a plausible reaction pathway for the reaction are discussed. The general and operationally simple methodology provides an alternative for the synthesis of a wide range of alk-2-ynamide derivatives under mild conditions. The present protocol is ecofriendly and practical, and it shows significant recyclability.

Continuous-Flow Synthesis of Deuterium-Labeled Antidiabetic Chalcones: Studies towards the Selective Deuteration of the Alkynone Core

Flow chemistry-based syntheses of deuterium-labeled analogs of important antidiabetic chalcones were achieved via highly controlled partial C≡C bond deuteration of the corresponding 1,3-diphenylalkynones. The benefits of a scalable continuous process in combination with on-demand electrolytic D2 gas generation were exploited to suppress undesired over-reactions and to maximize reaction rates simultaneously. The novel deuterium-containing chalcone derivatives may have interesting biological effects and improved metabolic properties as compared with the parent compounds.

Nitrogen-doped porous carbon materials: promising catalysts or catalyst supports for heterogeneous hydrogenation and oxidation

Developing novel and efficient catalysts is a critical step in common heterogeneous hydrogenation and oxidation reactions.