Catalyst as colour indicator for endpoint detection to enable selective alkyne trans-hydrogenation with ethanol

Methyl Formate, an Alternative Transfer Hydrogenating Agent for Chemoselective Reduction of N-Heteroarenes and Azoarenes

The search for efficient molecular hydrogen precursors and their catalytic exploration is necessary for the evolution of catalytic transfer hydrogenation. Methyl formate (MF) having high hydrogen content still remains unexplored for such transformations. Herein, we disclosed a bifunctional Ir(III)-complex catalyzed chemoselective TH protocol for N-heteroarenes and azoarenes using MF. A variety of substrates including ten bioactive molecules have been synthesized under mild reaction conditions. A probable mechanistic pathway was proposed based on control experiments and mechanistic studies.

Electrochemical hydrogenation and oxidation of organic species involving water

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactions involving water are summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Recent advances in the selective semi-hydrogenation of alkyne to (E)-olefins

Considering the potential importance and upsurge in demand, the selective semi-hydrogenation of alkynes to (E)-olefins has attracted significant interest. This article highlights the recent advances in newer technologies and important methodologies directed to (E)-olefins from alkynes developed from 2015 to 2023. Notable features summarised include the catalyst or ligand design and control of product selectivity based on precious and nonprecious metal catalysts for semi-hydrogenation to (E)-olefins. Mechanistic studies for various catalytic transformations, including synthetic application to bioactive compounds, are summarised.

Air-Stable Coordinatively Unsaturated Ruthenium(II) Complex for Ligand Binding and Catalytic Transfer Hydrogenation of Ketones from Ethanol

Coordinatively unsaturated complexes are interesting from a fundamental level for their formally empty coordination site and, in particular, from a catalytic perspective as they provide opportunities for substrate binding and transformation. Here, we describe the synthesis of a novel underligated ruthenium complex [Ru(cym)(N,N')]+, 3, featuring an amide-functionalized pyridylidene amide (PYA) as the N,N'-bidentate coordinating ligand. In contrast to previously investigated underligated complexes, complex 3 offers potential for dynamic modifications, thanks to the flexible donor properties of the PYA ligand. Specifically, they allow both for stabilizing the formally underligated metal center in complex 3 through nitrogen π-donation and for facilitating through π-acidic bonding properties the coordination of a further ligand L to the ruthenium center to yield the formal 18 e- complexes [Ru(cym)(N,N')(L)]+ (4: L = P(OMe)3; 5: L = PPh3; 6: L = N-methylimidazole; 7: L = pyridine) and neutral complex [RuCl(cym)(N,N')] 8. Analysis by 1H NMR and UV-vis spectroscopies reveals an increasing Ru-L bond strength along the sequence pyridine <1-methylimidazole < PPh3 < P(OMe)3 with binding constants varying over 3 orders of magnitude with log(Keq) values between 2.8 and 5.7. The flexibility of the Ru(PYA) unit and the ensuing accessibility of saturated and unsaturated species with one and the same ligand are attractive from a fundamental point of view and also for catalytic applications, as catalytic transformations rely on the availability of transiently vacant coordination sites. Thus, while complex 3 does not form stable adducts with O-donors such as ketones or alcohols, it transiently binds these species, as evidenced by the considerable catalytic activity in the transfer hydrogenation of ketones. Notably, and as one of only a few catalysts, complex 3 is compatible with EtOH as a hydrogen source. Complex 3 shows excellent performance in the transfer hydrogenation of pyridyl-containing substrates, in agreement with the poor coordination strength of this functional group to the ruthenium center in 3.

Protocol for (E)-selective semihydrogenation of alkynes using iridium-based catalyst

In this protocol, we describe highly (E)-selective alkyne semihydrogenation employing commercially available iridium complex and a bidentate phosphine ligand. We provide steps for (E)-stilbene synthesis, remaining formic acid neutralization, and determination of the (Z)/(E) ratio using gas chromatography analysis. We then detail (E)-stilbene purification using a short pad of silica and NMR analysis. The protocol is compatible with a wide range of functionalities and different types of alkynes. For complete details on the use and execution of this protocol, please refer to Kusy et al. (2022).1.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

Optical detection of alcohols with a Cu(I)HETPHEN complex by reversible aldehyde to hemiacetal conversion

A heteroleptic copper(I) bis(phenanthroline) complex with aldehyde groups at the 4,7 positions of the phenanthroline ligand was synthesized. The complex is responsive to alcohol, resulting in a distinct colour change caused by the facile reaction of the aldehyde group with alcohol, forming a hemiacetal product. The aldehyde species can be regenerated after heating the intermediate at 80 °C for 10 minutes, demonstrating the reusability of the complex for alcohol detection. This work presents a new strategy for applying transition metal complexes in small molecule sensing by installing functional groups in the secondary coordination sphere which reversibly react with analytes.

Fluorescent α-amino acids via Heck-Matsuda reactions of phenylalanine-derived arenediazonium salts

The Heck-Matsuda coupling reaction of arenediazonium salts derived from L-phenylalanine with various alkenes has been developed. A two-step process involving the preparation of a tetrafluoroborate diazonium salt from a 4-aminophenylalanine derivative, followed by a palladium(0)-catalysed Heck-Matsuda coupling reaction allowed access to a range of unnatural α-amino acids with cinnamate, vinylsulfone and stilbene side-chains. Analysis of the photophysical properties of these unnatural α-amino acids demonstrated that the (E)-stilbene analogues exhibited fluorescent properties with red-shifted absorption and emission spectra and larger quantum yields than L-phenylalanine.

Designed Nanomaterials for Electrocatalytic Organic Hydrogenation Using Water as the Hydrogen Source

ConspectusThe hydrogenation reaction is one of the most frequently used transformations in organic synthesis. Electrocatalytic hydrogenation by using water (H₂O) as the hydrogen source offers an efficient and sustainable approach to synthesize hydrogenated products under ambient conditions. Such a technique can avoid the use of high-pressure and flammable hydrogen gas or other toxic/expensive hydrogen donors, which usually cause environmental, safety, and cost concerns. Interestingly, utilizing easily available heavy water (D₂O) for deuterated syntheses is also attractive due to the widespread applications of deuterated molecules in organic synthesis and the pharmaceutical industry. Despite impressive achievements, electrode selection mainly relies on trial-and-error modes, and how electrodes dictate reaction outcomes remains elusive. Therefore, the rational design of nanostructured electrodes for driving the electrocatalytic hydrogenation of a series of organics via H₂O electrolysis is developed.In this Account, we review recent advances in the electrocatalytic hydrogenation of different types of organic functional groups, including C≡C, C≡N, C═C, C═O, and C-Br/I bonds, -NO₂, and N-heterocycles, with H₂O over nanostructured cathodes. First, the general reaction steps (reactant/intermediate adsorption, active atomic hydrogen (H*) formation, surface hydrogenation reaction, product desorption) are analyzed, and key factors are proposed to optimize hydrogenation performance (e.g., selectivity, activity, Faradaic efficiency (FE), reaction rate, and productivity) and inhibit side reactions. Then, ex situ and in situ spectroscopic tools to study key intermediates and interpret mechanisms are introduced. Third, based on the knowledge of key reaction steps and mechanisms, we introduce catalyst design principles in detail on how to optimize the adoption of reactants and key intermediates, promote the formation of H* from water electrolysis, inhibit hydrogen evolution and side reactions, and improve the selectivity, reaction rate, FEs, and space-time productivity of products. We then introduce some typical examples. (i) P- and S-modified Pd can decrease C═C adsorption and promote H* formation, enabling semihydrogenation of alkynes with high selectivity and FEs at lower potentials. Then, creating high-curvature nanotips to concentrate the substrates further speeds up the hydrogenation process. (ii) By introducing low-coordination sites into Fe and combining low-coordination sites and surface fluorine to modify Co to optimize the adsorption of intermediates and facilitate H* formation, hydrogenation of nitriles and N-heterocycles with high activity and selectivity is obtained. (iii) By forming isolated Pd sites to induce a specific σ-alkynyl adsorption of alkynes and steering S vacancies of Co₃S_4-x to preferentially adsorb -NO₂, hydrogenation of easily reduced group-decorated alkynes and nitroarenes with high chemoselectivity is realized. (iv) For gas reactant participated reactions, by designing hydrophobic gas diffusion layer-supported ultrasmall Cu nanoparticles to enhance mass transfer, improve H₂O activation, inhibit H₂ formation, and decrease ethylene adsorption, ampere-level ethylene production with a 97.7% FE is accomplished. Finally, we provide an outlook on the current challenges and promising opportunities in this area. We believe that the electrode selection principles summarized here provide a paradigm for designing highly active and selective nanomaterials to achieve electrocatalytic hydrogenation and other organic transformations with fascinating performances.

H2O as the Hydrogen Donor: Stereo-Selective Synthesis of E- and Z-Alkenes by Palladium-Catalyzed Semihydrogenation of Alkynes

It is very desirable to develop a facile controllable method for selective semihydrogenation of alkynes to alkenes with a cheap and safe hydrogen donor but remains a big challenge. H₂O is one of the best choices of the transfer hydrogenation agent of the world, and the development of methods for synthesizing E- and Z-alkenes using H₂O as the hydrogen source is worthwhile. In this article, a palladium-catalyzed synthesis of E- and Z-alkenes from alkynes using H₂O as the hydrogenation agent was reported. The use of di-tert-butylphosphinous chloride (t-Bu₂PCl) and triethanolamine/sodium acetate (TEOA/NaOAc) was essential for the stereo-selective semihydrogenation of alkynes. The general applicability of this procedure was highlighted by the synthesis of more than 48 alkenes, with good yields and high stereoselectivities.

Modulation of metal species as control point for Ni-catalyzed stereodivergent semihydrogenation of alkynes with water

A base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent transfer semihydrogenation of alkynes with water, delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives. Different from most precedents, in which E-alkenes derive from the isomerization of Z-alkene products, the isomers were formed in orthogonal catalytic pathways. Mechanistic studies suggest base as a key early element in modulation of the reaction pathways: by adding different bases, nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers. The practicability of the method is showcased with nearly 70 examples, including internal and terminal triple bonds, enynes and diynes, affording semi-hydrogenated products in high yields and selectivity.

Structural snapshots of an Al-Cu bond-mediated transformation of terminal acetylenes

The copper(i) alumanyl derivative, [{SiN^Dipp}Al-Cu(NHC^iPr)] (SiN^Dipp = {CH₂SiMe₂NDipp}₂; Dipp = 2,6-di-isopropylphenyl; NHC^iPr = N,N'-di-isopropyl-4,5-dimethyl-2-ylidene), reacts in a stepwise fashion with up to three equivalents of various terminal alkynes. This reactivity results in the sequential formation of cuprous (hydrido)(alkynyl)aluminate, (alkenyl)(alkynyl)aluminate and bis(alkynyl)aluminate derivatives, examples of which have been fully characterised. The process of alkene liberation resulting from the latter reaction step constitutes a unique case of alkyne transfer semi-hydrogenation in which the C-H acidic alkyne itself acts as a source of proton, with the Cu-Al bond providing the requisite electrons to effect reduction. This reaction sequence is validated by DFT calculations, which rationalise the variable stability of the initially formed heterobimetallic hydrides.

Advances in Selective Electrocatalytic Hydrogenation of Alkynes to Alkenes

Selective electrochemical hydrogenation of alkynes to alkenes under ambient conditions is a promising alternative to the traditional energy-intensive and high-cost thermocatalytic hydrogenation. However, the systematic summary on the electrocatalysts and electrolyzers remains lacked. Herein, we demonstrate a comprehensive review about recent achievements in the electrocatalysts including noble metal and non-noble-metal materials. Several effective strategies of catalyst design were developed to improve alkyne conversion, and alkene selectivity, for example, accelerating the formation of active hydrogen species, enhancing alkyne adsorption and suppressing the side reactions. Furthermore, the advantages and disadvantages of various electrolyzers are systematically discussed. Accordingly, major challenges and future trends in this field are proposed.

E-selective Semi-hydrogenation of Alkynes under Mild Conditions by a Diruthenium Hydride Complex

The synthesis, characterization and catalytic activity of a new class of diruthenium hydrido carbonyl complexes bound to the tBu PNNP expanded pincer ligand is described. Reacting tBu PNNP with two equiv of RuHCl(PPh3 )3 (CO) at 140 °C produces an insoluble air-stable complex, which was structurally characterized as [Ru2 (tBu PNNP)H(μ-H)Cl(μ-Cl)(CO)2 ] (1) using solid-state NMR, IR and X-ray absorption spectroscopies and follow-up reactivity. A reaction with KOtBu results in deprotonation of a methylene linker to produce [Ru2 (tBu PNNP* )H(μ-H)(μ-OtBu)(CO)2 ] (3) featuring a partially dearomatized naphthyridine core. This enables metal-ligand cooperative activation of H2 analogous to the mononuclear analogue, [Ru(tBu PNP*)H(CO)]. In contrast to the mononuclear system, the bimetallic analogue 3 catalyzes the E-selective semi-hydrogenation of alkynes at ambient temperature and atmospheric H2 pressure with good functional group tolerance. Monitoring the semi-hydrogenation of diphenylacetylene by 1 H NMR spectroscopy shows the intermediacy of Z-stilbene, which is subsequently isomerized to the E-isomer. Initial findings into the mode of action of this system are provided, including the spectroscopic characterization of a polyhydride intermediate and the isolation of a deactivated species with a partially hydrogenated naphthyridine backbone.

Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor

A ligand-promoted, palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor is developed. The chemical selectivity control is achieved based on ligand regulation. The use of triethanolamine and tetrahydrofuran at 80 °C under N2 is found to be critical for the transfer hydrogenation of terminal alkynes. The general applicability of this procedure is highlighted by the synthesis of 27 terminal alkenes in moderate to good yields.

σ-Alkynyl Adsorption Enables Electrocatalytic Semihydrogenation of Terminal Alkynes with Easy-Reducible/Passivated Groups over Amorphous PdSx Nanocapsules

Highly chemo- and regioselective semihydrogenation of alkynes is significant and challenging for the synthesis of functionalized alkenes. Here, a sequential self-template method is used to synthesize amorphous palladium sulfide nanocapsules (PdS_x ANCs), which enables electrocatalytic semihydrogenation of terminal alkynes in H₂O with excellent tolerance to easily reducible groups (e.g., C-I/Br/Cl, C═O) and the metal center deactivating skeletons (e.g., quinolyl, carboxyl, and nitrile). Mechanistic studies demonstrate that specific σ-alkynyl adsorption via terminal carbon and negligible alkene adsorption on isolated Pd²⁺ sites ensure successful synthesis of various alkenes with outstanding time-irrelevant selectivity in a wide potential range. The key hydrogen and carbon radical intermediates are validated by electron paramagnetic resonance and high-resolution mass spectrometry. Gram-scale synthesis of 4-bromostyrene and expedient preparation of deuterated alkene precursors and drugs with D₂O show promising applications. Impressively, PdS_x ANCs can be applied to the prevailing thermocatalytic semihydrogenation of functionalized alkyne using H₂.

A New Paradigm in Pincer Iridium Chemistry: PCN Complexes for (De)Hydrogenation Catalysis and Beyond

The discovery and development of organometallic catalysts is of paramount importance in modern organic synthesis, among which the ligand scaffolds play a crucial role in controlling the activity and selectivity. Over the past several decades, d⁸ transition-metal complexes of pincer ligands have been developed extensively thanks to their easy structural modification, versatile reactivities, and high stability. One paradigm is the bis(phosphine)-based pincer iridium complexes PCP-Ir, which are highly active for alkane dehydrogenation, partly due to their high thermostability. However, except for alkane dehydrogenation and related transformations, few applications of pincer iridium catalysis have been seen in organic synthesis. This mainly arises from the low functional-group compatibility and poor substrate scope and the limited catalytic chemistry that invariably involves Ir(I/III) redox processes initiated by oxidative addition of substrates to 14-electron (PCP)Ir fragments (the proposed catalytically active intermediates). In this Account, we describe our endeavor on the development of a new family of PCN-Ir complexes with initial intention on creating more efficient alkane dehydrogenation catalysts. The replacement of a soft, σ-donor phosphine arm in the PCP ligands by a harder, π-acceptor N-heteroarene (pyridine or oxazoline) not only provides an additional platform to modify the structural properties but also offers new modes of bond activation and novel reactivities and catalysis. One uniqueness of the PCN-Ir system lies in the formation, via ortho-C(sp²)-H cyclometalation of the pyridine unit in the PCN_Py ligand, of the neutral monohydride (PCC)Ir^IIIHL (L = neutral ligand), which catalyzes positional and stereoselective 1-alkene-to-(E)-2-alkene isomerization. Moreover, the PCN-Ir catalysts effect ethanol dehydrogenation without decarbonylation, allowing for transfer hydrogenation of unactivated alkenes and trans-selective semihydrogenation of internal alkynes with user-friendly ethanol as the H-donor. Another feature originates from the ability of the pentacoordinate hydrido chloride complex (PCN)Ir^IIIHCl to undergo reversible solvent-coordination-induced-ionization (SCII), furnishing a cationic monohydride [(PCN)Ir^IIIH(Sol)]⁺Cl^- bearing an uncoordinated Cl anion that effects selective hydrometalation of internal alkynes over the corresponding (Z)-alkenes; the resulting (PCN)Ir^III(vinyl)Cl complex undergoes amine-assisted formal alcoholysis involving the protonation of the Cl anion by the activated Ir^III-bound EtOH, again via the SCII pathway. Together these elementary reactions lay the foundation for cis-selective semihydrogenation of alkynes with EtOH. Further, the design of the oxazoline-containing chiral complexes (PCN_Oxa)Ir^IIIHCl enables asymmetric transfer hydrogenation of alkenes/ketones with ethanol. The efficient catalytic α-alkylation of unactivated esters/amides with alcohols is another case showing the benefit that the PCN-Ir catalyst can offer. These examples illustrate the profound impact of the pincer ligands on the reactivities and catalysis. We hope this Account will provide an in-depth view into the fundamentals of pincer iridium chemistry and ultimately broaden its applications in organic synthesis.

Controlled Selectivity through Reversible Inhibition of the Catalyst: Stereodivergent Semihydrogenation of Alkynes

Catalytic semihydrogenation of internal alkynes using H2 is an attractive atom-economical route to various alkenes, and its stereocontrol has received widespread attention, both in homogeneous and heterogeneous catalyses. Herein, a novel strategy is introduced, whereby a poisoning catalytic thiol is employed as a reversible inhibitor of a ruthenium catalyst, resulting in a controllable H2-based semihydrogenation of internal alkynes. Both (E)- and (Z)-alkenes were obtained efficiently and highly selectively, under very mild conditions, using a single homogeneous acridine-based ruthenium pincer catalyst. Mechanistic studies indicate that the (Z)-alkene is the reaction intermediate leading to the (E)-alkene and that the addition of a catalytic amount of bidentate thiol impedes the Z/E isomerization step by forming stable ruthenium thiol(ate) complexes, while still allowing the main hydrogenation reaction to proceed. Thus, the absence or presence of catalytic thiol controls the stereoselectivity of this alkyne semihydrogenation, affording either the (E)-isomer as the final product or halting the reaction at the (Z)-intermediate. The developed system, which is also applied to the controllable isomerization of a terminal alkene, demonstrates how metal catalysis with switchable selectivity can be achieved by reversible inhibition of the catalyst with a simple auxiliary additive.

Iridium-Catalyzed Selective trans-Semihydrogenation of 1,3-Enynes with Ethanol: Access to (E,E)-1,4-Diarylbutadienes

A trans-semihydrogenation of 1,3-enynes with ethanol as the hydrogen source was developed using a new (PCN)Ir complex as the precatalyst and tBuNH₂ as the cocatalyst. This catalyst system provides an efficient and atom-economical access to unsymmetrical (E,E)-1,4-diarylbutadienes with high yields and stereoselectivities. Monitoring the process revealed that a sequence of cis-semihydrogenation of the triple bond of 1,3-enynes (to form (E,Z)-butadienes) and (E,Z)-to-(E,E) isomerization occurs to form (E,E)-butadienes.

Catalytic and mechanistic studies of a highly active and E-selective Co(II) PNNH pincer catalyst system for transfer-semihydrogenation of internal alkynes

Herein we report the application of a Co(II) PNNH pincer catalyst system (PNNH = 2-(5-(t-butyl)-1H-pyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine) for the highly E-selective transfer semihydrogenation of internal diaryl alkynes using methanol and ammonia borane...

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a...

Revisiting the Balz-Schiemann Reaction of Aryldiazonium Tetrafluoroborate in Different Solvents under Catalyst- and Additive-Free Conditions

The thermal and photochemical Balz-Schiemann reaction in commonly used solvents was revisited under catalyst- and additive-free conditions. The study showed that using low- or non-polar solvents could improve the pyrolysis and photolysis of aryldiazonium tetrafluoroborates, enabling effective fluorination at a low temperature or under visible-light irradiation. PhCl and hexane were exemplified as cheap and reliable solvents for both reactions, providing good to excellent yields of aryl fluorides from the corresponding diazonium tetrafluoroborates. The combination of slight heating with visible-light irradiation was beneficial for the transformation of stable aryldiazonium tetrafluoroborates. Nevertheless, the electronic and steric nature of aryldiazonium tetrafluoroborates still had a pivotal effect on both fluorinations even in these solvents.

Converting copper sulfide to copper with surface sulfur for electrocatalytic alkyne semi-hydrogenation with water

Electrocatalytic alkyne semi-hydrogenation to alkenes with water as the hydrogen source using a low-cost noble-metal-free catalyst is highly desirable but challenging because of their over-hydrogenation to undesired alkanes. Here, we propose that an ideal catalyst should have the appropriate binding energy with active atomic hydrogen (H*) from water electrolysis and a weaker adsorption with an alkene, thus promoting alkyne semi-hydrogenation and avoiding over-hydrogenation. So, surface sulfur-doped and -adsorbed low-coordinated copper nanowire sponges are designedly synthesized via in situ electroreduction of copper sulfide and enable electrocatalytic alkyne semi-hydrogenation with over 99% selectivity using water as the hydrogen source, outperforming a copper counterpart without surface sulfur. Sulfur anion-hydrated cation (S²⁻-K⁺(H₂O)_n) networks between the surface adsorbed S²⁻ and K⁺ in the KOH electrolyte boost the production of active H* from water electrolysis. And the trace doping of sulfur weakens the alkene adsorption, avoiding over-hydrogenation. Our catalyst also shows wide substrate scopes, up to 99% alkenes selectivity, good reducible groups compatibility, and easily synthesized deuterated alkenes, highlighting the promising potential of this method.

Highly selective electrocatalytic semi-hydrogenation of alkynes over a noble-metal-free catalyst is highly desirable. Here, authors synthesize sulfur-containing copper nanowire sponges for selective electrocatalytic alkyne semi-hydrogenation using water as the hydrogen source.

Transfer hydrogenation of N-heteroarenes with 2-propanol and ethanol enabled by manganese catalysis

A convenient well-defined manganese catalyzed transfer hydrogenation of N-heteroarenes using 2-propanol and ethanol as hydrogen sources is developed. DFT calculations support an outer sphere hydrogenation mechanism.

The Immobilization of Pd(II) on Porous Organic Polymers for Semihydrogenation of Terminal Alkynes

Highly selective catalytic hydrogenation of alkynes to alkenes is a highly important reaction owing to its industrial and commercial application. Specifically, semihydrogenation of terminal alkynes has been more challenging than internal alkenes even using Lindlar catalysts. Also, the high reduction degree state metal-supported catalysts like Pd⁰/C, Pt⁰/C, and Ru⁰/C have been well-known to be used widely in hydrogenation due to their super activity. However, charcoal can absorb a large amount of water; Pd/C with 50% water is convenient on a large-scale synthesis. Charcoal generally bears oxygen groups on its surface, which are responsible for low selectivity and undesired products. Even typically, only 10-60% of the Pd metal atoms are exposed, they still suffer from poor stability in acids owing to leaching. Herein, we intend to design active and stable metal catalysts with features as the following to avoid leaching: having strong interaction with the support and coordinatively unsaturated metal sites or low valence state metals physically isolated from the acid environment. Herein, a highly efficient semihydrogenation of terminal alkynes to produce alkenes has been realized using a heterogeneous Pd(II)/POP-GIEC catalyst, imine-linked, crystalline, and porous organic polymer supporter modified by coordination of Pd(OAc)₂ to its walls under mild conditions. Surprisingly, for the first time, modified POP-supported low reduction degree Pd^II catalysts were synthesized efficiently, and they were successfully used in semihydrogenation of terminal alkynes. The substrate scope was studied and included both unfunctionalized as well as functionalized substituents on the para, ortho, and meta position of aromatic alkynes. The substrate having a substituent with the functionality of fluoro protected at the meta position was semihydrogenated with a high alkyne conversion of 100% and olefin selectivity (up to 99%).

Ruthenium-Catalyzed E-Selective Alkyne Semihydrogenation with Alcohols as Hydrogen Donors

Selective direct ruthenium-catalyzed semihydrogenation of diaryl alkynes to the corresponding E-alkenes has been achieved using alcohols as the hydrogen source. The method employs a simple ruthenium catalyst, does not require external ligands, and affords the desired products in > 99% NMR yield in most cases (up to 93% isolated yield). Best results were obtained using benzyl alcohol as the hydrogen donor, although biorenewable alcohols such as furfuryl alcohol could also be applied. In addition, tandem semihydrogenation–alkylation reactions were demonstrated, with potential applications in the synthesis of resveratrol derivatives.

Homogeneous catalytic transfer semihydrogenation of alkynes – an overview of hydrogen sources, catalysts and reaction mechanisms

Chemoselective semihydrogenation of alkynes to alkenes with E- or Z-stereoselectivity is among the most important transformations in the synthesis of highly functional organic building blocks.

Ligand-Promoted Iridium-Catalyzed Transfer Hydrogenation of Terminal Alkynes with Ethanol and Its Application

A ligand-promoted iridium-catalyzed transfer hydrogenation of terminal alkynes with ethanol and its application has been developed. Highly chemical selectivity control is achieved based on ligand regulation. 1,2-Bis(diphenylphosphino)ethane was found to be critical for the transfer hydrogenation of alkynes. The general applicability of this procedure is highlighted by the synthesis of 30 terminal alkenes with a good yield. In addition, we conducted drug effect studies of phenelzine using zebrafish as the vertebrate model. Phenelzine shows a significant effect on promoting vascular proliferation and inhibiting nerve growth. The results of these studies have an important reference value for promoting drug research in cerebrovascular diseases, epilepsy, mania, and psychosis.