Addition Of Alkynes Research Articles

Platinum-Centered Oligoynes Capped by Boron Difluoride Formazanate Dyes and Their Thin-Film Properties.

Since the Nobel prize winning discovery that polyacetylene could act as a semiconductor, there has been tremendous efforts dedicated to understanding and harnessing the unusual properties of 𝜋-conjugated polymers. Much of this research has focused on the preparation of oligoynes and polyynes with well-defined numbers of repeating alkyne units as models for carbyne. These studies are usually hampered by a structure-property relationship where the stability of the resulting materials decrease with the incorporation of additional alkyne units. Here, we describe a series of oligoynes, with up to 12 alkyne units, where electron-rich [Pt(PBu3)2]2+ units are incorporated into the center of oligoyne backbones which are capped by electron-poor BF2 formazanate dyes. These compounds exhibit excellent stability and solubility, panchromatic absorption, and redox activity characteristic of their structural components. These traits facilitated thin-film studies of extended oligoyne materials, where it is shown that incorporating [Pt(PBu3)2]2+ units leads to smoother films, decreased conductivity on the microscale, and increased conductivity on the nanoscale when compared to metal-free analogs. Remarkably, our oligoynes have superior conductivity compared to the ubiquitous poly(3-hexylthiophene) semiconductor.

Rare-Earth Dialkyls Supported by Silaimine-Cp Ligand: Synthesis, Reactivity, and Catalytic Addition of Alkynes and Amines to Carbodiimides

Rare-Earth Dialkyls Supported by Silaimine-Cp Ligand: Synthesis, Reactivity, and Catalytic Addition of Alkynes and Amines to Carbodiimides

Chiral bis(imidazoline) NCN pincer iridium(III)-catalyzed enantioselective alkynylation of trifluoropyruvates with terminal alkynes

Readily prepared chiral bis(imidazoline) NCN pincer iridium(III) complexes have been developed as the new and highly stereoselective catalysts for the direct asymmetric addition of terminal alkynes to trifluoropyruvates. With a catalyst loading of 5 mol%, a variety of optically active α-trifluoromethylated tertiary propargylic alcohols were thus produced in good yields with high enantioselectivity (27 examples, 74-96% ee). Both enantiomers of the catalysis products were obtained by using enantiomeric Ir(III) catalysts. In addition, gram scale synthesis of the product and its transformation to a potentially very useful 2H-1,2,3-triazole compound were accomplished. Control experiments suggested that the alkynylide Ir(III) intermediates were involved in the reactions.

On the Existence and Relevance of Copper(III) Fluorides in Oxidative Trifluoromethylation

AbstractNumerous reports invoke CuIII–F intermediates engaging in oxidative cross-couplings mediated by low/mid-valent copper and formal sources of ‘F+’ oxidants. These elusive and typically instable CuIII fluorides have been rarely characterized or spectroscopically identified, making their existence and participation within catalytic cycles somehow questionable. We have authenticated a stable organocopper(III) fluoride that undergoes Csp–CF3 bond formation upon addition of silyl-capped alkynes following a 2 e– CuIII/CuI redox shuttle. This finding strongly supports the intermediacy of CuIII fluorides in C–C coupling. We review herein the state of the art about well-defined CuIII fluorides enabling cross-coupling reactions.1 Introduction2 Brief History of Coupling-Competent CuIII Fluorides3 Design of an Isolable – yet Reactive – Organocopper(III) Fluoride4 Alkyne Trifluoromethylation: Scope and Mechanism5 Extension to Aryl–CF3 and C–Heteroatom Couplings6 Summary and Outlook

Numerical investigation of soot formation in methane/n-heptane laminar diffusion flame doped with hydrogen at elevated pressure

The addition of hydrogen in a dual-fuel mode based on natural gas and diesel offers great potential for improving engine efficiency and reducing emissions. Therefore, detailed numerical simulations have been used to explore the effects of soot formation characteristics of natural gas-diesel dual-fuel engines doped by hydrogen at elevated pressure. Numerical simulations are compared with available experimental data, the effects of H2 addition on soot formation in laminar CH4 + n-heptane, H2 + CH4 + n-heptane, FH2 + CH4 + n-heptane diffusion flames at 2, 4, 6 and 8 atm are simulated, FH2 is added to separate the H2 chemical effects. The results show that the dilution and thermal effects of H2 inhibit soot formation, while the chemical effects of H2 promote soot formation under different pressures. The addition of H2 increases the concentration of H and OH radicals, which promotes the formation of C2H2 and benzene (A1). By simplifying the reaction path and analyzing the production rate of A1, the mechanism of H2 addition to promote A1 formation is illustrated. The concentrations of polycyclic aromatic hydrocarbon (PAH) pyrene (A4), benzo(ghi)fluoranthene (BGHIF) and benzo(a)pyrene (BAPYR) are inhibited at higher pressures that result in lower inception and condensation rates. Therefore, the increase of hydrogen abstraction acetylene addition (HACA) rate is the main reason for the increase of soot formation under chemical effects. While the O2 oxidation rate decreases and the OH oxidation rate increases, that is due to the decrease of O2 concentration and the increase of OH concentration in the soot formation area under chemical effects.

Experimental and numerical investigations of soot formation in propane laminar coflow flames in O2/N2 and O2/CO2 atmospheres

Oxygen-rich combustion is a new type of clean combustion technology with important application prospects. At present, there are few detailed analyses on the mechanism changes of soot formation under oxygen enrichment of propane. In this paper, the effects of oxygen-rich (O2/N2, O2/CO2) combustion on soot formation in the propane laminar flow coaxial jet diffusion flame were investigated by using the experiment and numerical simulation. The flame image was taken by a color (CCD) camera in the visible band, and the two-dimensional distribution of temperature and soot volume fraction in the flame was reconstructed. In numerical simulation, the soot production model considers a detailed description of nucleation via collisions among heavy polycyclic aromatic hydrocarbons, particle aggregation, polycyclic aromatic hydrocarbons condensation, surface growth and oxidation through the hydrogen abstraction acetylene addition mechanism. The results show that the experimental results were compared with the numerical simulation results, and the numerical simulation results predict the temperature and soot change of oxygen-rich flame well. With the increase in oxygen concentration, the peaks of soot and temperature in the two oxygen-rich atmospheres gradually increased. With the increase in oxygen concentration, the peaks of soot and temperature in the two oxygen-rich atmospheres gradually increased. Comparing the combustion mechanism changes of the two oxygen-rich combustion systems, it was found that the hydrogen abstraction acetylene addition mechanism was the main cause of soot generation. The OH oxidation is dominated near the fuel nozzle side, and O2 oxidation is dominant downstream. With the substitution of CO2 for N2, the chemical effect of CO2 reduces the flame temperature and inhibits the formation mechanism and oxidation mechanism of soot to some extent. This in turn leaded to a reduction in the amount of soot produced.

Effects of different ammonia energy ratio on soot formation and oxidation in an ammonia diesel dual-fuel engine

Due to environmental pollution and energy crises, zero‑carbon fuel ammonia (NH3) has attracted extensive attention as an alternative fuel for engines. In this paper, the effects of ammonia energy ratio (AER) and injection strategy on particulate emission characteristics of an ammonia diesel dual-fuel engine were examined by merging experimental and simulation results; additionally, soot formation and oxidation mechanism were investigated. Results showed that the reduction in particulate emission was substantially higher than the increase in AER. When AER increased to 60 %, the reduction in particulate mass concentration reached 97.5 %. The initial soot formation area gradually moved to the bottom of the piston bowl with increasing AER. When the piston reached the top dead center, the high-soot-concentration area was shifted to the center of the piston bowl as AER increased. The contents of acetylene (C2H2) and methyl (CH3) reduced considerably, which restricted the formation of soot precursors. With AER increasing, the contents of nitric oxides (NOx) and other nitrogen-containing species increased and reacted with CH3 and other carbon-containing species, which effectively reduced the number of C in soot formation pathway, thereby lowering particulate emissions. As AER increased, hydroxyl (OH) involved in soot formation gradually decreased, and only 14 % of OH was involved in the oxidation of n-heptane at 60 % AER, which was favorable for reducing the soot formation rate. Furthermore, OH is a substantial species in soot oxidation. The introduction of ammonia caused an increase in OH, which facilitated the removal of soot. The decrease in hydrogenium (H) hindered the hydrogen–abstraction–acetylene–addition (HACA) reaction, further limiting the soot surface growth. By optimizing the injection timing and AER, particulate emission was lowered to 4.31 × 10−5 μg/cm3, and particle size was reduced by 64.2 % when AER was 60 %, injection timing was −20° CA ATDC, and injection pressure was 60 MPa.

Switchable Enantioselectivity in Conjugate Alkyne Addition of β,γ-Unsaturated α-Keto Esters by Asymmetric Binary Acid Catalysis.

Switchable enantioselectivity was uncovered in the enantioselective catalytic conjugate addition of β,γ-unsaturated α-keto esters with terminal alkynes to the chiral Lewis acid complex of In(BF4)3 and chiral phosphoric acid.

Study on effects of ethylene or acetylene addition on the stability of ammonia laminar diffusion flame by optical diagnostics and chemical kinetics

Improvement of ammonia combustion characteristics by carbon-based combustion promoters is currently emphasized, but the impact of carbon‑carbon multi-bond structure on ammonia combustion characteristics and reaction mechanisms has not been sufficiently investigated. In order to investigate the mechanism of molecular structures (C=C and C≡C) of combustion promoters on the stability of ammonia flames, the flame morphology, flame structure, NH3-H2 cracking, and C-N cross-reaction of ammonia/ethylene and ammonia/acetylene laminar diffusion flame are investigated based on a Gu¨lder burner by utilizing high-speed photography, planar laser-induced fluorescence (PLIF) and laser spontaneous Raman scattering (SRS) techniques. The results show that acetylene addition is more effective than ethylene to improve the flame stability. Combined with the flame structure analysis, it is shown that C=C mainly enhances the low-temperature reaction stage intensity of laminar flame, while C≡C can both enhance the intensity of low-temperature and high-temperature reaction stages, thereby enhancing the flame combustion exothermic process. Besides, C=C mainly strengthens the exothermic reactions in the upstream of the flame whereas C≡C can strengthen the exothermic reactions in the upstream and downstream of the flame simultaneously. Investigation of the NH3-H2 cracking reactions reveals that C≡C promotes H2 generation mainly by increasing NH3→H2 cracking, whereas C=C promotes H2 generation mainly by increasing NH2→H2 and NH→H cracking, hence improving the flame stability. Further analysis through the reaction flows revels that C=C acts mainly on H-containing species HCN/HNCO whereas C≡C mainly acts on non-H-containing species CN/NCO to influence the reaction pathways, but C-N cross-reaction does not play an important role in the characteristics of ammonia composite combustion (ACC).

Catalytic Enantioselective Alkyne Addition to Nitrones Enabled by Tunable Axially Chiral Imidazole-Based P,N-Ligands.

Although catalytic enantioselective alkyne addition is an established method for the synthesis of chiral propargylic alcohols and amines, addition to nitrones presents unique challenges, and no general chiral catalyst system has been developed. In this manuscript, we report the first Cu-catalyzed enantioselective alkyne addition to nitrones utilizing tunable axially chiral imidazole-based P,N-ligands. Our approach effectively overcomes difficulties in both reactivity and selectivity, resulting in a simple Cu-catalyzed protocol. The reaction accommodates a wide range of nitrones and alkynes, enabling the streamlined synthesis of chiral propargyl N-hydroxylamines via the enantioselective C-C bond formation. A diverse array of optically active nitrogen-containing compounds, including chiral hydroxylamines, can be accessed directly through facile transformations of the reaction products.

Green Light Promoted Iridium(III)/Copper(I)-Catalyzed Addition of Alkynes to Aziridinoquinoxalines Through the Intermediacy of Azomethine Ylides.

This manuscript describes the development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalytic system under green light-emitting diode (LED) photolysis (λmax =525 nm). This mild method features high levels of chemo- and regioselectivity and was used to generate 30 highly functionalized substituted dihydroquinoxalines in 36-98 % yield. This transformation was also carried asymmetrically using phthalazinamine-based chiral ligand to provide 9 chiral addition products in 96 : 4 to 86 : 14 e.r. The experimental and quantum chemical explorations of this reaction suggest a mechanism that involves Ir(III)-catalyzed triplet energy transfer followed by a ring-opening reaction ultimately leading to the formation of azomethine ylide intermediates. These azomethine intermediates undergo sequential protonation/copper(I) acetylide addition to provide the products.

Green Light Promoted Iridium(III)/Copper(I)‐Catalyzed Addition of Alkynes to Aziridinoquinoxalines Through the Intermediacy of Azomethine Ylides

AbstractThis manuscript describes the development of alkyne addition to the aziridine moiety of aziridinoquinoxalines using dual Ir(III)/Cu(I) catalytic system under green light‐emitting diode (LED) photolysis (λmax=525 nm). This mild method features high levels of chemo‐ and regioselectivity and was used to generate 30 highly functionalized substituted dihydroquinoxalines in 36–98 % yield. This transformation was also carried asymmetrically using phthalazinamine‐based chiral ligand to provide 9 chiral addition products in 96 : 4 to 86 : 14 e.r. The experimental and quantum chemical explorations of this reaction suggest a mechanism that involves Ir(III)‐catalyzed triplet energy transfer followed by a ring‐opening reaction ultimately leading to the formation of azomethine ylide intermediates. These azomethine intermediates undergo sequential protonation/copper(I) acetylide addition to provide the products.

Coordination-induced reductive elimination from a titanium(IV) complex.

Diamidopyridine-supported titanium dibenzyl complexes undergo coordination-induced C-C reductive elimination upon addition of alkynes and quantitative formation of titanacyclopentadienes. The distinct radical mechanism of this reductive mechanism gives new insights into C-C bond formation with titanium.

Visible-light-driven graphitic carbon nitride-catalyzed ATRA of alkynes: highly regio- and stereoselective synthesis of (E)-β-functionalized vinylsulfones

A visible-light-driven g-C3N4-catalyzed atom transfer radical addition (ATRA) of alkynes to synthesize valuable (E)-β-thio/seleno vinylsulfones is accomplished. g-C3N4 can be recovered and reused in five runs without loss of catalytic activity.

Phenalenyl growth reactions and implications for prenucleation chemistry of aromatics in flames.

The energetics and kinetics of phenalene and phenalenyl growth reactions were studied theoretically. Rate constants of phenalene and phenalenyl H-abstraction and C2H2 addition to the formed radicals were evaluated through quantum-chemical and rate-theory calculations. The obtained values, assigned to all π radicals, were tested in deterministic and kinetic Monte Carlo simulations of aromatics growth under conditions of laminar premixed flames. Kekulé and non-Kekulé structures of the polycyclic aromatic hydrocarbons (PAHs) evolving in the stochastic simulations were identified by on-the-fly constrained optimization. The numerical results demonstrated an increased PAH growth and qualitatively reproduced experimental observations of Homann and co-workers of non-decaying PAH concentrations with nearly equal abundances of even and odd carbon-atom PAHs. The analysis revealed that the PAH growth proceeds via alternating and sterically diverse acetylene and methyl HACA additions. The rapid and diverse spreading in the PAH population supports a nucleation model as PAH dimerization, assisted by the non-equilibrium phenomena, forming planar aromatics first and then transitioning to the PAH-PAH stacking with size.

Reaction mechanism of the ethynylation of formaldehyde on copper terminated Cu2O(100) surfaces: a DFT study.

1,4-Butanediol (BDO) is an important chemical raw material for a series of high-value-added products. And the ethynylation of formaldehyde is the key step for the production of BDO by the Reppe process. However, little work has been done to reveal the reaction mechanism. In this work, the reaction mechanism for the ethynylation of formaldehyde process on copper-terminated Cu2O(100) surfaces was investigated with density functional theory (DFT). The reaction network of the ethynylation of formaldehyde was constructed first and the adsorption properties of the related species were calculated. Then the energy barrier and reaction energy of the related reactions and the geometric configuration were calculated. It is a consecutive reaction including two processes. For the propargyl alcohol (PA) formation process, the most favorable pathway is the direct addition of acetylene to formaldehyde followed by a hydrogen transfer reaction. And the rate control step is the hydrogen transfer reaction with an energy barrier of 1.43 eV. For the 1,4-butynediol (BYD) formation process, the most competitive pathway is the addition of PA to CH2OH, including formaldehyde hydrogenation to form CH2OH, coupling addition, and dehydrogenation reaction. The rate control step of this pathway is the dehydrogenation reaction with an energy barrier of 1.51 eV.

Styrene thermal decomposition and its reaction with acetylene under shock tube pyrolysis conditions: An experimental and kinetic modeling study

Styrene is an important compound for polymer production and a key intermediate in gas-phase kinetics of polycyclic aromatic hydrocarbons (PAHs). For the first time, the pyrolysis of styrene with and without the presence of acetylene is investigated in a single-pulse shock tube coupled to gas chromatography and mass spectrometry. For each reaction system, quantitative speciation profiles are probed within the temperature range of 1100–1730 K, nominal pressure of 20 bar, and reaction duration of ∼ 4 ms. A kinetic model is built to simulate the results. The model explains how styrene is consumed under high-pressure pyrolytic conditions, how the secondary chemistry of intermediate products affect subsequent PAH formation, and how acetylene addition alters the reaction pathways. Throughout the temperature range, styrene breakdown is dominated by the bimolecular interaction between styrene and hydrogen atom, which produces benzene+vinyl or phenyl and ethylene through the stabilization of 2-phenylethyl and its subsequent dissociation. As a result, large amounts of phenyl accumulate, which react with styrene to form C14H12 species while simultaneously releasing H atoms through addition/elimination reactions. The reactivity of fuel consumption is preserved by the regeneration of H atoms as chain carriers. Several C14H10 compounds are formed as a result of the following breakdown of the C14H12 isomers, particularly stilbene, 1,1-diphenyl ethylene, and 9-methyl-9H-fluorene. The presence of acetylene as a co-reactant with styrene allows the Hydrogen-Abstraction-Acetylene-Addition (HACA) pathway to proceed from phenyl radical to enhance the production of phenylacetylene at very low temperatures and acenaphthylene. This hinders the formation of C14H12 isomers, exclusive products from pure styrene dissociation by competing with the styrene+phenyl routes.

A Direct Synthesis of Substituted Exocyclic 1H‐pyrrol‐3(2H)‐ones by Base‐Mediated Multicomponent [3+2] Cycloaddition

AbstractA one‐pot, three‐component, base‐mediated [3+2] cycloaddition reaction to synthesize 1H‐pyrrol‐3(2H)‐ones from readily available amino acid esters, aldehydes, and terminal alkynes was reported. Isolation of the intermediate and the detailed mechanistic study revealed the course of the reaction. This multi‐component reaction proceeds via imine formation followed by the nucleophilic addition of alkyne to form a propargylamine precursor. Base‐mediated conversion of propargylamine precursor into 1‐azadiene followed by in situ ketene formation leading to [3+2] cycloaddition that ultimately produces unusual 1H‐pyrrol‐3(2H)‐ones.

Synthesis of Highly Substituted Pyrrolo[1,2‐a]quinoline‐3,5‐diones through Ag(I) Catalyzed Cyclization of 4‐Hydroxyquinolinyl‐2‐ynones

AbstractAn efficient synthetic route to access highly substituted pyrrolo[1,2‐a]quinoline‐3,5‐diones in which the core is formed by fusion of quinolone and pyrrolone moieties is discussed. The method involves Ag(I) catalyzed cyclization of 4‐Hydroxyquinolinyl‐2‐ynones which in turn may be accessed from kynurenic acid derivatives through Weinreb amide intermediate, followed by alkyne addition. Studies involving substrates with different substitution pattern revealed that factors increasing the nucleophilicity of quinoline nitrogen or Lewis acid‐coordination of the ynone unit gives high yields in short reaction times. It was possible to execute tandem cyclization‐arylation sequence by using Pd(II) generated by oxidative addition of Pd(0) with aryl iodide as the electrophilic species to get substitution pattern as seen in Discoipyrrole A.

On the mechanisms affecting soot production in oxygen-depleted buoyant flames

The objective of this article is to apply a detailed polycyclic aromatic hydrocarbons (PAH)-based soot production model to investigate the effects of oxygen depletion on the overall soot production processes in laminar coflow ethylene diffusion flames. This task is accomplished by simulating the flames, studied experimentally by Sun et al. (Combust. Flame 211:96–111, 2020), burning under oxygen concentration in the oxidizer down to 16.8% and characterized by a constant volumetric stoichiometric air to fuel ratio to keep the residence time unchanged. This configuration allows isolating the effects of reducing oxygen on both soot formation and oxidation processes and avoiding the complex interactions between soot production and turbulence. Model predictions are in reasonable agreement with the experiments in terms of temperature, soot volume fraction, and primary particle diameter and capture quantitatively the effects of oxygen depletion on soot production. In all the flames, both the H-abstraction and acetylene addition (HACA) and PAH condensation contribute significantly to the soot mass growth, with the HACA slightly dominating the overall process. Reducing the oxygen concentration affects similarly all the formation and oxidation processes with a reduction in the range 30–40% from 21.0% to 18.9% and in the range from 60 to 70% as it is further reduced to 16.8%. Among the formation processes, the PAH condensation and surface growth by HACA have a similar sensitivity to oxygen depletion, followed by soot inception.