Oxidative Addition Research Articles

The impact of cobalt oxide additions and heat treatment on wollastonite for magnetic applications

Magnetic nanocomposite was prepared using the wet chemical precipitation approach with varying amounts of cobaltous oxide (CoO). The concentrations of CoO were 0.5, 3.5, 6.5, and 9.5 g per 100 % wollastonite composition. Samples were sintered separately at 1000 and 1200 °C. X-ray diffraction analysis (XRD) of the sintered parent sample revealed the formation of wollastonite CaSiO3 and larnite Ca2SiO4, as well as a minor silicon oxide SiO2 phase. In CoO-doped samples, Co-åkermanite Ca2CoSi2O7 and other phases were formed. The XRD and scanning electron microscope SEM confirm the samples' submicron and nanocrystalline microstructure. The Fourier transform infrared spectroscopy (FTIR) and Raman spectra (RS) of investigated samples sintered at 1000 and 1200 °C revealed their bond structure. Both analyses confirmed that incorporating CoO into CaSiO3 significantly improved its vibrational modes, reflecting structural modifications. By increasing the cobalt oxide content from 3.5 to 9.5 wt%, the samples attain the ideal paramagnetic state, as demonstrated by the magnetic hysteresis (M − H) curve, which is linearly reversible. Formation of the Ca2CoSi2O7 significantly alters the magnetic characteristics of the samples, whether through increasing the cobalt oxide concentration up to 9.5 wt% or modifying the sintering temperature. This enables the prepared nonocomposites to be suitable for novel magnetic applications.

Isolation of a NHC-stabilized heavier nitrile and its conversion into an isonitrile analogue.

Nitriles (R-C≡N) have been investigated since the late eighteenth century and are ubiquitous encounters in organic and inorganic syntheses. In contrast, heavier nitriles, which contain the heavier analogues of carbon and nitrogen, are sparsely investigated species. Here we report the synthesis and isolation of a phosphino-silylene featuring an N-heterocyclic carbene-phosphinidene and a highly sterically demanding silyl group as substituents. Due to its unique structural motif, it can be regarded as a Lewis base-stabilized heavier nitrile. The Si-P bond displays multiple bond character and a bent R-Si-P geometry, the latter indicating fundamental differences between heavier and classical nitriles. In solution, a quantitative unusual rearrangement to a phosphasilenylidene occurs. This rearrangement is consistent with theoretical predictions of rearrangements from heavier nitriles to heavier isonitriles. Our preliminary reactivity studies revealed that both isomers exhibit highly nucleophilic silicon centres capable of oxidative addition and coordination to iron tetracarbonyl.

Study on the UV aging resistance of ZnO‐modified epoxy resin by experiments and MD simulation

AbstractThis study investigates the impact of zinc oxide nanoparticles on epoxy resin systems and the ultraviolet (UV) aging resistance of modified epoxy resin composites using molecular dynamics (MD) simulations and experimental methods. Initially, various epoxy resin cross‐linking models are established through MD simulations to understand the influence of different nano ZnO contents on resin modification, further validated by experiments. Subsequently, the UV radiation resistance of nano ZnO–epoxy resin composites is assessed by subjecting them to high‐intensity UV radiation equivalent to 3 years of natural environmental conditions, analyzing changes in tensile properties, impact performance, hardness, and glass transition temperature of epoxy resin before and after UV radiation exposure. The findings suggest that the addition of nano zinc oxide reduces the impact of UV radiation on epoxy resin, with optimal UV radiation resistance observed at a nano zinc oxide mass fraction of 0.3 wt%.

MOLECULAR MECHANISM OF PHYSICAL AND MECHANICAL IMPROVEMENT IN GRAPHENE/GRAPHENE OXIDE-EPOXY COMPOSITE MATERIALS.

The performance provided by graphene (Gr) and graphene oxide (GO) additives can be improved by achieving strong adhesion and uniform dispersion in the epoxy resin matrix. In this study, molecular modeling and simulation of DGEBA/DETA based epoxy nanocomposites containing Gr and GO additives were performed. Density functional theory and molecular dynamics simulations were used to investigate interfacial interaction energies and Young's Modulus. Improvement in the interaction energies was studied by controlling the epoxy:hardener ratio, type and the number of oxygen-containing functional groups on the GO, the mass percentage of Gr/GO filler in the epoxy matrix, size and dispersion of GO in the cell. It was demonstrated that functional groups with up to 10% oxygen content in GO significantly increase interfacial interaction energy for large size Gr/GO. Increasing DETA type amine ratio in the preparation of epoxy polymers increases the interaction energy for high oxygen content while decreasing the interaction energy for low oxygen content in GO for small size GO with edge functional groups. The performance of material dramatically decreased even at high DETA hardener and high GO mass percentages when the aggregation factor of Gr/GO was included in simulations that explain lower Gr/GO percentages in the experimental studies.

Bis(imidazolidine)-Derived NCN Nickel-Pincer-Catalyzed Asymmetric Reactions.

A bis(imidazolidine)-derived NCN nickel-pincer complex (tBu-PhBidine-Ni-OTf: NCN-Ni-OTf) was synthesized by the oxidative addition of imidazolidine-containing aryl triflate to Ni(cod)2 in MeCN. NCN-Ni-OTf exhibited asymmetric induction in three reactions. In the Friedel-Crafts reaction of indoles with N-Boc imines, 3-indolylmethanamine products were obtained in 79% yield with 99% ee. In a conjugate addition reaction of malononitrile to nitroalkenes, products were obtained in 95% yield with 75% ee. In iodolactonization, the pincer-Ni complex showed catalytic activity superior to that of tBu-PhBidine-Pd-OTf.

Cyclometalated C^C* Platinum(IV) NHC Complexes.

We present a previously unknown series of cyclometalated platinum(IV) NHC complexes, obtained by oxidative addition of iodine, iodomethane, and different benzyl bromides to platinum(II) complexes with cyclometalated C^C* dibenzofuran, dibenzothiophene, and phenylimidazole ligands together with an acetylacetonate ligand. All compounds were characterized by standard techniques (1H, 13C, and 195Pt NMR and elemental analysis), and for three complexes, solid-state structures could be obtained. DFT calculations (B3LYP(d3)/def2-TZVPP including dispersion interactions in dichloromethane and acetone) were performed to investigate the mechanism of the oxidation and explain the exclusive formation of the observed trans products.

Preparation of Benzo[a]fluorenes via Pd-Catalyzed Annulation of 5-(2-Bromophenyl)pent-3-en-1-ynes.

A palladium-promoted cascade cyclization of 5-(2-bromophenyl)pent-3-en-1-ynes is developed for the synthesis of benzo[a]fluorene derivatives. The reaction proceeds with oxidative addition of C-Br, insertion, C-H activation, and reductive elimination in sequential steps.

Rapid Aminations of Functionalized Aryl Fluorosulfates in Water

AbstractAryl fluorosulfates of varying complexities have been used in amination reactions in water using a new Pd oxidative addition complex (OAC‐1) developed specifically to match the needs of the fine chemicals industry, not only in terms of functional group tolerance, but also reflecting time considerations associated with these important C−N couplings. Also especially noteworthy is that they replace both PFAS‐related triflates and nonaflates, which are today out of favor due to recent government regulations. The new complex based on the BippyPhos ligand is used at low loadings and under aqueous micellar conditions. Moreover, it is easily prepared and stable to long term storage. DFT calculations on the OAC precatalyst compare well with the X‐ray structure of the crystals with π‐complexation to the aromatic system of the ligand and also confirm the NMR data showing a mixture of conformers in solution that differ from the X‐ray structure in rotation of the phenyl and t‐butyl ligand substituents. An extensive variety of coupling partners, including pharmaceutically relevant APIs, readily participate under mild and environmentally responsible reaction conditions.

Anti-selective Cyclopropanation of Nonconjugated Alkenes with Diverse Pronucleophiles via Directed Nucleopalladation.

A facile approach to obtaining densely functionalized cyclopropanes is described. The reaction proceeds under mild conditions via the directed nucleopalladation of nonconjugated alkenes with readily available pronucleophiles and gives excellent yields and good anti-selectivity using I2 and TBHP as oxidants. Pronucleophiles bearing a diverse collection of electron-withdrawing groups, including -CN, -CO2R, -COR, -SO2Ph, -CONHR, and -NO2, are well tolerated. Internal alkenes, which are generally challenging substrates in other cyclopropanation methods, provide excellent yields and good diastereoselectivity in this methodology, allowing for controlled access to cyclopropanes substituted at all three C atoms. DFT calculations and mechanistic experiments reveal that the major mechanistic pathway involves the initial α-iodination of the nucleophile, followed by anti-carbopalladation and intramolecular C(sp3)-I oxidative addition. Strain-release-promoted C(sp3)-C(sp3) reductive elimination then furnishes the cyclopropanated product.

Optimization of Iron Oxide (Fe2O3) Addition Parameters on the Physical Properties of Al-Si Alloys as an Advanced Material Innovation

Aluminum-silicon alloys are widely used in the industrial world, one of which is because they have high wear resistance. The aim of this research is to determine the physical and mechanical properties of the Al-Si alloy after strengthening by mixing reinforcing materials. The research method uses Taguchi optimization and analysis of the physical properties of the Al-Si alloy test results. The results showed that the highest hardness value was obtained in the 7th experiment, namely with a rotation variation of 2000 rpm, temperature of 6000C, and holding time of 60 seconds. This result is in line with the results of the tensile strength test, where the highest tensile strength was also obtained in the 7th experiment. This result is supported by the results of other researchers, which show that the higher the rotation in the casting results in higher hardness. The results of the microphotographs show that all alloy materials have an even distribution of grains, the grain size appears small, and the dendrites in the raw Al-Si alloy appear small compared to other materials. The macro photo results show that all alloy materials have fractures that appear brittle, as evidenced by the fact that these fractures provide light reflection.

Study on ultrasonic assisted intensive leaching of germanium from germanium concentrate using HCl/NaOCl

Ultrasonic radiation is widely used in the enhancement of leaching process with outstanding advantages in leaching efficiency. In this study, a germanium concentrate was leached with NaClO and the influence of factors such as ultrasound power and oxidant addition on the leaching efficiency of germanium from the concentrate were investigated. The leaching efficiency of germanium reached 96.8% at the initial concentration of hydrochloric acid of 8 mol/L, the oxidant dosage of 1.5 g/L NaClO, the liquid-solid volume/mass ratio of 6 mL/g, the ultrasonic power density of 13.3 W/cm3, and the stirring speed of 300 rpm for 30 min at 60 °C. The leaching efficiency was 4.50% higher at a shorter leaching time and lower temperature, than that of the conventional process, which was mainly attributed to the ultrasonic multiple effects and NaClO. Meanwhile, NaClO can effectively oxidize As(III) into non-volatile As(V), remove arsenic in germanium, facilitate the subsequent distillation, improve the leaching efficiency, and be more environmentally friendly.

Hemilabile and Redox-Active Quinone Ligands Unlock sp3-Rich Couplings in Nickel-Catalyzed Olefin Carbosulfenylation.

A three-component coupling approach toward structurally complex dialkylsulfides is described via the nickel-catalyzed 1,2-carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N-S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N-S electrophile containing an N-methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol%. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox-active ligands that tune the steric and electron properties of the metal throughout the catalytic cycle. DFT calculations show that the duroquinone (DQ) ligand adopts different coordination modes in different stages of the Ni-catalyzed 1,2-carbosulfenylation-binding as an η6 capping ligand to stabilize the precatalyst/resting state and prevent catalyst decomposition, binding as an X-type redox-active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, while binding as an η1 L-type ligand to promote N-S oxidative addition at a relatively more electron-rich and sterically less crowded Ni(I) center.

Hemilabile and Redox‐Active Quinone Ligands Unlock sp3‐Rich Couplings in Nickel‐Catalyzed Olefin Carbosulfenylation

A three‐component coupling approach toward structurally complex dialkylsulfides is described via the nickel‐catalyzed 1,2‐carbosulfenylation of unactivated alkenes with organoboron nucleophiles and alkylsulfenamide (N–S) electrophiles. Efficient catalytic turnover is facilitated using a tailored N–S electrophile containing an N‐methyl methanesulfonamide leaving group, allowing catalyst loadings as low as 1 mol%. Regioselectivity is controlled by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, amides, sulfinamides, phosphoramides, and carbamates. Key to the development of this transformation is the identification of quinones as a family of hemilabile and redox‐active ligands that tune the steric and electron properties of the metal throughout the catalytic cycle. DFT calculations show that the duroquinone (DQ) ligand adopts different coordination modes in different stages of the Ni‐catalyzed 1,2‐carbosulfenylation—binding as an η6 capping ligand to stabilize the precatalyst/resting state and prevent catalyst decomposition, binding as an X‐type redox‐active durosemiquinone radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, while binding as an η1 L‐type ligand to promote N–S oxidative addition at a relatively more electron‐rich and sterically less crowded Ni(I) center.

Reactive Condensation of Cr Vapor on Aluminosilicates Containing Alkaline Oxides

This study is part of a series with the objective of improving fundamental understanding of reactive condensation of Chromium (Cr) vapors, which are generated from Cr containing alloys used in many high-temperature (>500 °C) process environments and can form potentially problematic condensed hexavalent (Cr(VI)) species downstream. This study specifically focuses on the effects of alkaline oxide additives in aluminosilicate fibers on Cr condensation and speciation. Cr vapors were generated by flowing high-temperature (800 °C) air containing 3% water vapor over chromia (Cr2O3) powder, with aluminosilicate fiber samples positioned downstream where the temperature decreases (<500 °C). Total condensed Cr and ratios of oxidation states were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) and diphenyl carbazide (DPC) colorimetric/direct UV–vis spectrophotometric analyses. Results indicate presence of hexavalent Cr (Cr(VI)) species condensed on all samples investigated. The ratio of Cr(VI) to total Cr detected was consistently higher on aluminosilicate fiber samples containing alkaline oxide (CaO and MgO) additions. Computational thermodynamic equilibrium modelling corroborated experimental results showing stabilities of Ca and Mg chromate (Cr(VI)) compounds. Comparative results and analyses are presented and discussed to help inform mechanistic understanding and future related research and engineering efforts.

THE INFLUENCE OF NITROUS OXIDE ADDITION TO THE AIR CHARGE ON THE INDICATORS OF A SPARK IGNITION ENGINE UNDER FULL LOAD OPERATION

The article presents the methodology and research results on the influence of nitrous oxide addition to the air charge on the energy and environmental indicators, as well as the fuel economy of a spark ignition engine with feedback and a three-way catalytic converter under full load conditions. Full load engine modes are often used in conditions of intense traffic of vehicles in cities and settlement. Increasing energy indicators is relevant for sports vehicles and stationary energy installations operating at full load. When determining the most efficient method of achieving high engine energy indicators, it is necessary to take into account the method's impact on the engine's environmental indicators and fuel economy. Several methods for increasing the energy indicators of spark ignition engines are known. One of the most utilized methods is enriching the fuel-air mixture. Engine operation on enriched fuel-air mixture leads to increased gasoline consumption and deterioration of environmental indicators, especially when using a catalytic converter. Therefore, research into methods that simultaneously improve the energy and environmental indicators of the engine in the mentioned operating modes without increasing fuel consumption is relevant. One such method is the use of oxygen-containing compounds, in particular nitrous oxide, added to the air charge. The article proposes a methodology for assessing the method's impact on engine performance indicators in relative terms compared to fuel-air mixture enrichment. We conducted a study of indicator indicators of engine operation, namely: energy indicators based on average indicator pressure, fuel efficiency indicators based on indicator coefficient of useful action, environmental indicators based on concentrations of pollutants in exhaust gases. Calculations using experimental data showed that by adding various amounts of nitrous oxide to the engine's air charge, it is possible to achieve higher energy indicators, improve environmental indicators without worsening fuel economy compared to fuel-air mixture enrichment.

Nano Fe3O4 improved the electron donating capacity of dissolved organic matter during sludge composting

The effect of Fe3O4 nanoparticles (Fe3O4 NPs) on the electron transfer process in aerobic composting systems remains unexplored. In this study, we compared the electron transfer characteristics of DOM in sludge composting without additives (group CK) and with the addition of 50 mg/kg Fe3O4 NPs additive (group Fe). It was demonstrated that the electron transfer capacity (ETC) and electron donating capacity (EDC) of compost-derived DOM increased by 13%–29% and 40%–47%, respectively, with the addition of Fe3O4 NPs during sludge composting. Analyzing the composition and structure of DOM revealed that Fe3O4 NPs promoted the formation of humic acid-like substances and enhanced the aromatic condensation degree of DOM. Correlation analysis indicated that the increase in EDC of DOM was closely associated with the phenolic group in DOM and influenced by quinone groups and the degree of aromatization of DOM. The higher EDC and the structural evolution of DOM in group Fe reduced the bioaccessibility of Cu, Cr, Ni, Zn. This study contributes to a deeper understanding of the redox evolutionary mechanism of DOM in sludge composting and broadens the application of iron oxides additives.

Synergistic adsorption-photocatalytic degradation of methylene blue by Fe3O4/HKUST-1 composite modified with graphene oxide

Abstract Methylene blue (MB) is the most commonly used cationic dye, but the complex structure of MB makes it harder to be removed from the wastewater by conventional techniques. The integration of adsorption and photocatalytic has been proposed to overcome the drawbacks of the sole technology for more efficient and eco-friendly removal. A magnetic MOF composite, Fe3O4/HKUST-1, was successfully synthesized using the solvothermal method. The addition of graphene oxide (GO) uses the in situ method. XRD and FTIR results revealed the presence of GO, which was dispersed into the composite. SEM images for the composite showed GO(20)/Fe3O4/HKUST-1 was octahedral with Fe3O4 and GO distributed on the surface and between HKUST-1. When the initial concentration of MB was 50 mg/L, the composites exhibited high MB removal efficiency (92,75%) under irradiation through the combination of adsorption-photocatalytic. The effective removal of Fe3O4/HKUST-1 combined with the photocatalyst properties of GO, makes the composite highly efficient for applications in water purification. The adsorption kinetics of MB on the GO(20)/Fe3O4/HKUST-1 were well-fitted with the pseudo-second-order kinetic model.

Effect of samarium oxide addition on the structural, thermal, and optical properties and photoluminescence of lithium borate glass

The samples were prepared in compliance with the form 33 Li2O–66 B2O3—(1-x) AgF—x Sm2O3, where x = 0, 0.25, 0.5, and 0.75. Powdered samples were converted to a glassy state via melting and quenching. The glassiness of the prepared samples was examined using X-ray diffraction (XRD) and Differential Thermal Analysis (DTA). From the absorption spectra of the prepared glass samples, the band gap in the optical spectrum changed slightly in the range of 3.45, whereas the Urbach energy decreased from 0.32 to 0.267 eV. The fluctuations of the optical band gap and Urbach energy can be attributed to variations in the glass structure. Sm3 + emitted intense reddish-orange light under blue and UV light excitation. There are six excitation bands in the Sm3+ excitation spectrum situated in the blue and UV regions, peaking at 361.7, 374, 400, 417, 462, and 475 nm, which are attributed to the transitions from 6H5/2 to 4D3/2, 6P7/2, 6P3/2, 6P5/2, 4I13/2, and 4I11/2 respectively. The transition from 6H5/2 to 6P3/2 had the highest intensity and was associated with a peak at 400 nm. The bright yellow, reddish-orange, and red emission bands of the Sm3+ ions in the oxide glasses are related to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 emission transitions, respectively.

Role of oxidants in the anodic oxidation of 2024 aluminum alloy by dominating anodic and cathodic processes

The addition of oxidants into the electrolyte of Al anodic oxidation can alter the anodic and cathodic reactions, further affects the quality of the oxide film. In this paper, the role of two typical oxidants of H2O2 and Na2MoO4 in the microstructure and corrosion resistance of the oxide film on 2024 aluminum alloy was investigated by the scanning electron microscopy (SEM), Mott Schottky plots and electrochemical impedance spectroscopy (EIS). The addition of H2O2 increases the oxygen evolution amount on the anode Al and more oxygen can participate in the oxide film formation to improve the compactness. The addition of Na2MoO4 results in the deposit of MoO2 on the cathode plate to accelerate the hydrogen evolution reaction by the catalytic action of the MoO2, which further accelerates the anodic reaction to form a thick oxide film. As a result, the corrosion resistance of the oxide film is significantly improved by adding H2O2 or Na2MoO4 due to the promotion of film thickness and compactness.

Enhancement of the Sensing Properties of Chitosan Films as an Acetone Gas Sensor with the Addition of Tin Oxide (SnO2)

Enhancement of the Sensing Properties of Chitosan Films as an Acetone Gas Sensor with the Addition of Tin Oxide (SnO2)