Aminyl Research Articles

Silyl Radical Generation from Silylboronic Pinacol Esters through Substitution with Aminyl Radicals.

A novel strategy was developed to generate silyl radicals from silylboronic pinacol esters (SPEs) through nucleohomolytic substitution of boron with aminyl radicals. We successfully applied this strategy to obtain diverse organosilicon compounds using SPEs and N-nitrosamines under photoirradiation without any catalyst. The ability to access silyl radicals offers a new perspective for chemists to rapidly construct Si-X bonds.

The (±)-5-Aza[1.0]triblattane Skeleton via Azetine Cycloaddition.

The first synthesis of the 5-aza[1.0]triblattane skeleton was achieved through a [4 + 2] cycloaddition approach using a suitably protected azetine and cyclopentadiene. A series of azetines were synthesized to explore both stability and suitable N-protection. The key step following cycloaddition utilized a noninitiated protonated aminyl radical cyclization to install the final 5-azatriblattane bond, but it was found to be considerably more unstable than the 6-aza isomer under acidic conditions.

Synthesis of quinazolinone scaffolds via a zinc(II)-stabilized amidyl radical-promoted deaminative approach.

Herein, we report a solely ligand centered redox controlled protocol, utilizing a bench stable zinc compound, for the efficient coupling of o-amino amides/esters with nitriles to afford diverse quinazolinone scaffolds and their synthetic utility was showcased via post-modification to access therapeutically relevant compounds. Importantly, mechanistic probes established the reaction pathway that proceeds via aminyl radical.

A thiolated copper-hydride nanocluster with chloride bridging as a catalyst for carbonylative C-N coupling of aryl amines under mild conditions: a combined experimental and theoretical study.

Atomically precise copper nanoclusters (Cu NCs), an emerging class of nanomaterials, have garnered significant attention owing to their versatile core-shell architecture and their potential applications in catalytic reactions. In this study, we present a straightforward synthesis strategy for [Cu29(StBu)12(PPh3)4Cl6H10][BF4] (Cu29) NCs and explore their catalytic activity in the carbonylative C-N coupling reaction involving aromatic amines and N-heteroarenes with dialkyl azodicarboxylates. Through a combination of experimental investigations and density functional theory studies, we elucidate the radical mechanisms at play. The crucial step in the catalytic process is identified as the decomposition of diisopropyl azodicarboxylates on the surface of Cu29 NCs, leading to the generation of oxyacyl radicals and the liberation of nitrogen gas. Subsequently, an oxyacyl radical abstracts a hydrogen atom from aniline, initiating the formation of an aminyl radical. Finally, the aminyl radical reacts with another oxyacyl radical, culminating in the synthesis of the desired carbamate product. This detailed analysis provides insights into the intricate catalytic pathways of Cu29 NCs, shedding light on their potential for catalyzing carbonylative C-N coupling reactions.

Theoretical study on the concerted catalysis of Ir/Ni for amino radical transfer for C(sp2)-C(sp3) bond formation.

Thomas C. Maier's group has reported a synergistic Ir/Ni catalysis method for the synthesis of C(sp2)-C(sp3) bonds through an amino radical transfer (ART) strategy to generate alkyl radicals. This work employed density functional theory (DFT) to investigate the reaction mechanism, including the redox mechanism of Ir complexes in the generation process of amino radicals, analyzed the role and rationale behind alkyl boronic esters becoming dominant reaction pathways in the ART process, and discussed the competitive reaction mechanisms between oxidative addition and radical capture during C(sp2)-C(sp3) cross-coupling with Ni complexes. Through this theoretical calculation study, we aim to provide a theoretical foundation for constructing key carbon radical intermediates using ART and Ni-complex catalyzed free-radical-involved C(sp2)-C(sp3) cross-coupling reactions.

NIR-absorbing and emitting α,α-nitrogen-bridged BODIPY dimers with strong excitonic coupling.

Three new distinct NIR α,α-NH-bridged BODIPY dimers were prepared by a direct nucleophilic substitution reaction. The synergistic effects of the nitrogen bridges and strong excitonic coupling between each BODIPY unit play major roles in enhancing the delocalization of an electron spin over the entire BODIPY dimers. The in situ formed aminyl radical dimer showed an absorption maximum at 1040 nm.

Multi-speciation and ignition delay time measurements of ammonia oxidation behind reflected shock waves

Ammonia (NH3) oxidation was studied using emission and laser absorption diagnostics in a shock tube. Experiments were carried out using stoichiometric mixtures of NH3 and O2 highly dilute in Ar seeded with CO2 at post-reflected-shock conditions from 1700–2500K near 2atm. Five optical diagnostics in the infrared (IR), visible, and ultraviolet (UV) were implemented to measure NH3 (before and after shock-heating), NO, electronically excited amino radicals (NH2∗), electronically excited hydroxyl radicals (OH∗), and temperature during oxidation. To mitigate mixture uncertainty due to NH3 adsorption, a scanned-wavelength laser absorption diagnostic near 10.4μm was developed to measure initial NH3 concentration. A two-color, fixed-wavelength laser absorption diagnostic near 225 nm was developed to measure quantitative NO and NH3 time-histories. A detailed spectroscopic model of the NO A2Σ+←X2Π system was used to provide NO absorption cross-sections at both wavelengths, and NH3 absorption cross-sections were measured at the conditions of interest. Emission from NH2∗ near 600 nm was collected to provide qualitative insight into radical formation prior to ignition, and emission from OH∗ near 308 nm was used to determine ignition delay times (IDTs). A two-color, fixed-wavelength laser absorption diagnostic at 4.17μm and 4.19μm was developed to measure temperature using small quantities of seeded CO2. Measured time-histories are compared against predictions from two kinetic models. Experimental results and model predictions show several discrepancies, both in terms of timescales and absolute quantities. Sensitivity analysis shows that the reactions H + O2⇌ O + OH, NH3 + M ⇌ NH2 + H + M, and NH3 + H ⇌ NH2 + H2 are dominant across all conditions, and that NH3 pyrolysis reactions in general drive much of the chemistry. Direct, low-scatter rate constant measurements of the NH3 + M ⇌ NH2 + H + M reaction and additional multi-speciation measurements of NH3 pyrolysis and oxidation at combustion-relevant temperatures and pressures are recommended.Novelty and significance statementThe novelty of this work is exemplified most strongly by the use of UV laser absorption diagnostics to measure NH3 and NO during high-temperature oxidation of NH3. Simultaneous measurements of temperature via CO2 laser absorption at two wavelengths and light emission from NH2∗ and OH∗ are also novel. Simultaneous, time-resolved, quantitative measurements of NH3, NO, and temperature and qualitative measurements of NH2∗ and OH∗ light emission are of significant utility as a model validation-suited data set. Additionally, the data presented herein and the associated findings provide evidence of current chemical kinetic model deficiencies pertaining to NH3 chemistry and suggest avenues for model improvement.

Surface regulation of silicon dioxide nanoparticle and its tribological properties as additive in base oils with different polarity

Silica nanoparticle primarily surface-capped by amino radical was further modified by polyisobutylene succinic anhydride. The tribological properties of RNS-1A-PIBSA nanoparticle as additive in the three kinds of base oils were evaluated and compared with an oscillating reciprocal friction and wear tester (SRV-5). In DIOS with a high polarity, however, RNS-1A-PIBSA nanoparticle has nearly no influence on the friction reducing ability of the base oil. Namely, the lowly polar base oil PAO6 and moderately polar base oil AN5 do not disturb the adsorption of the nano-additive on rubbed metal surface and the formation of relatively thick deposited film; the highly polar base oil DIOS, however, competes with the nano-additive and hinders the adsorption of the nano-additive thereon.

Molecular dynamics simulation of amine formation in plasma-enhanced chemical vapor deposition with hydrocarbon and amino radicals

Molecular dynamics simulations were performed to examine the amine formation in carbon-based polymer films deposited by plasma-enhanced chemical vapor deposition (PECVD) with methane (CH4) and nitrogen (N2) gases. In the simulations, the interactions between the deposited film surface and incident precursors were examined, where nitrogen species were assumed to be supplied only as amino radicals (NH2) such that the amount of primary amine (−NH2) could be maximized in the deposited film. Carbon was supplied as CH2 or CH3 radicals as well as CH2+ or CH3+ ions with an ion kinetic energy up to 100 eV, as typical in such PECVD experiments. It has been found that, even under such “ideal” conditions for the maximum primary-amine content, hydrogen (H) atoms of incident NH2 radicals tend to be transferred to surrounding C atoms in the polymerization process, leaving a relatively small amount of primary amine (the concentration ratio of primary amino groups NH2 to nitrogen atoms N ∼10%) in the deposited polymer films. The simulation results indicate that an increase of NH2 radicals in the gas phase of PECVD hardly increases the primary-amine content in the deposited films and, therefore, the primary-amine content may not depend strongly on the plasma conditions as long as a sufficient amount of nitrogen and hydrogen is supplied during the plasma polymerization process. The primary-amine content predicted by the simulations was found to be consistent with earlier experimental observations.

Proposal of a new mechanism of ammonia on the coking inhibition of n-decane under supercritical conditions

The coking problem of hydrocarbon fuel pyrolysis is the key factor affecting the application of active cooling technology for high-speed aircraft. The purpose of this work is to investigate the coking inhibition performance and coking mechanism of using ammonia as an additive during the thermal cracking. In this study, the pyrolysis and coking characteristics of supercritical n-decane were experimentally studied using an electrically heated tube. ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer), GC–MS (Gas Chromatograph Mass Spectrometer), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), TPO (Temperature Programmed Oxidation), and Raman spectroscopy are applied to characterize the anti-coking performance of the additives. The results show that the additive hardly affects the cracking of the fuel under high-temperature conditions, but the coke mass deposited on the inner surface of the tube is significantly reduced, and the coking inhibition rate can reach 80% at 750 °C. The addition of additives reduced the graphitization degree and oxidative activity of the coke. The maximum oxidation temperature of the coke obtained at 750 °C was reduced by 145 °C, and the ID/IG value of the Raman spectroscopy peak-fitting was 3.29. The new mechanism of the effect of additives on the formation of coking precursors and the deposition of coke on the surface of the tube wall is proposed. Ammonia can react with Ni of the inner metal tube and radicals generated by fuel cracking to form a carbonized film, achieving the effect of inhibiting metal catalytic coking. Meanwhile, the amino radicals generated by ammonia dehydrogenation can regulate the coking reaction path by forming a stable p-π conjugate structure with unsaturated radicals. Therefore, the research will contribute to a deeper comprehension of the coking inhibition mechanism and the development of more effective coking inhibitors, providing new technical support for active cooling technologies.

Deterioration behavior of graphene-modified epoxy-primer-coated aluminum alloy in a UVA acidic alternation immersion environment

The modification of epoxy primers with graphene can significantly improve their anticorrosion properties and reduce environmental pollution. In this study, the modified epoxy primers with different graphene contents were prepared and tested in a UVA acidic alternation immersion environment. The deterioration characteristics under different corrosion times were analyzed in terms of their microscopic morphology, electrochemical characteristics, and molecular structure. It was shown that graphene nanoplates can impede the penetration of corrosive media, promote the cathodic protection of fillers, and easily cross-link with amino radicals to improve the binding force at the interface. The coated surface of graphene nanoplates with a content of 1.0 wt% was flatter than those with a content of 0.5 wt% and 2.0 wt%. After corrosion, the roughness of the surfaces all increased significantly. Especially, the coatings with graphene contents of 0.5 wt% increased nearly three times. And the impedance improvement of the coatings with graphene contents of 0.5 wt% and 1.0 wt% is more significant, both reaching more than 6 × 1011 Ω·cm2. The most obvious corrosion inhibiting effect was the coatings with a graphene content of 1.0% wt.

Efficient and Selective Photogeneration of Stable N-Centered Radicals via Controllable Charge Carrier Imbalance in Cesium Lead Halide Nanocrystals.

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N-H bond dissociation. The negative charge of the halide ions on the NC's lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

ЭЛЕКТРОННОЕ СТРОЕНИЕ ГОМОЛОГИЧЕСКИХ РЯДОВ ПЕРВИЧНЫХ АМИНОВ И АМИНИЛЬНЫХ РАДИКАЛОВ

Электронное строение молекул моноалкиламинов R-NH2 и соответствующих радикалов R-N●H изучено в рамках квантовой теории атомов в молекулах. Представлены значения зарядов и объемов атомных групп. Проведено сравнение влияния на углеводородную цепь функциональных групп, содержащих атомы O-, N-, S-. The electronic structure of the molecules of monoalkylamines R-NH2 and the corresponding radicals R-N●H has been studied in the framework of the quantum theory of atoms in molecules. The values of charges and volumes of atomic groups are presented. The effect of functional groups containing O-, N-, S- atoms on the hydrocarbon chain is compared.

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes.

Two air-stable organic radicals derived from oxalyl chloride and cAAC were synthesized, resulting in the unexpected formation of a known (amino)(carboxy) radical cation ([2]BF4) and the oxidative formation of a 1,2-dicarbonyl radical cation ([3]BF4) from a neutral 3-oxetanone compound (4). The highly strained and newly discovered 4 was obtained by a single-electron reduction of [3]BF4 with a mild reducing agent. This result differs from the generation of NHC-based 1,2-dicarbonyl radicals, indicating the uniqueness of cAAC.

Multistructural torsional anharmonicity and pressure-dependent kinetic studies on methanol/ethanol reaction with amino radical: Implication for combustion modeling

The blending of ammonia with alternative fuel alcohols has recently received increasing interest and it has been shown that their cross-reactions significantly influence the ignition process. In the present work, the detailed electronic structure calculations and kinetic studies for the reactions of CH3OH/C2H5OH with NH2 were performed. The rate constants were calculated by Master Equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) over a pressure range of 10−1–105 Torr for the pressure-dependent effect caused by reactant complex. The multistructural torsional anharmonicity effects of the reaction were analyzed and the high-pressure limiting rate constants were calculated over a wide temperature range of 250–2000 K by using multistructural variational transition state theory. All calculations considered the tunneling effect. The results show that the CH3OH/NH2 system exhibits pressure-dependent below 550 K, while the pressure-dependent of the C2H5OH/NH2 system can be safely neglected. Besides, the multistructural torsional anharmonicity effect is pronounced for the C2H5OH/NH2 system, especially at intermediate and high temperatures. The channel for the formation of CH2CH2OH is underestimated and the branching ratio of this channel exceeds that of CH3CH2O and CH3CHOH under the multistructural influence at high temperatures. Thus, we updated the kinetic model and further investigation on ignition delay times and sensitivity analysis. The discrepancies in rate constants caused by the kinetic methods mentioned above seems to have a non-negligible effect on the combustion modeling.

Blue Light Irradiated Metal-, Oxidant-, and Base-Free Cross-Dehydrogenative Coupling of C(sp2)-H and N-H Bonds: Amination of Naphthoquinones with Amines.

Herein, we report a blue-light-driven amination of C(sp2)-H bond of naphthoquinones and quinones with the N-H bond of primary and secondary amines for the synthesis of 2-amino-naphthoquinones and 2-amino-quinones. The coupling of naphthoquinones with a wide array of aliphatic, aromatic, chiral, primary, and secondary amines having electron donating (-CH3, -OCH3, -SCH3), withdrawing (-F, -Cl, -Br, -I), and CO2H, -OH, -NH2 groups with acidic protons selectively occurred to afford C-N coupled 2-amino-naphthoquinones in 60-99% yields and hydrogen gas as a byproduct in methanol solvent without using any additional reagents, additives, and oxidant under the blue light irradiation. Mechanistic insight by DFT computation, controlled experiments, kinetic isotopic effect, and substitution effect of the substrates suggest that the reaction proceeds by radical pathway in which naphthoquinone forms a highly oxidizing naphthoquinonyl biradical upon irradiation of blue light (457 nm). Consequently, electron transfer from electron-rich amine to an oxidizing naphthoquinonyl biradical leads to a naphthoquinonyl radical anion and aminyl radical cation, followed by proton transfer and delocalization leading to a carbon-centered naphthoquinonyl radical. The cross-coupling of naphthoquinonyl carbon-centered and aminyl nitrogen radicals forms a C-N bond, with subsequent elimination of hydrogen gas (which was also confirmed by GC-TCD), affording 2-amino-1,4-naphthoquinone under metal-, reagent-, base-, and oxidant-free conditions.

Synthesis of a Carbene-Stabilized (Diphospha)aminyl Radical and Its One Electron Oxidation and Reduction to Nonclassical Nitrenium and Amide Species

Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAACMePNPCAACMe 4 (CAACMe = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) by a facile one-pot, seven-electron reduction of hexachlorophosphazene chloride [Cl3PNPCl3][Cl]. The PNP radical 4 features a conjugated framework with spin density primarily localized on the central nitrogen atom as well as the flanking carbenes. Unlike other tripnictogen radicals, 4 undergoes facile one-electron oxidation and reduction to yield nonclassical nitrenium and amide species [5]+ and [6]-, respectively. The cation [5]+ exhibits conformational flexibility in the solution state between the expected W-shaped geometry [5b]+ and a previously unobserved linear heteroallene-type structure [5a]+, which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [5a]+ is favored over [5b]+ both enthalpically (ΔH = -2.9 × 103 ± 80 J mol-1) and entropically (ΔS = 4.2 ± 0.25 J mol-1 K-1). The formal amide [6]- displays remarkable flexibility in its coordination chemistry due to the presence of multiple Lewis basic centers, as evidenced by the structure of its potassium complex K262, which exhibits μ, κ-P, κ-P, and η3-PNP coordination modes. Protonation of [6]- leads to the formation of an amine 7, which features a trigonal planar geometry around nitrogen.

Alkyl Radical Generation from Alkylboronic Pinacol Esters through Substitution with Aminyl Radicals.

Alkylboronic pinacol esters (APEs) are highly versatile reagents in organic synthesis. However, the direct generation of alkyl radicals from commonly used, bench-stable APEs has not been well explored. In this communication, alkyl radical generation from APEs through reaction with aminyl radicals is reported. The aminyl radicals are readily generated by visible-light-induced homolytic cleavage of the N-N bond in N-nitrosamines, and C radical generation occurs through nucleohomolytic substitution at boron. As an application, the highly efficient photochemical radical alkyloximation of alkenes with APEs and N-nitrosamines under mild conditions is presented. A wide range of primary, secondary, and tertiary APEs engage in this transformation that is easily scaled up.

Emerging Metabolic Profiles of Sulfonamide Antibiotics by Cytochromes P450: A Computational-Experimental Synergy Study on Emerging Pollutants.

Metabolism, especially by CYP450 enzymes, is the main reason for mediating the toxification and detoxification of xenobiotics in humans, while some uncommon metabolic pathways, especially for emerging pollutants, probably causing idiosyncratic toxicity are easily overlooked. The pollution of sulfonamide antibiotics in aqueous system has attracted increasing public attention. Hydroxylation of the central amine group can trigger a series of metabolic processes of sulfonamide antibiotics in humans; however, this work parallelly reported the coupling and fragmenting initiated by amino H-abstraction of sulfamethoxazole (SMX) catalyzed by human CYP450 enzymes. Elucidation of the emerging metabolic profiles was mapped via a multistep synergy between computations and experiments, involving preliminary DFT computations and in vitro and in vivo assays, profiling adverse effects, and rationalizing the fundamental factors via targeted computations. Especially, the confirmed SMX dimer was shown to potentially act as a metabolism disruptor in humans, while spin aromatic delocalization resulting in the low electron donor ability of amino radicals was revealed as the fundamental factor to enable coupling of sulfonamide antibiotics by CYP450 through the nonconventional nonrebound pathway. This work may further strengthen the synergistic use of computations prior to experiments to avoid wasteful experimental screening efforts in environmental chemistry and toxicology.

Synthesis of silylamine and siloxyamine compounds: A novel approach to flame retardancy of polypropylene and Epoxy resins

A series of innovative flame retardants containing N-Si and N-O-Si bonds have been synthesized. Their chemical structures were verified by nuclear magnetic resonance (NMR) spectroscopy and thermal stabilities determined by thermogravimetric analysis (TGA). The results indicate that their thermal and hydrolytic stabilities could be adjusted by fine tuning their silylamine (N-Si) and siloxyamine (N-O-Si) skeletons. Thus, the substituents bonded to the phthalimides, such as diphenylmethylsilyl, dimethylphenylsilyl, diphenyl‑tert-butylsilyl, triisopropylsilyl or diphenylmethylsiloxy; whichever was attached to the imide played a significant role on its thermal and hydrolytic properties. Upon thermal dissociation, the N-Si and N-O-Si compounds were shown to yield aminyl, silyl and oxygen-centered radicals that provided fire proofing effect in polypropylene (PP) films alone and a synergistic effect in combination with conventional phosphorous flame retardant in PP, linear low-density polyethylene (LLDPE) and epoxy resins (EP). Their efficacy as flame retardants alone in thin PP films were evaluated according to the DIN4102-B2 test. Both N-Si and N-O-Si significantly slowed down the burning of PP films. Moreover, their potential as adjuvants with a conventional phosphorous based flame retardant, i.e., spirocyclic phosphonate (AFLAMMIT® PCO 900) in PP and EP resins was evaluated according to the UL-94 V fire standard. A synergistic effect was observed when the phosphorous flame retardant was combined with either N-Si or N-O-SI containing compounds, since none of the flame retardants by themselves could provide V-0 rating in the UL94-V test in PP, LLDPE or EP resins even at much higher loadings. The thermogravimetric analysis carried out under inert atmosphere revealed enhanced and earlier onset of decomposition and thermal activation of phosphorous based flame retardant in the presence of N-Si or N-O-Si in comparison to spirocyclic phosphonate, N-Si or N-O-Si used alone, respectively. The interaction of the phosphorus flame retardant with N-Si was verified by 31P NMR.