Precursor Anions Research Articles

Mechanistic insight into the kinetic fragmentation of norpinonic acid in the gas phase: an experimental and density functional theory (DFT) study

Abstract. Norpinonic acid has been known as an important α-pinene atmospheric secondary organic aerosol (SOA) component. It is formed in the reaction of α-pinene, β-pinene or verbenone with atmospheric oxidizing reagents. In the presented study, tandem mass spectrometry techniques were used to determine the exact norpinonic acid fragmentation pathway in the gas phase. The precursor anion – deprotonated norpinonic acid (m/z 169), generated in an electrospray (ESI) source – was introduced into the collision cell of the mass spectrometer and fragmented using the energy-resolved collision-induced dissociation (ER-CID) technique. The experimental energy values of degradation processes were determined via analysis of the breakdown curves. Quantum chemical calculations of the reaction models were also constructed, including calculation of all transition states. Comparison between the experimental and the theoretical threshold energies calculated at a ωB97XD/6-311+G(2d,p) theoretical level has shown a good correlation. Two basic pathways of the fragmentation of the parent anion [M-H]− (m/z 169) were observed. Firstly this leads to the decarboxylation product (m/z 125) and secondly to the loss of a neutral molecule (C4H6O), together with the formation of the anion m/z 99. On the other hand, the breakdown of the anion m/z 125 gives rise to the m/z 69, 57 and 55 ions. To confirm structures formed during ER-CID experiments, the gas-phase proton transfer reactions were examined of all norpinonic acid anionic fragments with a series of neutral reagents, characterized by proton affinity (PA) values. Based on PA difference analysis, the most possible chemical structures were proposed for the observed fragment anions.

Photocatalytic CO2 Reduction Using Zinc Indium Sulfide Aggregated Nanostructures Fabricated under Four Anionic Conditions.

Zinc indihuhium sulfide (ZIS), among various semiconductor materials, shows considerable potential due to its simplicity, low cost, and environmental compatibility. However, the influence of precursor anions on ZIS properties remains unclear. In this study, we synthesized ZIS via a hydrothermal method using four different anionic precursors (ZnCl2/InCl3, Zn(NO3)2/In(NO3)3, Zn(CH3CO2)2/In(CH3CO2)3, and Zn(CH3CO2)2/In2(SO4)3), resulting in distinct morphologies and crystal structures. Our findings reveal that ZIS produced from Zn(CH3CO2)2/In2(SO4)3 (ZIS-AceSO4) exhibited the highest photocatalytic CO2 reduction efficiency, achieving a CO production yield of 134 μmol g-1h-1. This enhanced performance is attributed to the formation of more zinc and indium vacancy defects, as confirmed by EDS analysis. Additionally, we determined the energy levels of the valence band maximum (VBM) and the conduction band minimum (CBM) via UPS and absorption spectra, providing insights into the band alignment essential for photocatalytic processes. These findings not only deepen our understanding of the anionic precursor's impact on ZIS properties but also offer new avenues for optimizing photocatalytic CO2 reduction, marking a significant advancement over previous studies.

Spontaneous Formation of Strained Anti-Bredt Bridgehead Alkenes upon Computational GeometryOptimization of Bicyclic β-Halo Carbanions

Bridgehead alkenes are polycyclic molecules bearing at least one C=C bond that includes a bridgehead carbon atom. For small bicyclic systems, these bonds are highly strained due to geometric constraints placed on the sp2 hybridized carbon atoms. These small, strained molecules have been termed “anti-Bredt” alkenes. β-halo carbanions have served as convenient precursors to bridgehead alkenes in experimental studies. We observed that upon attempted computational geometric optimizations (ωB97X-D/aug-cc-pVDZ) of the precursors, spontaneous elimination of the halide occurs along with formation of the anti-Bredt alkene in many cases. Such computational eliminations were shown to faithfully mimic experimentally obtained results. Computational elimination was not observed for [1.1.1] or [2.1.1] frameworks, in agreement with predictions that these bridgehead alkenes are too strained to be formed. However, computational elimination from the [2.2.1] framework was observed to form 1-norbornene, a compound suggested in experimental work to be a reactive intermediate. Similarly, [3.1.1] frameworks and higher led to eliminations upon computational geometric optimization, in agreement with experimental findings. Natural bond order (NBO) calculations of the starting geometries proved to be excellent predictors as to whether elimination would take place. Those precursor compounds exhibiting delocalization energies in the order of 10 kcal/mol between the lone-pair electrons of the carbon atom and σ*C-Br were generally found to undergo elimination. Thus, computational optimization of β-halo substituted bicyclic precursor anions can be used to predict whether strained anti-Bredt alkenes are likely to be formed, thereby saving valuable time and costs in the experimental lab.

Influence of inevitable iron precursor anions on MIL-100(Fe) structure and its La(Ⅲ) adsorption performance

The influence of iron precursor anions on the structure and properties of MIL-100(Fe) has often been overlooked. In this study, iron chloride hexahydrate and iron nitrate nonahydrate were used to synthesize MIL-100(Fe)-Cl and MIL-100(Fe)-N, respectively. Characterization comparisons revealed that MIL-100(Fe)-Cl exhibited a higher organic ligand content and a larger specific surface area. Subsequently, the adsorption properties of both materials for the rare-earth element lanthanum (La(Ⅲ)) were investigated. MIL-100(Fe)-Cl demonstrated superior La(Ⅲ) adsorption performance, with a maximum adsorption capacity of 54.7 mg·g−1, which is more than twice that of MIL-100(Fe)-N at 25.5 mg·g−1. The adsorption rate of MIL-100(Fe)-Cl for low-concentration La(Ⅲ) approached 100 % and sustained effective adsorption under weakly acidic conditions. The La(Ⅲ) adsorption processes on MIL-100(Fe)-Cl and MIL-100(Fe)-N were spontaneous and endothermic, involving both physisorption and chemisorption. Notably, a strong chemical interaction occurred during La(Ⅲ) adsorption by MIL-100(Fe)-Cl, whereas ion exchange was predominant in MIL-100(Fe)-N. Through further exploration of the adsorption mechanism via FT-IR and XPS characterizations, the main chemical active sites were the uncoordinated –COOH and terminal –OH groups of the Fe trimer. This study underscores the significant impact of different iron precursors on the synthesis of MIL-100(Fe), highlighting the need for careful selection of these materials in precursor choice.

Formation of FeNi-based nanowire-assembled superstructures with tunable anions for electrocatalytic oxygen evolution reaction

Anion modification has been considered as a strategy to improve water splitting efficiency upon oxygen evolution reaction (OER). However, constructing a novel catalysis system with high catalytic activity and precise structures is still a huge challenge due to the tedious procedure of precursor synthesis and anion selection. Here, a bimetallic (FeNi) nanowire self-assembled superstructure was synthesized using the Hoffmann rearrangement method, and then functionalized with four anions (P, Se, S, and O). Notably, the Fe3Se4/Ni3Se4 catalyst shows a high conductivity, enhances the adsorption of intermediate products, accelerates the rate-determining step, and consequently results to improved electrocatalytic performance. Using the Fe3Se4/Ni3Se4 catalyst exhibits enhanced performance with overpotential of 316 mV at 10 mA/cm2, in stark contrast to Fe2P/Ni2P (357 mV), Fe7S8/NiS (379 mV), and Fe3O4/NiO (464 mV). Moreover, the formation mechanism of superstructure and the relationship between electronegativities and electrocatalytic properties, are elucidated. Accordingly, this work provides an efficient approach to Hoffmann-type coordination polymer catalyst for oxygen evolution towards a near future.

Exploration of anion effects in solvothermal synthesis using in situ X-ray diffraction.

Solvothermal synthesis presents a facile and highly flexible approach to chemical processing and it is widely used for preparation of micro- and nanosized inorganic materials. The large number of synthesis parameters in combination with the richness of inorganic chemistry means that it is difficult to predict or design synthesis outcomes, and it is demanding to uncover the effect of different parameters due to the sealed and complex nature of solvothermal reactors along with the time demands related to reactor cleaning, sample purification, and characterization. This study explores the effect on formation of crystalline products of six common anions in solvothermal treatment of aqueous and ethanolic precursors. Three different cations are included in the study (Mn2+, Co2+, Cu2+) representing chemical affinities towards different regions of the periodic table with respect to the hard soft acid base (HSAB) classification and the Goldschmidt classification. They additionally belong to the commonly used 3d transition metals and display a suitable variety in solvothermal chemistry to highlight anion effects. The results of the solvothermal in situ experiments demonstrate a clear effect of the precursor anions, with respect to whether crystallization occurs or not and the characteristics of the formed phases. Additionally, some of the anions are shown to be redox active and to influence the formation temperature of certain phases which in turn relates to the observed average crystallite sizes.

Harnessing plasma-generated reactive species for the synthesis of different phases of molybdenum oxide to study adsorption and photocatalytic activity.

This study employs plasma-liquid interaction technique to synthesize different phases of molybdenum oxide using air and argon as plasma-forming gases. In situ plasma-generated nitrogen species primarily NO3-/NO2- and hydrogen species (H+) facilitate the reduction of the molybdenum precursor anion (Mo7O24-). The reduced Mo species subsequently reacts with reactive oxygen species, forming MoO6 octahedra, which is the building block of a molybdenum oxide crystal. Varied concentrations of NO3-/NO2- and H+ species in air and argon plasma treatment significantly influence the growth process. Air plasma synthesis yields hexagonal molybdenum oxide microrods, which upon calcination changes its phase to orthorhombic 2D layered structure. Moreover, the argon plasma synthesized sample exhibits a mixed phase of hexagonal and orthorhombic molybdenum oxide due to the heavy argon ion bombardment, inducing material porosity and surface oxygen vacancies. The mixed-phase material exhibits superior adsorption and photo-degradation towards cationic dye compared to the other two phases. The higher photocatalytic performance may be responsible for the extended lifetime of the photo-generated charge carriers possessed by the mixed-phase material. Radical scavenging tests have identified holes and hydroxyl radicals as the key reactive species that take part in the photo-degradation process.

Modulating the Morphological Features of Hydrothermally Derived Nickel Cobaltite for Supercapacitor Application: Role of Precursor Anions.

Morphologically engineered porous electrodes show great promise in energy applications as they exhibit improved electrochemical activity owing to increased electrical conductivity, increased surface area, and a shorter path length for ion transport. Herein, the role of precursors (chlorides, acetates and nitrates) on the crystallinity and textural features of Nickel Cobaltite, obtained by the controlled precipitation through hydrothermal synthesis, is studied. The synthesis yielded urchin like structures with morphological variations in substructures based on the precursor anion types. The surface area values obtained for nickel cobaltite derived from the chloride (NCO-C), nitrate (NCO-N), and acetate precursors (NCO-A) were 30,110 and 115 m2 g-1 , confirming the influence of anions on the textural features. The time dependant electrolyte (2 M KOH) infiltration behaviour on the electrode surfaces based on contact angle measurements is invoked to correlate its morphological and textural attributes with the electrolyte transport kinetics. The electrochemical performances were derived from cyclic voltammetry, galvanostatic charge discharge analysis and impedance measurements. The electrolyte infiltration studies established a dependence on the precursor anion. NCO-A facilitated faster electrolyte infiltration time of 7800 ms compared to 16200 ms and 54,000 ms for NCO-N and NCO-C electrodes, respectively. Furthermore, NCO-A exhibited a greater specific capacitance of 802 F g-1 than NCO-N (500 F g-1 ) and NCO-C (342 F g-1 ). The morphology modulation coupled with optimal porosity led to conducive pathways for reversible electrolyte infiltration resulting in increased capacitive contribution in NCO-A. The study revealed that the size of intercalating anions exercised a significant impact on the morphological and electrochemical features, signifying the importance of synthetic approaches in determining the functional properties of electrode materials.

Nuclear wave-packet-propagation-based study of the electron-coupled, proton-transfer process in the charge-transfer state of FHCl exhibiting three electronic states in full-dimensional space.

The charge-transfer (CT) excited state of FHCl (F+H-Cl-), generated by the photodetachment of an electron from its precursor anion (FHCl-) by a photon energy of ∼9.5eV, is a realistic prototype of two bidirectional-coupled reaction pathways, namely the proton-transfer (PT) and electron-transfer (ET) channels, that produce F + HCl and FH + Cl combinations, respectively. The early-time dynamics of the CT was studied via the time-dependent propagations of nuclear wave packets comprising three nonadiabatically coupled electronic states defined within a three-dimensional space. The detailed analyses of the early-time dynamics revealed an interesting phenomenon in which the onset of PT was ∼80fs earlier than that of ET, indicating that PT dominated ET in this case. A more significant finding was that the proper adjustment of the electronic-charge distribution for the onset of ET was obtained ∼80fs after the onset of PT; this adjustment was mediated by the initial movement of the H atom, i.e., the F-H vibration mode. To avail experimental observables, the branching ratio, χ = PT/(PT + ET), and absorption spectrum generating the neutral FHCl molecule from its precursor anion were also simulated. The results further demonstrated the dependences of the χs and spectrum on the change in the initial vibration level of the precursor anion, as well as the isotopic substitution of the connecting H atom with deuterium, tritium, and muonium.

Bimetallic oxide nanoparticles contained hollow spheres with sodium as a core: a promising energy storage advanced structure

The bimetallic oxide nanoparticles as outer shell with sodium entrapped as a core part of a hollow porous core–shell (HoPoCs) can be a promising battery electrode composition. Till now, scientists are struggling to synthesize ternary metal oxide hollow spheres due to the reactions between diverse cations and anions of different metal precursors. Also, the extremely reactive character of sodium prevents it from remaining alone without compound formation is unveiled. Here for the first time, we entrapped sodium and synthesized bimetallic nanoparticles contained outer shell hollowsphere (Na@ZnO@MoO2) successfully by sorption (absorption + adsorption) of two metal precursors (sodium molybdate dihydrate and zinc chloride) in two steps without adding any reaction inhibiting agent. As a result, significantly Na is entrapped as a core and ZnO and MoO2 nanoparticles forming the outer shell of the sphere. ‘Na’ entrapment is confirmed by X-ray photoelectron spectroscopy and high-angle annular dark-field scanning transmission electron microscopy elemental mapping. We employed our sodium entrapped HoPoCs bimetallic oxide nanoparticles sphere (Na@ZnO@MoO2) as a battery anode getting advantages from their structural specialty shows excellent battery properties promising for application in energy storage technologies. The initial specific capacity of these HoPoCs-Na@ZnO@MoO2 sphere is 940 mAh/g (1C), with exceptional stability (790 mAh/g) after 1000 cycles at a current density of 2C) and excellent rate capability. This approach will motivate the synthesis of other superior reactive element entrapped core–shell metal oxides for next-generation rechargeable batteries and other advanced suitable applications like microreactor, protector of explosive materials, and so on.

Anodic deposition of highly efficient nickel iron oxide electrocatalysts for water oxidation and role of anions in catalyst deposition

Nickel iron oxide has acquired significant interest as a highly efficient electrocatalyst for the oxygen evolution reaction. Although anodic deposition is beneficial for its preparation, anodically deposited nickel iron oxide presents poor performance, and the detailed mechanism of its formation is ambiguous, limiting its extensive applications. In this study, we examined the anodic deposition of nickel iron oxide using electroanalytical techniques combined with an electrochemical quartz crystal microbalance. In particular, the effects of anions were investigated to determine whether the formation of a nickel iron oxide film sensitively depends on the counter anions of the metal precursors. The anions not only provide buffering to retain the solution pH but also play a significant role in scavenging the surface protons to facilitate the growth of the catalyst film. We established a modified protocol to anodically deposit nickel iron oxide electrocatalysts excellent for water oxidation, with the best ever reported performance. These findings presented important but previously neglected aspects of anodic deposition, providing implications for nonprecious metal electrocatalysts.

Facile preparation of nanostructured ZnO via low-temperature hydrothermal method upon changing the precursor anion: The study of structural, morphological, and optical properties

The synthesis of ZnO nanostructures was carried out via a low-temperature hydrothermal route; using three different zinc precursors: ZnSO4, ZnCl2, and Zn(ac)2. X-ray diffraction analysis confirmed that all synthesized samples have high purity wurtzite hexagonal structure. The calculation of lattice parameters indicated that the precursor’s anion and the hydrothermal time strongly affected the lattice parameters. The SO42- anion capped the polar surface growth, which leads to 2D nanostructures. However, the Cl- anion boosted growth along the c axis and inhibited the lateral axes, which lead to 1D nanostructures. The microstrain and crystallite size of the samples were determined using the Williamson-Hall (W-H), Size-Strain Plot, and Halder-Wagner (H-W) methods. The SEM images indicated morphological differences in the formation of the synthesized samples, confirming that the anion of the precursor and the hydrothermal time play a determining role in the shape of the ZnO nanostructures. All the ZnO samples show strong absorption in the ultraviolet region with an onset of absorbance in the range 250–335 nm; blue shifting was observed for all samples indicating a large bandgap, such as Eg(Cl-) > Eg(SO42-) > Eg(C2H3O2-) and the Urbach energy that reflects the disorder was calculated, such thatEu(ZA6) > Eu(ZS6) > Eu(ZC6). There was a correlation between optical and structural proprieties: the bandgap decreased with increasing microstrain, however, Urbach energy increased.

Fragmentation pathways of deprotonated ortho-hydroxybenzyl alcohol.

The ortho, meta, and para isomers of hydroxybenzyl alcohol can be unequivocally distinguished by the collision-induced dissociation mass spectra of their anions. The presence of a prominent peak at m/z 121 for an elimination of a dihydrogen molecule renders the ortho-isomer spectrum markedly different from those of its meta and para congeners. Investigations carried out with deuterium-labeled isotopologues of the ortho isomer verified that the labile hydrogen atom on the hydroxyl group and one of the benzylic hydrogen atoms are specifically removed in the formation of the m/z 121 ion. The ortho-isomer spectrum also showed a prominent peak at m/z 93. Experimental data indicated that the m/z 93 product ion originates either from a two-step H2and CO elimination mechanism or from a direct loss of a HCHO molecule from the precursor anion. The intensity ratio of the m/z 93 and 94 peaks in the spectrum recorded from the m/z 124 ion generated from a sample of o-hydroxybenzyl alcohol dissolved in D2O supported the notion that the direct HCHO loss is the more dominant pathway for the generation of the phenolate ion under low activation conditions. In contrast, the two-step mechanism becomes the more dominant pathway under high collisional activation conditions. The spectrum also showed a weak peak at m/z 105 for a water loss. Based on computational data, the m/z 105 ion generated in this way appears to be a composite generated from a common ion-neutral complex intermediate in which a hydroxyl anion is positioned equidistantly between one of the benzylic hydrogens and a nearby hydrogen atom of the benzene ring. Upon activation, the complex dissociates to form either a phenide or a quinone methide anion. The reaction forming a carbon dioxide adduct under ion-mobility conditions was used to support the proposed water-loss mechanism.

Probing the Exit Channel of the OH + CH3OH → H2O + CH3O Reaction by Photodetachment of CH3O-(H2O).

Transition state dynamics of bimolecular reactions can be probed by photodetachment of a precursor anion when the Franck-Condon region of the corresponding neutral potential energy surface is near a saddle point. In this study, photodetachment of anions at m/z = 49 enabled investigation of the exit channel of the OH + CH3OH → H2O + CH3O reaction using photoelectron-photofragment coincidence spectroscopy. High-level coupled-cluster calculations of the stationary points on the anion surface show that the methoxide-water cluster CH3O-(H2O) is the stable minimum on the anion surface. Photodetachment at a 3.20 eV photon energy leads to long-lived H2O(CH3O) complexes and H2O + CH3O products consistent with both direct dissociative photodetachment and resonance mediated processes on the neutral surface. The partitioning of total kinetic energy in the system indicates that water stretch and bend excitation is induced in dissociative photodetachment and evidence for long-lived complexes consistent with vibrational Feshbach resonances is reported.

Anion Dependent Particle Size Control of Platinum Nanoparticles Synthesized in Ethylene Glycol.

The polyol synthesis is a well-established method to form so-called “surfactant-free” nanoparticles (NPs). In the present study, the NP size resulting from the thermal reduction of the precursors H2PtCl6, H2Pt(OH)6, or Pt(acac)2 in presence of the bases NaOH or Na(acac) at different concentrations is studied. It is shown that the size control depends more strongly on the nature of the precursor (metal salt) than on the anion present in the base. The latter is surprising as the concentration of the base anion is often an important factor to achieve a size control. The reduction of H2PtCl6 or H2Pt(OH)6 in presence of NaOH and Na(acac) confirm the observation that the NP size is determined by the OH−/Pt molar ratio and expands it to the base anion/Pt molar ratio. In contrast, the reduction of Pt(acac)2 in presence of the bases NaOH (previous reports) or Na(acac) (shown in the present work) leads to larger NPs of ca. 3 nm, independent of the concentration of the base anions. Hence, the anion effect observed here seems to originate predominantly from the nature of the precursor (precursor anion dependence) and only for certain precursors as H2PtCl6 or H2Pt(OH)6 the size control depends on the base anion/Pt molar ratio.

Bioinspired perovskite quantum dots microfibers from microfluidics

As perovskite quantum dots (PeQDs) are performing their outstanding characteristics, incremental efforts have been devoted to such materials. Here, inspired by the spider spinning process, we present novel PeQDs microfibers with tailorable morphologies and functions from a multi-injection microfluidic approach. The microfibers were generated by introducing PeQDs precursors into each barrel of the inner capillary array and mixing them in the spindle middle channel, where the poly(vinylidene fluoride) (PVDF) dissolved in N,N-dimethyl formamide (DMF) was also injected as their sheath fluid. During this process, the PeQDs were in situ synthesized with the connection of precursor cations and anions in the core fluid; while the PVDF formed solidified microfibers to encapsulate PeQDs with the fast dispersion of DMF into the outer aqueous solution. Thus, the good encapsulation of PeQDs was achieved in PVDF microfibers, which effectively protected them from different hostile environments. Because of the highly tunable spinning processes, the microfibers exhibited controllable diameters and helical geometric structures, and the encapsulated PeQDs could yield adjustable emission peaks. Based on the PeQDs microfibers, we have explored their potential as luminescent materials in barcodes and as flexible photodetectors, which make such microfibers highly versatile for different areas.

Wavepacket propagations for the early time dynamics of proton-coupled electron transfer in the charge-transfer state of NH3Cl complex.

A charge-transfer (CT) excited state of NH3Cl, generated by photo-detachment of an electron from the anionic NH3Cl- precursor, can be represented as H2N+-H-Cl- and proceeds to two chemical reactions: one reaction generating NH2 and HCl resulting from a proton transfer (PT) and the other reaction producing NH3 and a Cl atom resulting from an electron transfer (ET); both are coupled to form a typical proton-coupled electron transfer (PCET) process. The early time dynamics of this CT were studied using time-dependent wavepacket propagation on three nonadiabatically coupled electronic states in a reduced three-dimensional space. The electronic states were treated using the XMS-CASPT2/aug-cc-pVTZ ab initio methodology. The population dynamics of the three coupled electronic states were analyzed in detail to reveal the initial stage of the PCET process up to ∼100 fs, while the branching ratio, χ = PT/(ET+PT), was determined after wavepacket propagations of up to 2000 fs. Another main result is the dependence of χ on the vibration levels of the initial precursor anion and the isotope substitution of the connecting H atom with deuterium and tritium. Our study reveals the detailed microscopic features of the PCET process embedded in the CT state of the NH3Cl complex and certain systematic dependences of the branching ratio χ on the above factors.

Decomposition of Bis(acetylacetonate)zinc(II) by Slow Electrons.

The production of zinc-containing nanostructures has a large variety of applications. Using electron beam techniques to degrade organometallic molecules for that purpose is perhaps one of the most versatile methods. In this work, we investigate the scattering of low-energy (<12 eV) electrons with bis(acetylacetonate)zinc(II) molecules. We show that core excited and high-lying shape resonances are mainly responsible for the production of the precursor anions as well as the ligand negative fragments, which are observed exclusively at electron energies of >3 eV. The mechanisms for electron capture and then molecular dissociation are discussed in terms of density functional theory studies.

Gas-Phase Dissociation Chemistry of Deprotonated RGD.

We investigate the structure and dissociation pathways of the deprotonated amphoteric peptide arginylglycylasparic acid, [RGD-H]-. We model the pertinent gas-phase structures and fragmentation chemistry of the precursor anions and predominant sequence-informative bond cleavages (b2+H2O, c2, and z1 peaks) and compare these predictions to our tandem mass spectra and infrared spectroscopy experiments. Formation of the b2+H2O anions requires rate-limiting intramolecular back biting to cleave the second amide bond and generate an anhydride structure. Facile cleavage of the newly formed ester bond with concerted expulsion of a cyclic anhydride neutral generates the product structure. IR spectroscopy supports this b2+H2O anion having structures that are essentially identical to C-terminally deprotonated arginylglycine, [RG-H]-. Formation of the c2 anion is predicted to require concerted expulsion of CO2 from the aspartyl side chain carboxylate and cleavage of the N-Calpha bond to produce a proton-bound dimer of arginylglycinamide and acrylate. Proton transfers within the dimer then enable predominant detection of a c2 anion with the negative charge nominally on the central, glycine nitrogen (amidate structure) as the proton affinity of this structure is predicted to be lower than acrylate by ∼27 kJ mol-1. Alternate means of cleaving the same N-Calpha bond produce deprotonated cis-1,4-dibut-2-enoic acid z1 anion structures. These lowest energy processes involve C-H proton mobilization from the aspartyl side chain prior to N-Calpha bond cleavage consistent with proposals from the literature.

Intermediate formation enabled regioselective access to amide in the Pd-catalyzed reductive aminocarbonylation of olefin with nitroarene

An efficient route for the palladium-catalyzed reductive aminocarbonylation of olefins with nitroarenes was developed using carbon monoxide (CO) as both reductant and carbonyl source, which enables facile access to amides with excellent regioselectivity and broad substrate scope. It is found that the counter anions of the Pd catalyst precursors significantly affect the reaction chemoselectivity and amide regioselectivity. Branched amides were mainly obtained with K2PdCl4 as the metal catalyst, and phosphine ligands had no influence on the regioselectivity but affected the catalytic reactivity. However, phosphine ligands had significant effects on aminocarbonylation regioselectivity when Pd(CH3CN)4(OTf)2 was used; monodentate phosphines tended to form branched amides, and bidentate phosphines mainly formed linear amides. Trapping experiments, primary kinetic studies, and control reactions with all possible <I>N</I>-species reduced from nitroarene indicated that the catalytic synthesis of branched and linear amides produced nitrene (further converted to enamide) and aniline, respectively, different from the previous ligand-controlled regioselective synthesis of amides via the aminocarbonylation of olefins with amines. Furthermore, the proposed synthesis route could be applied in the synthesis of gram-scale propanil under mild conditions.