Cationic Catalysis Research Articles

A Tamed Intermediate: The Pivotal Role of Cp* in Hypercoordinate Boron Cation Catalysis

A Tamed Intermediate: The Pivotal Role of Cp* in Hypercoordinate Boron Cation Catalysis

Selective pore regulation of activated carbon using trace carbonate-assisted catalytic activation: Revealing the effect of cation catalysis on pore topology

Activated carbon is an important adsorbent for the adsorption removal of water or gas pollutants due to its low cost, high efficiency, and large-scale production potential; however, currently commercial activated carbon prepared through physical or chemical activation commonly shows a single microporous characteristic, making it difficult to match different kinds of pollutants. Here, we propose a convenient and cost-effective pore regulation strategy by introducing a trace carbonate catalysis process into the activation reaction, in which we find that the types of cations (Na, K, Ca) in carbonate have a significant impact on the pore topology of coal-based activated carbon, further revealing the role of cation induced catalytic gasification in pore regulation. Therein, K and Ca enhance the formation of micropores and meso-/macropores respectively, while Na promotes the pore development across the entire size range resulting in a hierarchically porous structure with high specific surface area. Kinetic analysis, density functional theory calculations, and three-dimensional pore fractal network characterization reveal that the pore development is collectively determined by the gasification reaction rate and depth. Evaluated as adsorbents, the obtained NaAC sample by Na catalysis demonstrates excellent adsorption capacities for both small-molecule toluene (467 mg g−1) and large-molecule tetracycline (374 mg g−1). This work for the first time elucidates the cation-induced gasification effect and provides a simple and cost-effective method for regulating the pore topology of activated carbon with only trace catalyst dosage.

Polymer-supported strong Lewis acid phosphonium cation catalysis applied to sydnone synthesis.

Organochlorophosphonium P(V) species are strong Lewis acids deriving from a low-lying σ* orbital at P opposite to Cl. Herein, applying this strong acidity to heterogenous reactivity, we introduce polymer-supported phosphorus(V)-mediated Lewis acid catalysis. Key to this innovation is the use of a recyclable solid support Merrifield resin P(V) Lewis acid catalyst with demonstrated utility for the one-pot synthesis of sydnones. This concept of pnictogen P(V) Lewis acid catalysis is simple to apply, selective, and benefits from mild conditions with short reaction times. Further, experimental and computational findings reveal the crucial mechanistic role of phosphonium cation P(V) species in these reactions.

Probing gas phase catalysis by atomic metal cations with flow tube mass spectrometry.

The evolution and applications of flow tube mass spectrometry in the study of catalysis promoted by atomic metal ions are tracked from the pioneering days in Boulder, Colorado, to the construction and application of the ICP/SIFT/QqQ and ESI/qQ/SIFT/QqQ instruments at York University and the VISTA-SIFT instrument at the Air Force Research Laboratory. The physical separation of various sources of atomic metal ions from the flow tube in the latter instruments facilitates the spatial resolution of redox reactions and allows the separate measurement of the kinetics of both legs of a two-step catalytic cycle, while also allowing a view of the catalytic cycle in progress downstream in the reaction region of the flow tube. We focus on measurements on O-atom transfer and bond activation catalysis as first identified in Boulder and emphasize fundamental aspects such as the thermodynamic window of opportunity for catalysis, catalytic efficiency, and computed energy landscapes for atomic metal cation catalysis. Gas-phase applications include: the catalytic oxidation of CO to CO2 , of H2 to H2 O, and of C2 H4 to CH3 CHO all with N2 O as the source of oxygen; the catalytic oxidation of CH4 to CH3 OH with O3 ; the catalytic oxidation of C6 H6 with O2 . We also address the environmentally important catalytic reduction of NO2 and NO to N2 with CO and H2 by catalytic coupling of two-step catalytic cycles in a multistep cycle. Overall, the power of atomic metal cations in catalysis, and the use of flow tube mass spectrometry in revealing this power, is clearly demonstrated.

Geochemical Characteristics of Catalytic Hydrogenation of Low-Mature Kerogen Under Deep Fluids

There is increasingly valued attention on whether the matter and energy carried in the deep fluids can significantly change the hydrocarbon (HC) generation of low-mature source rocks. Previous studies suggest that the upward movement of deep fluids to sedimentary basins will change the HC generation evolution mode of low-mature source rocks, and the matter and energy carried by the fluid will transform the evolution process as transient events. However, there is a lack of quantitative evaluation of the specific changes of gaseous HC generation in the process of modification. In this study, the effect of deep fluids on HC generation and evolution of low maturity source rocks were quantitatively studied through simulation experiments of the gold tube closed system. We quantitatively selected hydrogen and catalysts (ZnCl2 and MoS2) to conduct catalytic hydrogenation of kerogen and explore the quantitative effects of deep fluids on HC generation in low-mature source rocks. Through the experimental results, it is found that catalytic hydrogenation has significant changes in a HC generation transformation of organic matter (OM). With the increase of catalytic hydrogenation reaction intensity, the maximum gaseous HC generation yield is 3.16–3.24 times that of the control groups without hydrogenation. In the relatively low-temperature stage (<400°C), the competitive hydrogenation effect occurs and the drying coefficient is high. After the high-temperature stage, a large amount of hydrogen participates in the reaction, which significantly promotes the increase of gaseous HCs and decreases the drying coefficient. ZnCl2 or MoS2 can change the relative content ratio of isomerism and isomorphism of butane and pentane, suggesting that cationic catalysis plays a greater role. In the reaction process, OM plays the most important role in the contribution to HC generation, exogenous hydrogen is more likely to participate in HC generation reaction than water and has the potential contribution to HC generation in Fischer-Tropsch synthesis (FFT) under catalytic conditions. The results of this study effectively verify that exogenous hydrogen and metal elements in deep fluids significantly modify the thermal evolution of low-mature source rocks, and enhance the HC generation potential in the high-temperature stage.

Enantioselective transition metal catalysis directed by chiral cations.

Enantioselective transition metal catalysis directed by chiral cations is the amalgamation of chiral cation catalysis and organometallic catalysis. Thus far, three strategies have been revealed: ligand scaffolds incorporated on chiral cations, chiral cations paired with transition metal ‘ate’-type complexes, and ligand scaffolds incorporated on achiral anions. Chiral cation ion-pair catalysis has been successfully applied to alkylation, cycloaddition, dihydroxylation, oxohydroxylation, sulfoxidation, epoxidation and C–H borylation. This development represents an effective approach to promote the cooperation between chiral cations and transition metals, increasing the versatility and capability of both these forms of catalysts. In this review, we present current examples of the three strategies and suggest possible inclusions for the future.

Cationic Catalysis during the Discharge of Carbonate Anions in Molten Salts

In the recent years, much attention has been focused on the synthesis of various carbon nanomaterials (CNMs) because of their wide range of potential applications. These materials have been fabricated by different methods such as the laser and arc evaporation of graphite, catalytic pyrolysis of hydrocarbons, disproportionation of CO on metal-catalysts etc. Promising method for synthesis of CNMs is high-temperature electrochemical synthesis (HTES) in molten salts. Although much research has been devoted to this subject, little is known about the mechanism of HTES and which fundamental reactions taking place during this process.In this work an attempt to confirm the mechanism of cation-anion interaction between the CO3 2- anion and the strongly polarizing cations (Li+, Ca2+, Mg2+) is made. The mechanism of these interactions has a complex nature. Cation-anion interaction can result either in the formation of cationized anions (metal complexes) or in anion dissociation both under the direct influence of cations and through the intermediate stage of formation of "short-lived" metal complexes.To test this hypothesis, the quantum chemistry modeling and the cyclic voltammetry experiments were done. It has been shown by the quantum chemistry method that by changing the cationic composition of the electrolyte, one can transform anionic carbonate complexes into a new active state – cationized carbonate complexes. Experimental confirmation of cation-anion interaction was studied in the chloride melts Na,K,Cs|Cl, Na,K,Rb|Cl, Na,K|Cl by the cyclic voltammetry method at temperature ranges of 550–580 °C and of 700–800 °C, which are much lower than the thermal decomposition temperature. The electrolyses was carried out in electrolytes under potentiostatic conditions at a potential of -1.1 V at the concentrations of lithium, calcium and magnesium chlorides, corresponding to the clear observation of cathodic waves. According to the data of a chemical and an X-ray phase analysis a black powder of the cathodic product was carbon. The morphology of electrolytical carbon is presented in the figure below.Based on the obtained results the following conclusions can be done: In the Na,K,Rb|Cl melt containing weakly polarizing Na+, K+, Rb+ cations, the CO3 2- anion shows no electrochemical activity in the temperature range of 570–700 °C. This is accounted for by the large values of the activation barriers to the two- and four-electron reduction of CO3 2-.The addition of strongly polarizing cations (cations with high specific charge) results in the activation of the carbonate ion, which is caused by a large excess of Li+ and Ca2+ cations. In the case of Mg2+ cations, the carbonate ion shows electroactivity at much lower concentrations.Independent of the polarizing power of the cation (melt acidity), the CO3 2- reduction process in molten chlorides occurs in the same potential range of -0.7 to -0.9 V versus a silver reference electrode.The CO3 2- electroreduction process under the action of strongly polarizing cations occurs at temperatures much lower than the thermal decomposition temperature of the corresponding carbonate. This suggests that the formation of CO2 is not the result of thermal decomposition, but is a consequence of the polarizing action of cations. Figure 1

Cationic Catalysis during the Discharge of Carbonate Anions in Molten Salts

The paper presents a quantum-chemical model and experimental confirmation of cation catalysis mechanism during the cathodic discharge of carbonate anion in chloride melt. The model of cationized carbonate complex, which describes the effect of the acid-base properties of the melt on the electronic, energetic, structural, and electrochemical properties of the carbonate anion, was proposed. Cation-anion interaction between CO3 2- anion and the strongly polarizing cations (Li+, Ca2+, Mg2+) result either in the formation of cationized anions (metal complexes) or in anion dissociation. Dissociation of CO3 2- anions can occur directly or through an intermediate stage of formation of "short-lived" metal complexes. The changes in the electrochemical behavior of CO3 2- anion were studied by voltammetry by the sequential addition of cations with different polarizing (electrostatic) force to the Na,K,Rb|Cl eutectic. The potentiostatic electrolyses carried out in three electrolytes Na,K,Rb|Cl–Na2CO3–LiCl(CaCl2,MgCl2) at a same potential of -1.1 V against Ag/AgCl reference electrode gave a carbon powder.

Brønsted Acid‐Catalyzed Intramolecular α‐Arylation of Ketones with Phenolic Nucleophiles via Oxy‐Allyl Cation Intermediates

Nucleophilic addition to the oxy‐allyl cation intermediate has emerged as a promising methodology for functionalization of the α‐position of carbonyl compounds in an umpolung fashion. However, a structure of available carbon nucleophiles to trap the catalytically generated oxy‐allyl cation has been limited to highly nucleophilic ones. Herein, we report the Brønsted acid‐catalyzed α‐arylation of ketones employing less explored phenolic nucleophiles as carbon nucleophiles in the oxy‐allyl cation catalysis, affording ketones bearing an all carbon quaternary center at the α‐position.

A longitudinally expanded Ni-based metal-organic framework with enhanced double nickel cation catalysis reaction channels for a non-enzymatic sweat glucose biosensor.

Nickel-based metal-organic frameworks (Ni-MOFs) have attracted increasing attention in non-enzymatic glucose sensing. However, the insufficient active Ni cation sites from a stacked MOF layer, the unclear Ni catalysis mechanism, and the severe liquid alkaline electrolyte remain challenging for practical applications. In this work, the sonication-induced longitudinal-expansion of Ni-MOFs increases the active nickel ion sites, which not only enhances the current response to glucose detection, but also shows the oxidation peak evolution of nickel ions with different sonication times, revealing the mechanism of different glucose detection channels. The Ni-MOF sonicated for 60 min (60 min Ni-MOF) displays enhanced Ni(iii)/Ni(ii) and more significant Ni(iv)/Ni(iii) double nickel cation channels for catalyzing glucose into glucolactone compared to the 0 min Ni-MOF (without sonication), showing optimized glucose detection ability with a high sensitivity of 3297.10 μA mM-1 cm-2, a low detection limit of ∼8.97 μM (signal-to-noise = 3) and a wide linear response range from 10 to 400 μM from the cyclic voltammetry test as well as a high sensitivity of 3.03 μA mM-1 cm-2, a low detection limit of ∼1.16 μM (signal-to-noise = 3) and a wide linear response range from 10 to 2000 μM from the chronoamperometry test. More importantly, an all-solid-state glucose biosensor using a PVA/NaOH solid-state electrolyte and a disposable 60 min Ni-MOF working electrode is assembled for non-enzymatic sweat glucose detection.

Promoting Ni(II) Catalysis with Plasmonic Antennas

Plasmonic metal NPs such as Au and Ag are proven to channel visible-light photon energy to nearby metal complexes effectively and allow the conventional metal cationic catalysts to work at moderate temperatures under light irradiation. A key finding is that reactant molecules can be significantly concentrated at the active sites simply by light and thus increase the chance of activation. The merging of plasmonic antenna and metal cationic catalysis will be an inspiring strategy for designing efficient photocatalytic systems.

The effect of multielectron transfer on the direction for the mechanism of heterogeneous reactions during the synthesis for nanomaterials from tungstate melts under the conditions of cationic catalysis

On the basis of ab initio analysis of the calculation of impact of the cation composition tungstate-containing melt on structural peculiarities of EAP, the differences in the structure at implementation of sequential and simultaneous six-electron transfer are determined. According to the results of calculations of charge on the atoms of “isolated” tungstate-ion during transfer of 6 electrons in the electrode reaction on “isolated” tungstate-anion, the W atom is the only centre of electronic attack. At the electroreduction of cationised complexes, the electron charge is transferred to the cations and to the W atom, indicating the existence of two centres of electronic attack.

Triarylmethyl Cation Catalysis: A Tunable Lewis Acid Organo­catalyst for the Synthesis of Bisindolylmethanes

Triarylmethyl cations serve as tunable organocatalysts for the synthesis of bisindolylmethanes. The catalyst structure can be modified to increase or decrease reactivity as needed to match the requirements of the substrate. High yields are achieved for a variety of substrates by using these green catalysts. Catalyst tuning allows for the use of less reactive electrophiles by increasing the reactivity of the catalyst. Acid-sensitive products can be isolated under these mild reaction conditions.

Oxyallyl Cation Catalysis

Oxyallyl Cation Catalysis

Oxy-Allyl Cation Catalysis: An Enantioselective Electrophilic Activation Mode.

A generic activation mode for asymmetric LUMO-lowering catalysis has been developed using the long-established principles of oxy-allyl cation chemistry. Here, the enantioselective conversion of racemic α-tosyloxy ketones to optically enriched α-indolic carbonyls has been accomplished using a new amino alcohol catalyst in the presence of electron-rich indole nucleophiles. Kinetic studies reveal that the rate-determining step in this S(N)1 pathway is the catalyst-mediated α-tosyloxy ketone deprotonation step to form an enantiodiscriminant oxy-allyl cation prior to the stereodefining nucleophilic addition event.

ChemInform Abstract: The Carbocation: A Forgotten Lewis Acid Catalyst

AbstractReview: [39 refs.

The Carbocation: A Forgotten Lewis Acid Catalyst

AbstractA Lewis acid that has received negligible attention as a catalyst is the carbocation. The carbocation is isoelectronic to boron and owes its Lewis acidity to a low‐lying empty pC orbital. In terms of reactivity and stability carbocations are very versatile Lewis acids, from the extremely unstable methylium cation to the water‐stable tris(N,N‐dimethylaniline) methylium ion (crystal violet). Although the Lewis acid properties of carbocations have been extensively studied since the discovery of the tropolium ion more than 130 years ago there is only a handful examples on the application of carbocations as Lewis acid catalysts. Herein, the research on triarylmethylium (trityl)‐cation catalysis is summarized. In light of the reports the trityl ion emerges as a highly efficient and highly versatile Lewis acid catalyst capable of catalyzing different classes of reactions often with high selectivity and low catalyst loadings (for some reactions down to ppm levels).

Lotus leaf inspired robust superhydrophobic coating from strawberry-like Janus particles

We demonstrate a one-step approach toward the large-scale fabrication of robust superhydrophobic coatings using strawberry-like hemispherical Janus particles. Hemispherical Janus particles are capable of self-organizing into a layer on substrates. Nanoscale roughness on the hydrophobic hemispherical side determines the superhydrophobic performance. The imidazolin group on the hydrophilic flat side determines the coating strength by covalent binding onto substrates via cations initiating the crosslinking of the intermediate epoxy resins. The coating can tolerate organic solvents and high water flushing speeds. If the hydrophobic side is smooth, then the coating is highly adhesive to water. This procedure can fabricate unique coatings on a diverse range of substrates with varied compositions and shapes. A new coating made from self-assembling, strawberry-shaped Janus nanoparticles can turn ordinary surfaces into ultra-water-repellent materials. This first finding by Zhenzhong Yang and colleagues at the Chinese Academy of Sciences involves using a sol-gel process to synthesize tiny silica shells with ‘Janus’, or two-faced properties. Thanks to the presence of special surfactants, one side of the nanoparticle forms a curved, bumpy surface resembling that of a strawberry, whereas the other side is flat. The team modified the flat, hydrophilic surface with a reactive precursor and then sprayed an aqueous dispersion of the particles onto an epoxy-coated glass sheet. Water evaporation caused the flat silica side to covalently anchor to the epoxy, exposing a uniform coating of superhydrophobic bumps. These coatings are attractive because they are remarkably robust and could be applied to complex substrates at industrially relevant scales. Schematic synthesis of the robust superhydrophobic coating from strawberry-like Janus hemispherical particles: (a) the dispersion of aqueous particles is sprayed onto the E-51 layer on the substrate; (b) the Janus particles self-orientate to form a layer; and (c) after the epoxy resin is cured by cationic catalysis, the robust superhydrophobic coating is fabricated.

Microwave Assist Synthesis Methyl Ferulate through a Cationic Exchange Resin Catalysis Routine

Methyl ferulate was synthesized by methanol and ferulic acid with strongly acidic cation exchange resin as catalyst under microwave irradiation. The effect of catalyst activity was investigate by single factor experiment. Amount of catalyst, microwave treatment time, microwave output power and methanlo/ ferulic acid ratio were investigate by single factor experiment and orthogonal experiments. The optimal reaction conditions were ferulic acid being 0.1mol, molar radio of ethanol to ferulic acid being 5:1, mass percent of resin being 30％ of the reagent, microwave power being 300W, reaction time being 25 min. The yield of product was 81.2％ under the potimal conditions. The catalytic characteristics of regenerated catalyst were stable and the yield of product may keep greater than 76% after the 732# resin used five times.

Magnetic Anisotropy and Magneto-Transport Properties of Co–Ni–N Granular Alloys Thin Films

The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film. Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy. From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range Keff=(−21.5÷36.6)×104 J⋅m−3 and the coercivity varied between Hc=(13÷67) kA⋅m−1 depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%) of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive magnetic field sensors.