Kind Of Catalysis Research Articles

Organosulphur and organoselenium compounds as ligands for catalytic systems in the Sonogashira coupling.

Sonogashira coupling is a reaction of aryl/vinyl halides with terminal alkynes. It is used for the synthesis of conjugated enynes. Generally, copper (Cu) is required as a mediator for this reaction. It requires a long reaction time, high catalyst loading, or expensive ligands. Recently, homogeneous, heterogeneous, and nanocatalysts have been developed using organosulphur and organoselenium compounds as building blocks. Preformed complexes of metals with organosulphur and organoselenium ligands are used for homogeneous catalysis. Heterogeneous catalytic systems have also been developed using Cu, Pd, and Ni as metals. The nanocatalytic systems (synthesized using such ligands) include copper selenides and stabilized palladium(0) nanospecies. This article aims to cover the developments in the field of the processes and techniques used so far to generate catalytically relevant organic ligands having sulphur or selenium donor sites, the utility of such ligands in the syntheses of homogeneous, heterogeneous, and nanocatalytic systems, and critical analysis of their application in the catalysis of this coupling reaction. The results of catalysis are analyzed in terms of the effects of the S/Se donor, halogen atom of aryl halide, the effect of the presence/absence of electron-withdrawing or electron-donating groups or substituents on the aromatic ring of haloarenes/substituted phenylacetylenes, as well as the position (ortho or para) of the substitution. Substrate scope is discussed for all the kinds of catalysis. The supremacy of heterogeneous and nanocatalytic systems indicates promising future prospects.

Single-Particle Measurements of Nanocatalysis with Dark-Field Microscopy

Due to the complexity of heterogeneous reactions and heterogeneities of individual catalyst particles in size, morphology, and the surrounding medium, it is very important to characterize the structure of nanocatalysts and measure the reaction process of nanocatalysis at the single-particle level. Traditional ensemble measurements, however, only provide averaged results of billions of nanoparticles (NPs), which do not help reveal structure–activity relationships and may overlook a few NPs with high activity. The advent of dark-field microscopy (DFM) combined with plasmonic resonance Rayleigh scattering (PRRS) spectroscopy provides a powerful means for directly recording the localized surface plasmon resonance (LSPR) spectrum of single plasmonic nanoparticles (PNPs), which also enables quantitative measurements. In recent years, DFM has developed rapidly for a series of single-particle catalytic reactions such as redox reactions, electrocatalytic reactions, and DNAzyme catalysis, with the ability to monitor the catalytic reaction process in real time and reveal the catalytic mechanism. This review provides a comprehensive overview of the fundamental principles and practical applications of DFM in measuring various kinds of catalysis (including chemocatalysis, electrocatalysis, photocatalysis, and biocatalysis) at the single-particle level. Perspectives on the remaining challenges and future trends in this field are also proposed.

Advanced Synthesis Using Photocatalysis Involved Dual Catalytic System

AbstractCombining visible‐light photoredox catalysis with other kinds of catalysis is a powerful strategy to address the barriers met in reactions driven by single catalyst. Under environmentally benign condition, photoredox catalysis produces radical species via visible light irradiation. These species then work with other catalysts, often resulting in unconventional reactivities, by which the scope of reaction could be expanded. Interest focusing on photocatalysis in the synthetic chemistry community has grown tremendously over the past five years, and one of the most striking emerging features is the development of dual catalytic approaches. This minireview summarizes the progress on this theme, mainly including dual catalytic systems merging photoredox activation with acid/base catalysts.

Short-Chained Platinum Complex Catalyzed Hydrosilylation under Thermomorphic Conditions: Heterogeneous Phase Separation at Ice Temperature.

Homogeneous catalysts PtCl2[5,5′-bis-(n-ClCF2(CF2)3CH2OCH2)-2,2′-bpy] (2A) and PtCl2[5,5′-bis-(n-HCF2(CF2)3CH2OCH2)-2,2′-bpy] (2B), which contained short fluorous chains, were synthesized and used in catalysis of hydrosilylation of alkynes. In these reactions the thermomorphic mode was effectively used to recover these catalysts from the reaction mixture up to eight cycles by taking advantage of heterogeneous phase separation at ice temperature. This kind of catalysis had previously been observed in fluorous catalysts of platinum containing about 50% F-content, but in this work the percentage of F-content is decreased to only about 30%, by which we termed them as “very light fluorous”. Our new type of catalyst with limited number of F-content is considered as the important discovery in the fluorous technology field as the reduced number of fluorine atoms will help to be able to comply the EPA 8-carbon rule. The metal leaching after the reaction has been examined by ICP-MS, and the testing results show the leaching of residual metal to be minimal. Additionally, comparing these results to our previous work, fluorous chain assisted selectivity has been observed when different fluorous chain lengths of the catalysts are used. It has been found that there exists fluorous chain assisted better selectivity towards β-(E) form in the Pt-catalyzed hydrosilylation of non-symmetric terminal alkyne when the Pt catalyst contains short fluorous chain (i.e., 4 Cs). Phenyl acetylenes showed the opposite regioselectivity due to pi-pi interaction while using the same catalyst via Markovnikov’s addition to form terminal vinyl silane, which is then a major product for Pt-catalyzed hydrosilylation of terminal aryl acetylene with triethylsilane. Finally, the kinetic studies indicate that the insertion of alkyne into the Pt-H bond is the rate-determining step.

Copper-mediated synergistic catalytic titanium dioxide nanofilm with nitric oxide generation and anti-protein fouling for enhanced hemocompatibility and inflammatory modulation

Nitric oxide (NO) has become a highly compelling therapeutic gas for treating vascular diseases due to its versatile functions to vascular responses. Currently, NO biomimetic materials are successfully established through loading catalyst (i.e., Se, Cu) with the vehicle to decompose endogenous NO donors in blood continuously. However, current NO biomimetic materials are susceptible to the non-specific protein fouling, resulting in undesired therapeutic inefficiency with the observation of attenuated or even blocked NO catalytic activities. Herein, we produced a multifunctional nanofilm with dual catalysis based on the vascular stent platform via simply doping one kind of metal (Cu) as cocatalyst into anatase TiO2 crystal. Beneficial synergistic interactions between two kinds of catalysis are reported in this work. The nanofilm surface is endowed with photoinduced super hydrophilic conversion and controlled NO catalytic release simultaneously. The super hydrophilic surface shows the excellent self-cleaning ability to resist protein fouling. Importantly, the maintenance of the protein-resistant surface can effectively improve the NO catalytic release and reduce inflammatory stimuli, contributing to enhanced hemocompatibility. The optimum doping amount of Cu (TiO2@Cu1, 0.77 wt.%) is determined through the characterization of adjustable photoinduced hydrophilic conversion and appropriate NO catalytic generation within the effective physiological concentration. After vascular implantation in rats, the TiO2@Cu1 nanofilms achieved elevated performances on antithrombosis, reducing the intima hyperplasia area and promoting rapid reendothelialization at 4 weeks. This study provides a valuable guideline for NO-biomimetic materials used for blood contact devices and paves the way for the surface modification for vascular implants.

Metal Catalysis with Microwaves in Organic Synthesis: a Personal Account

In the last 25 years, the influence of microwave (MW) irradiation in chemical synthesis has intrigued chemists for the exceptional results obtained in shortening reaction times. Inspired by recent papers that demonstrate the existence of a non‐thermal effect in some MW assisted reactions, we examine herein a series of reactions catalysed by homogeneous and heterogeneous metals occurring under MW irradiation. The review contains examples of hydroformylation, hydrogenation (including enantioselective versions with 98 % ee), hydrogenolysis, hydrogen transfer and borrowing hydrogen reactions carried out under MWs and metal catalysis. An increase in the influence of MW irradiation was often observed in reactions performed with heterogeneous catalysts such as Pd/C. In these cases, a “microwave catalysis” can be possible. The increase in the (apparent) reaction rate requires the contribution of MW irradiation that modifies the catalyst surface, driving the reaction progress as occurring in other kinds of catalysis.

Molecular Switching by Electron Holes

In this issue of Chem, Hecht and co-workers show how hole catalysis yields quantitative Z → E isomerization of azobenzenes, a paradigmatic molecular switch, to reach quantum yields larger than 1 in the case of photoinitiated catalysis. This versatile oxidative catalysis paves the way for its use in biological environments and condensed matter.

Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

Supported bimetallic nanoparticles (SBN) are extensively used as efficient redox catalysts. This kind of catalysis particularly using SBN has attracted immense research interest compared to their parent metals due to their unique physico-chemical properties. The primary objective of this contribution is to provide comprehensive overview about SBN and their application as promising catalysts. The present review contains four sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of SBN as promising catalysts for different applications. Section 2 reviews the preparation and characterization methods of SBN for a wide range of catalytic reactions. Section 3 concentrates on our own results related to the application of SBN in heterogeneous catalysis. In this section, the oxidation of cyclohexane to adipic acid (an eco-friendly and novel approach) will be discussed. In addition, the application of bimetallic Pd catalysts for vapor phase toluene acetoxylation in a fixed bed reactor will also be highlighted. Acetoxylation of toluene to benzyl acetate is another green route to synthesize benzyl acetate in one step. Finally, Section 4 describes the summary of the main points and also presents an outlook on the application of SBN as promising catalysts for the production of valuable products.

Electrochemical tuning of vertically aligned MoS 2 nanofilms and its application in improving hydrogen evolution reaction

The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li(+) ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity.

Mechanisms of Formation of Hemiacetals: Intrinsic Reactivity Analysis

The reaction mechanism of the hemiacetal formation from formaldehyde and methanol has been studied theoretically at the B3LYP/6-311++G(d,p) level. In addition to the study of the reaction between the isolated reactants, three different kinds of catalysis have been explored. The first one examines the use of assistants, especially bridging water molecules, in the proton transfer process. The second one attempts to increase the local electrophilicity of the carbon atom in formaldehyde with the presence of a Brønsted acid (H(+) or H(3)O(+)). The last one considers the combined effect of both catalytic strategies. The reaction force, the electronic chemical potential, and the reaction electronic flux have been characterized for the reaction path in each case. In general, it has been found that structural rearrangements represent an important energetic penalty during the activation process. The barriers for the reactions catalyzed by Brønsted acids show a high percentage of electronic reorganization contribution. The catalytic effects for the reactions assisted by water molecules are due to a reduction of the strain in the transition state structures. The reaction that includes both acid catalysis and proton assistance transfer shows the lowest energy barrier (25.0 kJ mol(-1)).

New ternary immobilization of chiral sulfonato-(salen)manganese(III) complex for aqueous asymmetric oxidation reactions

This article reports our study on asymmetric epoxidation of unfunctionalized alkenes and asymmetric oxidation of sulfides catalyzed by a new triply immobilized (salen)Mn(III) system, when commercial sodium hypochlorite and hydrogen peroxide were loaded as terminal oxidant, respectively. A chiral sulfonato-(salen)Mn(III) complex was grafted onto a novel polysiloxane, then axially coordinated by 3-aminopropyl functionalized silica gel (40–63μm, 1mmolg−1 NH2 loading) as a secondary anchoring mode, and eventually dispersed into ionic liquid BMImX (BMIm+=1-n-butyl-3-methylimidazolium; X−=PF6−, BF4−, NO3−) for purpose of catalyst recycling. Catalysts were fully characterized by 1H NMR, FT-IR, molar conductivity, elemental analysis, nitrogen adsorption, aqueous particle size and zeta potential analysis, along with XRD. Interestingly, lateral immobilization led to a novel catalyst structure featuring parallel stacking of one-dimensional planers, whereas the lateral together with axial immobilization made supported complex nano-sized crystallite particles (diameter 24.2nm). After stepwise screening, doubly-immobilized catalyst and BMImBF4, in combination, showed best enantiomeric excess (e.e.) values and most stable recycling behavior in two kinds of catalysis, but generally sulfoxidation had better turnover frequencies than epoxidation reaction.

Pd(II)-Catalyzed Synthesis of Carbolines by Iminoannulation of Internal Alkynes via Direct C−H Bond Cleavage Using Dioxygen as Oxidant

A palladium-catalyzed iminoannulation of internal alkynes via direct C-H bond cleavage was developed. Dioxygen was employed as a clean oxidant in this kind of catalysis. Carbolines were synthesized from tert-butylimines of N-substituted indole-2-carboxaldehydes or indole-3-carboxaldehydes.

Comparison of Catalytic Efficiency of Some Industrial Nanosized Titanium Dioxides in Heterogeneous Photodegradation by Chemometric Analysis

Due to its high intrinsic efficiency, heterogeneous catalysis is widely used in waste water treatments employing mixed catalysts. However, in this kind of catalysis it is extremely difficult to separate the suspended catalyst from the solution at the end of the procedure due to the small dimension of the particles. In environmental applications, the most used catalyst is titanium dioxide because of its great catalytic efficiency. The present research concerns the efficiency evaluation of TiO2 catalysts, estimated on the extent of photodegradation of target molecules after a radiation treatment (solar, UV, microwave) carried out in a dedicated apparatus. Experimental variables are: 1) catalyst type (TiO2 particles of different size), 2) catalyst concentration (0.1, 0.2, 0.5, 1.0 g/L), 3) exposure time (45 and 90 min), and 4) target molecules (five industrial textile dyes: Acid Blue 29, Alizarin Red S, Procion Red MX-5B, Reactive Blue 2, Acid Green 25). The efficiency of the photodegradation process has been evaluated by a UV/ Vis spectrophotometry comparing the spectra of the target substances obtained before and after the degradation process itself, therefore monitoring the cracking of the chromophore groups. Obtained data matrix was analysed with chemometric tools. The aim of this work was to identify the correlation between photodegradation efficiency and experimental variables. It has been also evaluated the possibility of substituting nanomaterial catalysts with catalysts characterized by bigger particle size keeping the degradation efficiency unaltered: this evaluation has been performed because the non- nanoparticles are more easily separable from suspension, making the water clarification post-processes easier. Keywords: TiO2, Titanium dioxide, Heterogeneous photocatalysis, Photodegradation, Chemometric analysis, Dyes, Efficiency study, Nanosize, Deep UV, UV/Vis measure

A note on the quantum-theoretic basis of primary of primary genetic activity.

In previous work (Bull. Math. Biophysics,23, 393–403, 1960) it was shown that, if primary genetic processes are of an essentially microphysical nature, the objects bearing the primary genetic information must act in a catalytic fashion. At the same time it was pointed out that the kind of catalysis involved in the primary genetic process was fundamentally different, in specific ways, from that occurring, e.g., in enzyme systems. The present work demonstrates that, if the information-bearing objects of the general theory are identified with molecules of DNA, and the primary gene products are considered to be RNA of the “messenger” variety, then the predictions of the general theory can be compared with experimental data from various recently isolated polymerase systems, which appear to “copy” a sequence of nucleotides from DNA into RNAin vitro, and with certainin vivo microbial systems. It is found that these data provide detailed support for the conclusions drawn from the general theory. However, it is emphasized that the identification of the information-bearing objects and primary gene products as DNA and RNA respectively, which allows us to compare the theory with the cited data, is by no means the only identification which can be made; i.e., other interpretations of the general theory are certainly not precluded.

The isomerization of β,γ-to α,β-unsaturated steroidal ketones

The isomerization of 12 steroidal Δ 5(6)- and Δ 5(10)-3-ketones to the corresponding Δ 4-3-ketones has been studied quantitatively under acid and enzymatic catalysis. Under both kinds of catalysis the Δ 5(10-series reacted more slowly. At pH 1 the difference in half-time periods for the two series was a factor of 10–38, but under enzymatic catalysis the difference was magnified to a factor varying from 29 to a few hundred, the exact values being dependent on precise structural features. Recently Talalay et al. 1 reported the rates of enzymatic isomerization of several of the Δ 5(10)-compounds which we have measured, and our values are in agreement with theirs. The mechanisms of the two types of isomerization are discussed, and two new compounds, 5-estrene-3,17-dione and the diacetate of 17α-methyl-3,5-estradiene-3,17β-diol, are reported.