Journal articles: 'Transition metals; Catalytic systems'

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Filardo, Giuseppe, Alessandro Galia, Franco Rivetti, Onofrio Scialdone, and Giuseppe Silvestri. "Catalytic systems based on transition metals for the carbonylation of methanol to dimethylcarbonate." Electrochimica Acta 42, no. 13-14 (January 1997): 1961–65. http://dx.doi.org/10.1016/s0013-4686(97)85467-9.

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Pal, Pratibha, Jyh-Ming Ting, Shivani Agarwal, Takayuki Ichikawa, and Ankur Jain. "The Catalytic Role of D-block Elements and Their Compounds for Improving Sorption Kinetics of Hydride Materials: A Review." Reactions 2, no. 3 (September 18, 2021): 333–64. http://dx.doi.org/10.3390/reactions2030022.

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The goal of finding efficient and safe hydrogen storage material motivated researchers to develop several materials to fulfil the demand of the U.S. Department of Energy (DOE). In the past few years, several metal hydrides, complex hydrides such as borohydrides and alanates, have been researched and found efficient due to their high gravimetric and volumetric density. However, the development of these materials is still limited by their high thermodynamic stability and sluggish kinetics. One of the methods to improve the kinetics is to use catalysts. Among the known catalysts for this purpose, transition metals and their compounds are known as the leading contender. The present article reviews the d-block transition metals including Ni, Co, V, Ti, Fe and Nb as catalysts to boost up the kinetics of several hydride systems. Various binary and ternary metal oxides, halides and their combinations, porous structured hybrid designs and metal-based Mxenes have been discussed as catalysts to enhance the de/rehydrogenation kinetics and cycling performance of hydrogen storage systems.

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Strekalova, Sofia, Mikhail Khrizanforov, and Yulia Budnikova. "Evaluation of Transition Metal Catalysts in Electrochemically Induced Aromatic Phosphonation." Molecules 24, no. 9 (May 11, 2019): 1823. http://dx.doi.org/10.3390/molecules24091823.

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Voltammetry provides important information on the redox properties of catalysts (transition metal complexes of Ni, Co, Mn, etc.) and their activity in electrocatalytic reactions of aromatic C–H phosphonation in the presence of a phosphorus precursor, for example, dialkyl-H-phosphonate. Based on catalytic current growth of oxidation or reduction of the metal catalysts (CoII, MnII, NiII, MnII/NiII, MnII/CoII, and CoII/NiII), quantitative characteristics of the regeneration of catalysts were determined, for example, for MnII, NiII and MnII/NiII, CoII/NiII pairs. Calculations confirmed the previously made synthetic observations on the synergistic effect of certain metal ions in binary catalytic systems (MnIIbpy/NiIIbpy and NiIIbpy/CoIIbpy); for mixtures, the observed rate constants, or TOF, were 690 s−1 and 721 s−1, respectively, and product yields were higher for monometallic catalytic systems (up to 71% for bimetallic catalytic systems and ~30% for monometallic catalytic systems). In some cases, the appearance of pre-waves after adding H-phosphonates confirmed the preceding chemical reaction. It also confirmed the formation of metal phosphonates in the time scale of voltammetry, oxidizing or reducing at lower potentials than the original (RO)2P(O)H and metal complex, which could be used for fast diagnostics of metal ion and dialkyl-H-phosphonate interactions. Electrochemical transfer of an electron to (from) metal phosphonate generates a phosphonyl radical, which can then react with different arenes to give the products of aromatic C–H phosphonation.

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Nesterov, Dmytro, and Oksana Nesterova. "Polynuclear Cobalt Complexes as Catalysts for Light-Driven Water Oxidation: A Review of Recent Advances." Catalysts 8, no. 12 (December 2, 2018): 602. http://dx.doi.org/10.3390/catal8120602.

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Photochemical water oxidation, as a half-reaction of water splitting, represents a great challenge towards the construction of artificial photosynthetic systems. Complexes of first-row transition metals have attracted great attention in the last decade due to their pronounced catalytic efficiency in water oxidation, comparable to that exhibited by classical platinum-group metal complexes. Cobalt, being an abundant and relatively cheap metal, has rich coordination chemistry allowing construction of a wide range of polynuclear architectures for the catalytic purposes. This review covers recent advances in application of cobalt complexes as (pre)catalysts for water oxidation in the model catalytic system comprising [Ru(bpy)3]2+ as a photosensitizer and S2O82− as a sacrificial electron acceptor. The catalytic parameters are summarized and discussed in view of the structures of the catalysts. Special attention is paid to the degradation of molecular catalysts under catalytic conditions and the experimental methods and techniques used to control their degradation as well as the leaching of cobalt ions.

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Hirao, Toshikazu, and Toru Amaya. "Synthesis and Application of Redox-Active Hybrid Catalytic Systems Consisting of Polyanilines and Transition Metals." Synlett 2011, no. 04 (February 11, 2011): 435–48. http://dx.doi.org/10.1055/s-0030-1259541.

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Chen, Xiao, and Changhai Liang. "Transition metal silicides: fundamentals, preparation and catalytic applications." Catalysis Science & Technology 9, no. 18 (2019): 4785–820. http://dx.doi.org/10.1039/c9cy00533a.

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Transition metal silicides as low-cost and earth-abundant inorganic materials are becoming indispensable constituents in catalytic systems for a variety of applications and exhibit excellent properties for sustainable industrial process.

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Khalimon, Andrey, Kristina Gudun, and Davit Hayrapetyan. "Base Metal Catalysts for Deoxygenative Reduction of Amides to Amines." Catalysts 9, no. 6 (May 28, 2019): 490. http://dx.doi.org/10.3390/catal9060490.

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The development of efficient methodologies for production of amines attracts significant attention from synthetic chemists, because amines serve as essential building blocks in the synthesis of many pharmaceuticals, natural products, and agrochemicals. In this regard, deoxygenative reduction of amides to amines by means of transition-metal-catalyzed hydrogenation, hydrosilylation, and hydroboration reactions represents an attractive alternative to conventional wasteful techniques based on stoichiometric reductions of the corresponding amides and imines, and reductive amination of aldehydes with metal hydride reagents. The relatively low electrophilicity of the amide carbonyl group makes this transformation more challenging compared to reduction of other carbonyl compounds, and the majority of the reported catalytic systems employ precious metals such as platinum, rhodium, iridium, and ruthenium. Despite the application of more abundant and environmentally benign base metal (Mn, Fe, Co, and Ni) complexes for deoxygenative reduction of amides have been developed to a lesser extent, such catalytic systems are of great importance. This review is focused on the current achievements in the base-metal-catalyzed deoxygenative hydrogenation, hydrosilylation, and hydroboration of amides to amines. Special attention is paid to the design of base metal catalysts and the mechanisms of such catalytic transformations.

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L. Simakova, Irina, Andrey V. Simakov, and Dmitry Yu. Murzin. "Valorization of Biomass Derived Terpene Compounds by Catalytic Amination." Catalysts 8, no. 9 (August 29, 2018): 365. http://dx.doi.org/10.3390/catal8090365.

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This review fills an apparent gap existing in the literature by providing an overview of the readily available terpenes and existing catalytic protocols for preparation of terpene-derived amines. To address the role of solid catalysts in amination of terpenes the same reactions with homogeneous counterparts are also discussed. Such catalysts can be considered as a benchmark, which solid catalysts should match. Although catalytic systems based on transition metal complexes have been developed for synthesis of amines to a larger extent, there is an apparent need to reduce the production costs. Subsequently, homogenous systems based on cheaper metals operating by nucleophilic substitution (e.g., Ni, Co, Cu, Fe) with a possibility of easy recycling, as well as metal nanoparticles (e.g., Pd, Au) supported on amphoteric oxides should be developed. These catalysts will allow synthesis of amine derivatives of terpenes which have a broad range of applications as specialty chemicals (e.g., pesticides, surfactants, etc.) and pharmaceuticals. The review will be useful in selection and design of appropriate solid materials with tailored properties as efficient catalysts for amination of terpenes.

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Zhou, Wei, Lei Zhong, and Wei Dong Li. "Progress in Development of Catalyst Systems for Coordinated Polymerization of Olefins." Advanced Materials Research 900 (February 2014): 11–14. http://dx.doi.org/10.4028/www.scientific.net/amr.900.11.

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The research progresses about polyolefin catalyst systems in recent years are summarized. Focusing on the type and properties of the catalytic polymerization of the olefin polymerization catalyst, including typical Ziegler-Natta catalysts, metallocene catalysts and post-transition metal catalyst system. Then the new post-transition metal catalyst is introduced.

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Jang, Jisun, Sangmoon Byun, B. Moon Kim, and Sunwoo Lee. "Arylsilylation of aryl halides using the magnetically recyclable bimetallic Pd–Pt–Fe3O4 catalyst." Chemical Communications 54, no. 28 (2018): 3492–95. http://dx.doi.org/10.1039/c7cc09926f.

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Amaya, Toru, and Toshikazu Hirao. "ChemInform Abstract: Synthesis and Application of Redox-Active Hybrid Catalytic Systems Consisting of Polyanilines and Transition Metals." ChemInform 42, no. 27 (June 9, 2011): no. http://dx.doi.org/10.1002/chin.201127242.

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Nesterov, Dmytro S., and Oksana V. Nesterova. "Catalytic Oxidations with Meta-Chloroperoxybenzoic Acid (m-CPBA) and Mono- and Polynuclear Complexes of Nickel: A Mechanistic Outlook." Catalysts 11, no. 10 (September 25, 2021): 1148. http://dx.doi.org/10.3390/catal11101148.

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Selective catalytic functionalization of organic substrates using peroxides as terminal oxidants remains a challenge in modern chemistry. The high complexity of interactions between metal catalysts and organic peroxide compounds complicates the targeted construction of efficient catalytic systems. Among the members of the peroxide family, m-chloroperoxybenzoic acid (m-CPBA) exhibits quite complex behavior, where numerous reactive species could be formed upon reaction with a metal complex catalyst. Although m-CPBA finds plenty of applications in fine organic synthesis and catalysis, the factors that discriminate its decomposition routes under catalytic conditions are still poorly understood. The present review covers the advances in catalytic C–H oxidation and olefine epoxidation with m-CPBA catalyzed by mono- and polynuclear complexes of nickel, a cheap and abundant first-row transition metal. The reaction mechanisms are critically discussed, with special attention to the O–O bond splitting route. Selectivity parameters using recognized model hydrocarbon substrates are summarized and important factors that could improve further catalytic studies are outlined.

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Jung, Jieun, and Susumu Saito. "Recent Advances in Light-Driven Carbon–Carbon Bond Formation via Carbon Dioxide Activation." Synthesis 53, no. 18 (August 3, 2021): 3263–78. http://dx.doi.org/10.1055/a-1577-5947.

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AbstractCarbon dioxide (CO2) is an attractive renewable one-carbon (C1) feedstock in terms of its earth abundance, low cost, and non-toxicity. Developing new catalytic systems to realize the practical insertion of CO2 into organic molecules has been of great importance for ecological economics. In recent years, outstanding improvements have been carried out in the field of light-driven catalytic carboxylation via the activation of CO2 as the key reagent. In this short review, the recent developments of light-promoted carboxylation utilizing CO2 to synthesize value-added chemicals using a dual visible-light photoredox/transition-metal catalyst or a photoredox catalyst are highlighted.1 Introduction2 Visible-Light-Driven Carboxylation Using Transition-Metal Photocatalysts2.1 Transition-Metal-Catalyzed Carboxylation of Alkenes2.2 Transition-Metal-Catalyzed Carboxylation of C(sp2)–X (X = Cl, Br, OTf) Bonds2.3 Transition-Metal-Catalyzed Carboxylation of Alkynes2.4 Transition-Metal-Catalyzed Carboxylation of Carbons Attached to Nitrogen3 Light-Driven Carboxylation via Organo-Photocatalysis3.1 Photocatalytic Carboxylation of Alkenes3.2 Photocatalytic Carboxylation of C(sp3)–H Bonds4 Conclusion

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Suprun, W. Ya, R. B. Sheparovych, Yu M. Hrynda, O. Yu Khavunko, and I. A. Opeida. "Supported transition metals oxides and N-hydroxyphthalimide as binary catalytic systems for the liquid-phase oxidation of cumene." Molecular Catalysis 510 (June 2021): 111683. http://dx.doi.org/10.1016/j.mcat.2021.111683.

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Lunardon, Marco, JiaJia Ran, Dario Mosconi, Carla Marega, Zhanhua Wang, Hesheng Xia, Stefano Agnoli, and Gaetano Granozzi. "Hybrid Transition Metal Dichalcogenide/Graphene Microspheres for Hydrogen Evolution Reaction." Nanomaterials 10, no. 12 (November 28, 2020): 2376. http://dx.doi.org/10.3390/nano10122376.

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A peculiar 3D graphene-based architecture, i.e., partial reduced-Graphene Oxide Aerogel Microspheres (prGOAM), having a dandelion-like morphology with divergent microchannels to implement innovative electrocatalysts for the hydrogen evolution reaction (HER) is investigated in this paper. prGOAM was used as a scaffold to incorporate exfoliated transition metals dichalcogenide (TMDC) nanosheets, and the final hybrid materials have been tested for HER and photo-enhanced HER. The aim was to create a hybrid material where electronic contacts among the two pristine materials are established in a 3D architecture, which might increase the final HER activity while maintaining accessible the TMDC catalytic sites. The adopted bottom-up approach, based on combining electrospraying with freeze-casting techniques, successfully provides a route to prepare TMDC/prGOAM hybrid systems where the dandelion-like morphology is retained. Interestingly, the microspherical morphology is also maintained in the tested electrode and after the electrocatalytic experiments, as demonstrated by scanning electron microscopy images. Comparing the HER activity of the TMDC/prGOAM hybrid systems with that of TMDC/partially reduced-Graphene Oxide (prGO) and TMDC/Vulcan was evidenced in the role of the divergent microchannels present in the 3D architecture. HER photoelectron catalytic (PEC) tests have been carried out and demonstrated an interesting increase in HER performance.

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Genoni, Andrea, Giuseppina La Ganga, Andrea Volpe, Fausto Puntoriero, Marilena Di Valentin, Marcella Bonchio, Mirco Natali, and Andrea Sartorel. "Water oxidation catalysis upon evolution of molecular Co(iii) cubanes in aqueous media." Faraday Discussions 185 (2015): 121–41. http://dx.doi.org/10.1039/c5fd00076a.

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The increasing global energy demand has stimulated great recent efforts in investigating new solutions for artificial photosynthesis, a potential source of clean and renewable solar fuel. In particular, according to the generally accepted modular approach aimed at optimising separately the different compartments of the entire process, many studies have focused on the development of catalytic systems for water oxidation to oxygen. While in recent years there have been many reports on new catalytic systems, the mechanism and the active intermediates operating the catalysis have been less investigated. Well-defined, molecular catalysts, constituted by transition metals stabilised by a suitable ligand pool, could help in solving this aspect. However, in some cases molecular species have been shown to evolve to active metal oxides that constitute the other side of this catalysis dichotomy. In this paper, we address the evolution of tetracobalt(iii) cubanes, stabilised by a pyridine/acetate ligand pool, to active species that perform water oxidation to oxygen. Primary evolution of the cubane in aqueous solution is likely initiated by removal of an acetate bridge, opening the coordination sphere of the cobalt centres. This cobalt derivative, where the pristine ligands still impact on the reactivity, shows enhanced electron transfer rates to Ru(bpy)₃³⁺(hole scavenging) within a photocatalytic cycle with Ru(bpy)₃²⁺as the photosensitiser and S₂O₈²⁻as the electron sink. A more accentuated evolution occurs under continuous irradiation, where Electron Paramagnetic Resonance (EPR) spectroscopy reveals the formation of Co(ii) intermediates, likely contributing to the catalytic process that evolves oxygen. All together, these results confirm the relevant effect of molecular species, in particular in fostering the rate of the electron transfer processes involved in light activated cycles, pivotal in the design of a photoactive device.

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Mai, Shaoyu, Changqing Rao, Ming Chen, Jihu Su, Jiangfeng Du, and Qiuling Song. "Merging gold catalysis, organocatalytic oxidation, and Lewis acid catalysis for chemodivergent synthesis of functionalized oxazoles from N-propargylamides." Chemical Communications 53, no. 75 (2017): 10366–69. http://dx.doi.org/10.1039/c7cc05746f.

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Novel catalytic systems consisting of cationic gold complexes, N-hydroxyphthalimide (NHPI), and transition-metal-based Lewis acids have been developed for the one-pot synthesis of functionalized oxazoles.

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Chernikova, O. M., H. D. Mateik, and Y. V. Ogorodnik. "Influence atoms of Co, Ni, Cu on the catalytic activity of small Pt clasters: First principles calculations." Physics and Chemistry of Solid State 21, no. 3 (September 30, 2020): 415–19. http://dx.doi.org/10.15330/pcss.21.3.415-419.

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Based on the calculations from the first principles, we obtained the distributions of valence electron densities and electronic energy spectra for small Ptn clusters (where n = 1-5 atoms). According to the results of calculations, it is determined that the inclusion of oxygen atoms or atoms of other kinds in small Ptn clusters, as a rule, affect the catalytic activity of research systems. It is established that during doping of small platinum clusters by atoms of 3-d transition metals (Cu, Ni, Co), the electronic structure of the cluster and the band gap change. This in turn helps to increase the catalytic activity of platinum.

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Lykaki, Maria, Sofia Stefa, Sόnia Carabineiro, Pavlos Pandis, Vassilis Stathopoulos, and Michalis Konsolakis. "Facet-Dependent Reactivity of Fe2O3/CeO2 Nanocomposites: Effect of Ceria Morphology on CO Oxidation." Catalysts 9, no. 4 (April 19, 2019): 371. http://dx.doi.org/10.3390/catal9040371.

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Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species.

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Mayet, Nolwenn, Karine Servat, K. Boniface Kokoh, and Teko W. Napporn. "Probing the Surface of Noble Metals Electrochemically by Underpotential Deposition of Transition Metals." Surfaces 2, no. 2 (April 9, 2019): 257–76. http://dx.doi.org/10.3390/surfaces2020020.

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The advances in material science have led to the development of novel and various materials as nanoparticles or thin films. Underpotential deposition (upd) of transition metals appears to be a very sensitive method for probing the surfaces of noble metals, which is a parameter that has an important effect on the activity in heterogeneous catalysis. Underpotential deposition as a surface characterization tool permits researchers to precisely determine the crystallographic orientations of nanoparticles or the real surface area of various surfaces. Among all the work dealing with upd, this review focuses specifically on the main upd systems used to probe surfaces of noble metals in electrocatalysis, from poly‒ and single-crystalline surfaces to nanoparticles. Cuupd is reported as a tool to determine the active surface area of gold‒ and platinum‒based bimetallic electrode materials. Pbupd is the most used system to assess the crystallographic orientations on nanoparticles’ surface. In the case of platinum, Bi and Ge adsorptions are singled out for probing (1 1 1) and (1 0 0) facets, respectively.

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Lee, Ha-Eun, Dopil Kim, Ahrom You, Myung Hwan Park, Min Kim, and Cheoljae Kim. "Transition Metal-Catalyzed α-Position Carbon–Carbon Bond Formations of Carbonyl Derivatives." Catalysts 10, no. 8 (August 2, 2020): 861. http://dx.doi.org/10.3390/catal10080861.

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α-Functionalization of carbonyl compounds in organic synthesis has traditionally been accomplished via classical enolate chemistry. As α-functionalized carbonyl moieties are ubiquitous in biologically and pharmaceutically valuable molecules, catalytic α-alkylations have been extensively studied, yielding a plethora of practical and efficient methodologies. Moreover, stereoselective carbon–carbon bond formation at the α-position of achiral carbonyl compounds has been achieved by using various transition metal–chiral ligand complexes. This review describes recent advances—in the last 20 years and especially focusing on the last 10 years—in transition metal-catalyzed α-alkylations of carbonyl compounds, such as aldehydes, ketones, imines, esters, and amides and in efficient carbon–carbon bond formations. Active catalytic species and ligand design are discussed, and mechanistic insights are presented. In addition, recently developed photo-redox catalytic systems for α-alkylations are described as a versatile synthetic tool for the synthesis of chiral carbonyl-bearing molecules.

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Kuriakose, Nishamol, and Kumar Vanka. "Can main group systems act as superior catalysts for dihydrogen generation reactions? A computational investigation." Dalton Transactions 45, no. 14 (2016): 5968–77. http://dx.doi.org/10.1039/c5dt01058f.

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The density functional theory (DFT) calculations reveal the potential of newly proposed main group germanium hydride systems to effect important chemical transformations, such as the catalytic cleavage of the O–H bond in water and alcohols, with significantly greater efficiency than the existing, state-of-the-art post-transition metal based systems.

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Palella, Alessandra, Katia Barbera, Francesco Arena, and Lorenzo Spadaro. "Clean Syn-Fuels via Hydrogenation Processes: Acidity–Activity Relationship in O-Xylene Hydrotreating." ChemEngineering 4, no. 1 (January 6, 2020): 4. http://dx.doi.org/10.3390/chemengineering4010004.

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Transition metal sulfide catalysts are actually the most performing catalytic materials in crude oil hydrotreating (HDT), for energetic purposes. However, these systems suffer from several drawbacks that limit their exploitation. Aiming to meet the even more stringent environmental requirement, through a remarkable improvement of HDT performance in the presence of refractory feedstock (i.e., in terms of activity, selectivity, and stability), a deeper knowledge of the structure–activity relationship of catalysts must be achieved. Therefore, in this study, CoMo/γ-Al2O3 and NiMo/γ-Al2O3 catalysts were characterized and tested in the o-xylene hydrogenation model reaction, assessing the influence of both support acidity and catalyst acid strength on reaction pathway by employing γ-Al2O3 and Y-Type zeolite as acid reference materials. A clear relationship between concentration and strength of acid sites and the performance of the catalytic materials was established. Cobalt based catalyst (CoMoSx) proves a higher acidic character with respect to Nickel (NiMoSx), prompting isomerization reactions preferentially, also reflecting a greater o-xylene conversion. The different chemical properties of metals also affect the catalytic pathway, leading on the CoMoSx system to the preferential formation of p-xylene isomer with respect to m-xylene.

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Heindl, Jason E., Michael E. Hibbing, Jing Xu, Ramya Natarajan, Aaron M. Buechlein, and Clay Fuqua. "Discrete Responses to Limitation for Iron and Manganese in Agrobacterium tumefaciens: Influence on Attachment and Biofilm Formation." Journal of Bacteriology 198, no. 5 (December 28, 2015): 816–29. http://dx.doi.org/10.1128/jb.00668-15.

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ABSTRACTTransition metals such as iron and manganese are crucial trace nutrients for the growth of most bacteria, functioning as catalytic cofactors for many essential enzymes. Dedicated uptake and regulatory systems have evolved to ensure their acquisition for growth, while preventing toxicity. Transcriptomic analysis of the iron- and manganese-responsive regulons ofAgrobacterium tumefaciensrevealed that there are discrete regulatory networks that respond to changes in iron and manganese levels. Complementing earlier studies, the iron-responsive gene network is quite large and includes many aspects of iron-dependent metabolism and the iron-sparing response. In contrast, the manganese-responsive network is restricted to a limited number of genes, many of which can be linked to transport and utilization of the transition metal. Several of the target genes predicted to drive manganese uptake are required for growth under manganese-limited conditions, and anA. tumefaciensmutant with a manganese transport deficiency is attenuated for plant virulence. Iron and manganese limitation independently inhibit biofilm formation byA. tumefaciens, and several candidate genes that could impact biofilm formation were identified in each regulon. The biofilm-inhibitory effects of iron and manganese do not rely on recognized metal-responsive transcriptional regulators, suggesting alternate mechanisms influencing biofilm formation. However, under low-manganese conditions thedcpAoperon is upregulated, encoding a system that controls levels of the cyclic di-GMP second messenger. Mutation of this regulatory pathway dampens the effect of manganese limitation.IMPORTANCEResponses to changes in transition metal levels, such as those of manganese and iron, are important for normal metabolism and growth in bacteria. Our study used global gene expression profiling to understand the response of the plant pathogenAgrobacterium tumefaciensto changes of transition metal availability. Among the properties that are affected by both iron and manganese levels are those required for normal surface attachment and biofilm formation, but the requirement for each of these transition metals is mechanistically independent from the other.

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Gulyás, Henrik, Ivan Rivilla, Simona Curreli, Zoraida Freixa, and Piet W. N. M. van Leeuwen. "Highly active, chemo- and enantioselective Pt-SPO catalytic systems for the synthesis of aromatic carboxamides." Catalysis Science & Technology 5, no. 7 (2015): 3822–28. http://dx.doi.org/10.1039/c5cy00627a.

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Platinum complexes of the chiral non-racemizing SPO ligand 1 have been discovered to be the first artificial transition metal complexes providing kinetic resolution in the hydration of a racemic chiral nitrile.

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Mysore Ramesha, Bharadwaj, and Vera Meynen. "Advances and Challenges in the Creation of Porous Metal Phosphonates." Materials 13, no. 23 (November 26, 2020): 5366. http://dx.doi.org/10.3390/ma13235366.

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In the expansive world of porous hybrid materials, a category of materials that has been rather less explored than others and is gaining attention in development is the porous metal phosphonates. They offer promising features towards applications which demand control over the inorganic–organic network and interface, which is critical for adsorption, catalysis and functional devices and technology. The need to establish a rationale for new synthesis approaches to make these materials in a controlled manner is by itself an important motivation for material chemists. In this review, we highlight the various synthetic strategies exploited, discussing various metal phosphonate systems and how they influence the properties of porous metal phosphonates. We discuss porous metal phosphonate systems based on transition metals with an emphasis on addressing challenges with tetravalent metals. Finally, this review provides a brief description of some key areas of application that are ideally suited for porous metal phosphonates.

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BILA, Evgenia, Daryna SOLTYS, and Mykola OBUSHAK. "THREE-COMPONENT REACTIONS OF UNSATURATED COMPOUNDS WITH ARENEDIASONIUM SALTS AND NEUTRAL NUCLEOPHILS. ARYLSULFONYLATION." Proceedings of the Shevchenko Scientific Society. Series Сhemical Sciences 2020, no. 60 (February 25, 2020): 31–54. http://dx.doi.org/10.37827/ntsh.chem.2020.60.031.

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The results of recent achievements on the interaction of arenediazonium salts with unsaturated compounds in the presence of neutral nucleophiles are summarized. New examples of multicomponent transformations with the participation of such neutral nucleophiles as CO (arylcarbonylation), NO (arylnitrosylation), aceto¬nitrile (aminoarylation), SO2 (arylsulfonylation) and others are given. These reactions can be applied to alkenes, alkynes, aromatic compounds. Mild reaction conditions allow the use of reagents with different functional groups. Reactions of this type open up the possibility of one-step production of complex poly¬functional compounds. Catalytic systems are quite diverse for these transformations: it is catalysis involving transition metals, platinum group metals. Prospects for the use of arenediazonium salts in multicomponent transfor¬ma-tions according to the concepts of «green» chemistry are outlined – it is photoinitiation by visible and ultraviolet radiation, acid-base catalysis. The role of catalysis in the process, the role of complex intermediates and reaction mechanisms are analyzed. For most processes, the SET reaction mechanism is implemented through the formation of an alkene intermediate ion radical, the stability of which depends on the nature of the substituent near the double bond. Particular attention is paid to arylsulfonylation reactions, because the arylsulfonyl group is one of the many important biologically active molecules. Arylsulfonylation reactions of alkenes with the participation of transition metals or under conditions of metal-free catalysis are considered. Examples of arylsulfonylation of the C=C bond using sulfinic acids, their salts and hydrazides are given. An available method for producing functionalized sulfones is the multicomponent interaction of arenediazonium salts, alkenes and SO2. The arylsulfonylation reaction occurs as a series of successive reactions involving the generation of a catalyst, the decomposition of arenediazonium cations, the addition of an aryl group, a nucleophile to a multiple bond, and the formation of the final products. The use of functionalized alkenes allows to obtain functionalized arylsulfones in one step. This functionalization expands the scope of use of arylsulfones, in particular, for studies of biological activity. The progress made in the development of effective strategies for the production of arylsulfones opens new opportunities for further research.

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Suarez, Hugo, Adrian Ramirez, Carlos J. Bueno-Alejo, and Jose L. Hueso. "Silver-Copper Oxide Heteronanostructures for the Plasmonic-Enhanced Photocatalytic Oxidation of N-Hexane in the Visible-NIR Range." Materials 12, no. 23 (November 22, 2019): 3858. http://dx.doi.org/10.3390/ma12233858.

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Volatile organic compounds (VOCs) are recognized as hazardous contributors to air pollution, precursors of multiple secondary byproducts, troposphere aerosols, and recognized contributors to respiratory and cancer-related issues in highly populated areas. Moreover, VOCs present in indoor environments represent a challenging issue that need to be addressed due to its increasing presence in nowadays society. Catalytic oxidation by noble metals represents the most effective but costly solution. The use of photocatalytic oxidation has become one of the most explored alternatives given the green and sustainable advantages of using solar light or low-consumption light emitting devices. Herein, we have tried to address the shortcomings of the most studied photocatalytic systems based on titania (TiO2) with limited response in the UV-range or alternatively the high recombination rates detected in other transition metal-based oxide systems. We have developed a silver-copper oxide heteronanostructure able to combine the plasmonic-enhanced properties of Ag nanostructures with the visible-light driven photoresponse of CuO nanoarchitectures. The entangled Ag-CuO heteronanostructure exhibits a broad absorption towards the visible-near infrared (NIR) range and achieves total photo-oxidation of n-hexane under irradiation with different light-emitting diodes (LEDs) specific wavelengths at temperatures below 180 °C and outperforming its thermal catalytic response or its silver-free CuO illuminated counterpart.

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Vemula, Sandeep R., Michael R. Chhoun, and Gregory R. Cook. "Well-Defined Pre-Catalysts in Amide and Ester Bond Activation." Molecules 24, no. 2 (January 9, 2019): 215. http://dx.doi.org/10.3390/molecules24020215.

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Over the past few decades, transition metal catalysis has witnessed a rapid and extensive development. The discovery and development of cross-coupling reactions is considered to be one of the most important advancements in the field of organic synthesis. The design and synthesis of well-defined and bench-stable transition metal pre-catalysts provide a significant improvement over the current catalytic systems in cross-coupling reactions, avoiding excess use of expensive ligands and harsh conditions for the synthesis of pharmaceuticals, agrochemicals and materials. Among various well-defined pre-catalysts, the use of Pd(II)-NHC, particularly, provided new avenues to expand the scope of cross-coupling reactions incorporating unreactive electrophiles, such as amides and esters. The strong σ-donation and tunable steric bulk of NHC ligands in Pd-NHC complexes facilitate oxidative addition and reductive elimination steps enabling the cross-coupling of broad range of amides and esters using facile conditions contrary to the arduous conditions employed under traditional catalytic conditions. Owing to the favorable catalytic activity of Pd-NHC catalysts, a tremendous progress was made in their utilization for cross-coupling reactions via selective acyl C–X (X=N, O) bond cleavage. This review highlights the recent advances made in the utilization of well-defined pre-catalysts for C–C and C–N bond forming reactions via selective amide and ester bond cleavage.

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Zhang, Zhuolei, Ji Su, Ana Sanz Matias, Madeleine Gordon, Yi-Sheng Liu, Jinghua Guo, Chengyu Song, et al. "Enhanced and stabilized hydrogen production from methanol by ultrasmall Ni nanoclusters immobilized on defect-rich h-BN nanosheets." Proceedings of the National Academy of Sciences 117, no. 47 (November 9, 2020): 29442–52. http://dx.doi.org/10.1073/pnas.2015897117.

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Employing liquid organic hydrogen carriers (LOHCs) to transport hydrogen to where it can be utilized relies on methods of efficient chemical dehydrogenation to access this fuel. Therefore, developing effective strategies to optimize the catalytic performance of cheap transition metal-based catalysts in terms of activity and stability for dehydrogenation of LOHCs is a critical challenge. Here, we report the design and synthesis of ultrasmall nickel nanoclusters (∼1.5 nm) deposited on defect-rich boron nitride (BN) nanosheet (Ni/BN) catalysts with higher methanol dehydrogenation activity and selectivity, and greater stability than that of some other transition-metal based catalysts. The interface of the two-dimensional (2D) BN with the metal nanoparticles plays a strong role both in guiding the nucleation and growth of the catalytically active ultrasmall Ni nanoclusters, and further in stabilizing these nanoscale Ni catalysts against poisoning by interactions with the BN substrate. We provide detailed spectroscopy characterizations and density functional theory (DFT) calculations to reveal the origin of the high productivity, high selectivity, and high durability exhibited with the Ni/BN nanocatalyst and elucidate its correlation with nanocluster size and support–nanocluster interactions. This study provides insight into the role that the support material can have both regarding the size control of nanoclusters through immobilization during the nanocluster formation and also during the active catalytic process; this twofold set of insights is significant in advancing the understanding the bottom-up design of high-performance, durable catalytic systems for various catalysis needs.

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Buncel, Erwin, Ruby Nagelkerke, and Gregory RJ Thatcher. "Alkali metal ion catalysis in nucleophilic displacement by ethoxide ion on p-nitrophenyl phenylphosphonate: Evidence for multiple metal ion catalysis." Canadian Journal of Chemistry 81, no. 1 (January 1, 2003): 53–63. http://dx.doi.org/10.1139/v02-202.

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In continuation of our studies of alkali metal ion catalysis and inhibition at carbon, phosphorus, and sulfur centers, the role of alkali metal ions in nucleophilic displacement reactions of p-nitrophenyl phenylphosphonate (PNPP) has been examined. All alkali metal ions studied acted as catalysts. Alkali metal ions added as inert salts increased the rate while decreased rate resulted on M+ complexation with 18-crown-6 ether. Kinetic analysis indicated the interaction of possibly three potassium ions, four sodium ions, and five lithium ions in the transition state of the reactions of ethoxide with PNPP. Pre-association of the anionic substrate with two metals ions in the ground state gave the best fit to the experimental data of the sodium system. Thus, the study gives evidence of the role of several metal ions in nucleophilic displacement reactions of ethoxide with anionic PNPP, both in the ground state and in the transition state. Molecular modeling of the anionic transition state implies that the size of the monovalent cation and the steric requirement of the pentacoordinate transition state are the primary limitations on the number of cations that can be brought to bear to stabilize the transition state and catalyze nucleophilic substitution at phosphorus. The bearing of the present work on metal ion catalysis in enzyme systems is discussed, in particular enzymes that catalyze phosphoryl transfer, which often employ multiple metal ions. Our results, both kinetic and modeling, reveal the importance of electrostatic stabilization of the transition state for phosphoryl transfer that may be effected by multiple cations, either monovalent metal ions or amino acid residues. The more such cations can be brought into contact with the anionic transition state, the greater the catalysis observed.Key words: alkali metal ion catalysis, nucleophilic displacement at phosphorus, multiple metal ion catalysis, phosphoryl transfer.

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Chen, Chueh-An, Chiao-Lin Lee, Po-Kang Yang, Dung-Sheng Tsai, and Chuan-Pei Lee. "Active Site Engineering on Two-Dimensional-Layered Transition Metal Dichalcogenides for Electrochemical Energy Applications: A Mini-Review." Catalysts 11, no. 2 (January 21, 2021): 151. http://dx.doi.org/10.3390/catal11020151.

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Two-dimensional-layered transition metal dichalcogenides (2D-layered TMDs) are a chemically diverse class of compounds having variable band gaps and remarkable electrochemical properties, which make them potential materials for applications in the field of electrochemical energy. To date, 2D-layered TMDs have been wildly used in water-splitting systems, dye-sensitized solar cells, supercapacitors, and some catalysis systems, etc., and the pertinent devices exhibit good performances. However, several reports have also indicated that the active sites for catalytic reaction are mainly located on the edge sites of 2D-layered TMDs, and their basal plane shows poor activity toward catalysis reaction. Accordingly, many studies have reported various approaches, namely active-site engineering, to address this issue, including plasma treatment, edge site formation, heteroatom-doping, nano-sized TMD pieces, highly curved structures, and surface modification via nano-sized catalyst decoration, etc. In this article, we provide a short review for the active-site engineering on 2D-layered TMDs and their applications in electrochemical energy. Finally, the future perspectives for 2D-layered TMD catalysts will also be briefly discussed.

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Nghiem, Tai-Lam, Deniz Coban, Stefanie Tjaberings, and André H. Gröschel. "Recent Advances in the Synthesis and Application of Polymer Compartments for Catalysis." Polymers 12, no. 10 (September 24, 2020): 2190. http://dx.doi.org/10.3390/polym12102190.

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Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. To prevent the deactivation of catalysts in water or avoid unwanted cross-reactions, catalysts are often site-isolated in nanopockets or separately stored in compartments. These concepts have inspired the design of a range of synthetic nanoreactors that allow otherwise unfeasible catalytic reactions in aqueous environments. Since the field of nanoreactors is evolving rapidly, we here summarize—from a personal perspective—prominent and recent examples for polymer nanoreactors with emphasis on their synthesis and their ability to catalyze reactions in dispersion. Examples comprise the incorporation of catalytic sites into hydrophobic nanodomains of single chain polymer nanoparticles, molecular polymer nanoparticles, and block copolymer micelles and vesicles. We focus on catalytic reactions mediated by transition metal and organocatalysts, and the separate storage of multiple catalysts for one-pot cascade reactions. Efforts devoted to the field of nanoreactors are relevant for catalytic chemistry and nanotechnology, as well as the synthesis of pharmaceutical and natural compounds. Optimized nanoreactors will aid in the development of more potent catalytic systems for green and fast reaction sequences contributing to sustainable chemistry by reducing waste of solvents, reagents, and energy.

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Tao, Lei, Yu-Yang Zhang, Sokrates T. Pantelides, and Shixuan Du. "Tuning the Catalytic Activity of a Quantum Nutcracker for Hydrogen Dissociation." Surfaces 3, no. 1 (January 20, 2020): 40–47. http://dx.doi.org/10.3390/surfaces3010004.

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A quantum nutcracker, a recently proposed catalytic system for hydrogen dissociation, consists of two inert components: an organic molecule such as a transition metal phthalocyanine and an inert surface such as Cu or Au. The reaction takes place at the interface between the two components, which are weakly bonded by Van der Waals (VdW) forces. Here, we explore a method used to tune the reaction barrier in a quantum nutcracker system for hydrogen dissociation. By employing density-functional-theory calculations, we find that the H2 entry barrier, which is the rate-limiting barrier, is reduced by replacing the phthalocyanine by porphyrin derivatives such as octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP). The system remains active if a dissociated H atom is adsorbed on the transition metal ion. Metallic two-dimensional materials such as NbS2 and CoS2 are good candidates for the quantum nutcracker. The present design of a quantum nutcracker for hydrogen dissociation provides new opportunities with which to induce catalytic activity in VdW-bonded systems.

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Zheng, Yun, Xiaojuan Wan, Xin Cheng, Kun Cheng, Zhengfei Dai, and Zhihong Liu. "Advanced Catalytic Materials for Ethanol Oxidation in Direct Ethanol Fuel Cells." Catalysts 10, no. 2 (February 1, 2020): 166. http://dx.doi.org/10.3390/catal10020166.

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Direct ethanol fuel cells (DEFCs) have emerged as promising and advanced power systems that can considerably reduce fossil fuel dependence, and thus have attracted worldwide attention. DEFCs have many apparent merits over the analogous devices fed with hydrogen or methanol. As the key constituents, the catalysts for both cathodes and anodes usually face some problems (such as high cost, low conversion efficiency, and inferior durability) that hinder the commercialization of DEFCs. This review mainly focuses on the most recent advances in nanostructured catalysts for anode materials in DEFCS. First, we summarize the effective strategies used to achieve highly active Pt- and Pd-based catalysts for ethanol electro-oxidation, including composition control, microstructure design, and the optimization of support materials. Second, a few non-precious catalysts based on transition metals (such as Fe, Co, and Ni) are introduced. Finally, we outline the concerns and future development of anode catalysts for DEFCs. This review provides a comprehensive understanding of anode catalysts for ethanol oxidation in DEFCs.

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Sánchez-López, Perla, Yulia Kotolevich, Serguei Miridonov, Fernando Chávez-Rivas, Sergio Fuentes, and Vitalii Petranovskii. "Bimetallic AgFe Systems on Mordenite: Effect of Cation Deposition Order in the NO Reduction with C3H6/CO." Catalysts 9, no. 1 (January 8, 2019): 58. http://dx.doi.org/10.3390/catal9010058.

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Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV–Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag+ is reduced with the participation of the Fe2+/Fe3+ ions transition and is present in the form of a Ag reduced state in different proportions of Agm clusters and Ag0 NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C3H6/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO.

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37

Liang, G., J. Huot, S. Boily, A. Van Neste, and R. Schulz. "Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2–Tm (Tm=Ti, V, Mn, Fe and Ni) systems." Journal of Alloys and Compounds 292, no. 1-2 (November 1999): 247–52. http://dx.doi.org/10.1016/s0925-8388(99)00442-9.

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38

Manos, Donatos, Kleopatra Miserli, and Ioannis Konstantinou. "Perovskite and Spinel Catalysts for Sulfate Radical-Based Advanced Oxidation of Organic Pollutants in Water and Wastewater Systems." Catalysts 10, no. 11 (November 10, 2020): 1299. http://dx.doi.org/10.3390/catal10111299.

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Since environmental pollution by emerging organic contaminants is one of the most important problems, gaining ground year after year, the development of decontamination technologies of water systems is now imperative. Advanced oxidation processes (AOPs) with the formation of highly reactive radicals can provide attractive technologies for the degradation of organic pollutants in water systems. Among several AOPs that can be applied for the formation of active radicals, this review study focus on sulfate radical based-AOPs (SR-AOPs) through the heterogeneous catalytic activation of persulfate (PS) or peroxymonosulfate (PMS) using perovskite and spinel oxides as catalysts. Perovskites and spinels are currently receiving high attention and being used in substantial applications in the above research area. The widespread use of these materials is based mainly in the possibilities offered by their structure as it is possible to introduce into their structures different metal cations or to partially substitute them, without however destroying their structure. In this way a battery of catalysts with variable catalytic activities can be obtained. Due to the fact that Co ions have been reported to be one of the best activators of PMS, special emphasis has been placed on perovskite/spinel catalysts containing cobalt in their structure for the degradation of organic pollutants through heterogeneous catalysis. Among spinel materials, spinel ferrites (MFe2O4) are the most used catalysts for heterogeneous activation of PMS. Specifically, catalysts with cobalt ion in the A position were reported to be more efficient as PMS activators for the degradation of most organic pollutants compared with other transition metal catalysts. Substituted or immobilized catalysts show high rates of degradation, stability over a wider pH area and also address better the phenomena of secondary contamination by metal leaching, thus an effective method to upgrade catalytic performance.

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Ahmad, Dalla Tiezza, and Orian. "In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments." Catalysts 9, no. 8 (August 9, 2019): 679. http://dx.doi.org/10.3390/catal9080679.

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Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)3IndRh] (Ind = (C9H7)−, indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C5H5)−, cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)3 group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis.

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van Dijk, Alberdina A., Eugene V. Makeyev, and Dennis H. Bamford. "Initiation of viral RNA-dependent RNA polymerization." Journal of General Virology 85, no. 5 (May 1, 2004): 1077–93. http://dx.doi.org/10.1099/vir.0.19731-0.

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This review summarizes the combined insights from recent structural and functional studies of viral RNA-dependent RNA polymerases (RdRPs) with the primary focus on the mechanisms of initiation of RNA synthesis. Replication of RNA viruses has traditionally been approached using a combination of biochemical and genetic methods. Recently, high-resolution structures of six viral RdRPs have been determined. For three RdRPs, enzyme complexes with metal ions, single-stranded RNA and/or nucleoside triphosphates have also been solved. These advances have expanded our understanding of the molecular mechanisms of viral RNA synthesis and facilitated further RdRP studies by informed site-directed mutagenesis. What transpires is that the basic polymerase right hand shape provides the correct geometrical arrangement of substrate molecules and metal ions at the active site for the nucleotidyl transfer catalysis, while distinct structural elements have evolved in the different systems to ensure efficient initiation of RNA synthesis. These elements feed the template, NTPs and ions into the catalytic cavity, correctly position the template 3′ terminus, transfer the products out of the catalytic site and orchestrate the transition from initiation to elongation.

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Banerjee, Abhinandan, and Robert W. J. Scott. "Optimization of transition metal nanoparticle-phosphonium ionic liquid composite catalytic systems for deep hydrogenation and hydrodeoxygenation reactions." Green Chemistry 17, no. 3 (2015): 1597–604. http://dx.doi.org/10.1039/c4gc01716a.

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Rydel-Ciszek, Katarzyna, Tomasz Pacześniak, Izabela Zaborniak, Paweł Błoniarz, Karolina Surmacz, Andrzej Sobkowiak, and Paweł Chmielarz. "Iron-Based Catalytically Active Complexes in Preparation of Functional Materials." Processes 8, no. 12 (December 20, 2020): 1683. http://dx.doi.org/10.3390/pr8121683.

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Iron complexes are particularly interesting as catalyst systems over the other transition metals (including noble metals) due to iron’s high natural abundance and mediation in important biological processes, therefore making them non-toxic, cost-effective, and biocompatible. Both homogeneous and heterogeneous catalysis mediated by iron as a transition metal have found applications in many industries, including oxidation, C-C bond formation, hydrocarboxylation and dehydration, hydrogenation and reduction reactions of low molecular weight molecules. These processes provided substrates for industrial-scale use, e.g., switchable materials, sustainable and scalable energy storage technologies, drugs for the treatment of cancer, and high molecular weight polymer materials with a predetermined structure through controlled radical polymerization techniques. This review provides a detailed statement of the utilization of homogeneous and heterogeneous iron-based catalysts for the synthesis of both low and high molecular weight molecules with versatile use, focusing on receiving functional materials with high potential for industrial application.

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Piola, Lorenzo, Fady Nahra, and Steven P. Nolan. "Olefin metathesis in air." Beilstein Journal of Organic Chemistry 11 (October 30, 2015): 2038–56. http://dx.doi.org/10.3762/bjoc.11.221.

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Since the discovery and now widespread use of olefin metathesis, the evolution of metathesis catalysts towards air stability has become an area of significant interest. In this fascinating area of study, beginning with early systems making use of high oxidation state early transition metal centers that required strict exclusion of water and air, advances have been made to render catalysts more stable and yet more functional group tolerant. This review summarizes the major developments concerning catalytic systems directed towards water and air tolerance.

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Zhu, Lei, Haojie Yu, Li Wang, Yusheng Xing, and Bilal Ul Amin. "Advances in the Synthesis of Polyolefin Elastomers with “Chain-walking” Catalysts and Electron Spin Resonance Research of Related Catalytic Systems." Current Organic Chemistry 25, no. 8 (April 28, 2021): 935–49. http://dx.doi.org/10.2174/1385272825666210126100641.

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In recent years, polyolefin elastomers play an increasingly important role in industry. The late transition metal complex catalysts, especially α-diimine Ni(II) and α-diimine Pd(II) complex catalysts, are popular “chain-walking” catalysts. They can prepare polyolefin with various structures, ranging from linear configuration to highly branched configuration. Combining the “chain-walking” characteristic with different polymerization strategies, polyolefins with good elasticity can be obtained. Among them, olefin copolymer is a common way to produce polyolefin elastomers. For instance, strictly defined diblock or triblock copolymers with excellent elastic properties were synthesized by adding ethylene and α-olefin in sequence. As well as the incorporation of polar monomers may lead to some unexpected improvement. Chain shuttling polymerization can generate multiblock copolymers in one pot due to the interaction of the catalysts with chain shuttling agent. Furthermore, when regarding ethylene as the sole feedstock, owing to the “oscillation” of the ligands of the asymmetric catalysts, polymers with stereo-block structures can be generated. Generally, the elasticity of these polyolefins mainly comes from the alternately crystallineamorphous block structures, which is closely related to the characteristic of the catalytic system. To improve performance of the catalysts and develop excellent polyolefin elastomers, research on the catalytic mechanism is of great significance. Electron spin resonance (ESR), as a precise method to detect unpaired electron, can be applied to study transition metal active center. Therefore, the progress on the exploration of the valence and the proposed configuration of catalyst active center in the catalytic process by ESR is also reviewed.

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Peckh, Kamil, and Beata Orlińska. "Transition Metal Salts of Carboxylated Multiwalled Carbon Nanotubes in Combination with N-hydroxyphthalimide as Catalytic Systems for Hydrocarbon Oxidation." Materials 14, no. 9 (April 29, 2021): 2314. http://dx.doi.org/10.3390/ma14092314.

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In this study, the transition metal (Co (II), Cu (II), and Mn (II)) salts of carboxylated carbon nanotubes were synthesized and characterized (the determined metal contents were in the range of 0.89–1.16%). The catalytic activity and the possibility for recovery and reuse of the obtained heterogeneous salts were then studied in the solvent-free oxidation of ethylbenzene with oxygen. The oxidation processes were carried out at 80 °C under atmospheric pressure in the presence of N-hydroxyphthalimide. The highest conversion of ethylbenzene, 27%, was obtained with a system consisting of the Cu (II) salt of the carboxylated carbon nanotubes, N-hydroxyphthalimide, and the azo initiator AIBN.

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Grafova, Iryna A., Andrei V. Grafov, Umberto Costantino, Fabio Marmottini, and Marcos L. Dias. "Layered Double Hydroxides as Supports for Norbornene Addition Polymerisation Catalysts." Zeitschrift für Naturforschung B 58, no. 11 (November 1, 2003): 1069–74. http://dx.doi.org/10.1515/znb-2003-1106.

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Abstract Addition polymerisation of norbornene with transition metal catalysts activated by methylaluminoxane was first realised on heterogeneous catalytic systems. Advanced inorganic functional polymers possessing anion-exchange properties - layered double hydroxides of Al and Zn of hydrotalcitetype - were applied as supports. They possess high polarity and are selective towards polar molecules like organometallic compounds. The activity of immobilised nickel catalysts was found to be higher than that of the homogeneous one. A certain catalytic activity was also found for group 4 phthalocyanines. The polynorbornenes obtained were characterised by gel permeation chromatography and SEM microimaging. The support’s morphology influences the shape, density, and dimensions of the resulting polymer particles.

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Leimkühler, Silke. "Transition Metals in Catalysis: The Functional Relationship of Fe–S Clusters and Molybdenum or Tungsten Cofactor-Containing Enzyme Systems." Inorganics 9, no. 1 (January 13, 2021): 6. http://dx.doi.org/10.3390/inorganics9010006.

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Following the “Molybdenum and Tungsten Enzyme conference—MoTEC2019” and the satellite meeting on “Iron–Sulfur for Life”, we wanted to emphasize the link between iron–sulfur clusters and their importance for the biosynthesis, assembly, and activity of complex metalloenzymes in this Special Issue of Inorganics, entitled “Transition Metals in Catalysis: The Functional Relationship of Fe–S Clusters and Molybdenum or Tungsten Cofactor-Containing Enzyme Systems” [...]

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Suggs, Kelvin, and Alfred Z. Msezane. "Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals." International Journal of Molecular Sciences 21, no. 18 (September 13, 2020): 6714. http://dx.doi.org/10.3390/ijms21186714.

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The fundamental mechanism underlying negative-ion catalysis involves bond-strength breaking in the transition state (TS). Doubly-charged atomic/molecular anions are proposed as novel dynamic tunable catalysts, as demonstrated in water oxidation into peroxide. Density Functional Theory TS calculations have found a tunable energy activation barrier reduction ranging from 0.030 eV to 2.070 eV, with Si2−, Pu2−, Pa2− and Sn2− being the best catalysts; the radioactive elements usher in new application opportunities. C602− significantly reduces the standard C60− TS energy barrier, while graphene increases it, behaving like cationic systems. According to their reaction barrier reduction efficiency, variation across charge states and systems, rank-ordered catalysts reveal their tunable and wide applications, ranging from water purification to biocompatible antiviral and antibacterial sanitation systems.

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Mannu, Alberto, Arnald Grabulosa, and Salvatore Baldino. "Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes." Catalysts 10, no. 2 (February 1, 2020): 162. http://dx.doi.org/10.3390/catal10020162.

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The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl2(η6-arene)(P)] and cationic [Rh(PP)2]X (X = anion; P and PP = mono- and bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features.

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Franciò, Giancarlo, Ulrich Hintermair, and Walter Leitner. "Unlocking the potential of supported liquid phase catalysts with supercritical fluids: low temperature continuous flow catalysis with integrated product separation." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2057 (December 28, 2015): 20150005. http://dx.doi.org/10.1098/rsta.2015.0005.

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Solution-phase catalysis using molecular transition metal complexes is an extremely powerful tool for chemical synthesis and a key technology for sustainable manufacturing. However, as the reaction complexity and thermal sensitivity of the catalytic system increase, engineering challenges associated with product separation and catalyst recovery can override the value of the product. This persistent downstream issue often renders industrial exploitation of homogeneous catalysis uneconomical despite impressive batch performance of the catalyst. In this regard, continuous-flow systems that allow steady-state homogeneous turnover in a stationary liquid phase while at the same time effecting integrated product separation at mild process temperatures represent a particularly attractive scenario. While continuous-flow processing is a standard procedure for large volume manufacturing, capitalizing on its potential in the realm of the molecular complexity of organic synthesis is still an emerging area that requires innovative solutions. Here we highlight some recent developments which have succeeded in realizing such systems by the combination of near- and supercritical fluids with homogeneous catalysts in supported liquid phases. The cases discussed exemplify how all three levels of continuous-flow homogeneous catalysis (catalyst system, separation strategy, process scheme) must be matched to locate viable process conditions.

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Journal articles on the topic 'Transition metals; Catalytic systems'

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