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Catalysts, Volume 7, Issue 12 (December 2017)

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Cover Story (view full-size image) Among all the synthesized nano-TiO2, curved nanoparticles are of prominent interest for various [...] Read more.
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Open AccessArticle Effect of Iminodiacetic Acid-Modified Nieuwland Catalyst on the Acetylene Dimerization Reaction
Catalysts 2017, 7(12), 394; https://doi.org/10.3390/catal7120394
Received: 19 November 2017 / Revised: 16 December 2017 / Accepted: 16 December 2017 / Published: 19 December 2017
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Abstract
The iminodiacetic acid-modified Nieuwland catalyst not only improves the conversion of acetylene but also increases the selectivity of monovinylacetylene (MVA). A catalyst system containing 4.5% iminodiacetic acid exhibited excellent performance, and the yield of MVA was maintained at 32% after 24 h, producing
[...] Read more.
The iminodiacetic acid-modified Nieuwland catalyst not only improves the conversion of acetylene but also increases the selectivity of monovinylacetylene (MVA). A catalyst system containing 4.5% iminodiacetic acid exhibited excellent performance, and the yield of MVA was maintained at 32% after 24 h, producing an increase in the yield by 12% relative to the Nieuwland catalyst system. Based on a variety of characterization methods analysis of the crystal precipitated from the catalyst solution, it can be inferred that the outstanding performance and lifetime of the catalyst system was due to the presence of iminodiacetic acid, which increases the electron density of Cu+ and adjusts the acidity of the catalytic solution. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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Open AccessArticle Application of Heterogeneous Catalysts in the First Steps of the Oseltamivir Synthesis
Catalysts 2017, 7(12), 393; https://doi.org/10.3390/catal7120393
Received: 17 November 2017 / Revised: 7 December 2017 / Accepted: 12 December 2017 / Published: 17 December 2017
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Abstract
The first steps of oseltamivir synthesis from quinic acid involve acetalization and ester formation. These reactions are catalyzed by either acids or bases, which may be accomplished by heterogeneous catalysts. Sulfonic solids are efficient acid catalysts for acetalization and esterification reactions. Supported tetraalkylammonium
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The first steps of oseltamivir synthesis from quinic acid involve acetalization and ester formation. These reactions are catalyzed by either acids or bases, which may be accomplished by heterogeneous catalysts. Sulfonic solids are efficient acid catalysts for acetalization and esterification reactions. Supported tetraalkylammonium hydroxide or 1,5,7-triazabicyclo[4.4.0]dec-5-ene are also efficient base catalysts for lactone alcoholysis and in this work, these catalysts have been applied in two alternative synthetic routes that lead to oseltamivir. The classical route consists of an acetalization, followed by a lactonization, and then a lactone alcoholysis. This achieves a 66% isolated yield. The alternative route consists of esterification followed by acetalization and is only efficient when an acetone acetal is used. Full article
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Open AccessArticle Preparation of Manganese Lignosulfonate and Its Application as the Precursor of Nanostructured MnOx for Oxidative Electrocatalysis
Catalysts 2017, 7(12), 392; https://doi.org/10.3390/catal7120392
Received: 6 November 2017 / Revised: 11 December 2017 / Accepted: 13 December 2017 / Published: 15 December 2017
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Abstract
The synthesis of manganese lignosulfonates by a two-step method has been reported. It was based on the conversion of technical sodium derivative of lignosulfonate to its hydrogen form i.e., lignosulfonic acid and its further reaction with manganese hydroxide. The obtained product was electroactive,
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The synthesis of manganese lignosulfonates by a two-step method has been reported. It was based on the conversion of technical sodium derivative of lignosulfonate to its hydrogen form i.e., lignosulfonic acid and its further reaction with manganese hydroxide. The obtained product was electroactive, and could be applied as the precursor of electroactive manganese oxide. The product showed a reversible redox activity in the potential range of 0 to 1 V vs. an Ag/AgCl reference electrode. The electroactivity of the obtained product can be tentatively assigned to the redox activity of both the electrodeposited MnOx and the presence of lignosulfonate-derived quinones since the energy dispersive spectroscopy (EDS) confirmed the presence of organic matter in the deposit. It also showed substantial electrocatalytic activity towards the anodic oxidation of hydrogen peroxide. This suggests that manganese lignosulfonates could be a valuable compound for the electrochemical preparation of electroactive layers that are suitable in the development of electrochemical sensors. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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Open AccessArticle Mixed Zinc/Manganese on Highly Reduced Graphene Oxide: A Highly Active Nanocomposite Catalyst for Aerial Oxidation of Benzylic Alcohols
Catalysts 2017, 7(12), 391; https://doi.org/10.3390/catal7120391
Received: 29 November 2017 / Revised: 11 December 2017 / Accepted: 12 December 2017 / Published: 15 December 2017
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Abstract
Nanocomposites of highly reduced graphene oxide (HRG) and ZnOx nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method. The prepared sample calcined at 300 °C yielded i.e., ZnOx(1%)–MnCO3/(X%)HRG (where X =
[...] Read more.
Nanocomposites of highly reduced graphene oxide (HRG) and ZnOx nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method. The prepared sample calcined at 300 °C yielded i.e., ZnOx(1%)–MnCO3/(X%)HRG (where X = 0–7), calcination at 400 °C and 500 °C, yielded different manganese oxides i.e., ZnOx(1%)–MnO2/(X%)HRG and ZnOx(1%)–Mn2O3/(X%)HRG respectively. The prepared catalyst were subjected to catalytic evaluation and a comparative catalytic study between carbonates and oxides for the liquid-phase aerobic oxidation of benzylic alcohols to corresponding aldehydes using molecular oxygen as an eco-friendly oxidant without adding additives or bases. The influence of various parameters such as percentage of HRG, reaction time, catalyst amount, calcination and reaction temperature was systematically examined to optimize reaction conditions using oxidation of benzyl alcohol as a substrate model. It was found that the catalytic performance is remarkably enhanced after using HRG as catalyst co-dopant for the aerobic oxidation of alcohols, possibly owing to the presence of carbon defects and oxygenated functional groups on HRG surface. The as-synthesized catalysts were characterized by SEM, EDX, XRD, Raman, TGA, BET, and FT-IR. Under optimal conditions, the catalyst with composition ZnOx(1%)–MnCO3/(1%)HRG calcined at 300 °C exhibited remarkable specific activity (57.1 mmol·g−1·h−1) with 100% conversion of benzyl alcohol and more than 99% product selectivity within extremely short time (7 min). The as-prepared catalyst was re-used up to five consecutive times without significant decrease in its activity and selectivity. To the best of our knowledge, the achieved specific activity is the highest so far compared to the earlier reported catalysts used for the benzyl alcohol oxidation. A wide range of substituted benzylic and aliphatic alcohols were selectively oxidized into their corresponding aldehydes with complete convertibility and selectivity in short reaction times without over-oxidation to the acids. Due to their significant low cost, superior reproducibility, excellent catalytic efficiency, the ZnOx(1%)–MnCO3/(X%)HRG nanocomposites possess several application prospect in other organic chemistry reactions. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessArticle A Green Route to Copper Loaded Silica Nanoparticles Using Hyperbranched Poly(Ethylene Imine) as a Biomimetic Template: Application in Heterogeneous Catalysis
Catalysts 2017, 7(12), 390; https://doi.org/10.3390/catal7120390
Received: 24 November 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and
[...] Read more.
Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation. Full article
(This article belongs to the Special Issue Nanostructured Materials for Applications in Heterogeneous Catalysis)
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Open AccessFeature PaperArticle In Silico Switch from Second- to First-Row Transition Metals in Olefin Metathesis: From Ru to Fe and from Rh to Co
Catalysts 2017, 7(12), 389; https://doi.org/10.3390/catal7120389
Received: 20 November 2017 / Revised: 9 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
Density functional theory (DFT) calculations have been used to investigate the behavior of different transition metals from Groups 8 (Fe and Ru) and 9 (Co and Rh) in an already well-known catalytic mechanism, which is based on an Ru(SIMes)(PPh3)Cl2=CH(Ph)
[...] Read more.
Density functional theory (DFT) calculations have been used to investigate the behavior of different transition metals from Groups 8 (Fe and Ru) and 9 (Co and Rh) in an already well-known catalytic mechanism, which is based on an Ru(SIMes)(PPh3)Cl2=CH(Ph) complex. As expected, Ru has proven to perform better than their Fe, Co, and Rh counterparts. Even though the topographic steric maps analysis shows no difference in sterical hindrance for any of the metal centers, geometrically, the Fe-based species show a high rigidity with shorter and stronger bonds confirmed by Mayer Bond Orders. The systems bearing Co as a metallic center might present a reactivity that is, surprisingly, too high according to conceptual DFT, which would consequently be a drawback for the formation of the fundamental species of the reaction pathway: the metallacycle intermediate. Full article
(This article belongs to the Special Issue Catalysis of Olefin Metathesis)
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Open AccessFeature PaperArticle Understanding the Heteroatom Effect on the Ullmann Copper-Catalyzed Cross-Coupling of X-Arylation (X = NH, O, S) Mechanism
Catalysts 2017, 7(12), 388; https://doi.org/10.3390/catal7120388
Received: 14 November 2017 / Revised: 7 December 2017 / Accepted: 11 December 2017 / Published: 13 December 2017
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Abstract
Density Functional Theory (DFT) calculations have been carried out in order to unravel the governing reaction mechanism in copper-catalyzed cross-coupling Ullmann type reactions between iodobenzene (1, PhI) and aniline (2-NH, PhNH2), phenol (2-O, PhOH) and
[...] Read more.
Density Functional Theory (DFT) calculations have been carried out in order to unravel the governing reaction mechanism in copper-catalyzed cross-coupling Ullmann type reactions between iodobenzene (1, PhI) and aniline (2-NH, PhNH2), phenol (2-O, PhOH) and thiophenol (2-S, PhSH) with phenanthroline (phen) as the ancillary ligand. Four different pathways for the mechanism were considered namely Oxidative Addition–Reductive Elimination (OA-RE), σ-bond Metathesis (MET), Single Electron Transfer (SET), and Halogen Atom Transfer (HAT). Our results suggest that the OA-RE route, involving CuIII intermediates, is the energetically most favorable pathway for all the systems considered. Interestingly, the rate-determining step is the oxidative addition of the phenyl iodide to the metal center regardless of the nature of the heteroatom. The computed energy barriers in OA increase in the order O < S < NH. Using the Activation Strain Model (ASM) of chemical reactivity, it was found that the strain energy associated with the bending of the copper(I) complex controls the observed reactivity. Full article
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Open AccessCommunication Catalytic Enantioselective Addition of Me2Zn to Isatins
Catalysts 2017, 7(12), 387; https://doi.org/10.3390/catal7120387
Received: 15 November 2017 / Revised: 7 December 2017 / Accepted: 8 December 2017 / Published: 13 December 2017
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Abstract
Chiral α-hydroxyamide L5 derived from (S)-(+)-mandelic acid catalyzes the enantioselective addition of dimethylzinc to isatins affording the corresponding chiral 3-hydroxy-3-methyl-2-oxindoles with good yields and er up to 90:10. Furthermore, several chemical transformations were performed with the 3-hydroxy-2-oxindoles obtained. Full article
(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)
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Open AccessArticle Removal of NOX Using Hydrogen Peroxide Vapor over Fe/TiO2 Catalysts and an Absorption Technique
Catalysts 2017, 7(12), 386; https://doi.org/10.3390/catal7120386
Received: 17 October 2017 / Revised: 25 November 2017 / Accepted: 5 December 2017 / Published: 13 December 2017
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Abstract
In this study, we proposed an innovative oxidation–absorption method for low-temperature denitrification (160–240 °C), in which NO is initially catalytically oxidized by hydrogen peroxide (H2O2) vapor over titania-based catalysts, and the oxidation products are then absorbed by NaOH solution.
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In this study, we proposed an innovative oxidation–absorption method for low-temperature denitrification (160–240 °C), in which NO is initially catalytically oxidized by hydrogen peroxide (H2O2) vapor over titania-based catalysts, and the oxidation products are then absorbed by NaOH solution. The effects of flue gas temperature, molar H2O2/NO ratio, gas hourly space velocity (GHSV), and Fe substitution amounts of Fe/TiO2 catalysts on the denitrification efficiency were investigated by a well-designed experiment. The results indicated that the Fe/TiO2 catalyst exhibited a combination of remarkable activity and deep oxidation ability (NO converted into harmless NO3). In order to comprehend the functional mechanism of the Fe dopant’s local environment in TiO2 support, the promotional effect of the calcination temperature of Fe/TiO2 on the denitration performance was also studied. A tentative synergetic mechanism could be interpreted from two aspects: (1) Fe3+ as a substitute of Ti4+, leading to the formation of enriched oxygen vacancies at the surface, could significantly improve the adsorption efficiency of •OH; (2) the isolated surface Fe ion holds a strong adsorption affinity for NO, such that the adsorbed NO could be easily oxidized by the pre-formed •OH. This process offers a promising alternative for current denitrification technology. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessArticle Cu Nanoparticles/Fluorine-Doped Tin Oxide (FTO) Nanocomposites for Photocatalytic H2 Evolution under Visible Light Irradiation
Catalysts 2017, 7(12), 385; https://doi.org/10.3390/catal7120385
Received: 12 August 2017 / Revised: 29 September 2017 / Accepted: 29 September 2017 / Published: 12 December 2017
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Abstract
Copper nanoparticles/fluorine-doped tin oxide (FTO) nanocomposites were successfully prepared by a simple hydrothermal method. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), UV-visible diffuse-reflectance spectrum (UV-VIS DRS), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectra, and X-ray photoelectron spectroscopy (XPS).
[...] Read more.
Copper nanoparticles/fluorine-doped tin oxide (FTO) nanocomposites were successfully prepared by a simple hydrothermal method. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), UV-visible diffuse-reflectance spectrum (UV-VIS DRS), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The obtained Cu/FTO nanocomposites exhibit high photocatalytic activity for H2 evolution under visible light (λ > 420 nm) irradiation. When the content of Cu is 19.2 wt % for FTO, the Cu/FTO photocatalyst shows the highest photocatalytic activity and the photocatalytic H2 evolution rate is up to 11.22 μmol·h−1. Meanwhile, the photocatalyst exhibits excellent stability and repeatability. It is revealed that the transfer efficiency of the photogenerated electrons is improved greatly because of the intense interaction between Cu NPs and FTO. Furthermore, a possible mechanism is proposed for enhanced photocatalytic H2 evolution of Cu/FTO photocatalysts under visible light irradiation. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Catalytic Performance of Co3O4 on Different Activated Carbon Supports in the Benzyl Alcohol Oxidation
Catalysts 2017, 7(12), 384; https://doi.org/10.3390/catal7120384
Received: 22 September 2017 / Revised: 7 October 2017 / Accepted: 7 October 2017 / Published: 12 December 2017
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Abstract
Co3O4 particles were supported on a series of activated carbons (G60, CNR, RX3, and RB3). Incipient wetness method was used to prepare these catalysts. The effect of the structural and surface properties of the carbonaceous supports during oxidation of benzyl
[...] Read more.
Co3O4 particles were supported on a series of activated carbons (G60, CNR, RX3, and RB3). Incipient wetness method was used to prepare these catalysts. The effect of the structural and surface properties of the carbonaceous supports during oxidation of benzyl alcohol was evaluated. The synthetized catalysts were characterized via IR, TEM, TGA/MS, XRD, TPR, AAS, XPS, and N2 adsorption/desorption isotherm techniques. Co3O4/G60 and Co3O4/RX3 catalysts have high activity and selectivity on the oxidation reaction reaching conversions above 90% after 6 h, without the presence of promoters. Catalytic performances show that differences in chemistry of support surface play an important role in activity and suggest that the presence of different ratios of species of cobalt and oxygenated groups on surface in Co3O4/G60 and Co3O4/RX3 catalysts, offered a larger effect synergic between both active phase and support increasing their catalytic activity when compared to the other tested catalysts. Full article
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Open AccessArticle Hydrodeoxygenation of Methyl Laurate over Ni Catalysts Supported on Hierarchical HZSM-5 Zeolite
Catalysts 2017, 7(12), 383; https://doi.org/10.3390/catal7120383
Received: 30 September 2017 / Revised: 25 November 2017 / Accepted: 30 November 2017 / Published: 11 December 2017
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Abstract
The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained
[...] Read more.
The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained micropores, were created to facilitate mass transfer performance. There are very good correlations between the decline of the relative zeolite crystallinity and the loss of micropores volume. The Ni nanoclusters were uniformly confined in the mesopores of hierarchical HZSM-5 by the excessive impregnation method. The direct deoxygenation in N2 and hydrodeoxygenation in H2 of the methyl laurate were compared respectively over the Ni/HZSM-5 catalysts. In the N2 atmosphere, the deoxygenation rate of the methyl laurate on the Ni/HZSM-5 catalyst is relatively slow. In the presence of H2, the synergistic effect between the hydrogenation function of the metal and the acid function of the zeolite supports can make the deoxygenation level more obvious. The yield of hydrocarbon products gradually reached the maximum with the appropriate treatment concentration of 1M NaOH, which could be attributed to the improved mass transfer in the hierarchical HZSM-5 supports. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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Open AccessArticle Effects of Preparation Method on the Structure and Catalytic Activity of Ag–Fe2O3 Catalysts Derived from MOFs
Catalysts 2017, 7(12), 382; https://doi.org/10.3390/catal7120382
Received: 30 October 2017 / Revised: 4 December 2017 / Accepted: 5 December 2017 / Published: 9 December 2017
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Abstract
In this work, Ag–Fe2O3 catalysts were successfully prepared using several different methods. Our main intention was to investigate the effect of the preparation methods on the catalysts’ structure and their catalytic performance for CO oxidation. The catalysts were characterized by
[...] Read more.
In this work, Ag–Fe2O3 catalysts were successfully prepared using several different methods. Our main intention was to investigate the effect of the preparation methods on the catalysts’ structure and their catalytic performance for CO oxidation. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2-temperature program reduction (H2-TPR) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Ag–Fe catalysts prepared by impregnating Ag into MIL-100 (Fe) presented the best catalytic activity, over which CO could be completely oxidized at 160 °C. Based on the characterization, it was found that more metallic Ag species and porosity existed on Ag–Fe catalysts, which could efficiently absorb atmospheric oxygen and, thus, enhance the CO oxidation. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessArticle Novel Allyl Cobalt Phosphine Complexes: Synthesis, Characterization and Behavior in the Polymerization of Allene and 1,3-Dienes
Catalysts 2017, 7(12), 381; https://doi.org/10.3390/catal7120381
Received: 16 November 2017 / Revised: 1 December 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
Cited by 1 | PDF Full-text (2885 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Novel allyl cobalt complexes, i.e., (η3-C4H7)(η4-C4H6)Co(PCyPh2) (1), (η3-C4H7)(η4-C4H6)Co(PMePh2) (2) and (η
[...] Read more.
Novel allyl cobalt complexes, i.e., (η3-C4H7)(η4-C4H6)Co(PCyPh2) (1), (η3-C4H7)(η4-C4H6)Co(PMePh2) (2) and (η3-C5H9)(η4-C5H8)Co(PMePh2) (3), were synthesized by reacting CoCl2(PRPh2)2 (R = methyl, cyclohexyl) with 1,3-butadiene or isoprene in presence of metallic zinc. The complexes were fully characterized by Nuclear Magnetic Resonance (NMR) spectroscopy (1H and 2D experiments); in case of 1, single crystals, suitable for X-ray analysis, were obtained and the molecular structure was determined. The allyl cobalt phosphine complexes alone gave highly crystalline 1,2 polymers from 1,2-propadiene, but they did not polymerize 1,3-dienes. Nevertheless, in the presence of a stoichiometric amount of methylaluminoxane (MAO), they were able to polymerize 1,3-butadiene and substituted 1,3-butadienes such as isoprene, (E)-1,3-pentadiene, (E)-1,3-hexadiene, and (E)-3-methyl-1,3-pentadiene. Specifically, 1/MAO gave predominantly syndiotactic 1,2 polymers from 1,3-butadiene and terminally substituted 1,3-butadienes (e.g., 1,3-pentadiene and 1,3-hexadiene), but it was practically not active in the polymerization of internally substituted 1,3-butadienes (e.g., isoprene and 3-methyl-1,3-pentadiene); 2/MAO and 3/MAO exhibited instead an opposite behavior, giving predominantly isotactic 1,2 polymers from 3-methyl-1,3-pentadiene, and showing very low activity in the polymerization of 1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. The results obtained are interesting from the mechanistic point of view, and some hypotheses to explain this particular behavior were formulated. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessReview Direct Carboxylation of C(sp3)-H and C(sp2)-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions
Catalysts 2017, 7(12), 380; https://doi.org/10.3390/catal7120380
Received: 20 October 2017 / Revised: 21 November 2017 / Accepted: 24 November 2017 / Published: 7 December 2017
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Abstract
This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze
[...] Read more.
This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze representative examples from the literature, including transition-metal catalyzed carboxylation of benzylic and allylic C(sp3)-H functionalities using CO2 which is at a “nascent stage”. Examples of light-driven carboxylation reactions of unactivated C(sp3)-H bonds are also considered. Concerning C(sp3)-H and C(sp2)-H deprotonation reactions mediated by bases with subsequent carboxylation of the carbon nucleophile, few examples of catalytic processes are reported in the literature. In spite of this, several examples of base-promoted reactions integrating “base recycling” or “base regeneration (through electrosynthesis)” steps have been reported. Representative examples of synthetically efficient, base-promoted processes are included in the review. Full article
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