Catalysts

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11 pages, 1719 KiB

Open AccessFeature PaperArticle

Iron-Borophosphate Glass-Catalyzed Regioselective Hydrothiolation of Alkynes under Green Conditions

by Nicoli Catholico, Eduarda A. Tessari, Isis J. A. Granja, Martinho J. A. de Sousa, Jorlandio F. Felix, Flávia Manarin, Marcelo Godoi, Jamal Rafique, Ricardo Schneider, Sumbal Saba and Giancarlo V. Botteselle

Catalysts 2023, 13(7), 1127; https://doi.org/10.3390/catal13071127 - 20 Jul 2023

Viewed by 1302

Abstract

Vinyl sulfides are an important class of organic compounds that have relevant synthetic and biological applications. The best-known approach to realize these compounds is the hydrothiolation of alkynes under different conditions using metals, toxic and carcinogenic solvents. The development of new catalysts using [...] Read more.

Vinyl sulfides are an important class of organic compounds that have relevant synthetic and biological applications. The best-known approach to realize these compounds is the hydrothiolation of alkynes under different conditions using metals, toxic and carcinogenic solvents. The development of new catalysts using materials that are environmentally friendly, low in cost, and easy to handle is highly desirable for this reaction. In this regard, glasses have become an important class of materials, since they can be used as a catalyst for chemical reactions. We prepared and characterized an inexpensive and robust iron-doped borophosphate glass (Fe@NaH₂PO₄-H₃BO₃ glass). This eco-friendly material was successfully applied as a catalyst for the hydrothiolation of alkynes under solvent-free conditions, affording the desired vinyl sulfides in good-to-excellent yields, with high stereoselectivity. This method of synthesis is attractive because it enables the reuse of the iron-glass catalyst and the scaling up of reactions. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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13 pages, 2607 KiB

Open AccessFeature PaperArticle

An Asymmetric Dinuclear Bis(ansa-Zirconocene) Complex: Synthesis and Performance in Olefin (co-)Polymerization

by Lars N. Jende, Thierry Roisnel, Virginie Cirriez, Alexandre Welle, Evgueni Kirillov and Jean-Francois Carpentier

Catalysts 2023, 13(7), 1108; https://doi.org/10.3390/catal13071108 - 15 Jul 2023

Cited by 2 | Viewed by 1297

Abstract

A synthetic strategy to access asymmetric dinuclear bis(ansa-metallocene) pre-catalysts is described. As a key step, the Pd-catalyzed Suzuki cross-coupling of 9,9-bis(trimethylsilyl)-fluoren-2-yl-boronic acid with a substituted 2-bromo-9H-fluorene generates an asymmetric 2,2′-bifluorene platform, which can be individually functionalized at [...] Read more.

A synthetic strategy to access asymmetric dinuclear bis(ansa-metallocene) pre-catalysts is described. As a key step, the Pd-catalyzed Suzuki cross-coupling of 9,9-bis(trimethylsilyl)-fluoren-2-yl-boronic acid with a substituted 2-bromo-9H-fluorene generates an asymmetric 2,2′-bifluorene platform, which can be individually functionalized at the two differentiated 9-positions. Herein, as a first demonstration of this strategy, we report the asymmetric dinuclear bis(ansa-zirconocene) complex 2,2′-[{Me₂C(Flu)(Cp)}ZrCl₂][{Me₂C(^7-tBuFlu)(Cp)}ZrCl₂], which has been characterized with NMR spectroscopy and high-resolution mass spectrometry. The performance of this bimetallic pre-catalyst when combined with MAO has been evaluated in ethylene, propylene, and ethylene/1-hexene (co-)polymerization. This pre-catalyst is revealed to be less productive than the mononuclear reference pre-catalyst {Me₂C(^2,7-tBuFlu)(Cp)}ZrCl₂, likely because of higher steric hindrance induced by the linkage at the difluorenyl platform. The resulting (co-)polymers featured only slight differences in terms of molecular weights, tacticity, and comonomer incorporation. No bimodal molecular weight distribution was achieved at any produced polymer; this might have originated from the close similarity of the connected Cp/Flu moieties or a rapid chain-transfer phenomenon between the different active sites which were quite close to each other. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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16 pages, 2201 KiB

Open AccessArticle

Novel Copper(II) Complexes with BIAN Ligands: Synthesis, Structure and Catalytic Properties of the Oxidation of Isopropylbenzene

by Iakov S. Fomenko, Olga S. Koshcheeva, Nina I. Kuznetsova, Tatyana V. Larina, Marko I. Gongola, Medhanie Afewerki, Pavel A. Abramov, Alexander S. Novikov and Artem L. Gushchin

Catalysts 2023, 13(5), 849; https://doi.org/10.3390/catal13050849 - 8 May 2023

Cited by 6 | Viewed by 2226

Abstract

Two new isomeric complexes [CuBr₂(R-bian)] (R = 4-Me-Ph (1), 2-Me-Ph (2)) were obtained by reacting copper(II) bromide with 1,2-bis[(2-methylphenyl)imino]acenaphthene ligands and characterized. The crystal structure of 2 was determined by X-ray diffraction analysis. The copper atom has [...] Read more.

Two new isomeric complexes [CuBr₂(R-bian)] (R = 4-Me-Ph (1), 2-Me-Ph (2)) were obtained by reacting copper(II) bromide with 1,2-bis[(2-methylphenyl)imino]acenaphthene ligands and characterized. The crystal structure of 2 was determined by X-ray diffraction analysis. The copper atom has a distorted square-planar environment; the ω angle between the CuN₂ and CuBr₂ planes is 37.004°. The calculated ω parameters for optimized structures 1 and 2 were 76.002° and 43.949°, indicating significant deviations from the ideal tetrahedral and square-plane geometries, respectively. Molecules 2 form dimers due to non-covalent Cu···Br contacts, which were analyzed by DFT calculations. The complexes were also characterized by cyclic voltammetry and UV-Vis spectroscopy. A quasi-reversible Cu(II)/Cu(I) redox event with E_1/2 potentials of 0.81 and 0.66 V (vs. SHE) was found for 1 and 2, respectively. The electronic absorption spectra showed the presence of Cu(I) species as a result of the partial reduction of the complexes in the acetonitrile solution. Both complexes were tested as homogenous catalysts for the oxidation of isopropylbenzene (IPB) in acetonitrile at low temperatures. Differences in the mechanism of the catalytic reaction and the composition of the reaction products depending on the oxidizing ability of the catalyst were revealed. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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20 pages, 12373 KiB

Open AccessFeature PaperArticle

Divergent Reactivity of D-A Cyclopropanes under PTC Conditions, Ring-Opening vs. Decyanation Reaction

by Giorgiana Denisa Bisag, Pietro Viola, Luca Bernardi and Mariafrancesca Fochi

Catalysts 2023, 13(4), 760; https://doi.org/10.3390/catal13040760 - 16 Apr 2023

Viewed by 2053

Abstract

The divergent reactivity of D-A cyclopropane, under PTC conditions, is herein reported. Thus, a ring-opening or a decyanation reaction can be achieved by reacting 2-arylcyclopropane-1,1-dicarbonitriles 1 with thioacetic acid in different reaction conditions. The use of solid Cs₂CO₃ leads unexpectedly [...] Read more.

The divergent reactivity of D-A cyclopropane, under PTC conditions, is herein reported. Thus, a ring-opening or a decyanation reaction can be achieved by reacting 2-arylcyclopropane-1,1-dicarbonitriles 1 with thioacetic acid in different reaction conditions. The use of solid Cs₂CO₃ leads unexpectedly to the synthesis of new D-A cyclopropane derivatives via a decyanation reaction, followed by diastereoselective acetylation, whereas the use of an aqueous solution of Cs₂CO₃ results in a typical ring-opening reaction with the formation of S-thiolate products. Therefore, the use of tailored reaction conditions allows one to obtain either cyclic or open-chain products in moderate to good yields. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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20 pages, 2696 KiB

Open AccessArticle

Dynamic EPR Studies of the Formation of Catalytically Active Centres in Multicomponent Hydrogenation Systems

by Yuliya Yu. Titova

Catalysts 2023, 13(4), 653; https://doi.org/10.3390/catal13040653 - 27 Mar 2023

Cited by 1 | Viewed by 1868

Abstract

The formation of catalytically active nano-sized cobalt-containing structures in multicomponent hydrogenation systems based on Co(acac)₂ complex and various cocatalysts, namely, AlEt₃, AlEt₂(OEt), Li-n-Bu, and (PhCH₂)MgCl, has been studied for the first time in detail [...] Read more.

The formation of catalytically active nano-sized cobalt-containing structures in multicomponent hydrogenation systems based on Co(acac)₂ complex and various cocatalysts, namely, AlEt₃, AlEt₂(OEt), Li-n-Bu, and (PhCH₂)MgCl, has been studied for the first time in detail using dynamic EPR spectroscopy. It is shown that after mixing the initial components, paramagnetic structures are formed, which include a fragment containing Co(0) with the electronic configuration 3d⁹, as well as a fragment bearing an aluminium, lithium, or magnesium atom, depending on the nature of the used cocatalyst. Such bimetallic paramagnetic sites are stabilized by acetylacetonate ligands. In addition, the paramagnetic complex contains the arene molecule(s), and the cobalt atom is bonded with the atom of the corresponding non-transition through the alkyl group of the co-catalyst, in particular through the carbon atom in the α-position with respect to the atom of the non-transition element. Due to the high reactivity of the described intermediates, they, under the conditions of hydrogenation catalysis, are transformed into nano-sized cobalt-containing structures that act as carriers of the catalytically active sites. Furthermore, because of the high reactivity and paramagnetism, such intermediates can be detected only by the EPR technique. The paper describes the whole experimental way of interpreting the EPR signals corresponding to the intermediates, precursors of catalytically active structures. In addition, a possible mathematical model based on the obtained experimental EPR data is presented. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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14 pages, 5092 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Straightforward and Efficient Deuteration of Terminal Alkynes with Copper Catalysis

by Xènia Tarrach, Jingzhou Yang, Mohammad Soleiman-Beigi and Silvia Díez-González

Catalysts 2023, 13(4), 648; https://doi.org/10.3390/catal13040648 - 23 Mar 2023

Cited by 1 | Viewed by 2162

Abstract

The mild and effective preparation of deuterated organic molecules is an active area of research due to their important applications. Herein, we report an air-stable and easy to access copper(I) complex as catalyst for the deuteration of mono-substituted alkynes. Reactions were carried out [...] Read more.

The mild and effective preparation of deuterated organic molecules is an active area of research due to their important applications. Herein, we report an air-stable and easy to access copper(I) complex as catalyst for the deuteration of mono-substituted alkynes. Reactions were carried out in technical solvents and in the presence of air, to obtain excellent deuterium incorporation in a range of functionalised alkynes. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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17 pages, 2757 KiB

Open AccessFeature PaperArticle

Synthesis of N-Substituted Pyrroles Catalyzed by Low-Cost and Commercially Available Aluminas

by Omar Portilla-Zúñiga, Óscar M. Bautista-Aguilera, José J. Martínez, Hugo Rojas, Mario A. Macías, Isabel Iriepa, Adrián Pérez-Redondo, Ángel Sathicq, Juan-Carlos Castillo and Gustavo P. Romanelli

Catalysts 2023, 13(3), 603; https://doi.org/10.3390/catal13030603 - 16 Mar 2023

Viewed by 2219

Abstract

The Paal-Knorr reaction of acetonylacetone with primary amines catalyzed by CATAPAL 200 under conventional heating at 60 °C for 45 min afforded N-substituted pyrroles in 68–97% yields. The pyrrole 3g was studied by single-crystal and powder X-ray diffraction. The high percentage of [...] Read more.

The Paal-Knorr reaction of acetonylacetone with primary amines catalyzed by CATAPAL 200 under conventional heating at 60 °C for 45 min afforded N-substituted pyrroles in 68–97% yields. The pyrrole 3g was studied by single-crystal and powder X-ray diffraction. The high percentage of Brønsted–Lewis acid sites (23%) and pore diameter (37.8 nm) of CATAPAL 200 favor the formation of the pyrrole ring because an increase in Brønsted acid sites efficiently catalyzes condensation and dehydration processes. This protocol is distinguished by its operational simplicity, high yields, reduced reaction time, no solvent required, stoichiometric amounts of reactants, low catalyst loading, and clean reaction profile. In addition, the CATAPAL 200 is cheap and commercially available leading to an efficient and lower-cost chemical transformation. The reusability of the catalyst for up to five cycles without appreciable loss of its catalytic activity makes the present protocol sustainable and advantageous compared to conventional methods. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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17 pages, 6992 KiB

Open AccessFeature PaperArticle

Polydopamine-Coated Polyurethane Foam as a Structured Support for the Development of an Easily Reusable Heterogeneous Photocatalyst Based on Eosin Y

by Han Peng, Thierry Romero, Philippe Bertani and Vincent Ritleng

Catalysts 2023, 13(3), 589; https://doi.org/10.3390/catal13030589 - 15 Mar 2023

Cited by 4 | Viewed by 1838

Abstract

An easy-to-handle eosin Y-based heterogeneous photocatalyst was prepared by post-functionalization of a polydopamine-coated open cell polyurethane foam (PDA@PUF) via the silanization of the adhesive layer with 3-(triethoxysilyl)propan-1-amine (APTES) and the subsequent EDC-mediated coupling of the resulting amino-functionalized foam with eosin Y. The obtained [...] Read more.

An easy-to-handle eosin Y-based heterogeneous photocatalyst was prepared by post-functionalization of a polydopamine-coated open cell polyurethane foam (PDA@PUF) via the silanization of the adhesive layer with 3-(triethoxysilyl)propan-1-amine (APTES) and the subsequent EDC-mediated coupling of the resulting amino-functionalized foam with eosin Y. The obtained macroscopic material, EY-APTES@PDA@PUF, showed good efficiency and excellent reusability, in an easy-to-carry “dip-and-play” mode for at least six runs as photocatalyst for the aerobic oxidation of 2-methyl-5-nitroisoquinolin-2-ium iodide to the corresponding isoquinolone. Subsequent investigation of the catalytic efficiency of EY-APTES@PDA@PUF for the oxidation of sulfides to sulfoxides, however, evidenced non-negligible eosin Y leaching, leading to a progressive deactivation of the catalytic foam in this case. Two alternative synthetic protocols for the preparation of the macroscopic photocatalyst were next explored to avoid eosin Y leaching. In both cases however, cycling tests also highlighted a progressive deactivation of the catalytic foams in sulfide-to-sulfoxide oxidation reactions. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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12 pages, 1591 KiB

Open AccessArticle

Bulky NHC–Cobalt Complex-Catalyzed Highly Markovnikov-Selective Hydrosilylation of Alkynes

by Małgorzata Bołt and Patrycja Żak

Catalysts 2023, 13(3), 510; https://doi.org/10.3390/catal13030510 - 2 Mar 2023

Cited by 9 | Viewed by 2515

Abstract

The hydrosilylation of alkynes is one of the most attractive and, at the same time, most challenging catalytic transformations, usually demanding the use of noble transition metals. We describe a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, [...] Read more.

The hydrosilylation of alkynes is one of the most attractive and, at the same time, most challenging catalytic transformations, usually demanding the use of noble transition metals. We describe a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting the highly effective hydrosilylation of a broad scope of alkynes and silanes. The application of bulky NHC ligands allowed a decrease in the amount of cobalt necessary for an effective reaction run to 2.5 mol% and provided excellent selectivity towards challenging α-vinylsilanes. The developed method tolerates a number of substituted aryl, alkyl, and silyl acetylenes. Moreover, it is suitable for both tertiary and secondary silanes. Our findings confirm that steric hindrance around the metal center can effectively increase the activity of a catalyst and ensure better selectivity than those of analogous complexes bearing smaller ligands. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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18 pages, 10105 KiB

Open AccessArticle

Electrocatalytic Oxidation of Nitrophenols via Ag Nanoparticles Supported on Citric-Acid-Modified Polyaniline

by Milad Khani, Ramaswami Sammynaiken and Lee D. Wilson

Catalysts 2023, 13(3), 465; https://doi.org/10.3390/catal13030465 - 22 Feb 2023

Cited by 4 | Viewed by 1664

Abstract

Citric-acid-modified polyaniline (P-CA) and P-CA modified with Ag nanoparticles (Ag@P-CA) were prepared via an in situ reduction method. The physicochemical properties of P-CA and Ag@P-CA were compared to unmodified polyaniline (PANI) and PANI-modified Ag nanoparticles (Ag@PANI). Ag@P-CA had a lower content of aniline [...] Read more.

Citric-acid-modified polyaniline (P-CA) and P-CA modified with Ag nanoparticles (Ag@P-CA) were prepared via an in situ reduction method. The physicochemical properties of P-CA and Ag@P-CA were compared to unmodified polyaniline (PANI) and PANI-modified Ag nanoparticles (Ag@PANI). Ag@P-CA had a lower content of aniline oligomers compared to Ag@PANI. P-CA and Ag@P-CA had a greater monolayer adsorption capacity for 2-nitrophenol and lower binding affinity as compared to PANI and Ag@PANI materials. X-ray photoelectron spectroscopy and cyclic voltammetry characterization provided reason and evidence for the higher conductivity of citric-acid-modified materials (P-CA and Ag@P-CA versus PANI and Ag@PANI). These results showed the potential utility for the optimization of adsorption/desorption and electron transfer steps during the electrochemical oxidation of nitrophenols. The oxidation process employs Ag@P-CA as the electrocatalyst by modifying polyaniline with Ag nanoparticles and citric acid, which was successfully employed to oxidize 2-nitrophenol and 4-nitrophenol with comparable selectivity and sensitivity to their relative concentrations. This work is envisaged to contribute significantly to the selective conversion of nitrophenols and electrocatalytic remediation of such waterborne contaminants. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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15 pages, 6497 KiB

Open AccessArticle

Layered Copper Hydroxide Salts as Catalyst for the “Click” Reaction and Their Application in Methyl Orange Photocatalytic Discoloration

by Rafael Marangoni, Rafael E. Carvalho, Monielly V. Machado, Vanessa B. Dos Santos, Sumbal Saba, Giancarlo V. Botteselle and Jamal Rafique

Catalysts 2023, 13(2), 426; https://doi.org/10.3390/catal13020426 - 16 Feb 2023

Cited by 4 | Viewed by 2550

Abstract

The 1,2,3-triazoles are an important class of organic compounds that are found in a variety of biologically active compounds. The most usual and efficient methodology to synthetize these compounds is the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC), preferably by use of click chemistry principles. Therefore, [...] Read more.

The 1,2,3-triazoles are an important class of organic compounds that are found in a variety of biologically active compounds. The most usual and efficient methodology to synthetize these compounds is the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC), preferably by use of click chemistry principles. Therefore, the development of simple, robust, easily accessible and efficient materials as catalysts for this kind of reaction is highly desirable. In this sense, layered hydroxide salts (LHS) emerge as an interesting alternative for the click reaction. Thus, we describe herein the preparation and characterization of copper (II) layered hydroxide salts and their application as catalysts for the CuAAC reaction under solvent-free conditions. This synthetic methodology of CuAAC reaction is attractive as it follows several concepts of green chemistry, such as being easy to perform, allowing purification without chromatographic column, the process forming no sub-products, affording the desired 1,2,3-traizoles in the specific 1,4-disubstituted position in high yield, and having a short reaction time. Moreover, the photocatalysis for the degradation of methyl orange was also highly efficient using the same catalyst. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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18 pages, 2630 KiB

Open AccessFeature PaperArticle

Heteroleptic Copper Complexes as Catalysts for the CuAAC Reaction: Counter-Ion Influence in Catalyst Efficiency

by Maria S. Viana, Clara S. B. Gomes and Vitor Rosa

Catalysts 2023, 13(2), 386; https://doi.org/10.3390/catal13020386 - 10 Feb 2023

Cited by 3 | Viewed by 2312

Abstract

A series of nine cationic heteroleptic aryl-BIAN-copper(I) (BIAN = bis-iminoacenaphthene) complexes with the general formula [Cu((E-C₆H₄)₂BIAN)(PPh₃)₂][X] (E = p-Me, p-iPr, o-iPr; X = BF₄, OTf, NO₃) [...] Read more.

A series of nine cationic heteroleptic aryl-BIAN-copper(I) (BIAN = bis-iminoacenaphthene) complexes with the general formula [Cu((E-C₆H₄)₂BIAN)(PPh₃)₂][X] (E = p-Me, p-iPr, o-iPr; X = BF₄, OTf, NO₃) 1^X–3^X were synthesized and fully characterized using several analytical techniques, including NMR spectroscopy and single-crystal X-ray diffraction. Except for complexes 2^BF₄ and 3^BF₄, which were already reported in our previous works, all remaining complexes are herein described for the first time. Two different strategies were used for the preparation of the complexes: complexes bearing BF₄⁻ or OTf⁻ counter-ions (1^BF₄, 1^OTf, 2^OTf, and 3^OTf) were obtained using the appropriate copper(I) precursors [Cu(NCMe)₄][BF₄] or [Cu(NCMe)₄][OTf], whereas for derivatives 1^NO₃–3^NO₃, [Cu(PPh₃)₂NO₃] was used. Their activity as catalysts for the copper azide-alkyne cycloaddition (CuAAC) was assessed alongside other high activity, previously reported Cu(I) complexes. Comparative studies to determine the influence of the counter-ion and of the aryl substituents were performed. All complexes behaved as active catalysts under neat reaction conditions, at 25 °C and in short reaction times without requiring the use of any additive, with complex 2^NO₃ being the most efficient derivative, along with other NO₃⁻-bearing complexes. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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28 pages, 22579 KiB

Open AccessArticle

An Efficient Asymmetric Cross-Coupling Reaction in Aqueous Media Mediated by Chiral Chelating Mono Phosphane Atropisomeric Biaryl Ligand

by Katarzyna Kapłon, Sławomir Frynas, Barbara Mirosław, Janusz Lipkowski and Oleg M. Demchuk

Catalysts 2023, 13(2), 353; https://doi.org/10.3390/catal13020353 - 4 Feb 2023

Cited by 2 | Viewed by 1865

Abstract

The enantiomerically pure ligand BisNap-Phos was obtained in a straightforward sequence of reactions beginning with inexpensive starting materials under the readily affordable conditions in high overall yield. An asymmetric BisNap-Phos-palladium complex-catalyzed Suzuki–Miyaura coupling leading to axially chiral biaryl compounds was described. [...] Read more.

The enantiomerically pure ligand BisNap-Phos was obtained in a straightforward sequence of reactions beginning with inexpensive starting materials under the readily affordable conditions in high overall yield. An asymmetric BisNap-Phos-palladium complex-catalyzed Suzuki–Miyaura coupling leading to axially chiral biaryl compounds was described. The reactions were carried out under mild conditions in aqueous and organic media. A series of atropisomeric biaryls were synthesized with excellent yields and high enantioselectivities (up to 86% ee). The methodology provides an efficient and practical strategy for the synthesis of novel multifunctionalized axially chiral biaryl compounds under mild environmentally friendly and easily affordable conditions. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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11 pages, 2461 KiB

Open AccessArticle

Copolymerization of Norbornene and Methyl Acrylate by Nickel Catalyst Bearing 2-(Diarylphosphino)-N-phenylbenzenamine Ligands

by Lixin Cao, Mingyuan Li and Zhengguo Cai

Catalysts 2023, 13(2), 311; https://doi.org/10.3390/catal13020311 - 31 Jan 2023

Cited by 1 | Viewed by 1711

Abstract

The synthesis of polar functionalized cyclic olefin copolymers (COCs) from the coordination copolymerization of norbornene (NB) and polar monomers catalyzed by late transition metal catalysts has been a recent research hotspot. However, few catalysts have achieved efficient copolymerization with commercial vinyl-type polar monomers, [...] Read more.

The synthesis of polar functionalized cyclic olefin copolymers (COCs) from the coordination copolymerization of norbornene (NB) and polar monomers catalyzed by late transition metal catalysts has been a recent research hotspot. However, few catalysts have achieved efficient copolymerization with commercial vinyl-type polar monomers, such as methyl acrylate (MA). In this contribution, nickel complexes bearing 2-(diarylphosphino)-N-phenylbenzenamine ligands were synthesized and applied as pre-catalysts to catalyze the (co)polymerization of norbornene. Upon the activation of methylaluminoxane (MAO), these nickel catalysts were active for norbornene polymerization with the highest activity achieved being 3.6 × 10⁶ g mol⁻¹ h⁻¹ and the highest number average molecular weight (M_n) of polynorbornene (PNB) reaching 27.4 × 10⁵ g mol⁻¹. Moreover, these nickel catalysts also promoted the copolymerization of norbornene and MA to furnish high-molecular-weight NB/MA copolymers (M_n up to 6.20 × 10⁴ g mol⁻¹) with reasonable MA contents (3.07−5.90 mol%). The molecular weight of PNB and NB/MA copolymers obtained by the present nickel catalysts are remarkably higher than those of the (co)polymers from our previous reported dimethyl substituted phosphinobenzenamine nickel catalyst, suggesting significant progress in this field. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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24 pages, 58766 KiB

Open AccessFeature PaperArticle

Tetranuclear Copper Complexes with Bulky Aminoalcohol Ligands as Catalysts for Oxidative Phenoxazinone Synthase-like Coupling of Aminophenol: A Combined Experimental and Theoretical Study

by Oksana V. Nesterova, Armando J. L. Pombeiro and Dmytro S. Nesterov

Catalysts 2022, 12(11), 1408; https://doi.org/10.3390/catal12111408 - 10 Nov 2022

Cited by 5 | Viewed by 2077

Abstract

The new copper(II) complexes [Cu₄(pa)₄(Bae)₄]·H₂O (1) and [Cu₄(eba)₄(Buae)₄]·H₂O (2) (Hpa = propionic acid, HBae = 2-benzylaminoethanol, Heba = 2-ethylbutyric acid and HBuae = [...] Read more.

The new copper(II) complexes [Cu₄(pa)₄(Bae)₄]·H₂O (1) and [Cu₄(eba)₄(Buae)₄]·H₂O (2) (Hpa = propionic acid, HBae = 2-benzylaminoethanol, Heba = 2-ethylbutyric acid and HBuae = 2-butylaminoethanol) were synthesizsed by the interaction of a copper salt with a methanol solution of the respective ligands. The single-crystal X-ray diffraction analysis reveals that both compounds have a {Cu₄(μ₃-O)₄} cubane-like core. Both compounds show pronounced phenoxazinone synthase-like activity towards the aerobic oxidation of o-aminophenol to phenoxazinone chromophore, with the maximum initial rates W₀ up to 3.5 × 10⁻⁷ M s⁻¹, and exhibit complex non-linear W₀ vs. [catalyst]₀ dependences. DFT//CCSD theoretical calculations (B3LYP/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP) were employed to investigate the most challenging steps of catalyst-free and copper-catalysed o-aminophenol oxidation (formation of o-aminophenoxyl radical). QTAIM analysis was used to study the key intermediates and weak interactions. Geometries and energies of intermediates and transition states were benchmarked against a series of popular DFT functionals. The results of the calculations demonstrate that a Cu^II–OO• copper-superoxo model catalyst decreases the calculated activation barrier from 28.7 to 19.9 kcal mol⁻¹ for the catalyst-free and copper-catalysed abstraction of the H atom from the hydroxyl group of o-aminophenol, respectively. Finally, both complexes 1 and 2 were studied as catalysts in the amidation of cyclohexane with benzamide to give N-cyclohexyl benzamide and N-methyl benzamide employing di-tert-butyl peroxide (DTBP) as the oxidant, with a conversion of 16%, and in the oxidation of cyclohexane to cyclohexanol with aq. H₂O₂, with a conversion of 12%. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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9 pages, 4383 KiB

Open AccessArticle

N-Iodosuccinimide as a Precatalyst for C–N Bond-Forming Reactions from Alcohols under Mild Reaction Conditions

by Njomza Ajvazi and Stojan Stavber

Catalysts 2022, 12(11), 1368; https://doi.org/10.3390/catal12111368 - 4 Nov 2022

Viewed by 2023

Abstract

We report an efficient and selective methodology for the direct cross-coupling of alcohols with N-nucleophiles mediated by N-iodosuccinimide (NIS) as the non-metal, commercially available, low-cost, and most effective precatalyst among the N-halosuccinimides (NXSs) under mild reaction conditions enhancing the green [...] Read more.

We report an efficient and selective methodology for the direct cross-coupling of alcohols with N-nucleophiles mediated by N-iodosuccinimide (NIS) as the non-metal, commercially available, low-cost, and most effective precatalyst among the N-halosuccinimides (NXSs) under mild reaction conditions enhancing the green chemical profiles of these reactions. The scale-up procedure was accomplished with almost quantitative yield, verifying the presented method’s synthetic applicability and potential for industrial application. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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9 pages, 4133 KiB

Open AccessFeature PaperArticle

Naturally Nano: Magnetically Separable Nanocomposites from Natural Resources for Advanced Catalytic Applications

by Rick A. D. Arancon, Zeid A. Al Othman, Thomas Len, Kaimin Shih, Leonid Voskressensky and Rafael Luque

Catalysts 2022, 12(11), 1337; https://doi.org/10.3390/catal12111337 - 1 Nov 2022

Viewed by 1383

Abstract

The present manuscript describes the use of silk cocoons as a structuring agent for the formation of an iron-based active phase for the controlled oxidation of benzyl alcohol. Different samples were prepared using different calcination temperatures. X-ray diffraction and transmission electron microscopy showed [...] Read more.

The present manuscript describes the use of silk cocoons as a structuring agent for the formation of an iron-based active phase for the controlled oxidation of benzyl alcohol. Different samples were prepared using different calcination temperatures. X-ray diffraction and transmission electron microscopy showed a higher proportion of alpha-Fe₂O₃ phase and a higher global crystallinity at superior calcination temperature. In terms of catalytic activity, the sample treated at 500 °C presented the highest conversion reaching 47%, with selectivity in benzaldehyde of 75.9%. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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19 pages, 11070 KiB

Open AccessFeature PaperArticle

Development of Silicon Carbide-Supported Palladium Catalysts and Their Application as Semihydrogenation Catalysts for Alkynes under Batch- and Continuous-Flow Conditions

by Tsuyoshi Yamada, Haruka Yamamoto, Kanon Kawai, Kwihwan Park, Norihiko Aono and Hironao Sajiki

Catalysts 2022, 12(10), 1253; https://doi.org/10.3390/catal12101253 - 17 Oct 2022

Cited by 5 | Viewed by 2322

Abstract

Silicon carbide (SiC)-supported palladium (Pd) catalysts [3% Pd/SiC and a 3% Pd-diethylenetriamine (DETA)/SiC complex] for chemoselective hydrogenation under batch- and continuous-flow conditions were developed. The alkyne, alkene, azide, nitro, and benzyloxycarbonyl-protected aromatic amine (N-Cbz) functionalities were chemoselectively reduced in the presence [...] Read more.

Silicon carbide (SiC)-supported palladium (Pd) catalysts [3% Pd/SiC and a 3% Pd-diethylenetriamine (DETA)/SiC complex] for chemoselective hydrogenation under batch- and continuous-flow conditions were developed. The alkyne, alkene, azide, nitro, and benzyloxycarbonyl-protected aromatic amine (N-Cbz) functionalities were chemoselectively reduced in the presence of 3% Pd/SiC. By contrast, benzyl ether, alkyl N-Cbz, epoxide, aromatic chloride, aromatic ketone, and tert-butyldimethylsilyl ether were tolerant to the 3% Pd/SiC-catalyzed hydrogenation. The combined use of 3% Pd/SiC and DETA demonstrated excellent chemoselectivity toward the semihydrogenation of various mono- and disubstituted alkynes under batch- and continuous-flow conditions. Furthermore, compared with the separate use of 3% Pd/SiC and DETA, the newly developed 3% Pd(DETA)/SiC-packed in a cartridge showed higher chemoselectivity toward the continuous-flow semihydrogenation of alkyne over 24 h. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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13 pages, 3255 KiB

Open AccessArticle

Copper Supported on MgAlO_x and ZnAlO_x Porous Mixed-Oxides for Conversion of Bioethanol via Guerbet Coupling Reaction

by Zongyang Liu, Jie Li, Yuan Tan, Luyao Guo and Yunjie Ding

Catalysts 2022, 12(10), 1170; https://doi.org/10.3390/catal12101170 - 4 Oct 2022

Cited by 5 | Viewed by 2152

Abstract

The direct conversion of biomass-derived ethanol to high-valued-added chemicals has attracted widespread attention recently due to the great economic and environmental advantages. In the present study, the conversion of bioethanol through the Guerbet coupling process was studied in a fixed-bed reactor for MgAlO [...] Read more.

The direct conversion of biomass-derived ethanol to high-valued-added chemicals has attracted widespread attention recently due to the great economic and environmental advantages. In the present study, the conversion of bioethanol through the Guerbet coupling process was studied in a fixed-bed reactor for MgAlO_x and ZnAlO_x mixed-oxides supported Cu catalysts. From the results, Cu adding into the system greatly enhance the dehydrogenation of ethanol and increase the H-transfer in the course of Guerbet coupling process. Simultaneously, the porous mixed-oxides provide the acid-base property of the catalysts for intermediate transformation. Notably, for Cu/MgAlO_x, the main product of ethanol conversion is butanol, but for Cu/ZnAlO_x, the primary product is ethyl acetate. Characterizations such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and CO₂ temperature programmed desorption (TPD) were carried out to evaluate the structure and property of the catalysts. In combination with the catalytic performances with the characterization results, the synergistic catalytic effect between metal sites and acid-base sites were elaborated. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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17 pages, 2123 KiB

Open AccessArticle

Mononuclear Oxidovanadium(IV) Complexes with BIAN Ligands: Synthesis and Catalytic Activity in the Oxidation of Hydrocarbons and Alcohols with Peroxides

by Iakov S. Fomenko, Marko I. Gongola, Lidia S. Shul’pina, Nikolay S. Ikonnikov, Andrey Yu. Komarovskikh, Vladimir A. Nadolinny, Yuriy N. Kozlov, Artem L. Gushchin and Georgiy B. Shul’pin

Catalysts 2022, 12(10), 1168; https://doi.org/10.3390/catal12101168 - 3 Oct 2022

Cited by 8 | Viewed by 2058

Abstract

Reactions of VCl₃ with 1,2-Bis[(4-methylphenyl)imino]acenaphthene (4-Me-C₆H₄-bian) or 1,2-Bis[(2-methylphenyl)imino]acenaphthene (2-Me-C₆H₄-bian) in air lead to the formation of [VOCl₂(R-bian)(H₂O)] (R = 4-Me-C₆H₄ (1), 2-Me-C₆H₄ [...] Read more.

Reactions of VCl₃ with 1,2-Bis[(4-methylphenyl)imino]acenaphthene (4-Me-C₆H₄-bian) or 1,2-Bis[(2-methylphenyl)imino]acenaphthene (2-Me-C₆H₄-bian) in air lead to the formation of [VOCl₂(R-bian)(H₂O)] (R = 4-Me-C₆H₄ (1), 2-Me-C₆H₄ (2)). Thes complexes were characterized by IR and EPR spectroscopy as well as elemental analysis. Complexes 1 and 2 have high catalytic activity in the oxidation of hydrocarbons with hydrogen peroxide and alcohols with tert-butyl hydroperoxide in acetonitrile at 50 °С. The product yields are up to 40% for cyclohexane. Of particular importance is the addition of 2-pyrazinecarboxylic acid (PCA) as a co-catalyst. Oxidation proceeds mainly with the participation of free hydroxyl radicals, as evidenced by taking into account the regio- and bond-selectivity in the oxidation of n-heptane and methylcyclohexane, as well as the dependence of the reaction rate on the initial concentration of cyclohexane. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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16 pages, 5105 KiB

Open AccessArticle

A New Series of Tungstophosphoric Acid-Polymeric Matrix Catalysts: Application in the Green Synthesis of 2-Benzazepines and Analogous Rings

by Edna X. Aguilera Palacios, Valeria Palermo, Angel G. Sathicq, Luis R. Pizzio and Gustavo P. Romanelli

Catalysts 2022, 12(10), 1155; https://doi.org/10.3390/catal12101155 - 1 Oct 2022

Cited by 2 | Viewed by 1468

Abstract

A new series of composite materials (PLMTPA) based on tungstophosphoric acid (TPA) included in a polymeric matrix of polyacrylamide (PLM), with a TPA:PLM ratio of 20/80, 40/60, and 60/40, were synthesized and well characterized by FT-IR, XRD, ³¹P MAS-NMR, TGA-DSC, and SEM-EDAX. [...] Read more.

A new series of composite materials (PLMTPA) based on tungstophosphoric acid (TPA) included in a polymeric matrix of polyacrylamide (PLM), with a TPA:PLM ratio of 20/80, 40/60, and 60/40, were synthesized and well characterized by FT-IR, XRD, ³¹P MAS-NMR, TGA-DSC, and SEM-EDAX. Their acidic and textural properties were determined by potentiometric titration and nitrogen adsorption–desorption isotherms, respectively. Considering ³¹P MAS-NMR and FT-IR analyses, the main species present in the samples is the [PW₁₂O₄₀]³⁻ anion that, according to XRD results, is highly dispersed in the polymeric matrix or appears as a noncrystalline phase. The thermogravimetric analysis revealed that PLMTPA materials did not undergo any remarkable chemical changes up to 200 °C. Additionally, the PLMTPA materials showed strong acid sites whose number increased with the increment of their TPA content. Finally, PLMTPA materials were used as efficient and recyclable noncorrosive catalysts for the synthesis of 2-benzazepines and related compounds. Good yields (55–88%) and high purity were achieved by a Pictet-Spengler variant reaction between N-aralkylsulfonamides and s-trioxane in soft reaction conditions: low toluene volume, at 70 °C, for 3 h. The described protocol results in a useful and environmentally friendly alternative with operative simplicity. The best catalyst in the optimized reaction conditions, PLMTPA60/40₁₀₀, was reused six times without appreciable loss of activity. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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18 pages, 2998 KiB

Open AccessArticle

2-(Arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline Cobalt(II) Dichloride Polymerization Catalysts for Polyethylenes with Narrow Polydispersity

by Zheng Zuo, Qiuyue Zhang, Mingyang Han, Ming Liu, Yang Sun, Yanping Ma and Wen-Hua Sun

Catalysts 2022, 12(10), 1119; https://doi.org/10.3390/catal12101119 - 27 Sep 2022

Cited by 3 | Viewed by 1588

Abstract

A series of 2-(arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline cobalt(II) chlorides (Co1–Co6) containing a fused ring and a more inert phenyl group as the substituent at the imino-C atom has been synthesized using a one-pot synthesis method and fully characterized by FT-IR and [...] Read more.

A series of 2-(arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline cobalt(II) chlorides (Co1–Co6) containing a fused ring and a more inert phenyl group as the substituent at the imino-C atom has been synthesized using a one-pot synthesis method and fully characterized by FT-IR and elemental analysis. The molecular structures of Co2 and Co5 have been confirmed by X-ray diffraction as having a distorted square pyramidal geometry around a cobalt core with a tridentate N,N,N-chelating ligand and two chlorides. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co6 exhibited high activities for ethylene polymerization. The least sterically hindered Co2 showed a maximum activity of 16.51 × 10⁶ g (PE) mol⁻¹ (Co) h⁻¹ at a moderate temperature 50 °C. Additionally, ortho-fluoride Co6 was able to maintain a high activity not only at 70 °C but also after 60 min at 50 °C, highlighting its excellent thermal-stability and long catalytic lifetime. The resultant polyethylene showed clearly narrower molecular weight distribution (PDI: 1.3–3.1) than those produced by structurally related cobalt counterparts, indicating the positive influence of benzhydryl substitution on the catalysis. Moreover, the molecular weight (1.7–386.6 kg mol⁻¹) of vinyl- or n-propyl-terminated polyethylene can be finely regulated by controlling polymerization parameters. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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10 pages, 3231 KiB

Open AccessArticle

Accelerated Photodegradation of Organic Pollutants over BiOBr/Protonated g-C₃N₄

by Juanjuan Liu, Heng Guo, Haoyong Yin, Qiulin Nie and Shihui Zou

Catalysts 2022, 12(10), 1109; https://doi.org/10.3390/catal12101109 - 25 Sep 2022

Cited by 9 | Viewed by 2141

Abstract

Interfacial engineering has emerged as an effective strategy to optimize the photocatalytic activity of heterojunctions. Herein, the interface between graphitic carbon nitride (g-C₃N₄) and BiOBr was readily regulated by a protonation treatment. The synthesized BiOBr/g-C₃N₄ heterojunctions [...] Read more.

Interfacial engineering has emerged as an effective strategy to optimize the photocatalytic activity of heterojunctions. Herein, the interface between graphitic carbon nitride (g-C₃N₄) and BiOBr was readily regulated by a protonation treatment. The synthesized BiOBr/g-C₃N₄ heterojunctions were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The results show that pretreating g-C₃N₄ in diluted HCl solution led to a partial protonation of g-C₃N₄, which ensured intimate contact and high dispersion of supported BiOBr without changing the surface area, bulk g-C₃N₄ structure, or visible light absorption. The abundant BiOBr/g-C₃N₄ interfaces remarkably improved the separation and transfer of photogenerated carriers, which produced more h⁺ and O₂^●− to accelerate the photocatalytic degradation of organic pollutants. The photocatalytic activities of the BiOBr/g-C₃N₄ heterojunctions were evaluated by the degradation of RhB under visible-light irradiation (λ ≥ 420 nm). The apparent reaction (pseudo-first-order) rate constant of BiOBr supported on partially protonated g-C₃N₄ (Bpg-C₃N₄-0.75) is ca. 3-fold higher than that of BiOBr supported on pristine g-C₃N₄ (Bg-C₃N₄), verifying interfacial engineering as an effective strategy to optimize the catalytic activity of heterojunctions. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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7 pages, 1014 KiB

Open AccessArticle

Nickel-Catalyzed Ethylene Dimerization Based on PNP(NR₂)₂ Ligands

by Chengang Cao, Haonan Fan, Jingyi Zhang, Jing Ma and Tao Jiang

Catalysts 2022, 12(9), 1008; https://doi.org/10.3390/catal12091008 - 6 Sep 2022

Cited by 2 | Viewed by 1776

Abstract

Nickel (II) complexes stabilized by PNP(NR₂)₂ (L¹: R = Methyl, L²: R = ethyl, L³: R = isopropyl) ligands were synthesized and characterized. A narrow range of products was observed for catalytic systems [...] Read more.

Nickel (II) complexes stabilized by PNP(NR₂)₂ (L¹: R = Methyl, L²: R = ethyl, L³: R = isopropyl) ligands were synthesized and characterized. A narrow range of products was observed for catalytic systems containing nickel complexes and ethyl aluminum dichloride (EADC). All exhibit considerable activity in the ethylene dimerization to produce 1-butene. Precatalyst 1 is the most conducive for ethylene dimerization, producing 83.4% C₄ (1-C₄ 36.8%) and 103.0 × 10⁵ g/(molNi·h) in terms of its activity under the appropriate conditions. By adjusting the conditions of the catalytic system for precatalyst 2, high C₄ selectivity (88.1%) with reasonable activity (76.9 × 10⁵ g/(molNi·h)) can be obtained. The X-ray single-crystal analysis of complexes presents mononuclear bidentate coordination at the Ni center, and the relationship between certain bite angles may also imply catalytic performance. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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13 pages, 2464 KiB

Open AccessArticle

Perfluoroaryl Zinc Catalysts Active in Cyclohexene Oxide Homopolymerization and Alternating Copolymerization with Carbon Dioxide

by Yuri C. A. Sokolovicz, Antonio Buonerba, Carmine Capacchione, Samuel Dagorne and Alfonso Grassi

Catalysts 2022, 12(9), 970; https://doi.org/10.3390/catal12090970 - 29 Aug 2022

Cited by 4 | Viewed by 1924

Abstract

The zinc complex Zn(C₆F₅)₂(toluene) (1) behaves as a very active and selective catalyst in cyclohexene oxide (CHO) polymerization to produce poly(cyclohexene oxide) (PCHO) by the trans-ring-opening of CHO with remarkable TOF values at room [...] Read more.

The zinc complex Zn(C₆F₅)₂(toluene) (1) behaves as a very active and selective catalyst in cyclohexene oxide (CHO) polymerization to produce poly(cyclohexene oxide) (PCHO) by the trans-ring-opening of CHO with remarkable TOF values at room temperature. The ring-opening copolymerization (ROCOP) of CO₂ with CHO catalysed by 1 yields poly(cyclohexene carbonate) (PCHC) when using benzyl alcohol (BnOH) as an initiator at 120 °C. The ¹H NMR monitoring of the in situ reaction of 1 with BnOH highlighted the formation of the dinuclear species [(C₆F₅)₂Zn₂(BnO)₂ (2) that was isolated and found an active catalyst in the ROCOP of CO₂ with CHO in the absence of initiators. Interestingly, PCHCs by 2 in solventless conditions show polydispersity index (M_w/M_n) values close to 2, corresponding to those expected for a single-site catalyst; on the contrary, a broader polydispersity index of the polymer products was found in toluene solution, suggesting the formation of new zinc catalysts during the polymerization reaction. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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23 pages, 3045 KiB

Open AccessArticle

LLDPE-like Polymers Accessible via Ethylene Homopolymerization Using Nitro-Appended 2-(Arylimino)pyridine-nickel Catalysts

by Desalegn Demise Sage, Qiuyue Zhang, Ming Liu, Gregory A. Solan, Yang Sun and Wen-Hua Sun

Catalysts 2022, 12(9), 961; https://doi.org/10.3390/catal12090961 - 29 Aug 2022

Cited by 4 | Viewed by 1793

Abstract

Four examples of para-nitro substituted 2-(arylimino)pyridine-nickel(II) bromide complexes of general formula, [2-{(2,6-R-4-NO₂C₆H₂)N=CMe}C₅H₄N]NiBr₂, but differentiable by the steric/electronic properties displayed by the ortho-groups [R = i-Pr (Ni1), [...] Read more.

Four examples of para-nitro substituted 2-(arylimino)pyridine-nickel(II) bromide complexes of general formula, [2-{(2,6-R-4-NO₂C₆H₂)N=CMe}C₅H₄N]NiBr₂, but differentiable by the steric/electronic properties displayed by the ortho-groups [R = i-Pr (Ni1), Et (Ni2), CHPh₂ (Ni3), CH(4-FPh)₂ (Ni4)], have been prepared in good yield. For comparative purposes, the meta-nitro complex, [2-{(2,6-i-Pr₂-3-NO₂-4-(4-FPh)₂C₆H)N=CMe}C₅H₄N]NiBr₂ (Ni5), has also been synthesized. The molecular structures of mononuclear Ni3·xH₂O (x = 2, 3) and bromide-bridged dinuclear Ni4 and Ni5 are disclosed. Upon activation with either ethylaluminum dichloride (EtAlCl₂) or modified methylaluminoxane (MMAO), all precatalysts displayed good catalytic performance at operating temperatures between 30 °C and 60 °C with higher activities generally seen using EtAlCl₂ [up to 4.7 × 10⁶ g PE (mol of Ni)⁻¹ h⁻¹]: Ni2 ~ Ni5 > Ni1 ~ Ni4 > Ni3. In terms of the resultant polyethylene (PE), Ni4/EtAlCl₂ formed the highest molecular weight of the series (M_w up to 1.4 × 10⁵ g mol⁻¹) with dispersities (M_w/M_n) ranging from narrow to broad (M_w/M_n range: 2.2–24.4). Moreover, the melting temperatures (T_m) of the polymers generated via EtAlCl₂ activation fell in a narrow range, 117.8–126.0 °C, which resembles that seen for industrial-grade linear-low density polyethylene (LLDPE). Indeed, their ¹³C NMR spectra revealed significant amounts of uniformly distributed long-chain branches (LCBs), while internal vinylene groups constituted the major type of chain unsaturation [vinylene:vinyl = 5.3:1 (EtAlCl₂) and 9.9:1 (MMAO)]. Full article

(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)

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