Recycling Of Homogeneous Catalysts Research Articles

Fe (III)–porphyrin complex as an efficient and recyclable homogeneous catalyst for the synthesis of pyrano thiazole 6-carbonitrile derivatives in aqueous medium

In this study, the Fe(III)–porphyrin complex (FePOphy complex) was successfully utilized as an efficient and recyclable catalyst for a one-pot, three-component reaction involving aromatic aldehydes, 2,4-thiazolidenedione, and malononitrile. This reaction led to the synthesis of pyrano thiazole 6-carbonitrile derivatives under environmentally friendly conditions. The structures of the formed compounds were determined through elemental and spectral analyses including infrared (IR, 1H NMR and 13C NMR, CHN and mass spectrometry, confirming the successful synthesis of the desired products. The reactions were conducted in a compassionate environment using a green solvent (H2O/EtOH). The outcomes demonstrated the excellent catalytic activity and selectivity of the complexes, which led to good yields of the intended products. As a result, the study offers useful information on the FePOphy complex’ synthetic uses, and the creation of effective and environmentally acceptable catalysts, and emphasizes their potential as powerful catalysts for a variety of organic transformations. This strategy’s simplicity, safety, commercially accessible catalyst, stability, fast reaction time, and outstanding yields may be used in the industry in the future.

Recycling of Homogeneous Catalysts─Basic Principles, Industrial Practice, and Guidelines for Experiments and Evaluation

Recycling of Homogeneous Catalysts─Basic Principles, Industrial Practice, and Guidelines for Experiments and Evaluation

Microwave-Induced Chemical Recycling of Colored Polyester Textile Wastes Promoted by Zn[(L)Proline]2, as a Recyclable Homogeneous Catalyst

Microwave-Induced Chemical Recycling of Colored Polyester Textile Wastes Promoted by Zn[(L)Proline]2, as a Recyclable Homogeneous Catalyst

Cobalt(III)–porphyrin Complex as an Efficient and Recyclable Homogeneous Catalyst for the Synthesis of Tetrahydro-2-oxa-4-thia-diazapentalen-5-one Derivatives in Aqueous Medium

Abstract: In this study, we successfully synthesized the CoPHrn complex as an efficient and recyclable catalyst for the one-pot, three-component reaction of aromatic aldehydes, 2,4-thiazolidenedione, and hydroxylamine hydrochloride, leading to the synthesis of tetrahydro- 2-oxa-4-thia-diazapentalen-5-one derivatives under environmentally friendly conditions. The structures of the newly formed compounds were determined through elemental and spectral analyses. This methodology offers significant advantages, including its ecofriendliness, cost-effectiveness, operational simplicity, extensive reusability, and applicability, as well as the easy recovery of the catalyst using straightforward methods. Additionally, a series of tetrahydro-2-oxa-4-thia-diazapentalen-5-one derivatives were successfully synthesized. Notably, this novel procedure demonstrates remarkable benefits in terms of safety, simplicity, stability, mild reaction conditions, short reaction times, excellent yields, and high purity, all achieved without the use of hazardous solvents.

Functional polythioamides derived from thiocarbonyl fluoride.

Polythioamide is a unique type of sulfur-containing polymers with advanced functionalities. Nonetheless, the prevailing synthetic methods, reliant upon elemental sulfur, tend to react readily with unsaturated functional groups, thereby limiting the scope of eligible substrates. Inspired by the highly efficient sulfur-fluoride exchange (SuFEx) polymerization through discrete hubs, we present herein a pioneering and versatile approach to the synthesis of polythioamides from diboronic acids, secondary diamines, and thiocarbonyl fluoride as the central connective hub.Well-defined structures, including previously inaccessible unsaturated substrates, were realized. These newly devised polythioamides can efficiently and selectively bind to metal ions and were applied in precious metal recovery. Further development results in PdII-crosslinked single-chain nanoparticles serving as recyclable homogeneous catalysts, demonstrating the vast potential of these unprecedented polythioamides. We anticipate that thiocarbonyl fluoride could emerge as a potent hub for facilitating the intricate synthesis of sulfur-containing polymers.

Functional Polythioamides Derived from Thiocarbonyl Fluoride**

AbstractPolythioamide is a unique type of sulfur‐containing polymer with advanced functionalities. Nonetheless, the elemental sulfur commonly used in their synthesis tends to react readily with unsaturated functional groups, thereby limiting the scope of eligible substrates. Inspired by the highly efficient sulfur‐fluoride exchange (SuFEx) polymerization through discrete hubs, we present herein a pioneering and versatile approach to the synthesis of polythioamides from diboronic acids, secondary diamines, and thiocarbonyl fluoride as the central connective hub. Well‐defined structures, including previously inaccessible unsaturated substrates, were realized. These newly devised polythioamides can efficiently and selectively bind to metal ions and were applied in precious‐metal recovery. Further development resulted in PdII‐crosslinked single‐chain nanoparticles serving as recyclable homogeneous catalysts, thus demonstrating the vast potential of these unprecedented polythioamides. We anticipate that thiocarbonyl fluoride could emerge as a potent hub for facilitating the intricate synthesis of sulfur‐containing polymers.

Synthesestrategien für die Funktionalisierung homogener Katalysatoren zur Verbesserung ihrer Abtrennbarkeit

AbstractDas Recycling von homogenen Katalysatoren unter Beibehaltung einphasiger Bedingungen ist eine ständige Herausforderung, der sich viele Reaktionen stellen müssen, wenn sie den Schritt in die industrielle Anwendung schaffen sollen. Zwar gibt es eine Fülle von verschiedenen synthetischen Ansätzen für bessere, wiederverwendbare homogene Katalysatoren, doch der Literatur fehlt bisher ein knapper Überblick über die verschiedenen Katalysatormodifikationen. Dieser Übersichtsbeitrag soll diese Lücke schließen, indem die bestehenden Synthesewege zu polaren, unpolaren, fluorhaltigen und molekulargewichtsvergrößerten Katalysatoren zusammengefasst und die jeweiligen Syntheserouten mit Schwerpunkt auf modularen und Late‐Stage‐Ansätzen untersucht werden. Darüber hinaus zeigen wir das Potenzial für eine allgemein anwendbare Bibliothek auf, die es ermöglicht, Katalysatoren durch einfache Modifikationen auf die jeweils gewünschte Recyclingstrategie abzustimmen.

Synthesis Strategies towards Tagged Homogeneous Catalysts to Improve Their Separation.

The recycling of homogeneous catalysts while keeping them in the homogeneous matrix is an ongoing challenge many reactions face if they are to take the step into industrial application. While a plethora of different synthetic approaches towards better, recyclable homogeneous catalysts exist, the literature shows a gap when one searches for a concise overview of the different catalyst modifications. This review is designed to close that gap by summarising the existing synthesis pathways towards polar, non-polar, fluorous, and molecular-weight-enlarged catalysts and examining their respective synthesis routes with a focus on modular and late-stage approaches. Furthermore, we map out the potential for a generally applicable tag library that allows straightforward catalyst modifications to tune them for each desired recycling strategy.

Optically Controlled Recovery and Recycling of Homogeneous Organocatalysts Enabled by Photoswitches

AbstractWe address a critical challenge of recovering and recycling homogeneous organocatalysts by designing photoswitchable catalyst structures that display a reversible solubility change in response to light. Initially insoluble catalysts are UV‐switched to a soluble isomeric state, which catalyzes the reaction, then back‐isomerizes to the insoluble state upon completion of the reaction to be filtered and recycled. The molecular design principles that allow for the drastic solubility change over 10 times between the isomeric states, 87 % recovery by the light‐induced precipitation, and multiple rounds of catalyst recycling are revealed. This proof of concept will open up opportunities to develop highly recyclable homogeneous catalysts that are important for the synthesis of critical compounds in various industries, which is anticipated to significantly reduce environmental impact and costs.

Optically Controlled Recovery and Recycling of Homogeneous Organocatalysts Enabled by Photoswitches.

We address a critical challenge of recovering and recycling homogeneous organocatalysts by designing photoswitchable catalyst structures that display a reversible solubility change in response to light. Initially insoluble catalysts are UV-switched to a soluble isomeric state, which catalyzes the reaction, then back-isomerizes to the insoluble state upon completion of the reaction to be filtered and recycled. The molecular design principles that allow for the drastic solubility change over 10 times between the isomeric states, 87 % recovery by the light-induced precipitation, and multiple rounds of catalyst recycling are revealed. This proof of concept will open up opportunities to develop highly recyclable homogeneous catalysts that are important for the synthesis of critical compounds in various industries, which is anticipated to significantly reduce environmental impact and costs.

The hydroformylation of 1-butene on phosphine modified 1Rh/MOF-5 prepared by different immobilization strategies

Immobilization of the Rh active sites in novel porous materials has attracted attentions for solving the problems of separation and recycling of homogeneous catalysts. In this work, a comparative study of phosphine modified 1Rh/MOF-5 using three different methods was reported, namely 1Rh-P/MOF-5, 1Rh/MOF-5-P and 1Rh/MOF-5-PPh3. Similar with the traditional methods, PPh3 was etched on Rh particles by impregnation in 1Rh-P/MOF-5 and encapsulated in the pores by solvothermal method in 1Rh/MOF-5-P. Moreover, we proposed a novel post-synthesis strategy for grafting phenyl phosphine on the organic linkers in 1Rh/MOF-5-PPh3. The position of phenyl phosphine in MOFs and the effect of phosphine on the Rh active sites in hydroformylation were investigated by XRD, IR, XPS, TGA and DRIFTS. 1Rh/MOF-5-PPh3 exhibited the best catalytic activity and stability than 1Rh-P/MOF-5 and 1Rh/MOF-5-P in the hydroformylation of 1-butene. Different P/Rh ratio in P-modified 1Rh/MOF-5 led to the spatial environment change around the Rh active sites. This study showed details in the role of phosphine ligands played in hydroformylation reactions and provided some guidance for MOFs materials in the immobilization of homogeneous catalysts.

PolyE-IL Is an Efficient and Recyclable Homogeneous Catalyst for the Synthesis of 5-Hydroxymethyl Furfural in a Green Solvent.

5-Hydroxymethyl furfural (5-HMF) is a potential platform molecule with multidimensional applications and can be produced from biomass-based hexose sugars. In the present article, polyethyleneimine (PEI)-functionalized polymeric Bronsted acid ionic liquid (PolyE-IL) catalyst has been explored for fructose dehydration in the presence of isopropyl alcohol (IPA) as a green and low-boiling-point (LBP) organic solvent. The use of homogeneous PolyE-IL catalyst provides several specific advantages in terms of high yield, conversion, selectivity, ease of catalyst separation, recycle and reuse, and so forth. PEI with various Bronsted acid counterions such as H2SO4, H3PO4, TsOH, TfOH, and TFA provides the corresponding variables of PolyE-IL such as [PEI]+[HSO3]-, [PEI]+[H2PO4]-, [PEI]+[CF3CO2]-, [PEI]+[TfO]-, and [PEI]+[TsO]-, which are tested for fructose dehydration in the presence of IPA. Of the tested catalysts, only PolyE-IL with [HSO4]-, [CF3CO2]-, [TfO]-, and [TsO]- counterions showed the formation of 5-HMF. [PEI]+[HSO4]- showed the maximum yield of 5-HMF (61%) and selectivity (70%) with (87%) fructose conversion. Thus, further process optimization study was conducted to obtain the maximum yield, conversion, and selectivity. The intensified process provides a maximum yield of 5-HMF of 75% with 85% fructose conversion and 90% selectivity. The catalyst recyclability study showed the consistency in 5-HMF yield (75%), conversion (85%), and selectivity (90%) for five consecutive recycle runs. However, the study of reaction kinetics showed the first-order kinetics with an activation energy of 12.4 kJ/mole by using [PEI]+[HSO4]- catalyst. Thus, the use of an easily recyclable and robust catalyst provides an efficient route for production of 5-HMF in the presence of a green solvent.

Electrochemical recycling of homogeneous catalysts.

Homogeneous catalysts have rapid kinetics and keen reaction selectivity. However, their widespread use for industrial catalysis has remained limited because of challenges in reusability. Here, we propose a redox-mediated electrochemical approach for catalyst recycling using metallopolymer-functionalized electrodes for binding and release. The redox platform was investigated for the separation of key platinum and palladium homogeneous catalysts used in organic synthesis and industrial chemical manufacturing. Noble metal catalysts for hydrosilylation, silane etherification, Suzuki cross-coupling, and Wacker oxidation were recycled electrochemically. The redox electrodes demonstrated high sorption uptake for platinum-based catalysts (Qmax up to 200 milligrams of platinum per gram of adsorbent) from product mixtures, with up to 99.5% recovery, while retaining full catalytic activity over multiple cycles. The combination of mechanistic studies and electronic structure calculations indicate that selective interactions with anionic intermediates during the catalytic cycle played a key role in the separations. Last, continuous flow cell studies support the scalability and favorable technoeconomics of electrochemical recycling.

Pushing Boundaries—Selective Cooling Crystallization as Tool for Selectivity Compensation and Product Purification Using a Recyclable Pd/Xantphos Catalyst in the Methoxycarbonylation of Methyl 10‐Undecenoate

AbstractThe homogeneously catalyzed methoxycarbonylation of methyl 10‐undecenoate allows for the synthesis of dimethyl 1,12‐dodecandioate as an interesting bio‐based drop‐in alternative for 1,12‐dodecandioic acid as polymer building block. Although the benchmark catalyst system of Pd/1,2‐bis((di‐tert‐butylphosphino)methyl)benzene and methane sulfonic acid is very active and selective, long‐term stability over a potential catalyst recycling is limited. In this work, modifications of this catalyst system in terms of protonation of the ligand and its replenishment during recycling are first investigated, proving that the reaction system is tolerant against minor changes. Finally, the commercially available ligand Xantphos, featuring higher stability but comes with a rather low l:b selectivity of 70:30, is applied. However, through the application of cooling crystallization, 58 g product (52% isolated yield) with an overall purity of 94% is obtained from the crude reaction solution without further treatment and a ∑TON of 4000 after ten reaction runs, while catalyst loss into the product is low.Practical Applications: Selective syntheses on the basis of renewable resources are a powerful tool for the production of value products in terms of green chemistry. Thereby, homogeneous transition metal catalysts are beneficial regarding selectivity. However, their separation and recycling are challenging due to their limited stability. The combination of a stable, commercially available catalyst with a selective purification method allows for isolation and purification from a crude reaction mixture without the need for any auxiliary or further purification steps. In this work, cooling crystallization is applied for subsequent purification of the linear diester dimethyl 1,12‐dodecandioate. Thereby, a lower selectivity from the methoxycarbonylation reaction using the stable Xantphos ligand is compensated and combined with recycling of the homogeneous catalyst. Thus, the development of an integrated process covering a stable catalyst system in the reaction, and high selectivity in the purification is the key toward an efficient homogeneous catalyst recycling.

Selective and quantitative functionalization of unprotected α-amino acids using a recyclable homogeneous catalyst

<h2>Summary</h2> A new Ir(III)-NHC catalyst is reported that shows remarkable activity in the <i>N</i>-alkylation of unprotected amino acids. The catalytic system gives excellent selectivity toward monoalkylated α-amino acids and a high degree of retention of stereochemistry. A wide range of unprotected nonnatural amino acids have been prepared. These compounds represent an array of building blocks that could be used for the direct synthesis of peptidomimetics. The synthesis of amino-acid-based surfactants is also reported. This catalytic method gives the amino acid products in quantitative yield; hence, tedious purifications by derivatization are therefore avoided. Furthermore, although the catalyst is a homogeneous metal complex, it can be recycled and reused for several runs. This also contributes to the efficiency and sustainability of the method.

Effect of Liquid–Liquid Interfacial Area on Biphasic Catalysis Exemplified by Hydroformylation

Biphasic catalysis enables the effective recycling of homogeneous catalysts by their immobilization in an additional liquid phase immiscible with the products. The introduced liquid–liquid interfacial area implies mass transfer limitations that play an important role in understanding these catalytic systems, with many rate enhancement strategies revolving around optimizing said area. In this contribution, the relationship between liquid–liquid interfacial area and catalytic activity is elucidated by applying a methodology that utilizes an image-based in situ measurement of the transient droplet size distribution. When the industrially highly relevant aqueous biphasic hydroformylation of the long-chain olefin 1-octene is taken as the model reaction, it is found that the product nonanal and the addition of the ligand increases the interfacial area by a factor of up to 5. The rate of conversion is found to depend on the stirring speed. By variation of the catalyst concentration, it is shown that an accumulation of the catalyst species at the interface is unlikely. Using a mathematical model, it is highlighted that the effect of the aqueous–organic interfacial area on the catalytic activity is not linear as was previously assumed in the literature. Instead, a change in the interfacial composition is proposed that causes a shift in the dependence of catalytic activity on said area. Thus, the dynamic physical properties of a lean gas–liquid–liquid system were linked to the catalytic performance of the system.

Reusable homogeneous metal- and additive-free photocatalyst for high-performance aerobic oxidation of alcohols to carboxylic acids

How to realize the recycling of homogeneous catalysts has been a great challenge for chemists. In this background, a new pyridinium compound was synthesized and applied in selective photocatalytic oxidation. This photocatalytic system is advantageous in accelerating the transformation of alcohols into acids by two consecutive routes, including (1) photocatalytic oxidation of alcohols to aldehydes; (2) photocatalytic oxidation and autoxidation of aldehydes to acids. By activating molecular oxygen into •O2− and 1O2, the system displays advantages of high efficiency and simplicity, as well as environment-friendly nature without metals or additives. Attractively, this compound as a homogeneous catalyst can be reused by direct filtration of products profiting from its high performance and stability. The present work develops a new approach to achieve an efficient and recyclable aerobic oxidation of alcohols into acids by using pyridinium-based photocatalysts and provides a valuable insight into the separation and recycling of homogeneous catalysts for economic compatibility and industrial application.

Efficient Solvent-Free Synthesis of Cyclic Carbonates from the Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by New Imidazolinium Functionalized Metal Complexes Under 0.1 MPa

A series of imidazolinium functionalized metal complexes were prepared as efficient and recyclable homogeneous catalysts for the synthesis of cyclic carbonates via the coupling reaction of carbon dioxide and epoxides in the absence of co-catalysts and solvent. Due to the synergistic effect between the metal center as Lewis acid and the imidazolinium groups with halide anions as Lewis base, these catalysts exhibited excellent catalytic capability. Particularly, high turnover frequency (TOF) values of (1174, 1240 and 1262 h−1) for bifunctional catalysts (2c, 2i and 2j, respectively) were achieved via adjusting reaction parameters. These catalysts also showed excellent catalytic performances under atmospheric pressure. Recyclability test showed that this kind of bifunctional catalyst can be easily recovered and reused for at least five times without dramatic loss of activity and selectivity. The optimum reaction conditions were also screened as (120 °C, 1.0 MPa CO2 and 2 h). The catalyst could also be applied to a variety of substrates and be used for a long time with high catalytic activities. We also performed the Kinetic studies, which suggested that the activity of catalysts following the order I− > Br− > Cl−. Moreover, a plausible reaction mechanism by imidazolinium functionalized metal complexes was proposed.

Peroxo-Cerium(IV)-Containing Polyoxometalates: [CeIV6(O2)9(GeW10O37)3]24-, a Recyclable Homogeneous Oxidation Catalyst.

The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [CeIV6(O2)9(GeW10O37)3]24- (1). Polyanion 1 consists of a cyclic [Ce6(O2)9]6+ assembly that is stabilized by three dilacunary [GeW10O37]10- Keggin fragments. The title polyanion 1 is solution-stable, on the basis of 183W nuclear magnetic resonance, and was shown to act as a recyclable homogeneous catalyst for the selective, microwave-activated sulfoxidation of the model substrate methionine to the sulfoxide in the absence and to the sulfone in the presence of hydrogen peroxide. Solution and solid-state Raman as well as solid-state infrared studies of 1 demonstrated the complete loss (and regain) of the nine peroxo groups in situ during the catalytic cycle, suggesting that the peroxo-free {Ce6(GeW10)3} skeleton remains most likely intact during the catalytic cycle. Solid-state X-ray photoelectron spectroscopy measurements showed that peroxo loss is accompanied by reduction of the cerium ions from +4 to +3, which is fully reversible. Density functional theory calculations are in complete agreement with all of these observations and furthermore suggest that the reduction of the six cerium(IV) ions is accompanied by the formation of molecular dioxygen.

Homogeneous Catalyst Recycling and Separation of a Multicomponent Mixture Using Organic Solvent Nanofiltration

AbstractIn homogeneous catalysis, the application of organic solvent nanofiltration (OSN) has become a well‐known alternative to common recycling methods. Even though some OSN membranes are commercially available, their classification and the scope of application have to be determined for the specific solvent mixture. The commercial membrane Evoniks DuraMem® 300 was tested in a mixture of ethanol, ethyl acetate, and cyclohexane with magnesium triflate as possible catalyst. The cross permeate fluxes were measured for two transmembrane pressures and the hydrodynamic radii of the components were determined. Some of the components in the ternary mixture are retained, which makes the membrane also suitable for fractioning thereof.