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BACKGROUND Transition metal catalysis has, over recent decades, developed into one of the most important methods of constructing molecules. However, although efficient in the construction of complex molecules, these catalysts can be expensive as they are often based upon second- and third-row transition metals which have, for the most part, low terrestrial abundance. Present removal and recovery techniques for homogeneous catalysts tend, at best, to focus on recovering the metal center and to consider ligands as single-use components. Recovery of the whole catalyst would be more beneficial from economic and environmental points of view. RESULTS The integration of a membrane separation protocol with gold-catalyzed carboxylative cyclization of propargylamine was investigated. Filtration conditions were identified in membrane screening experiments with the dinuclear catalyst [Au2Cl2(L)] (Au-1) and the mononuclear catalyst [Au(IPr)Cl] (Au-2). Recovery of the whole catalyst was then investigated. Catalyst Au-1 proved unstable and led to metal recovery for reprocessing upon completion of the process. However, the membrane methodology does allow recovery of the catalyst within the reaction mixture which increases its efficiency. On the other hand, catalyst Au-2 proved more stable and can be recovered along with its ancillary ligands. CONCLUSIONS For both catalysts a membrane-based recovery protocol was successfully demonstrated. This protocol was either internal or external in that the Au complex along with its ligands can be recovered after reaction. This initial work shows the possibility that ligands do not always need to be considered as single-use components. (c) 2021 Society of Chemical Industry (SCI).

The deployment of photocatalysis for remediation of water has not yet been realized, although laboratory-scale studies have demonstrated promise. Accomplishing this requires the development of photocatalysis as a process, including studying its efficiencies in remedying water when high volumes of water are processed, and addressing the recovery, possible regeneration and reuse of the photocatalysts. To that end, this work is aimed at demonstrating the use of a custom-built mobile platform for disinfecting large quantities of water. The benchtop platform built is capable of processing 15.14 L (4 gallons) per minute of water, with possibility for further scale-up. Preliminary studies on the catalyst recovery, regeneration and reuse via gravity-assisted settling, centrifugation and air plasma treatment indicated that 77% of Aeroxide® P25 titania (TiO2) nanoparticle and 57% of porous TiO2 nanowire photocatalysts could be recovered and regenerated for further use. Overall, this study indicated that process improvements, including increasing the kinetics of the photocatalysis, and optimization of the efficacies of the catalyst recovery and regeneration processes will make it useful for water remediation on any scale. More importantly, the portable and flexible nature of the benchtop photocatalysis system makes it amenable for use in conjunction with existing technologies for remedying large quantities of water.

In the last decades the rapid advancement of solvent-resistant membranes and catalysis led to the development of more efficient and sustainable materials and processes. The present article critically assesses membrane-assisted catalysis in organic media, which is a multidisciplinary field combining materials science, reaction engineering, organic chemistry, and membrane science and technology. The membranes act either as catalysts directly accelerating the rate of the reaction or as selective barriers for separating homogeneous catalysts from the reaction mixture. The discussions are grouped based on the catalyst type, and introductory tables given for each group allow direct comparison of the literature with regards to reaction type, solvent(s) employed, type of membrane, catalyst rejection, highest conversion and volumetric productivity. Major achievements, limitations and inconsistencies in the field are presented along with future research directions and requirements.

The prevalence of homogeneous catalysts, to produce high value commodities in the surfactant and detergent range by upgrading inter alia syngas and short chain olefins, through metathesis, hydroformylation and hydrogeneration, is hampered by the expensive, waste generating and destructive thermal separation methods required for the recovery of these catalysts. By using the membrane technology of organic solvent nanofiltration (OSN), the successful recovery of two commercially available homogeneous catalysts, the rhodium-based complex, HRh(CO)(PPh3)3, and the cobalt-based complex, Co(C5H7O2)3, from the solvents representative of the hydroformylation and hydrogenation reactions, with the STARMEM 240 membrane, was performed. The energy-efficiency of OSN for homogeneous catalyst recovery, commonly alluded to in literature, was investigated by performing a technological evaluation between OSN and a conventional downstream recovery process such as distillation. It was found that, using the ST-240 membrane, catalyst concentrations in the permeate stream can be successfully reduced to near negligible amounts (

At 60–150 °C and 15–35 bar H2, two model reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, were explored in a multiphase system composed of an aqueous solution of reactants, a hydrocarbon, and commercial 5 % Ru/C as a heterogeneous catalyst. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, a quantitative conversion of LA was achieved with formation of γ-valerolactone or N-(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively. Additionally, the catalyst could be segregated in the hydrocarbon phase and recycled in an effective semi-continuous protocol. Under such conditions, formic acid additive affected the reactivity of LA through a competitive adsorption on the catalyst surface. This effect was crucial to improve selectivity for the reductive amination process. The comparison of 5 % Ru/C with a series of carbon supports demonstrated that the segregation phenomenon in the hydrocarbon phase, never previously reported, was pH-dependent and effective for samples displaying a moderate surface acidity.

Magnetic nanoparticle (MNP)-supported catalysis is a new method to facilitate catalyst separation and reuse. This technique has recently been introduced for organocatalysis. MNP-supported organocatalysts have been evaluated for their activity, selectivity, and recyclability in a range of chemical transformations, especially for asymmetric synthesis. The synthesis and application of Fe3O4 MNP-supported organocatalysis are highlighted in this short review article.

Bronsted acid ionic liquids (BAILs) have been prepared and applied for the first time - to the best of our knowledge - as efficient catalysts in the acetylation of glycerol with acetone to form solketal ((2,2-dimethyl-1,3-dioxolan-4-yl)methanol) at very mild reaction conditions (room temperature) and short reaction times. The BAILs showed a superior catalytic performance in terms of both conversion and selectivity compared to the common mineral acid methanesulfonic acid as well as to other reported homogeneous and heterogeneous catalysts. Catalyst reusability was demonstrated with one of the BAILs (BAIL-1), which was recovered and reused by a simple procedure in four consecutive reaction runs without any loss of catalytic activity and selectivity. Thus, the BAILs combine the advantages of both homogeneous and heterogeneous catalysis with respect to excellent conversion and selectivity as well as easy recyclability.

The development of heterogeneous catalytic processes is highly desirable in order to overcome some drawbacks of homogeneous catalysts, such as the separation and recycling of these catalysts. In this work, we report that Jacobsen type catalysts are efficient and selective for the oxidation of R-(+)-limonene to its corresponding diepoxides using in situ generated dimethyldioxirane (DMD) as oxidant. It was demonstrated that the solid NaHCO3 addition to the initial reaction mixture, improves the catalytic activity. Additionally, catalyst samples can be recovered and reused at least twice without significant loss of its initial catalytic activity. El desarrollo de procesos catalíticos heterogéneos es muy deseable dado que se pueden superar las dificultades que presentan los catalizadores homogéneos, tales como la separación y el reciclado de estos catalizadores. En este trabajo, reportamos que los catalizadores tipo Jacobsen son eficientes y selectivos para la oxidación de R-(+)-limoneno a sus correspondientes diepóxidos cuando dimetildioxirano generado in situ es utilizado como agente oxidante. Se demostró que la adición de NaHCO3 sólido, al inicio de la reacción, mejora la actividad catalítica. Además, el catalizador puede ser recuperado y reutilizado al menos dos veces sin pérdida significativa de su actividad catalítica inicial.

International audience; A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO2(HL5)]center dot MeOH center dot H2O (H2L5 = pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO2 moiety. A DFT study of this molecule and of the related [VO2(H2L5)] complex of V-IV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert-butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs. olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert-butoxido (tBuOO(-)) ligand, without the need to generate a peroxido (022) ligand.

Catalysts based on dendrimers and magnetic nanoparticles are becoming increasing utilized in the context of green and sustainable chemistry, because they are easily separated by precipitation or by using asimple magnet respectively, and they are recyclable. In this spirit, the thesis has been devoted to the synthesis, characterization and catalytic applications of iron oxide magnetic nanoparticles-immobilized molecular, nano-and dendritic catalysts involving Ru, Cu and Pd. Magnetically recyclable ruthenium(II) and Cu(I) complexes and Pd nanoparticles have provided excellent catalytic performances in terms of activity, stability and recyclability, using alkyne-azide cycloaddition and carbon-carbon cross coupling reactions. The synthesis of mono-and polymetallic palladium complexes containing the 2-pyridyl-1,2,3-triazole ligand or nonabranch-derived ligands has also been carried out, and their catalytic properties in coupling reactions has been studied; Les catalyseurs supportés sur des dendrimères et nanoparticules magnétiques acquièrent actuellement une importance accrue dans le contexte de la chimie verte et du développement durable car ils sont séparés facilement des produits de réaction par filtration ou à l’aide d’un aimant et recyclables. Dans cet esprit, la thèse a été dédiée à la synthèse, à la caractérisation et aux applications catalytiques de catalyseurs moléculaires, nano-et dendritiques immobilisés impliquant le ruthénium, le cuivre et le palladium. Les catalyseurs magnétiquement recyclables de ruthenium (II), de cuivre (I) et des nanoparticules de palladium ont produit d’excellentes performances en terme d’activité, de stabilité et de recyclabilité pour les réactions de cycloaddition entre les alcynes et les azotures et les réactions de couplage croisé carbone-carbone. Enfin, la synthèse de complexes mono-et polymétalliques du palladium contenant les ligands 2-pyridyl-1,2,3-triazole a également été réalisée et leurs proprietiés catalytiques ont été étudiées.

Esterification yields were significantly improved using calix[n]arenes catalysts under simple conditions. p-Sulfonic acid calix[4]arene and p-sulfonic acid calix[6]arene were powerful organocatalysts in several esterification reactions, which showed activity comparable or even superior to other well-established acids catalysts, such as, sulfuric acid, p-toluenesulfonic acid, and p-hydroxybezenesulfonic acid described in the literature.

11 pages; International audience; The use of dendritic structures for the grafting of core-shell g- Fe2O3/polymer 300 nm superparamagnetic nanoparticles (MNPs) has been performed with four metallodendrons that were functionalized with diphosphinopalladium complexes. The catalytic performance of these nanocatalysts was optimized for the Suzuki C-C cross-coupling reaction. These results demonstrated the importance of optimizing the catalytic efficiency of grafted MNPs by optimizing the dendritic structures and the nature of the peripheral phosphine ligands. All of these nanocatalysts showed remarkable reactivity towards bromoarenes and they were recovered and efficiently reused by magnetic separation with almost no loss of reactivity, even after 25 cycles.