A methods study of immobilization of PONOP pincer transition metal complexes on silica polyamine composites (SPC)

Recovery of Homogeneous Platinoid Catalysts from Pharmaceutical Media: Review on the Existing Treatments and the Perspectives of Membrane Processes

Catalyst recovery is a major challenge for reaching the objectives of green chemistry for industry. Indeed, catalysts enable quick and selective syntheses with high reaction yields. This is especially the case for homogeneous platinoid catalysts which are almost indispensable for cross-coupling reactions often used by the pharmaceutical industry. However, they are based on scarce, expensive, and toxic resources. In addition, they are quite sensitive and degrade over time at the end of the reaction. Once degraded, their regeneration is complex and hazardous to implement. Working on their recovery could lead to highly effective catalytic chemistries while limiting the environmental and economic impacts of their one-time uses. This review aims to describe and compare conventional processes for metal removal while discussing their advantages and drawbacks considering the objective of homogeneous catalyst recovery. Most of them lead to difficulty recycling active catalysts due to their ability to only treat metal ions or to chelate catalysts without the possibility to reverse the mechanism. However, membrane processes seem to offer some perspectives with limiting degradations. While membranes are not systematically the best option for recycling homogeneous catalysts, current development might help improve the separation between pharmaceutical active ingredients and catalysts and enable their recycling.

β-Cyclodextrin-Silica Hybrid: A Spatially Controllable Anchoring Strategy for Cu(II)/Cu(I) Complex Immobilization

The development of new strategies for spatially controllable immobilization has encouraged the preparation of novel catalysts based on the organic-inorganic hybrid concept. In the present paper, a Cu-based multi-structured silica catalyst has been prepared and fully characterized. The inclusion of Cu(II) in β-cyclodextrins has been exploited with the double aim to stabilize the metal and to act as a source of Cu(I) catalytic sites. Multi-technique characterization by infrared, UV-visible, electron microscopy and X-ray absorption spectroscopies of the fresh and exhaust catalysts provided information on the local structure, redox properties and stability of the investigated hybrid systems. The catalytic system showed that copper nanospecies were dispersed on the support and hardly affected by the catalytic tests, confirming the stabilizing effect of β-CD, and likely of the N1-(3-Trimethoxysilylpropyl) diethylenetriamine spacer, as deduced by X-ray absorption spectroscopy analysis. Overall, we demonstrate a feasible approach to efficiently anchor Cu(II) species and to obtain a reusable single-site hybrid catalyst well suited for Cu(I)-catalyzed alkyne-azide cycloaddition.

Preparation of a Series of Supported Nonsymmetrical PNP-Pincer Ligands and the Application in Ester Hydrogenation

In contrast to their symmetrical analogues, nonsymmetrical PNP-type ligand motifs have been less investigated despite the modular pincer structure. However, the introduction of mixed phosphorus donor moieties provides access to a larger variety of PNP ligands. Herein, a facile solid-phase synthesis approach towards a diverse PNP-pincer ligand library of 14 members is reported. Contrary to often challenging workup procedures in solution-phase, only simple workup steps are required. The corresponding supported ruthenium-PNP catalysts are screened in ester hydrogenation. Usually, industrially applied heterogeneous catalysts require harsh conditions in this reaction (250-350 °C at 100-200 bar) often leading to reduced selectivities. Heterogenized reusable Ru-PNP catalysts are capable of reducing esters and lactones selectively under mild conditions.

Core-shell Fe-SiO2-polyamine magnetic nanoparticles for metal recovery using a continuous flow pipeline reactor

A series of core-shell magnetic nanomaterials have been synthesized with the intent of applying them for metal ion capture in a newly designed pipeline reactor. The synthetic chemistry is an extension of a previously developed family of materials based on amorphous silica gel, which has been used in the mining and remediation industries. The nanoparticles were characterized by infrared spectroscopy and TEM and SEM techniques. The size of the starting magnetite core was critical to the behavior of the particles under metal sequestering conditions. The capture kinetics of the resulting nanoagregates is 10 times faster than related micro composites. All of the tests performed point to the future successful development of a technology that circumvents the disadvantages associated with the use of column based microparticles.

New Heterogeneous Rh-Containing Catalysts Immobilized on a Hybrid Organic-Inorganic Surface for Hydroformylation of Unsaturated Compounds

Anchoring Rh complexes to the surface of a silica polyamine composite, which has a poly(allylamine) covalently grafted to the surface of amorphous silica gel, yielded a material that proved to be an effective and novel heterogeneous catalyst for hydroformylation of unsaturated compounds. Surface amino groups of the material were modified with phosphines by covalent and ionic coupling. The modified materials were then treated with Rh(acac)(CO)₂, giving the catalysts K-1 and K-2. Catalysts were characterized by solid-state NMR spectroscopy, IR spectroscopy, XPS, TEM, and elemental analysis. The activity and stability of K-1 and K-2 were then studied for the hydroformylation of selected unsaturated compounds. Hydroformylation of terminal double bonds occurred selectively in the presence of internal double bonds. Characterization of the catalysts and the problems encountered with the supported catalysts are discussed. Catalyst K-1 is reusable and can be applied to the hydroformylation of linear olefins, styrene, 4-vinylcyclohexene, and dienes, as well as representative terpenes and other unsaturated hydrocarbons in a batch reactor.