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Organic Polymers, Oligomers, and Catalysis
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Cross-linked polystyrene is probably the most popular polymeric support for heterogenized catalysts. For instance, the chloromethylated cross-linked polystyrene, also named Merrifield resin, offers a convenient functionalization point. Thus, several ligands for designing homogeneous catalysts, including carbenes, xyliphos, and phosphines ligands were covalently immobilized on cross-linked polystyrene matrices. The corresponding Ru, Ir, and Pd catalysts were synthesized and their activity was tested for hydrogenation, ring closing metathesis and coupling reactions. Heterogenized Ru-based Grubbs and Hoveyda catalysts could reach comparable turnover numbers as their homogeneous counterparts for catalyzing various ring closing metathesis reactions [79]. However, no recycling could be performed, due to the degradation of the catalyst. Immobilization of iridium-based xyliphos complexes on polystyrene allowed catalyzing the asymmetric hydrogenation of imines [80]. In that case, the heterogenization process resulted in much less active catalysts than homogenous competitors, but a similar enantioselectivity of around 75% was obtained. Although several attempts for immobilizing palladium complexes on polystyrene have been performed, the formation of palladium nanoparticles after one catalytic run is suspected [81–86]. This type of polymer-supported nanoparticles is discussed later in this chapter.
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Published in Brajendra K. Sharma, Girma Biresaw, Environmentally Friendly and Biobased Lubricants, 2016
Kenneth M. Doll, Bryan R. Moser, Zengshe Liu, Rex E. Murray
The reaction proceeds by the cleavage and reformation of carbon–carbon double bonds and the simultaneous exchange of substituents. The fundamental metathesis transformations include self-metathesis, cross metathesis, ring-closing metathesis, ring-opening metathesis acyclic diene metathesis polymerization, and ring-opening metathesis polymerization. Application of metathesis chemistry to fats and oils was limited until the discovery of active ruthenium catalysts by Grubbs, which, in 2005, earned him the Nobel Prize in Chemistry [87]. Olefin metathesis is an appealing industrial reaction because it is cost effective and catalytic, generates almost no unusable by-products, and is easily scalable [88]. Major petrochemical applications of metathesis include conversion of relatively inexpensive propene into more valuable ethene and butene by the Shell Higher Olefins Process, to produce linear alpha olefins and their derivatives from oligomerized ethene [89].
An Approach for Development of Materials for Green Chemical Catalytic Processes: Green Catalysis
Published in Neha Kanwar Rawat, Iuliana Stoica, A. K. Haghi, Green Polymer Chemistry and Composites, 2021
Rimzhim Gupta, Akanksha Adaval, Sushant Kumar
These catalysts have shown to have high yields with easy removal through filtration and can also be reused without any loss in their catalytic activity. Rhodium and its complexes have been commonly used in several organic reactions like C-H bond activation, hydrogenation, hydroformylation, and carbonylation reactions. To follow in the steps of green chemistry, many solid supported catalysts have been developed. Petrukhina et al. have covalently anchored rhodium complex on functionalized resin for use in cyclopropanation reaction.69 Similarly, several immobilized catalysts on solid supports have been unearthed through subsequent and relentless research for rhodium-catalyzed reactions. A recent study reported the use of rhodium and palladium complex immobilized on functionalized graphene oxide being used in hydrogenation reactions.70,71 Ruthenium-catalyzed reactions are commonly being used for the synthesis of many organic molecules. As mentioned earlier, solid-supported ruthenium catalysts have found a breakthrough as they offer all the advantages of green chemistry, like ease of separation, reusability, and effortless handling. Grubs and Grubbs-Hoveyda ruthenium catalysts have been prepared on SBA silica and mesoporous silica supports for ring-closing metathesis reactions.72 Magnetic beads, organic polymers, inorganic oxides, and carbonaceous materials have been used as supports for hydrogenous catalytic reactions. A report published by Ge et al. reported the use of Grubbs–Hoveyda ruthenium complex for the one-pot reaction of olefin metathesis and functionalized 2H-atrazines were synthesized by ring contraction of isoxazols using the G–H II catalyst, as shown in Figure 8.6.94
PolyHIPEs for Separations and Chemical Transformations: A Review
Published in Solvent Extraction and Ion Exchange, 2019
Kathryn M. L. Taylor-Pashow, Julia G. Pribyl
A procedure to immobilize ruthenium olefin metathesis catalysts on the surface of polyHIPEs was recently reported.[60] Both first and second-generation Grubbs Ru catalysts were immobilized on the surface of polyHIPEs via alkylidene ligand exchange and tested for their ability to catalyze the ring-opening metathesis polymerization of norbornene and various norbornene derivatives. It was found that the supported catalysts did efficiently catalyze the ROMP reactions studied, which resulted in polyHIPEs grafted with brushes of the Ru catalyst initiated polynorbornyl compounds with up to 97% monomer incorporation. The authors noted that after the ROMP reactions were performed, the catalysts were not reusable for subsequent ROMP reactions but could be further used for other olefin metathesis reactions including ring-closing metathesis (RCM) and self-metathesis (SM).