Page 27 - חוברת תזות הנדסה ירוקה 2024

Study of Renewable Polysaccharide-based Heterogeneous Transition Metal Catalysts in Organic Synthesis.
Natalia Gliksberg; nataglik7@gmail.com
Prof. Adi Wolfson, Dr. Oshrat Levy-Ontman, and Dr. Eyal Tzur
Sami Shamoon College of Engineering, Be’er-Sheva and Ashdod
Organometallic catalysts play a crucial role in diverse applications across chemical, and pharmaceutical industries by accelerating reaction rates by means of the selective promotion of desired products and the reduction of activation energy. While homogeneous catalysis offers high activity and selectivity, it usually suffers from complex separation processes, necessary for isolating the catalyst from other products and residue substrates. To address this drawback, different recyclable heterogeneous systems were researched and developed, while novel polysaccharide- based heterogeneous catalysts were prepared and tested in Suzuki cross-coupling and metathesis reactions.
Renewable and biodegradable polysaccharides have attracted much attention recently, due to their unique properties and use for the immobilization of different complexes. In this study, kappa )k(, iota )i(, and lambda )λ( carrageenan and alginate were examined for their use to heterogenize three complexes. Two heterogeneous systems were developed and tested in Suzuki cross-coupling reactions and a third system in metathesis reaction.
The complexes of Pd)OAc(2 with two different ligands: PhenS and TXPTS, after immobilization in xerogels and hydrogels of various polysaccharides, were used in the Suzuki coupling reaction between phenylboronic acid and iodobenzene in the presence of sodium carbonate in ethanol. The heterogeneous system with Pd)OAc( *PhenS in ethanol yielded similar and even higher
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conversions than those of the homogeneous complex—up to 27% )after 24 h(. These results imply
that the polysaccharides also contribute to reaction performance. However, the recycling of the heterogeneous system showed a significant decrease in conversion, probably because the ligand has a high steric hindrance, causing its leaching. Thus, another ligand, TXPTS, of the phosphine family, with a structure similar to that of the ligand TPPTS )used successfully in many previous Suzuki reaction studies( was tested. In this system, while the homogeneous reaction in ethanol yielded a 61% conversion, after the immobilization of the complex in various polysaccharides, higher conversions were obtained: i-71%, k-69%, λ-70%, Alg-80%. As with the previous ligand, here too, the results show the contribution of the polysaccharides to the performance of the catalyst. In addition, this heterogeneous system showed mildly decreased conversion during the recycling of the heterogeneous catalyst and its leaching test showed that the complex had been leached. The two heterogeneous systems were characterized by various analyses: FTIR, XPS, and TGA. During the FTIR test of iota, chosen as a representative polysaccharide, no new covalent bonds between the sulfate ester group in the polysaccharide and the complex were identified; however, the TGA and XPS tests indicated the presence of the complex in the polysaccharide.
In the second part of the study, a heterogeneous system of ruthenium complex )FixCat(, was used and tested inthe metathesis reaction of olefins. The catalyst had been immobilized in λ
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