Metal nanoparticles embedded in ligand-functionalized water-soluble core-shell polymers for application in aqueous biphasic hydrogenation

Chantal Joseph Abou Fayssal

Research output: Book/ReportPh.D. thesis

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Abstract

Metallic nanoparticles (MNPs) garner substantial attention in the field of catalysis due to their remarkable high surface-to-volume ratio that indudes a high number of potential active sites. The confinement of MNPs significantly impacts their stability and catalytic performance. Biphasic applications are particularly attractive as they facilitate catalyst recovery and recycling by simple phase separation. Micellar catalysis, where the catalyst is tethered to the hydrophobic core of a surfactant, that self-assembles into micellar nanoreactors is of particular interest. Inspired by previous research work, this project focuses on the synthesis of unimolecular nanosized polymeric reactors and the confinement of rhodium nanoparticles (RhNPs) within their cores, for their application in aqueous biphasic hydrogenation. To circumvent extraction of the NPs upon recycling, as previously encountered with triphenylphosphine-functionalized polymer cores in the presence of O-based solvent, the use of triphenylphosphine oxide (TPPO) as core-anchor was developed. The aim was to have core-ligands which interact more strongly with the RhNPs surface, and thus provide a more efficient confinement and resultant higher performance for hydrogenation catalysis. Experiments were performed using core-crosslinked micelles with a polycationic (CCM-C) or polyanionic (CCM-A) shell, where TPPO functions were grafted by copolymerization with styrene of 4-styryldiphenylphosphine oxide (SDPPO), both synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The in-situ generation of the RhNPs using [Rh(COD)(μ-Cl)]2 as precursor proved unsuccessful, suggesting that RhI binding by TPPO to yield [RhCl(COD)(TPPO@CCMs)] was insufficiently strong to cleave the di-μ-Cl-bridge in the precurcor complex. However, two alternative approaches were successfully developed for the generation of RhNP-TPPO@CCMs, consisting of either an ex-situ synthesis of RhNPs in the presence of stabilizers followed by their transfer to the CCM cores, and a one-pot synthesis approach. The resulting RhNP-TPPO@CCMs latexes showed a very high catalytic activity for the aqueous biphasic hydrogenation of styrene, and they proved reusable in multiple catalytic runs without any perceptible RhNPs loss during the intermediate product extractions with diethyl ether. The RhNP-TPPO@CCMs latexes were also proven efficient for the hydrogenation of other alkenes, alkynes, and carbonyl substrates.
Original languageEnglish
PublisherDTU Chemistry
Number of pages236
Publication statusPublished - 2023

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