Hydrogen-bonded supramolecular polymers as dynamic scaffolds for catalysis

Abstract : Hydrogen-bonded supramolecular polymers based on benzene-1,3,5-tricarboxamide (BTA) and bis-urea recognition units were investigated as dynamic scaffolds for catalysis. The catalytic properties of a full set of ligands, including a series of eleven new bis-urea ligands, and complementary co-monomers have been investigated in various metal-catalyzed reactions. Co-polymers formed by mixing an achiral phosphine-functionalized monomer (the ligand) and a chiral phosphine-free additive (the co-monomer) were investigated as scaffolds for asymmetric catalysis. The aim was to transfer, amplify and switch the supramolecular chirality of the polymer scaffold to intrinsically achiral metal centres located at its periphery. BTA mixtures have been successfully applied in two different asymmetric reactions providing up to 85% and 80% e.e. in the rhodium-catalysed hydrogenation of dimethylitaconate and in the copper-catalysed hydrosilylation of 4’-nitro-acetophenone respectively. The BTA scaffold supporting the catalytic rhodium and copper centres display strong chirality amplification properties: i) for the rhodium catalysis, the amount of chiral co-monomer can be decreased down to one-fourth of that of the ligand without deteriorating the enantioselectivity of the reaction and ii) the chirality of the copper catalyst can be switched during the course of the catalytic reaction. In the case of the bis-urea platform, mixtures of monomers have been investigated in several asymmetric metal-catalysed reactions but selectivity was obtained only for the copper-catalyzed hydrosilylation of 4’-nitro-acetophenone (22% e.e). We also tested the use of supramolecular polymers in the context of organocatalysis: the possibility of tuning the activity of a thiourea catalytic centre by controlling its self-assembly behaviour was investigated. Overall, our studies clearly reveal the innovative properties of catalysts supported by hydrogen-bonded supramolecular polymers
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Xavier Caumes. Hydrogen-bonded supramolecular polymers as dynamic scaffolds for catalysis. Material chemistry. Université Pierre et Marie Curie - Paris VI, 2016. English. ⟨NNT : 2016PA066554⟩. ⟨tel-01534681⟩



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