Abstract
A water-soluble benzene-1,3,5-tricarboxamide (BTA) derivative that self-assembles into one-dimensional, helical, supramolecular polymers is functionalised at the periphery with one L-proline moiety. In water, the BTA-derivative forms micrometre long supramolecular polymers, which are stabilised by hydrophobic interactions and directional hydrogen bonds. Furthermore, we co-assemble a catalytically inactive, but structurally similar, BTA with the L-proline functionalised BTA to create co-polymers. This allows us to assess how the density of the L-proline units along the supramolecular polymer affects its activity and selectivity. Both the supramolecular polymers and co-polymers show high activity and selectivity as catalysts for the aldol reaction in water when using p-nitrobenzaldehyde and cyclohexanone as the substrates for the aldol reaction. After optimisation of the reaction conditions, a consistent conversion of 92 ± 7%, deanti of 92 ± 3%, and eeanti of 97 ± 1% are obtained with a concentration of L-proline as low as 1 mol%.
Highlights
Catalysts immobilised on soluble macromolecular scaffolds are enjoying renewed interest due to their spatial confinement of catalytic centres, enzyme like-construction, and facile recyclability.[1]
Bouteiller and coworkers reported that helical supramolecular polymers based on a benzene-1,3,5-tricarboxamide (BTA) scaffold with Rhbased catalysts attached to the periphery showed remarkable enantioselectivities for the asymmetric reduction of dimethyl
BTA 1 was obtained in high purity and moderate yield, as evidenced by NMR, IR and LC-MS (ESI, Fig. S1–S4†)
Summary
Catalysts immobilised on soluble macromolecular scaffolds are enjoying renewed interest due to their spatial confinement of catalytic centres, enzyme like-construction, and facile recyclability.[1]. A supramolecular approach – the application of reversible, non-covalent interactions – to construct a well-defined macromolecular scaffold has been proposed as a versatile method to control the proximity of catalytic sites.[2] An interesting system to achieve spatial modulation between catalytic sites was demonstrated by Stupp and coworkers. The hydrolysis of a model ester was evaluated using imidazole catalysts attached to the surface of nanofibers formed by aggregation of peptide amphiphiles.[3] A high density of reactive sites on the surface of the ordered supramolecular fibre led to a considerably higher hydrolysis rate than the catalysts in micelles or solution. Bouteiller and coworkers reported that helical supramolecular polymers based on a benzene-1,3,5-tricarboxamide (BTA) scaffold with Rhbased catalysts attached to the periphery showed remarkable enantioselectivities for the asymmetric reduction of dimethyl
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