The effects of interactions between proline and carbon nanostructures on organocatalysis in the Hajos–Parrish–Eder–Sauer–Wiechert reaction

Abstract

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. The non-covalent interactions of S-(-)-proline with the surfaces of carbon nanostructures (fullerene, nanotubes and graphite) change the nucleophilic-electrophilic and acid-base properties of the amino acid, thus tuning its activity and selectivity in the organocatalytic HajosParrish-Eder-Sauer-Wiechert (HPESW) reaction. Whilst our spectroscopy and microscopy measurements show no permanent covalent bonding between S-(-)-proline and carbon nanostructures, a systematic investigation of the catalytic activity and selectivity of the organocatalyst in the HPESW reaction demonstrates a clear correlation between the pyramidalisation angle of carbon nanostructures and the catalytic properties of S-(-)-proline. Carbon nanostructures with larger pyramidalisation angles have a stronger interaction wit h the nitrogen atom lone pair of electrons of the organocatalyst, thereby simultaneously decreasing the nucleophilicity and increasing the acidity of the organocatalyst. These translate into lower conversion rates but higher selectivities towards the dehydrated product of Aldol addition.

Hollow Mesoporous Organic Polymeric Nanobowls and Nanospheres: Shell Thickness and Mesopore-Dependent Catalytic Performance in Sulfonation, Immobilization of Organocatalyst, and Enantioselective Organocascade

“…Homogeneous organocatalysis has now become a thriving catalytic methodology paralleling metal catalysis and widespread applications in synthetic organic chemistry. − However, most organocatalytic processes require a high loading of catalyst and remain a major drawback with the tedious separation of expensive organocatalyst from the reaction mixture. From the viewpoint of green chemistry, polymers, − inorganic materials, − metal–organic frameworks (MOFs), − covalent-organic frameworks (COFs), − and ionic liquid , covalently and noncovalently supported − heterogeneous organocatalysts have been developed to achieve the reusability of expensive organocatalysts and ensure low environmental impacts. Nevertheless, these heterogeneous organocatalysts have at least one of the following disadvantages: (i) less effectiveness than the homogeneous counterpart, (ii) mass transfer limitations of reactants in catalyst carrier, and (iii) multiple synthetic manipulations to anchor the organocatalyst.…”