Bio-nanohybrid catalysts based on l-leucine immobilized in hydrotalcite and their activity in aldol reaction

• The organic/inorganic interactions between l-leucine immobilized into hydrotalcites were studied.
• By reconstruction method, the anionic form of l-leucine is immobilized in the interlayer space while by anionic exchange, both zwitterionic and anionic forms are immobilized.
• These nanohybrid materials are more active in the asymmetric aldol reaction than the mere l-leucine.
• Modulating reaction conditions (solvent, type of nanohybrid used, time) can lead to different reaction outcome.

Nanohybrid materials based on l-leucine (l-Leu) and hydrotalcites (HT) were prepared by the ion-exchange and reconstruction method, under mild synthesis conditions. The location, amount and the form of the immobilized l-Leu are affected not only by the time of synthesis, but also by temperature and ultrasound treatment. The XRD results demonstrate that the immobilization occurs in either a vertical or oblique orientation with respect to the HT layers. The catalytic activity of these materials was tested in the aldol addition reaction of cyclohexanone with different aromatic aldehydes, affording mainly the syn-diastereomer. Furthermore, the present study demonstrates that both diastereo- and enantioselectivity can be easily modulated by the appropriate combination of nanohybrid catalyst, solvent and reaction time.

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