Asymmetric Catalysis at the Mesoscale: Gold Nanoclusters
Embedded in Chiral Self-Assembled Monolayer as Heterogeneous Catalyst
for Asymmetric Reactions
- Publication date
- Publisher
Abstract
Research
to develop highly versatile, chiral, heterogeneous catalysts
for asymmetric organic transformations, without quenching the catalytic
reactivity, has met with limited success. While chiral supramolecular
structures, connected by weak bonds, are highly active for homogeneous
asymmetric catalysis, their application in heterogeneous catalysis
is rare. In this work, asymmetric catalyst was prepared by encapsulating
metallic nanoclusters in chiral self-assembled monolayer (SAM), immobilized
on mesoporous SiO<sub>2</sub> support. Using olefin cyclopropanation
as an example, it was demonstrated that by controlling the SAM properties,
asymmetric reactions can be catalyzed by Au clusters embedded in chiral
SAM. Up to 50% enantioselectivity with high diastereoselectivity were
obtained while employing Au nanoclusters coated with SAM peptides
as heterogeneous catalyst for the formation of cyclopropane-containing
products. Spectroscopic measurements correlated the improved enantioselectivity
with the formation of a hydrogen-bonding network in the chiral SAM.
These results demonstrate the synergetic effect of the catalytically
active metallic sites and the surrounding chiral SAM for the formation
of a mesoscale enantioselective catalyst