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Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO2 and Epoxides
journal contribution
posted on 2020-07-29, 18:08 authored by Lucie Červenková Št’astná, Alena Krupková, Roman Petrickovic, Monika Müllerová, Jindřich Matoušek, Martin Koštejn, Petra Cuřínová, Věra Jandová, Stanislav Šabata, Tomáš StrašákInsertion
of carbon dioxide into the structure of organic epoxides
leads to the formation of valuable cyclic carbonates and polycarbonates.
For the purpose of this process, we report here a series of recyclable
organocatalysts with superior activity. Carbosilane dendrimers (first
to third generation) are employed as a support to which periphery
ammonium or phosphonium centers are covalently attached to form a
dendritic ionic liquid (DIL). The obtained DILs were tested as homogeneous
catalysts in the cycloaddition of CO2 to epoxides with
respect to their activity and recyclability. The catalytic performance
of active sites is enhanced by the presence of a proximal hydroxyl
group, playing the role of a hydrogen bond donor. An experimentally
observed synergistic effect was confirmed by density functional theory
calculations. The activity of DILs is affected more by the structure
of onium salt than by the size of the support (dendrimer generation).
The dendritic catalysts of all tested generations could be recovered
by nanofiltration and repeatedly reused. In order to simplify the
separation of the catalysts, composite materials were prepared by
intercalating the more active ammonium dendrimers into the interlayer
space of a natural montmorillonite. The resulting heterogeneous catalysts
were easily separable by centrifugation while retaining a reasonable
level of activity.