Carbosilane dendrimers as renewable organocatalysts for the coupling of CO₂ and epoxides

Carbon dioxide attracts the attention of a scientific community due to an increasing demand for the reduction of greenhouse gases to support the fight against climatic changes. Moreover, CO₂ can be considered as a natural, inexpensive, abundant, non-toxic, and renewable resource of C1 feedstock. The Department of Bioorganic Compounds and Nanocomposites, among others, develops organocatalytic materials for chemical transformations using CO₂ as a substrate. In the recent publication (ACS Sustainable Chemistry & Engineering), dr. Strašák et al. proposed a novel catalytic system activating the cycloaddition of CO₂ to epoxides. The reaction provides cyclic carbonates, an important group of organic compounds. Further, the authors demonstrated two alternative protocols to recycle the catalytic material from reaction mixtures.

Unique properties of carbosilane dendrimers, a core interest of the Department of Bioorganic Compounds and Nanocomposites, were utilized to prepare a new class of macromolecules with a well-defined structure. Ammonium and phosphonium multivalent dendritic catalysts have comparable catalytic activities to their monovalent low-molecular-weight analogues even under mild conditions (without solvents or other additives). Furthermore, thanks to their size and shape, the dendritic catalysts can be easily and effectively separated from reaction mixtures via nanofiltration. Another approach to recycling uses the incorporation of dendritic catalysts into layered silicates – montmorillonites. The resulting nanocomposites are only slightly less active than the homogenous dendritic catalysts. As presented, the robust synthetic procedure can be adopted to prepare dendrimers with various types of catalytically active cationic groups at the periphery. Optionally, the polycationic dendrimers can be immobilized into anionic layered clays to form sophisticated nanocomposite catalysts without substantial loss of activity.

L. Červenková Št’astná, A. Krupková, R. Petrickovic, M. Müllerová, J. Matoušek, M. Koštejn, P. Cuřínová, V. Jandová, S. Šabata, and T. Strašák Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO₂ and Epoxides ACS Sustainable Chem. Eng. 2020, 8, 31, 11692–11703.
DOI: 10.1021/acssuschemeng.0c03367

Carbosilane dendrimers are effective and easily recyclable catalysts for CO₂ cycloaddition to epoxides in both homogeneous and heterogeneous modes.