Supported Polyhedral Oligomeric Silsesquioxane-Based (POSS) Materials as Highly Active Organocatalysts for the Conversion of CO2

Abstract

Very high turnover numbers (TON) and productivity values up to 7875 and 740 respectively have been obtained for the conversion of CO2 into cyclic carbonates by using hybrid materials based on imidazolium modified polyhedral oligomeric silsesquioxanes (POSS-Imi) grafted on amorphous silica (SiO2) and mesostructured SBA-15. The heterogeneous organocatalysts were easily prepared via a straightforward synthetic procedure allowing to generate high local concentration spots of imidazolium active sites surrounding the POSS core. This synthetic procedure is also a promising approach for the design of a wide library of hybrid functional materials. The materials do not possess other co-catalytic species with Lewis or Brønsted acid functionalities which still represents a challenging aspect for the outcome of the process. The recyclability of the catalysts was successfully verified for four consecutive runs. The catalytic versatility was proved with a wide range of epoxides and with the most challenging oxetane on large scale (105–210 mmol) showing higher performances in comparison with other unmodified imidazolium-based catalytic systems. The new hybrids based on supported POSS nanostructures allowed the sustainable conversion of carbon dioxide under solvents- and metal-free reaction conditions with a full selectivity toward cyclic carbonates.