Recent advances in the use of catalysts based on natural products for the conversion of CO2 into cyclic carbonates
The cycloaddition of carbon dioxide to epoxides is an efficient and clean method to obtain cyclic carbonates, which are used as green solvents, as electrolytes for lithium batteries and as intermediates for the synthesis of polymers and chemicals. This reaction requires a catalyst to overcome the low reactivity of carbon dioxide. The best catalysts for this transformation include a Lewis acid or hydrogen-bond donor to activate the epoxide and a Lewis base as a nucleophile to open the ring of the oxirane cycle. The most commonly used catalysts are alkali halides, ammonium and phosphonium salts, which are organocatalysts containing hydrogen-bond donor groups and metal-based systems. To increase the sustainability and decrease the toxicity of the catalytic systems, many bio-based products derived from natural sources have been used as catalysts or in combination with catalytic materials. The high functionality of natural products that contain amino and/or hydroxyl groups is used to activate an epoxide or reversibly capture carbon dioxide when used directly. But these products can also behave as auxiliaries, for instance, as ligands in metal-based complexes, as biopolymer active supports for catalysts, as components for the skeleton of metal organic frameworks or to form ionic liquids or as deep eutectic solvents serving as an active medium for catalytic reactions. In this literature review, we present a structured overview of the reported chemical catalytic systems containing any component derived from a natural product. We discuss the amino acid-based systems, cellulose, saccharides, lignin and lignocellulosic materials, choline-derived species, guanidine and guanidinium salts, and other less explored compounds. Special emphasis has been placed on mechanistic studies providing information about the role of each component in these multifunctional systems.