Sustainable synthesis of polymeric materials versus fine chemicals via CO₂ addition to epoxides

Increasing concerns about global warming and a potential energy crisis have prompted the search for new technologies for converting CO₂, a notorious greenhouse gas resulting from fossil fuel burning. Due to the high chemical inertness of CO₂ molecule, chemical reactions involving CO₂ activation usually face large energy barriers and require the development of highly effective catalysts.

In this context, the use of carbon dioxide as a source of C1 is a relevant topic in the scientific community and, over the last decade, there has been a remarkable scientific and technological advance in terms of the development of chemical processes for converting CO₂ into products with added value. We highlight the reaction of CO₂ addition to epoxides, from which it is possible to selectively obtain two types of products: cyclic carbonates and polycarbonates, both with relevant applications, such as green solvents and in plastic engineering, respectively.

In this work, we present our recent results on the application of metal complexes of tetrapyrrolic macrocycles (porphyrins and phthalocyanines) as catalysts in CO₂ addition reactions to epoxides. The effects of substrate, catalyst structure, as well as the reaction conditions (temperature and CO₂ pressure) on the modulation of the reaction selectivity will be discussed. So far, using cyclohexene oxide as substrate, Cr(III) porphyrin-based catalysts showed high activity and selectivity for polycarbonates while Al(III) cationic phthalocyanines led to the formation of polymers containing high ether linkage content. Furthermore, using styrene oxide as substrate, Zn(II) and Cu(II) phthalocyanine catalysts derived from natural-based terpene derivatives (menthol and myrtenol) led to the formation of cyclic carbonates with 100% selectivity.