Sustainable synthesis of polycarbonates and polyurethanes precursors by CO2 cycloaddition reactions catalyzed by supported ferrates

Ammonium tetrahalo-metallates of the first transition series elements were proven efficient catalysts in an ample scope of reactions, combining ease of preparation and storage, excellent catalytic activity and extremely low production costs [1][2][3][4]. In particular, ammonium ferrates showed remarkable performance in the synthesis of cyclic carbamates and carbonates when employed in the cycloaddition of CO2 to aziridines and epoxides, respectively. These reactions display interesting features in terms of eco-sustainability, since the coupling occurs with 100% of atom-economy, valorizing waste CO2 to yield value-added products. In continuation to our previous works on CO2 valorization, we present a heterogeneous implementation of this catalytic system. A simple and efficient protocol to functionalize Amberlyst® ionic exchange resins with [FeX3Y]- complexes was developed. The obtained materials can be fine-tuned both by choosing the preferred ferric halide and resin reticular size, controlling thus the selectivity of the reaction. The catalysts were therefore optimized to fully comply to the reaction’s requirements; mild reaction conditions, both in terms of CO2 pressure and reaction temperature, were achieved, to yield the desired products with high yields and selectivity (Figure 1). The already effective ferrates-based catalytic system was improved with a more industrially applicable heterogeneous solution. When applied to appropriate substrates, these catalysts can be used for the synthesis of polycarbonates and polyurethanes precursors. Cyclic carbonates [5] and carbamates[6] ring opening polymerization (ROP) indeed could be employed as a phosgene and isocyanate free synthesis of high value polymeric products, thus recycling human-waste CO2 in mass-produced chemicals