Robust pyrrole-containing Zinc complexes for the catalytic valorisation of CO2 into cyclic carbonates

SSCI-VIDE+CDURABLE:ING+LCH:ATU:MAPInternational audienceThe reaction of CO2 and epoxides to form organic carbonates requires Lewis base catalysts, such as tetrabutylammonium halides (TBAX). Their activity and selectivity towards cyclic carbonates can be strongly reinforced with Lewis acids, as for example, Salen or porphyrin metallic complexes. We developed a series of nitrogen Schiff base (N-SB) compounds1 that forms a family of ligands that combines properties of both, Salen flexibility and porphyrins nitrogen coordination sphere. Herein, we present the synthesis and characterization of pyrrole containing Nitrogen-Schiff Base (N-SB) ligands. XRay analysis showed monomeric or dimeric helical structures, according with the coordination mode of the zinc centre that can be tetra or pentacoordinated. Combined to TBAX, the zinc N-SB complexes proved to be efficient and selective co-catalysts for the valorisation of CO2 into cyclic carbonates. The optimization of the reaction parameters was carried out with styrene oxide, and solvent free reactions allowed very high yields (up to 97%) using very small catalyst/co-catalyt amounts (less than 0.2mol%)2. Moreover, the robustness of these zinc complexes allowed various catalytic runs four days long, without any purification, just adding new loadings of styrene oxide. The reaction scope was also enlarged to other epoxides