Robust pyrrole-Schiff base Zinc complexes as novel catalysts for the selective cycloaddition of CO2 to epoxides.

• Catalyzed cycloaddition of CO 2 over styrene oxide • More robust, Pyrrole-based Zn-N 4 SB were studied as Lewis acid catalysts • Good efficiency of Zn-N 4 SB along with tetrabutylammonium halides (NBu 4 X) • The optimized catalytic system can lead to TON up to 1400 and TOF up to 232 h⁻¹. • Study supported by DFT calculations A series of Zn (II) complexes with nitrogen Schiff base ligands (NSB) has been synthesized from pyrrole carboxaldehyde. The prepared complexes were fully characterized. Single crystal X-ray diffraction analysis showed various coordination modes, as monomers or as helical dimers according to the number of available nitrogen atoms surrounding the zinc cation. The complex structure optimizations were carried out using the density functional theory (DFT) with ADF program and the dimerization energies and the temperature effect were examined. The Zn complexes were used as Lewis acids (LA) combined with tetrabutylammonium halides (N 4 BuX) as Lewis bases (LB), for the catalytic valorization of CO 2 into cyclic carbonates. A new momomeric Zn-NSB was chosen to study the influence of different reaction parameters (temperature, CO 2 pressure, LA/LB molar ratio, catalyst amount). Thus, optimized conditions afforded the solvent-free selective formation of styrene cyclic carbonate in good yields (up to 98 %) and allowed the reuse of this Zn-NSB/N 4 BuX catalytic system without any loss of activity. [ABSTRACT FROM AUTHOR]