Influence of structural properties of zinc complexes with N4-donor ligands on the catalyzed cycloaddition of CO2 to epoxides into cyclic carbonates

Identifier:  imarina:9295068

Handle: https://hdl.handle.net/20.500.11797/imarina9295068

Authors:  El Aouni, N; Redondo, CL; Bin Yeamin, M; Aghmiz, A; Reguero, M; Masdeu-Bultó, AM

Abstract:
Zinc(II) complexes [Zn(L1-L5)Cl2] with tetra-aza donor ligands bearing phenanthroline and bipyridine bis(aniline) skeleton L1-L5 have been prepared and characterised. These ligands were selected to analyse the influence on the catalytic activity for the CO2-cycloaddition to epoxides of three parameters: the steric hindrance of the orto substituent of the aniline ring, the central skeleton and the nature of the non-aromatic amine. X-ray diffraction characterisation of [Zn(L1)Cl2] and [Zn(L2)Cl2] showed that the geometry is pentacoordinate while in the case of [Zn(L5)Cl2] a four-coordinate tetrahedral complex was formed. Computational calculations using density functional theory methods (DFT) agreed with these results. These complexes combined with tetrabutylammonium bromide (TBAB) are very selective for the CO2/terminal epoxides coupling to form cyclic carbonates providing activity up to TOF 565 h−1.