Synthesis, characterization and catalytic properties of heterogeneous iron(III) tetradentate Schiff base complexes for the aerobic epoxidation of styrene

A series of hybrid mesoporous SBA-15 materials containing four iron(III) Schiff base complexes of the type [FeL (x) (NO3)] (x = 4-7, L = N,N'-bis(salicylidene)ethylenediamine, N,N'-bis(salicylidene)diethylenetriamine, N,N'-bis(salicylidene)o-phenylenediamine, N,N'-bis(3-nitro-salicylidene)ethylenediamine) was synthesized by a post-grafting route. The XRD, N-2 adsorption/desorption and TEM measurements confirmed the structural integrity of the mesoporous hosts, and the spectroscopic characterization techniques (FT-IR, UV-vis spectroscopy, H-1 NMR) confirmed the ligands and the successful anchoring of iron(III) Schiff base complexes over the modified mesoporous support. Quantification of the supported ligand and metal was carried out by TG/DSC and ICP-AES techniques. The catalyst FeL7-SBA resulting from N,N'-bis(3-nitro-salicylidene)ethylenediamine) ligand was considerably active for the aerobic epoxidation of styrene, in which the highest conversion of styrene reached 83.6%, and the selectivity to styrene oxide was 83.0%. Moreover, it was also found that the catalytic activity increases with the decrease in the electron-donating ability of the Schiff bases, and the selectivity varies according to the types of substituents in the ligands.