Synthesis, Dioxygen Affinities and Biomimetic Catalytic Oxidation Performance of Crown Ether-tethered Schiff Base Transition-Metal Complexes

Abstract

Mono-Schiff bases containing crown ether ring ( HL 1 , HL 2 , HL 3 and HL 4 ) and their transition-metal complexes were synthesized and characterized by 1H NMR, IR, MS spectra and elemental analysis. The crystal structures of HL 1 , HL 3 and CoL 2 1 were determined from X-ray diffraction data. The oxygenation constants (Ko 2) of Schiff-base Co (II) complexes were measured over a range of −5 °C to 25 °C, and the values of ΔH 0 and ΔS 0 were also calculated based on Ko 2. In the presence of Mn (III) Schiff base complexes, the biomimetic catalytic oxidation for styrene to benzalhyde was carried out at 100% selectivity. Compared with the uncrowned analogue, the influence of crown ring and its bonding pattern, the distance between the coordination center and crown ring on the dioxygen affinities and biomimetic catalytic oxidation performance of the crowned Schiff base complexes were observed.