Synthesis, oxygenation and catalytic oxidation performance of crown ether-containing Schiff base-transition metal complexes

Mono-Schiff bases containing a crown ether 2 3 4 ring (HL1, HL2, HL3 and HL4) and their transition metal complexes were synthesized and characterized by H-1 NMR, IR, and mass spectroscopy as well as elemental analysis. The oxygenation constants (K-O2) of Schiff base-Co(II) complexes were measured over the range of -5 to +25 degreesC, and the values of DeltaHdegrees and AS' were calculated based on these K-O2 values. Using Mn(III)-Schiff base complexes, the biornimetic catalytic oxidation of styrene to benzaldehyde was carried out with 100% selectivity. Comparison of this complex with analogues not containing a crown ether moiety clearly demonstrated the influence of crown ether ring on the dioxygen affinities and biomimetic catalytic oxidation performance of the Schiff base complexes.