Synthesis, Oxygenation and Catalytic Epoxidation Performance of Transition-metal Hydroxamate with Benzo-15-Crown-5

Abstract

A series of novel hydroxamic acid complexes (ML ¹₂ ~ ML ³₂ , M=Co^II, Mn^IIICl) containing benzo-15-crown-5 and their analogues, ML ⁴₂ were successfully synthesized starting from benzo-15-crown-5 (B15C5) or 1,2-dimethoxybenzene. Their structures were characterized by ¹H-NMR, IR, and MS as well as by elemental analysis. Moreover, the saturated oxygen uptake of their cobalt(II) complexes,Col ¹₂ −Col ⁴₂ , in diethyleneglycol dimethyl ether was determined over the −5 to +20 °C range. The oxygenation constants (Ko₂) and thermodynamic parameters (ΔH⁰ and ΔS⁰) were calculated. Meanwhile, the corresponding Mn^(III) hydroxamates were employed as models of monooxygenase to catalyze PhCH=CH₂ epoxidation at ambient temperature and pressures. The effects of pendant B15C5 and adding sodium cation on the O₂-binding capabilities, and the catalytic oxidation performance of the complexes (ML ¹₂ ~ ML ³₂ ), were investigated and compared with the uncrowned analogue ML ⁴₂ . The results indicated that the B15C5-functionalized Co(II) complexes (CoL ¹₂ ~ CoL ³₂ ) showed high ) showed high activity in the dioxygen affinities, and the Mn ¹₂ Cl exhibited the best catalytic activity: th e conversion of PhCH=CH2 and epoxidation selectivity were up to 27.14%, 100% respectively.