Synthesis, Characterization and Reactivity of Cobalt(III)-Oxygen Complexes Bearing a Macrocyclic 15-TMC Ligand

Abstract

촉매 효소의 활성 자리인 금속-산소 결합체는 산소 활성화의 촉매 순환반응에서 발견되는 핵심적인 중간체이다. 이 연구에서는 [Co(15-TMC)(CH3CN)2]2+를 H2O2와 triethylamine를 반응시켜 단핵 Cobalt(III)-peroxo 화합물인 [Co(III)(15-TMC)(OO)]+를 합성하였다. 다양한 분광학적 기술을 통해 분광학적 특성들을 확인하였다. Cobalt(III)-peroxo 화합물인 [Co(III)(15-TMC)(OO)]+에 수소 이온을 첨가하면 Co-hydroperoxo 화합물인 [Co(III)(15-TMC)(OOH)]2+로 전환되었다. 그 후 [Co(III)(15-TMC)(OOH)]+는 산소-산소 결합이 균일하게 해리하는 작용과 TMC리간드의 산화작용을 거쳐 [Co(III)(15-TMC-O)(CH3CN)]2+ 로 전환되는 것을 확인했다. 이 화합물은 다양한 분광학적 기술과 X-ray 결정학으로 구조적·분광학적 특성을 확인할 수 있었다.;Mononuclear metal-dioxygen adducts are produced as key intermediates of dioxygen activation in the catalytic cycles of metalloenzymes. In this work, a side-on cobalt(III)-peroxo complex bearing a macrocyclic 15-TMC ligand, [CoIII(15-TMC)(O2)]+, was synthesized and characterized by various physicochemical methods, including UV-vis, ESI-MS, EPR and XAS/EXAFS. Upon protonation, this cobalt(III)-peroxo complex is cleanly converted to an end-on cobalt(III)-hydroperoxo complex, [CoIII(15-TMC)(OOH)]2+, which was confirmed by spectroscopic techniques, such as UV-vis and XAS/EXAFS. Interconversion between the cobalt(III)-peroxo complex and the cobalt(III)-hydroperoxo complex has been observed through acid-base chemistry. The cobalt(III)-hydroperoxo complex is responsible for aliphatic hydroxylation at the methyl group of the 15-TMC ligand to give oxygenated product, [CoIII(15-TMC-CH2-O)]2+. Kinetic studies and 18O-labeling experiments propose the homolytic O-O bond cleavage of the cobalt(III)-hydroperoxo complex for the aliphatic hydroxylation. Structural and spectroscopic studies and conversion processes give important information in aliphatic hydroxylation by metal-dioxygen adducts.