Synthesis, Structural and Spectroscopic Characterization and Reactivities of Mononuclear Cobalt(III)-Peroxo Complexes

Abstract

Metal-O2 부가물은 금속효소 및 생체모방 화합물에 의한 산소 활성화의 촉매 순환반응에서 발견되는 핵심적인 중간체이다. 이 연구에서는 [Co(12-TMC)(CH3CN)]2+와 [Co(13-TMC)(CH3CN)]2+를 H2O2와 triethylamine과 반응시켜 tetraazamacrocyclic ligand를 가진 단핵 cobalt(III)-peroxo 복합체, [Co(12-TMC)(O2)]+와 [Co(13-TMC)(O2)]+를 합성하였다. 다양한 분광학적 기술과 x-ray 결정학으로 단핵 cobalt(III)-peroxo 중간체의 구조적 • 분광학적 특성들을 확인할 수 있었고, 이러한 특성들은 peroxo ligand가 side-on η2 경향으로 결합되어있다는 것을 명확히 보여주었다. [Co(12-TMC)(O2)]+와 [Co(13-TMC)(O2)]+의 산소-산소 결합 stretching 진동수는 resonance Raman spectroscopy에 의해 902 cm-1로 밝혀졌다. 이 두 가지 복합체에서 산소-산소 결합 길이는 각각 1.4389(17)Å, 1.438(6)Å 으로 CoO2 core의 구조적 특성이 거의 동일하였다. Cobalt(III)-peroxo 복합체의 반응성을 살펴 본 결과, 이 복합체는 aldehyde를 산화 시키고 O2를 다른 금속으로 전달할 수 있었다. Aldehyde의 산화반응에서 두 cobalt-peroxo 복합체의 친핵성 반응성은 macrocyclic ligand의 고리 크기에 따라 크게 달라져 [Co(13-TMC)(O2)]+가 [Co(12-TMC)(O2)]+보다 더 빨리 반응하였다. O2-전달 반응에서는 cobalt(III)-peroxo 복합체에 결합되어있던 peroxo group이 manganese(II) 복합체로 전달되어 cobalt(II)와 mangance(III)-peroxo 복합체가 생성됨을 확인하였고, 그 반응성 또한 tetraazamacrocycle의 고리 크기에 크게 영향을 받아 aldehyde의 산화반응에서와 같은 양상을 보였다.;Metal-dioxygen adducts are key intermediates detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. In this study, mononuclear cobalt(III)-peroxo complexes bearing tetraazamacrocyclic ligands, [Co(12-TMC)(O2)]+ and [Co(13-TMC)(O2)]+, were synthesized by reacting [Co(12-TMC)(CH3CN)]2+ and [Co(13-TMC)(CH3CN)]2+, respectively, with H2O2 in the presence of triethylamine. The mononuclear cobalt(III)-peroxo intermediates were isolated and characterized by various spectroscopic techniques and X-ray crystallography, and the structural and spectroscopic characterization demonstrated unambiguously that the peroxo ligand is bound in a side-on η2 fashion. The O-O bond stretching frequency of [Co(12-TMC)(O2)]+ and [Co(13-TMC)(O2)]+ was determined to be 902 cm-1 by resonance Raman spectroscopy. The structural properties of the CoO2 core in both complexes are nearly identical; the O-O bond distances of [Co(12-TMC)(O2)]+ and [Co(13-TMC)(O2)]+ were 1.4389(17) Å and 1.438(6) Å, respectively. The cobalt(III)-peroxo complexes showed reactivities in the oxidation of aldehydes and O2-transfer reactions. In the aldehyde oxidation reactions, the nucleophilic reactivity of the cobalt-peroxo complexes was significantly dependent on the ring size of the macrocyclic ligands, with the reactivity of [Co(13-TMC)(O2)]+ > [Co(12-TMC)(O2)]+. In the O2-transfer reactions, the cobalt(III)-peroxo complexes transferred the bound peroxo group to a manganese(II) complex, affording the corresponding cobalt(II) and manganese(III)-peroxo complexes. The reactivity of the cobalt-peroxo complexes in O2-transfer was also significantly dependent on the ring size of tetraazamacrocycles, and the reactivity order in the O2-transfer reactions was the same as that observed in the aldehyde oxidation reactions.