Mechanistic Study on Non-Heme Iron Catalyzed Chlorine Dioxide Generation and O-O Bond Cleavage and O₂Transfer Reaction Possibilities of Mononuclear Metal-O₂Complexes

Abstract

Part I The chlorine oxyanions (ClOn-, n = 1 - 4) spanning oxidation states of +1 to +7 have found various uses from oxidizers in rocket fuels to bleaching agents. Of chlorine oxyanions used for chlorine dioxide (ClO2) production, Chlorate (ClO3-) is the common source. The primary commercial use of ClO2 is as an oxidizing agent for pulp bleaching, water disinfection and treatment. However, because of the fault with instability of ClO2, it is necessary for on-site production of ClO2 for practical application. We have reported that non-heme manganese catalysts offer a new method for the preparation of pure chlorine dioxide for on-site use. In this work, we studied the reaction of non-heme iron complex, [FeIII(TAML)]-, with sodium chlorite in acetate buffer solution by spectroscopic methods. As the results, chlorine dioxide was produced in a good yield in the reaction of [FeIII(TAML)]- complex with sodium chlorite and we found that the yield and rate of conversion from chlorite to chlorine dioxide by [FeIII(TAML)]- complex is much greater than that obtained from manganese non-heme catalysts. Part II Metalloenzymes activate dioxygen (O2) to carry out a diversity of biological reactions, including biotransformation of naturally occurring molecules, oxidative metabolism of xenobiotics, and oxidative phosphorylation. The dioxygen activation at the catalytic sites of the enzymes such as cytochrome P450 and dioxygenases, occurs through several steps, such as the binding of O2 at a reduced metal center, the generation of metal-superoxo and-peroxo species, and the O-O bond cleavage of metal-hydroperoxo species to form high-valent metal-oxo species which are further used as a strong oxidant in biological oxidative transformation of organic substrates. Thus, it is of importance to understand the factors determining the O-O bond cleavage vs O2 transfer processes after the formation of the dinuclear metal-peroxo bridging intermediates. To investigate the mechanistic pathways of O-O bond cleavage, O2-transfer processes and elucidate the factors determining one process from the other, we first synthesized and isolated a number of transition metal complexes bearing TMC ligand such as [M(O2)(n-TMC)]+ (M = Cr, Mn, Fe, Co, Ni ; n = 12, 14) and TAML ligand such as [M(O2)(TAML)]2- (M = Mn, Fe) according to the reported procedure. We performed the intermolecular O2-transfer reactions from [M(O2)(n-TMC)]+ intermediates to [M(TAML)]- and reverse reactions (e.g., from [M(O2)(TAML)]2- to [M(n-TMC)]2+) were also undertaken. In case of the reaction between [M(O2)(n-TMC)]+ (M = Cr, Mn, Fe, Co ; n = 14) and [M(TAML)]-, the O-O bond cleavage reactions were observed and metal-oxo or metal-hydroxo species have been detected whereas [Ni(O2)(n-TMC)]+ transferred peroxo moiety to [M(TAML)]-, thereby generating [M(O2)(TAML)]2- intermediates. To rationalize these contrasting observations, DFT-calculations will carry out to understand factors controlling these results.;생체 내에 존재하는 산소화 효소는 화학반응을 통하여 산소 분자를 물 분자로 환원시킴과 동시에 에너지를 생성하며, 또한 생명체가 필요로 하는 유기물을 합성하면서 생명을 유지한다. 이러한 산소화 효소의 화학반응에 관여하는 중간체 및 메커니즘에 대한 연구는 전 세계의 우수한 연구진에 의하여 활발히 진행되고 있으며, 효소 반응을 모방하는 모델 화합물을 이용한 촉매 시스템 개발이 중요한 분야로 각광을 받고 있다. 본 연구 1장에서는 마일드한 조건에서 비헴성 철 화합물을 촉매로 사용하여 아연소산 염과 반응을 하여 이산화 염소를 생성하였다. 이 결과는 이전에 보고된 비헴성 망간 화합물을 촉매로 사용하여 이산화 염 소를 생성시킨 논문과 비교하였을 때 아연소산 염에서 이산화염소로의 전환율 또한 높게 나왔으며 반응 시간 또한 짧게 걸린 것을 알 수 있었다. 현재 비헴성 철 화합물과 아연소산 염과의 반응의 정확한 메커니즘을 규명하기 위해 키네틱 모델링 연구가 진행 중에 있다. 본 연구 2장에서는 일련의 전이금속과 거대고리 배위자(n-TMC: n = 12, 14)를 사용하여 금속-활성산소(M-O2: M = 크로뮴, 망간, 철, 코발트, 니켈)화합물을 얻었다. 또한 TAML 배위자를 사용하여 금속-슈퍼옥소, -퍼옥소 화합물을 얻었다. 금속-활성산소(M-O2: M = 크로뮴, 망간, 철, 코발트, 니켈)화합물에 금속-TAML(M = 망간, 철) 화합물을 반응하여 산소-산소 결합 분해 반응 또는 산소 전달 반응 가능성에 대하여 알아보았다.