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Reaction of iron porphyrin complexes as biomimetic models for cytochrome P-450 원문보기

  • 저자

    오소영

  • 학위수여기관

    이화여자대학교 대학원

  • 학위구분

    국내석사

  • 학과

    분자생명과학부

  • 지도교수

  • 발행년도

    2000

  • 총페이지

    vi, 61 p.

  • 키워드

  • 언어

    kor

  • 원문 URL

    http://www.riss.kr/link?id=T8952147&outLink=K  

  • 초록

    Aprotic 용매에서 iron(III) porphyrin complexes와 tert-alkylhydroperoxides에 의한 탄화수소의 산화 반응을 진행할 때 대부분 tert-alkylhydroperoxides의 O-O결합이 균일하게 (알콕시 라디칼에 의한 반응) 분리된다고 발표되어 왔다.1-3 우리는 전기 음성적으로 치환된 Fe(TFT₄TMAP)(CF₃SO₃)5(meso-tetrakis(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-aniliniumyl)porphyrinato)iron(III)의 존재하에서 tert-alkyl hydroperoxides 즉 tert-butylhydroperoxide (t-BuOOH)와 2-methyl-1-phenyl-2-propylhydroperoxide (MPPH)를 사용하여 aprotic 용매인 CH₃CN에서 올레핀의 에폭시 반응을 시도하였다. 우리는 처음으로 aprotic 용매에서 tert-alkylhydroperoxides를 사용하여 라디칼이 관여하지 않은 에폭시 반응을 보여준다. 이 반응은 온도에 민감하게 영향을 받는 것을 관찰하였다. 낮은 온도일 때 높은 수율의 에폭사이드 생성물과 소량의 알코올과 케톤을 얻었으며 이는 라디칼이 관여하는 반응임을 배제할 수 있다. 반면 온도가 높아질 수록 라디칼 반응으로 나오는 allylic 생성물의 양이 많아짐을 보았다. 즉 온도에 따라 각기 다른 중간체가 존재하는 메커니즘을 가지고 있음을 추정할 수 있다. 저온에서 라디칼이 관여하지 않는 반응임을 확인하기 위하여 입체 특이성을 살펴 보았다. cis-stilbene을 사용하여 저온에서 에폭시 반응을 수행하였을 때 입체 특이성이 유지됨을 보였다. 이는 라디칼에 의한 Fenton-type의 반응이 아니라 이전자 산화 반응임을 증명해 주는 결과이다. 저온에서 예상할 수 있는 반응 중간체 Fe(III)-OOR과 (Porp)+. FeIV=O 종 중 어느 것이 중간체로 작용했는지 확인하기 위하여 cis-, trans-stilbene을 사용하여 경쟁반응을 시도하여 에폭시 반응의 중간체는 (Porp)+. FeIV=O 임을 밝혔다. 또한 18O이 포함된 물을 사용하여 실온에서의 반응 중간체를 추정하여 보았다. 실온에서의 주생성물인 t-BuOOH로부터의 alcohol과 MPPH로부터의 benzyl alcohol에 18O이 포함되어 있는 것으로 반응 중간체는 oxoiron(IV) porphyrin 임을 확인하였다.


    The reactions of iron(III) complexes of porphyrin and non-porphyrin ligands with alkyl hydroperoxides have been extensIVely studied as biomimetic models for heme- and nonheme-containing enzymes, with the intention of understanding the mechanism of O-O bond cleavage of alkyl hydroperoxides and developing radical-free (enzyme mimetic) oxidation reactions. It has been shown in a number of reports that oxidation of hydrocarbons by iron(III) porphyrin complexes and tert-alkyl hydroperoxides proceeds via O-O bond homolysis (i.e., free alkoxyl radical chemistry) in aprotic solvents. In addition, Ingold and co-workers evidenced, using 2-methyl-1-phenyl-2-propyl hydroperoxide (MPPH) as a mechanistic probe to distinguish between free alkoxyl radical chemistry and radical-free chemistry, that O-O bond homolysis is a predominant pathway in non-porphyrin iron complex-catalyzed oxidation of hydrocarbons by tert-alkyl hydroperoxides. Despite the intensIVe study for the last two decades, it has been rarely observed that simple iron complexes of porphyrin and non-porphyrin ligands are able to catalyze the oxidation of hydrocarbons by alkyl hydroperoxides via radical-free chemistry in aprotic solvents. Since we found recently that a highly electron-deficient iron(III) porphyrin complex, Fe(TF₄TMAP)(CF₃O₃)5 [TF₄TMAP = meso-tetrakis(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-aniliniumyl)porphinato dianion], catalyzes the epoxidation and hydroxylation of hydrocarbons by H₂O₂ via radical-free oxidation reactions in aprotic solvent, we therefore attempted the epoxidation of olefins with the iron porphyrin complex and tert-alkyl hydroperoxides such as tert-butyl hydroperoxide (t-BuOOH) and MPPH in CH₃CN. In the present study, we report that the epoxidation reactions were markedly influenced by reaction temperature and high yields of epoxide products with the retention of stereospecificity were obtained at low temperature. The reactions of iron(III) porphyrin complexes with various oxidants such as peroxyacids and hydroperoxides have been extensIVely studied for the past two decades, with the intention of elucidating the mechanisms of O-O bond actIVation and developing biomimetic oxygenation reactions. Since hydrogen peroxide (H₂O₂) is a biologically important and environmentally clean oxidant, use of the oxidant in catalytic oxygenation of hydrocarbons by iron porphyrin complexes has attracted much attention in the communities of bioinorganic and oxidation chemistry. Traylor et al. reported for the first time that the reactions of iron porphyrins with H₂O₂ in protic solvent such as CH₃OH generate oxoiron(IV) porphyrin cation radical complexes that epoxidize olefins to gIVe the corresponding oxide products. We and Mansuy et al. also showed recently that highly electron-deficient iron porphyrin complexes react with H₂O₂ to form intermediates that are capable of oxygenating olefins and unactIVated alkanes in aprotic solvent. Another oxidant that has been widely used in the mechanistic studies of O-O bond actIVation by iron(III) porphyrin complexes is peracids such as m-chloroperoxybenzoic acid (m-CPBA). It has been generally believed that iron porphyrins react with peracids to form high-valent iron(IV)oxo cation radical via O-O bond heterolysis in polar solvent such as CH₂CI₂. As far as we have been able to discern, there is no report that shows that both heterolysis and homolysis can occur concurrently in the m-CPBA reactions in polar solvent. In the present study, we report two novel results that were obtained using an electron-deficient iron(III) porphyrin complex containing different anionic axial ligands. Those are the remarkable anionic axial ligand effects on (1) the catalytic epoxidation and hydroxylation of hydrocarbons by aqueous 30% H₂O₂ in aprotic solvent and (2) the formation of two distinct oxoiron(IV) porphyrin intermeidates in m-CPBA reactions in polar solvent.


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