Ligand Topology Effect on the Reactivity of a Non-heme Iron(IV)-oxo species and C-H Bond Activation Putative Iron(III)-O-IPh Adduct

Abstract

[Part I] Nonheme iron(IV)-oxo 종들의 반응성은 여러 가지 산화반응으로 연구 되어져왔다. 이러한 반응들을 통해, iron(IV)-oxo 종의 반응성은 축방향 배위자 (axial ligand) 또는 iron(IV)-oxo의 이온 스핀 상태 등등으로 인해 영향을 받음을 보여줬다. 본 연구에서는, 배위자(ligand)의 토폴로지(topology)에 따라 반응성의 효과에 대한 연구와 그로 인해 생성되는 생성물에 대한 연구를 진행하였다. 실험조건으로는 [Fe(BQCN)(CH3CN)2](ClO4)2와 [Fe(BQCN)(CH3CN)2](OTf)2을 이용하여, cis-α-[FeIV(O)(BQCN)]2+와 cis-β-[FeIV(O)(BQCN)]2+을 형성시킨 뒤, cumene, ethyl benzene, toluene과 반응 시킴으로써 나오는 생성물들을 비교해 보았다. [Part II] 많은 합성 모방체들을 가지고 있는 철산화종(IV) (oxoiron(IV))은 다양한 분광학적 실험 방법으로 특성화 되어 왔다. 그리고 이 종들의 반응성은 많은 산화반응을 통해 연구되었다. 본 논문에서는 nonheme 철산화종(IV)인 13-membrered marcrocyclic ligand를 가진 [FeIV(O)(13-TMC)]2+와 중간체의 생성 ([FeII(13-TMC)](OTf)2 and PhIO) 과 그 종에 대한 화학적 특성을 연구한 내용이다. 또한 중간체에 대한 반응성에 대한 연구하였다.;[Part I] A number of nonheme iron(IV)-oxo complexes have been synthesized and characterized with various spectroscopic methods and X-ray crystallography. Reactivities of the nonheme iron(IV)-oxo complexes have also been investigated intensively in various oxidation reactions. it has been shown that reactivities of the iron(IV)-oxo complexes are markedly affected by supporting and axial ligands, spin states of the iron(IV) ion, redox-inactive metal ions, and solvents. One important factor that determines reactivities of the iron catalysts is the ligand structure around the iron center. Therefore, iron complexes with various ligand types have been synthesized and used as catalysts in oxidation reactions. One notable example is that linear tetradentate N4 ligands can coordinate to an octahedral iron center in three different topologies, cis-α, cis-β, and trans forms. Since nonheme iron(IV)-oxo complexes have been considered as active oxidants in the oxidation of organic substrates but the topology effect on their reactivities has never been explored previously, we synthesized nonheme iron(II) complexes with two different topologies, cis-α- and cis-β-[FeII(BQCN)(CH3CN)2]2+, and their corresponding iron(IV)-oxo complexes. The effect of ligand topology on the reactivities of nonheme iron(IV)-oxo complexes was investigated in C-H bond activation and oxygen atom-transfer reactions; cis-α-[FeIV(O)(BQCN)]2+ was more reactive than cis-β-[FeIV(O)(BQCN)]2+ in the oxidation reactions. The reactivity difference between the cis-α and cis-β isomers of [FeIV(O)(BQCN)]2+ was rationalized with the FeIV/III redox potentials of the iron(IV)-oxo complexes: the FeIV/III redox potential of the cis-α isomer was 0.11 V higher than that of the cis-β isomer. [Part II] High-valent iron(IV)-oxo species have been implicated as the key reactive intermediates in the catalytic cycles of dioxygen activation . and also high-valent iron(IV)-oxo intermediates have been indenfied as the active species in selective biotransformations in heme and non heme enzymes. Such species have been characterized for heme enzymes such as cytochrome P450 and α-KG dioxygenase . Iodosylbenzene (PhIO) has been widely used as a terminal oxidant in metal-complex-catalyzed oxidation reactions. In this study, I have investigated the formation, characterization and reactivity of intermediate (1) which precedes the formation of [FeIV(O)(13-TMC)] 2+ (2).