Versatile Reactivities of Non-heme Manganese(II) Complexes in Catalytic Oxidation Reactions and C-H Activation Reactions of Iodosylbenzene

Abstract

Non-heme Manganese(Ⅱ) 종 화합물은 iodosylbenzene에 의한 올레핀의 에폭시화 반응과 peracetic acid에 의한 올레핀, 알코올 등의 산화반응에 효과적인 촉매 반응성을 보인다. 이러한 산화 반응에는 금속촉매가 연계된 산화제가 관여하는 메커니즘이 진행된다고 여겨진다. 본 연구에서는 여러 가지 산화제와 기질을 사용하여 non-heme 리간드를 포함한 Manganese(II) 종 특히, Mn(BQEN)(CF₃SO₃)₂ 라는 새로운 화합물의 특성 규명 및 Mn(BQEN)(CF₃SO₃)₂ 를 사용한 올레핀 에폭시화 반응, 알코올의 산화 반응에 대한 실험을 진행하였다. 또한, 새로운 화합물인 Mn(BQEN)(CF₃SO₃)₂ 의 반응성을 기존에 있던 Mn(BPMEN)(CF₃SO₃)₂ 와 Mn(BPMCN)(CF₃SO₃)₂ 화합물의 반응성과 각각 비교해 보았다. 그 결과 지금까지 진행된 단핵종 Non-heme Manganese(Ⅱ) 화합물을 사용한 특정 기질의 경쟁적 산화반응의 결과와는 다른 새로운 결과를 도출 해 내었으며 그 메커니즘에 대한 심층적 연구가 진행 중 이다. Part. Ⅱ Iodosylbenzene의 반응성에 대한 실험적 연구와 이론적 연구의 조합은 iodosylbenzene이 그 자체로 hydrocarbon의 약한 C-H 결합을 활성화시켜 수소 원자 분리 반응(H-atom abstraction)을 진행 할 수 있음을 보여준다.;A non-heme manganese(II) complex shows a high catalytic activity in the epoxidation of olefins by iodosyl benzene and in the oxidation of olefins, alcohols and alkanes by peracetic acid; a mechanism involving metal-based oxidants is proposed for the oxidation reactions. Metal-catalyzed oxygenations of organic substrates are of significant importance in both synthetic chemistry and industrial processes. Since metalloenzymes catalyze the oxygenation reactions with high regio- and stereoselectivity under mild conditions, biomimetic oxygenation reactions using their model compounds have attracted much attention in the communities of bioinorganic and oxidation chemistry. For example, it has been demonstrated that synthetic iron complexes of heme and non-heme ligands are capable of mimicking the chemistry of cytochrome P450 (CYP450) and non-heme iron enzymes, respectively, and that the oxygenation reactions by the model compounds proceed via a mechanism involving metal-based oxidants (e.g., high-valent ironoxo intermediates). Similarly, manganese porphyrins have been extensively investigated as chemical models of CYP 450 in various oxygenation reactions. Manganese complexes bearing non-heme ligands, such as salen- and tacn-derived ligands, have shown promise as versatile catalysts in olefin epoxidation and alkane hydroxylation. Very recently, Stack and co-workers8 reported a highly efficient epoxidation reaction using peracetic acid as the terminal oxidant, in which terminal olefins are epoxidized to the corresponding epoxides in the presence of non-heme Mn(II)catalysts (e.g., Mn(BPMEN)(CF₃SO₃)₂ and Mn(BPMCN)(CF₃SO₃)₂). We now report a mononuclear non-heme manganese complex, Mn(BQEN)(CF₃SO₃)₂ (1), that shows a high catalyticactivity and stereo- and regioselectivity in the oxidation of olefins, alcohols and alkanes under mild conditions.