Aldehyde Deformylation by Nonheme Manganese(Ⅲ)-Peroxo Intermediates

Abstract

Mononuclear metal complex는 최근 oxidation catalyst로써의 metal complex와 biological system에서 oxygen activating biomolecule의 반응 메커니즘을 이해하기 위한 흥미로운 연구이다. Nonheme iron enzyme에서, ferric-peroxo종은 Rieske dioxygenase에 의한 aromatic 화합물의 cis-dihydroxylation 반응으로써 나타났다. 본 연구에서는 macrocyclic tetradentate N4 리간드 TMC (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)를 사용하여 side-on peroxo의 Mn(TMC) intermediate를 생성시킴으로써 그 특성과 반응성을 연구했다. Side-on peroxo Mn(Ⅲ)종은 UV-vis spectrophotometer, electron paramagnetic resonance, electrospray ionization mass spectrometer의 다양한 분광학적 방법을 통해 특성화된다. Side-on peroxo Mn(Ⅲ)종은 ESI-MS에서 (m/z) 343.1을 나타내며, 이것은 [Mn^(Ⅲ)(η-O₂)(TMC)]^(+)의 isotope distribution pattern과 일치한다 (calculated m/z 343). 또한 ^(18)○ 실험을 통해(^(18)○-labeled hydrogen peroxide) m/z 347.1로 치환됨을 확인하였다. [Mn^(Ⅲ)(η-O₂)(TMC)]^(+) intermediate의 X-ray crystal 구조는 Manganese와 dioxygen의 공유 결합을 보여준다 (○-○ : 1.404 Å, Mn-O : 1.884 Å). Mn(Ⅱ) complex에 의한 aldehyde oxidation은 side-on Mn(III) peroxo complex의 aldehyde oxidation 메커니즘을 이해하기 위해 시도되었다.;Mononuclear metal complexes are recent interest for understanding the reaction mechanisms of oxygen activating biomolecules in biological systems and utilizing metal complexes as oxidation catalyst. In nonheme iron enzymes, ferric-peroxo species has been proposed as an active oxidant responsible for the cis-dihydroylation of aromatic compounds catalyzed by Rieske dioxygenases. We have reported the characterization and reactivity of a mononuclear Mn peroxo complex, bearing a macrocyclic tetradentate N4 ligand, TMC (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) were studied by side-on peroxo Mn(TMC) intermediate. The side-on peroxo Mn(Ⅲ) species are characterized with various spectroscopic techniques such as UV-vis spectrophotometer, electron paramagnetic resonance, and electrospray ionization mass spectrometer. The electrospray ionization mass spectrum (ESI-MS) of side-on peroxo Mn(Ⅲ) species exhibited a prominent ion at a mass-to-charge ratio (m/z) of 343.1, with mass and isotope distribution pattern corresponding to [Mn^(Ⅲ)(η-O₂)(TMC)]^(+) (calculated m/z of 343). The mass peak at 347.1 up-shifted accordingly upon introduction of ^(18)○ (^(18)○-labeled hydrogen peroxide used). The X-ray crystal structure of [Mn^(Ⅲ)(η-O₂)(TMC)]^(+) intermediate reveals a coordination of Mn with dioxygen, with a 1.404 Å distance of ○-○ and 1.884 Å distance of Mn-O. A catalytic aldehyde oxidation by Mn(Ⅱ) complex was demonstrated to understand mechanisms of the aldehyde oxidation by side-on Mn(Ⅲ) peroxo complex.