FINAL REPORT For Japan-Korea Joint Research Project

Transcription

1 (Form4-2) FINAL REPRT For Japan-Korea Joint Research Project AREA 1. Mathematics & Physics 2. Chemistry & Material Science 3. Biology 4. Informatics & Mechatronics 5. Geo-Science & Space Science 6. Medical Science 7. Humanities & Social Sciences 1. Research Title: Biomimetics for 2 Activation: Metal-2 Chemistry 2. Term of Research: From July 1, 2010 To June 30, Total Budget a. Financial Support by JSPS: Total amount: 2,400 thousand yen 1 st Year 1,200 thousand yen 2 nd Year 800 thousand yen 3 rd Year 400 thousand yen b. ther Financial Support : Total amount: 0 thousand yen 4. Project rganization a. Japanese Principal Researcher Name Shunichi Fukuzumi Institution / Department Position, Department of Material and Life Science, Graduate School of Engineering Professor b. Korean Principal Researcher Name Jaeheung Cho Institution / Department Position, Department of Chemistry Assistant Professor 1

2 c. List of Japanese-side Participants (Except for Principal Researcher) Name Institution/Department Position Yusuke Yamada Associate Professor Tomoyoshi Suenobu Assistant Professor Kei hkubo Designated Associate Professor Yuma Morimoto Graduate Student d. List of Korean-side Participants (Except for Principal Researcher) Name Institution/Department Position Hye Yeon Kang Department of Chemistry and Nano Science, Graduate Student Jaeyoung Woo Department of Chemistry and Nano Science, Graduate Student 2

3 5. Number of Exchanges during the Final Fiscal Year* a. from Japan to Korea *Japanese fiscal year begins April 1. Name Home Institution Duration Host Institution Shunichi Fukuzumi June 30, 2012 Kei hkubo June 30, 2012 Total: 2 persons Total: 2 man-days Numbers of Exchanges during the Past Fiscal Years FY2010: Total 3 persons FY2011: Total 3 persons b. from Korea to Japan Name Home Institution Duration Host Institution none Total: 0 persons Total: 0 man-days Numbers of Exchanges during the Past Fiscal Years FY2010: Total 2 persons FY2011: Total 6 persons 3

4 6. bjective of Research The objective of this research is to clarify the "biological processes" of high-valent metal-oxygen species in the reactions of metalloenzymes through the biomimetic studies. The reactivity and mechanistic aspects of newly discovered metal-active oxygen species will be investigated in the biomimetic redox reactions, such as oxo-transfer, hydrogen atom abstraction, oxygenation, electron-transfer, and hydride-transfer reactions. In addition to the biomimetic processes, environmentally benign catalytic oxidation processes will also be investigated. Thus, the results obtained in studying biomimetic systems for dioxygen activation will not only unveil the chemistry of oxygenase enzymes but also create new technologies applicable to industrial oxidation processes. Cytochrome c oxidases (Ccs), with a bimetallic active-site consisting of a heme a and Cu (Fe a3 /Cu B ) are capable of catalyzing the four-electron reduction of dioxygen to water. Multicopper oxidases such as laccase can also activate dioxygen at a site containing a three-plus-one arrangement of four Cu atoms. Extensive efforts have been devoted to develop efficient catalysts for the four-electron reduction of dioxygen because of its great biological interest as well as technological significance such as in fuel cells. Electrocatalytic reduction of dioxygen has frequently been used to probe the catalytic reactivity of synthetic Cc model complexes and copper complexes by themselves have been reported to exhibit electroactivity for the four-electron reduction of dioxygen. In contrast to such heterogeneous systems, investigations on the catalytic reduction of dioxygen by metal complexes in homogeneous systems have provided deeper insight into the catalytic mechanism of the four-electron reduction of dioxygen by detecting reactive metal-dioxygen intermediates as well as by the information provided via detailed kinetics studies. With regard to copper-dioxygen intermediates, η 2 :η 2 -peroxo and bis-µ-oxo species have been extensively studied in reactions of low-valent metal complexes and dioxygen. However, even if the reaction of an η 2 :η 2 -peroxo species with a substrate (pathway (a) in Scheme 1) is followed, the reaction may undergo via the conversion to the bis-µ-oxo species, which may be much more reactive than the corresponding η 2 :η 2 -peroxo species (pathway (b) in Scheme 1). Thus, it has always been very difficult to clarify the actual reactive intermediate, which could be either the peroxo (pathway (a) in Scheme 1) or bis-µ-oxo species (pathway (b) in Scheme 1) in the reactions with substrates, unless the rate-determining step is the interconversion between them when the rate would be independent of concentrations of substrates. In these regards, the roles of the η 2 :η 2 -peroxo versus bis-µ-oxo species in the catalytic four-electron reduction of 2 have yet to be established. There has so far been no report on electron-transfer reactions of η 2 :η 2 -peroxo and bis-µ-oxo dicopper species. Cu II Cu II Cu III Cu III S (a) (b) S S ox 2Cu II or (Cu II ) 2 Scheme 1 S ox 4

5 7. Methodology A binuclear copper complex, [Cu II 2(N3)(H 2 ) 2 ](Cl 4 ) 4 [1; N3 = (-(CH 2 ) 3 -linked bis[(2-(2-pyridyl)ethyl)amine], and a mononuclear copper complex, [Cu II (BzPY1)(EtH)](Cl 4 ) 2 [2; BzPY1 = N,N-bis[2-(2-pyridyl)-ethyl]benzylamine], efficiently catalyze the four-electron reduction of 2 by decamethylferrocene (Fc * ) in the presence of trifluoroacetic acid (TFA) in acetone at 298 K. The spectroscopic detection of the intermediate and the dynamics reveal that the catalytic four-electron reduction of 2 by Fc * with 1 occurs via electron transfer from Fc * to 1, followed by the reaction of the resulting dicopper(i) complex with 2 to afford a η 2 :η 2 -peroxo intermediate (3), which is further reduced by electron transfer from Fc *. Alternatively a possible interconversion to a bis-µ-oxo dicopper(iii) species may occur, followed by fast electron-transfer reduction by Fc *. Electron-transfer reactions of ferrocene derivatives are known to occur via an outer-sphere pathway, in which the activation entropy is close to zero. If electron transfer from ferrocene derivatives to 3 proceeds directly via pathway (a) in Scheme 1, the activation entropy should be the same as electron transfer from ferrocene derivatives to 1. Thus, comparison of the activation entropies of electron transfer from ferrocene derivatives to 3 with those of the electron transfer to 1 provides a unique opportunity to distinguish between pathways (a) and (b) in Scheme 1. In the case of [Cu II (BzPY1)(EtH)](Cl 4 ) 2 (2), the catalytic four-electron reduction of 2 by Fc * comes about by reduction of 2, followed by the reaction of the resulting Cu(I) complex with 2 to afford a bis-µ-oxo dicopper(iii) species, which here is in fact the key intermediate, reduced by fast electron transfer from Fc *. 5