Catalytic Reduction of Dioxygen to Water with a Monomeric Manganese Complex at Room Temperature

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• 作者：Ryan L. Shook ; Sonja M. Peterson ; John Greaves ; Curtis Moore ; Arnold L. Rheingold ; A. S. Borovik
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：April 20, 2011
• 年：2011
• 卷：133
• 期：15
• 页码：5810-5817
• 全文大小：921K
• 年卷期：v.133,no.15(April 20, 2011)
• ISSN：1520-5126

文摘

There have been numerous efforts to incorporate dioxygen into chemical processes because of its economic and environmental benefits. The conversion of dioxygen to water is one such example, having importance in both biology and fuel cell technology. Metals or metal complexes are usually necessary to promote this type of reaction and several systems have been reported. However, mechanistic insights into this conversion are still lacking, especially the detection of intermediates. Reported herein is the first example of a monomeric manganese(II) complex that can catalytically convert dioxygen to water. The complex contains a tripodal ligand with two urea groups and one carboxyamidopyridyl unit; this ligand creates an intramolecular hydrogen-bonding network within the secondary coordination sphere that aids in the observed chemistry. The manganese(II) complex is five-coordinate with an N₄O primary coordination sphere; the oxygen donor comes from the deprotonated carboxyamido moiety. Two key intermediates were detected and characterized: a peroxo鈭抦anganese(III) species and a hybrid oxo/hydroxo鈭抦anganese(III) species (1). The formulation of 1 was based on spectroscopic and analytical data, including an X-ray diffraction analysis. Reactivity studies showed dioxygen was catalytically converted to water in the presence of reductants, such as diphenylhydrazine and hydrazine. Water was confirmed as a product in greater than 90% yield. A mechanism was proposed that is consistent with the spectroscopy and product distribution, in which the carboxyamido group switches between a coordinated ligand and a basic site to scavenge protons produced during the catalytic cycle. These results highlight the importance of incorporating intramolecular functional groups within the secondary coordination sphere of metal-containing catalysts.