An Osmium(III)/Osmium(V) Redox Couple Generating OsV(O)(OH) Center for cis-1,2-Dihydroxylation of Alkenes with H2O2: Os Complex with a Nitrogen-Based Tetradenta

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• 作者：Hideki Sugimoto ; Kazuhiro Kitayama ; Seiji Mori ; Shinobu Itoh
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：November 21, 2012
• 年：2012
• 卷：134
• 期：46
• 页码：19270-19280
• 全文大小：542K
• 年卷期：v.134,no.46(November 21, 2012)
• ISSN：1520-5126

文摘

For the synthesis of the 1,2-diols, cis-1,2-dihydroxylation of alkenes catalyzed by osmium(VIII) tetroxide (OsO₄) is a powerful method. However, OsO₄ is quite toxic due to its highly volatile and sublimable nature. Thus, the development of alternative catalysts for cis-1,2-dihydroxylation of alkenes is highly challenging. Our approach involves the use of a nitrogen-based tetradentate ligand, tris(2-pyridylmethyl)amine (tpa), for an osmium center to develop a new osmium catalyst and hydrogen peroxide (H₂O₂) as a cheap and environmentally benign oxidant. The new Os鈥搕pa complex acts as a very efficient turnover catalyst for syn-selective dihydroxylation of various alkenes (turnover number 1000) in aqueous media, and H₂O₂ oxidant is formally incorporated into the products quantitatively (100% atom efficiency). The reaction intermediates involved in the catalytic cycle have been isolated and characterized crystallographically as [Os^III(OH)(H₂O)(tpa)]²⁺ and [Os^V(O)(OH)(tpa)]²⁺ complexes. The observed syn-selectivity, structural characteristics of the intermediates, and kinetic studies have suggested a concerted [3 + 2]-cycloaddition mechanism between [Os^V(O)(OH)(tpa)]²⁺ and alkenes, which is strongly supported by DFT calculations.