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 Tetradentate Ligand
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 Tetradentate Ligand
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DOI：
10.1021/ja309566c
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发表时间：
2012-11-21
影响因子：
15
通讯作者：
Itoh, Shinobu
中科院分区：
文献类型：
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作者：
Sugimoto, Hideki;Kitayama, Kazuhiro;Itoh, Shinobu
四氧化锇催化的烯烃顺式-1，2-二羟基化反应是合成1，2-二醇的有效方法。然而，OsO 4由于其高度挥发性和可升华性而具有相当大的毒性。因此，开发用于烯烃的顺式-1，2-二羟基化的替代催化剂是非常具有挑战性的。我们的方法涉及使用氮基四齿配体，三（2-吡啶基甲基）胺（TPA），锇中心开发一种新的锇催化剂和过氧化氢（H2 O2）作为一种廉价和环境友好的氧化剂。新的Os tpa配合物作为一个非常有效的周转催化剂的顺式选择性二羟基化的各种烯烃（周转数类似于4000）在水介质中，和H2 O2氧化剂正式纳入产品定量（100%原子效率）。参与催化循环的反应中间体已被分离和晶体学表征为[Os-III（OH）（H2O）（tpa）]（2+）和[Os-V（O）（OH）（tpa）]（2+）配合物。实验结果表明，[Os-V（O）（OH）（tpa）]（2+）与烯烃之间存在[3 + 2]-协同环化反应机理。
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 tpa complex acts as a very efficient turnover catalyst for syn-selective dihydroxylation of various alkenes (turnover number similar to 4000) 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]-cycloacldition mechanism between [Os-V(O)(OH)(tpa)](2+) and alkenes, which is strongly supported by DFT calculations.