cis-Dihydroxylation of Alkenes with Oxone Catalyzed by Iron Complexes of a Macrocyclic Tetraaza Ligand and Reaction Mechanism by ESI-MS Spectrometry and DFT Calculations
cis-Dihydroxylation of Alkenes with Oxone Catalyzed by Iron Complexes of a Macrocyclic Tetraaza Ligand and Reaction Mechanism by ESI-MS Spectrometry and DFT Calculations
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DOI：
10.1021/ja100967g
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发表时间：
2010-09-29
影响因子：
15
通讯作者：
Che, Chi-Ming
中科院分区：
文献类型：
--
作者：
Chow, Toby Wai-Shan;Wong, Ella Lai-Ming;Che, Chi-Ming
[Fe-III（L-N4 Me 2）Cl-2]（1，L-N4 Me 2 = N，N-二甲基-2，11-二氮杂[3.3]（2，6）吡啶并吡喃）是一种催化剂，可用于在室温下以过硫酸氢钾为底物，催化烯烃的顺式二羟基化反应。在0.7或3.5摩尔%的1存在下，富电子烯烃（包括环辛烯、苯乙烯和直链烯烃）与过硫酸氢钾（2当量）反应5分钟，导致高达>99%的底物转化率，并以高达67%的产率提供顺式二醇产物，顺式二醇/环氧化物摩尔比高达16.8：1。对于缺电子烯烃，包括α，β-不饱和酯和α，β-不饱和酮，它们与过硫酸氢钾（2当量）在1（3.5摩尔%）催化下反应5分钟，以高达99%的产率和高达>99%的底物转化率得到顺式二醇。肉桂酸甲酯（9.7 g）与过硫酸氢钾（1当量）的大规模顺式-二羟基化得到顺式-二醇产物（8.4 g），产率为84%，底物转化率为85%。催化后脱金属释放的L-N_4 Me_2配体可与新加入的Fe（ClO_4）（2）中心点4 H（2）O反应，原位生成铁催化剂，可用于催化烯烃顺式二羟基化反应的重新启动。对富马酸二甲酯与过硫酸氢钾的顺式二羟基化反应进行了电喷雾质谱、同位素标记和密度泛函理论研究，发现反应中可能存在顺式HO Fe-v=O和/或顺式O =Fe-v=O物种;涉及顺式-HOFe-v =O和顺式-O =Fe-v=O物质的顺式-二羟基化反应均通过协调但高度异步的机理进行，其中涉及顺式-HO Fe-v=O的更有利，这是由于较小的活化势垒。
[Fe-III(L-N4Me2)Cl-2](1, L-N4Me2 = N,N-dimethyl-2,11-diaza[3.3](2,6)pyridinophane) is an active catalyst for cis-dihydroxylation of various types of alkenes with oxone at room temperature using limiting amounts of alkene substrates. In the presence of 0.7 or 3.5 mol % of 1, reactions of electron-rich alkenes, including cyclooctene, styrenes, and linear alkenes, with oxone (2 equiv) for 5 min resulted in up to >99% substrate conversion and afforded cis-diol products in up to 67% yield, with cis-diol/epoxide molar ratio of up to 16.8:1. For electron-deficient alkenes including alpha,beta-unsaturated esters and alpha,beta-unsaturated ketones, their reactions with oxone (2 equiv) catalyzed by 1 (3.5 mol %) for 5 min afforded cis-diols in up to 99% yield with up to >99% substrate conversion. A large-scale cis-dihydroxylation of methyl cinnamate (9.7 g) with oxone (1 equiv) afforded the cis-diol product (8.4 g) in 84% yield with 85% substrate conversion. After catalysis, the L-N4Me2 ligand released due to demetalation can be reused to react with newly added Fe(CIO4)(2)center dot 4H(2)O to generate an iron catalyst in situ, which could be used to restart the catalytic alkene cis-dihYdroxylation. Mechanistic studies by ESI-MS, isotope labeling studies, and DFT calculations on the 1-catalyzed cis-dihydroxylation of dimethyl fumarate with oxone reveal possible involvement of cis-HO Fe-v=O and/or cis-O=Fe-v=O species in the reaction; the cis-dihydroxylation reactions involving cis-HO Fe-v=O and cis-O=Fe-v=O species both proceed by a concerted but highly asynchronous mechanism, with that involving cis-HO Fe-v=O being more favorable due to a smaller activation barrier.