Modeling Rieske dioxygenases:: The first example of iron-catalyzed asymmetric cis-dihydroxylation of olefins
Modeling Rieske dioxygenases:: The first example of iron-catalyzed asymmetric cis-dihydroxylation of olefins
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DOI：
10.1021/ja015601k
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发表时间：
2001-07-11
影响因子：
15
通讯作者：
Que, L
中科院分区：
文献类型：
--
作者：
Costas, M;Tipton, AK;Que, L
Rieske双加氧酶是催化芳烃和烯烃双键的O2依赖性对映选择性顺式二羟基化的细菌酶。1这些酶利用单核非血红素铁中心与2-组氨酸-1-羧酸面部三联体基序配位，留下至少两个可用于催化的不稳定位点。2，3迄今为止，金属中心在酶机制中的作用还没有很好地建立，但最近报道的合成铁络合物，可以催化烯烃与H2 O2的顺式二羟基化，证明了单核铁活性位点的关键作用。4因此，我们开始努力开发合成催化剂，将这种化学模拟为传统重金属试剂（如OsO 4和RuO 4-）的潜在“绿色”替代品，这些试剂有效但由于其毒性而不太理想。我们通过用基于手性二胺骨架的线性四齿配体替换三足四齿配体来扩展这种化学（图1）。5在这篇报道中，我们首次证明了铁配合物催化的烯烃顺式-二羟基化反应。使用基于乙二胺骨架的配体是金属催化氧化反应中手性诱导的既定策略。6因此，我们首先探索了BPMEN配体框架形成能够催化烯烃顺式二羟基化的铁络合物的能力。为此，测试配合物[Fe-（BPMEN）（MeCN）2]（ClO 4）2（1）7和6-甲基取代的[Fe-（6-Me 2-BPMEN）（CF 3SO 3）2]（2）作为催化剂。在由1催化的反应中，通过注射泵将10当量的H2 O2加入到具有0.7M环辛烯的0.7mM络合物的乙腈溶液中，得到环辛烯氧化物和顺式二醇，相对于H2 O2的产率分别为75%和9%（表1）。因此，1是烯烃环氧化的优良催化剂。与此形成鲜明对比的是，2在相同条件下分别以15%和64%的产率得到环氧化物和顺式二醇。因此，如先前在Fe（TPA）催化剂中观察到的，4引入6-甲基-N-（2-甲基苯基）-2-甲基-N-（2-甲基苯基）
Rieske dioxygenases are bacterial enzymes that catalyze the O2-dependent enantioselective cis-dihydroxylation of arene and olefin double bonds. 1 These enzymes utilize a mononuclear nonheme iron center coordinated to a 2-histidine-1-carboxylate facial triad motif that leaves at least two labile sites available for catalysis. 2, 3 To date, the role of the metal center in the enzyme mechanism is not well established, but the recent report of a synthetic iron complex that can catalyze cis-dihydroxylation of olefins with H2O2 demonstrates a key role for the mononuclear iron active site. 4 We have thus embarked on an effort to develop synthetic catalysts that model this chemistry as a potential “green” alternative to traditional heavy metal reagents such as OsO4 and RuO4-, which are effective but less desirable due to their toxicity. We have extended this chemistry by replacing the tripodal tetradentate ligand with a linear tetradentate ligand based on a chiral diamine backbone (Figure 1). 5 In this report, we demonstrate the first enantioselective olefin cis-dihydroxylations catalyzed by an iron complex.The use of ligands based on an ethylenediamine backbone is an established strategy for chiral induction in metal-catalyzed oxidations. 6 We thus first explored the ability of the BPMEN ligand framework to form iron complexes capable of catalyzing olefin cis-dihydroxylation. To this end, the complexes [Fe-(BPMEN)(MeCN) 2](ClO4) 2 (1) 7 and the 6-methyl substituted [Fe-(6-Me2-BPMEN)(CF3SO3) 2](2) were tested as catalysts. In the reaction catalyzed by 1, addition via syringe pump of 10 equivalents of H2O2 to a 0.7 mM solution of the complex in acetonitrile with 0.7 M in cyclooctene afforded cyclooctene oxide and the cis-diol in respective yields of 75 and 9% relative to H2O2 (Table 1). Thus, 1 is an excellent catalyst for olefin epoxidation. In sharp contrast, 2 under the same conditions afforded epoxide and cis-diol in respective yields of 15 and 64%. Thus, as observed earlier in the Fe (TPA) catalysts, 4 the introduction of the 6-methyl