Stereospecific alkane hydroxylation with H2O2 catalyzed by an iron(II)-tris(2-pyridylmethyl)amine complex
Stereospecific alkane hydroxylation with H2O2 catalyzed by an iron(II)-tris(2-pyridylmethyl)amine complex
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DOI：
10.1021/ja9642572
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发表时间：
1997-06-25
影响因子：
15
通讯作者：
Que, L
中科院分区：
文献类型：
--
作者：
Kim, C;Chen, K;Que, L
脂肪族CH键的立体特异性官能化是化学和生物化学的一个重要目标。 1 虽然这种转化可以通过有机过氧化物以化学计量方式进行，2 使用金属配合物和廉价且环保的氧化剂（例如 O2、H2O2）来催化进行此类反应的前景引起了人们对这些努力的极大兴趣。 3, 4 后者受到细胞色素 P450 等金属酶的启发，5 利用血红素中心进行催化。铁卟啉配合物可用作烃类立体定向羟基化的催化剂； 6 然而，卟啉对氧化自降解的敏感性以及通常需要昂贵的氧化剂（如 PhIO）限制了这种方法的实用性。 7 我们长期以来对氧活化非血红素铁酶（例如甲烷单加氧酶8）的兴趣促使我们努力使用非血红素铁复合物来催化这种化学反应。 9, 10 铁络合物与过氧化物的组合通常被认为提供哈伯-韦斯化学，11 产生羟基（或烷氧基）自由基，引发自由基链自氧化反应。 12, 13 在这些反应中，烷烃通常提供醇 (A) 和酮 (K) 产物，A/K 比率约为 1，而烯烃则主要产生烯丙型氧化产物。这种反应性模式似乎不适用于 [Fe (TPA)(CH3CN) 2]-(ClO4) 2 14 (1, TPA) tris (2-pyridylmethyl) amine) 与 H2O2 的组合。在此，我们报告了其反应性的详细信息，并提供了 [Fe (TPA)(OOH)] 2+ 中间体的证据。配合物 1 是一种低自旋六配位 Fe (II) 配合物。 14 在环己烷与 [Fe2O (TPA) 2 (H2O) 2] 4+(2) 和 tBuOOH 羟基化所用的注射泵条件下，10 0.7 mM 1 与 10 当量 H2O2 和 1000 当量环己烷在 CH3CN 中反应，得到 3.0 当量环己醇和 0.7 当量环己酮。 15分钟的过程（表1）；在Ar或空气中获得基本上相同的结果。该反应活性与 [Fe (TTP) Cl]/PhIO6e (TTPH2
The stereospecific functionalization of aliphatic CH bonds is an important goal for chemistry and biochemistry. 1 While such transformations can be carried out by organic peroxides in a stoichiometric fashion, 2 the prospect of using metal complexes and cheap and environmentally friendly oxidants (eg, O2, H2O2) to carry out such reactions catalytically has aroused considerable interest in these endeavors. 3, 4 The latter has been inspired by metalloenzymes such as cytochrome P450, 5 which utilize a heme center for catalysis. Iron porphyrin complexes can be used as catalysts for stereospecific hydroxylation of hydrocarbons; 6 however, the susceptibility of the porphyrin to oxidative self-degradation and the usual requirement for an expensive oxidant like PhIO have limited the utility of this approach. 7 Our long-standing interest in oxygen activating nonheme iron enzymes such as methane monooxygenase8 has stimulated our efforts to use nonheme iron complexes to catalyze this chemistry. 9, 10 The combination of an iron complex with peroxides is often considered to afford Haber-Weiss chemistry, 11 generating hydroxyl (or alkoxyl) radicals that initiate radical chain autoxidation reactions. 12, 13 In these reactions, alkanes typically afford alcohol (A) and ketone (K) products with an A/K ratio of about 1, while alkenes yield mostly allylic oxidation products. This pattern of reactivity does not appear to hold for the combination of [Fe (TPA)(CH3CN) 2]-(ClO4) 2 14 (1, TPA) tris (2-pyridylmethyl) amine) with H2O2.Herein, we report the details of its reactivity and present evidence for an [Fe (TPA)(OOH)] 2+ intermediate. Complex 1 is a low-spin six-coordinate Fe (II) complex. 14 Under the syringe pump conditions used for the hydroxylation of cyclohexane with [Fe2O (TPA) 2 (H2O) 2] 4+(2) and tBuOOH, 10 0.7 mM 1 reacts with 10 equiv of H2O2 and 1000 equiv of cyclohexane in CH3CN to afford 3.0 equiv of cyclohexanol and 0.7 equiv of cyclohexanone in the course of 15 min (Table 1); essentially the same results are obtained under Ar or in air. This reactivity is comparable to that of [Fe (TTP) Cl]/PhIO6e (TTPH2