ALKANE FUNCTIONALIZATION AT NONHEME IRON CENTERS - STOICHIOMETRIC TRANSFER OF METAL-BOUND LIGANDS TO ALKANE
ALKANE FUNCTIONALIZATION AT NONHEME IRON CENTERS - STOICHIOMETRIC TRANSFER OF METAL-BOUND LIGANDS TO ALKANE
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DOI：
10.1021/ja00077a035
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发表时间：
1993-12-01
影响因子：
15
通讯作者：
QUE, L
中科院分区：
文献类型：
--
作者：
KOJIMA, T;LEISING, RA;QUE, L
合成了一系列[Fe（III）X2 L]+配合物（L = TPA，三（2-吡啶甲基）胺，或NTB*，三（N-乙基苯并咪唑-2-甲基）胺; X = Br，Cl，或N3），并研究了它们在室温下活化烷基氢过氧化物用于烷烃官能化的能力。测定了[FeCl 2（TPA）] ClO 4（2）和[Fe 2-OCl 2（TPA）2]（ClO 4）2（6）的晶体结构，而其他配合物则通过可见光谱和核磁共振光谱进行了表征。在环己烷存在下，用化学计量的烷基过氧化氢处理单核络合物，以良好的产率得到卤代环己烷。溴代和叠氮基环己烷的生产与单核催化剂的特征LMCT谱带的消失相关，所述特征LMCT谱带被转化成催化惰性的（μ-氧代）二铁物种。当烷基过氧化氢过量时，卤代烷的产率可达100%（以络合物计），但过量卤化物的加入对卤代烷的产率没有影响。卤代烷烃的形成被抑制的存在下的二甲基硫醚（形成DMSO），但不受影响的4-甲基-2，6-二叔丁基苯酚的加入，表明参与的反应机制中的两个电子的氧化剂。环己烷和金刚烷官能化的催化剂的选择性显着影响的三脚架配体和结合的卤化物的性质，但不是由氢过氧化物上的烷基。因此，我们提出活性物种为[O=Fe（L）（X）]2+，其可能与Fe 2 O（TPA）2（ClO 4）4与H2 O2反应产生的瞬态中间体有关（Leising等人，J.Am. 1991，113，3988-3990）。在提出的机制中，[O=Fe（L）（X）]2+从烷烃中夺取氢，然后将结合的卤化物转移到初始的烷基自由基。这种氧化配体转移反应已被提出为非血红素铁酶异青霉素N合酶在青霉素生物合成中噻唑烷环形成的机制。
A series of [Fe(III)X2L]+ complexes (L = TPA, tris(2-pyridylmethyl)amine, or NTB*, tris(N-ethylbenzimidazol-2-ylmethyl)amine; X = Br, Cl, or N3) has been synthesized and examined for their ability to activate alkyl hydroperoxides for the functionalization of alkanes at room temperature. The crystal structures of [FeCl2(TPA)]ClO4 (2) and [Fe2-OCl2(TPA)2](ClO4)2 (6) were determined, while other complexes were characterized by their visible and NMR spectra. Treatment of the mononuclear complexes with a stoichiometric amount of alkyl hydroperoxide in the presence of cyclohexane affords halocyclohexane in good yield. The production of bromo- and azidocyclohexane was correlated with the disappearance of the characteristic LMCT bands of the mononuclear catalysts, which were converted into catalytically inactive (mu-oxo)diferric species. The yield of haloalkane increased to 100% based on complex when an excess of alkyl hydroperoxide was used, but it was not affected by the addition of excess halide. The formation of haloalkane was inhibited by the presence of dimethyl sulfide (forming DMSO), but was unaffected by the addition of 4-methyl-2,6-di-tert-butylphenol, suggesting the involvement of a two-electron oxidant in the reaction mechanism. The selectivities of the catalysts for cyclohexane and adamantane functionalization were significantly affected by the nature of the tripodal ligand and the bound halide but not by the alkyl group on the hydroperoxide. We thus propose the active species to be [O=Fe(L)(X)]2+, which may be related to the transient intermediate generated from the reaction of Fe2O(TPA)2(ClO4)4 with H2O2 (Leising et al. J. Am. Chem. Soc. 1991, 113, 3988-3990). In the proposed mechanism, [O=Fe(L)(X)]2+ abstracts hydrogen from the alkane and then transfers the bound halide to the incipient alkyl radical. Such an oxidative ligand transfer reaction has been proposed for the mechanism of thiazolidine ring formation in penicillin biosynthesis by the nonheme iron enzyme isopenicillin N synthase.