Two-state reactivity in alkane hydroxylation by non-heme iron-oxo complexes
Two-state reactivity in alkane hydroxylation by non-heme iron-oxo complexes
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DOI：
10.1021/ja061609o
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发表时间：
2006-07-05
影响因子：
15
通讯作者：
Shaik, Sason
中科院分区：
文献类型：
--
作者：
Hirao, Hajime;Kumar, Devesh;Shaik, Sason
密度泛函理论用于探索四种合成非血红素铁(IV)-氧配合物与三种目标底物的烷烃羟基化机制（Kaizer， J.; Klinker， E. J.; Oh， N. Y.; Rohde； J.- U.; Song， W. J.; Stubna， A.; Kim， J.; Munck， E.; Nam， W.; Que， L., Jr. J.）。化学。社会科学学报，2004,26 (4):472-473；罗德，J. U.；Que， L. Jr. andrew。化学。Int。编辑。2005,44,2255-2258.)。铁氧试剂具有三态基态和低洼五态激发态。如果反应在两个自旋态上进行，即两态反应性（TSR），则可以理解实验和理论反应性趋势集；提出了一种合适的新模型。TSR模型做出了可检验的预测：(a)如果发生五价态的交叉，羟基化作用将有效协同；然而，如果该过程只发生在三重态表面，则会发生逐步羟基化，并且会观察到自由基中间体产生的副产物（例如，立体化学的损失）。(b)在穿越到五态过渡态的情况下，可以预期典型隧穿的动力学同位素效应。(c)在两种表面对速率有影响的情况下，可以预期中间的KIEs和激进的加扰模式反映了这两种过程。(d)溶剂对这些反应的影响预计很大。
Density functional theory is used to explore the mechanisms of alkane hydroxylation for four synthetic non-heme iron(IV)-oxo complexes with three target substrates (Kaizer, J.; Klinker, E. J.; Oh, N. Y.; Rohde; J.- U.; Song, W. J.; Stubna, A.; Kim, J.; Munck, E.; Nam, W.; Que, L., Jr. J. Am. Chem. Soc. 2004, 126, 472-473; Rohde, J.- U.; Que, L., Jr. Angew. Chem. Int. Ed. 2005, 44, 2255-2258.). The iron-oxo reagents possess triplet ground states and low-lying quintet excited states. The set of experimental and theoretical reactivity trends can be understood if the reactions proceed on the two spin states, namely two-state reactivity (TSR); an appropriate new model is presented. The TSR model makes testable predictions: (a) If crossing to the quintet state occurs, the hydroxylation will be effectively concerted; however, if the process transpires only on the triplet surface, stepwise hydroxylation will occur, and side products derived from radical intermediates would be observed (e. g., loss of stereochemistry). (b) In cases of crossing en route to the quintet transition state, one expects kinetic isotope effects (KIEs) typical of tunneling. (c) In situations where the two surfaces contribute to the rate, one expects intermediate KIEs and radical scrambling patterns that reflect the two processes. (d) Solvent effects on these reactions are expected to be very large.