Kinetics and mechanism of iridium-catalyzed dehydrogenation of primary amines to nitriles
Kinetics and mechanism of iridium-catalyzed dehydrogenation of primary amines to nitriles
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DOI：
10.1021/om701148t
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发表时间：
2008-05-12
期刊：
影响因子：
2.8
通讯作者：
Brookhart, Maurice
中科院分区：
文献类型：
--
作者：
Bernskoetter, Wesley H.;Brookhart, Maurice
以叔丁基乙烯为氢受体，用[C6H3-2,6-(OPBU2)- b -t)]IrH2催化脱氢制腈族伯胺。通过一系列的动力学和同位素标记实验，以及沿反应途径分离的中间体，研究了催化机理。转换频率与胺的浓度呈一阶依赖关系，与腈呈反一阶依赖关系，与叔丁基乙烯呈零阶依赖关系。胺脱氢的机理是由催化剂静息态的铱(1)腈配合物经过两个循环前极限平衡，然后由瞬态铱(1)酰胺氢化物进行缓慢的ss-氢化物消除。测定异丁胺在41℃温度范围内的化学计量脱氢速率常数，确定h -双匕首消除-氢化物的激活参数为24.8(9)kcal/mol， s -双匕首消除-氢化物的激活参数为-10(2)eu。一系列对取代苯胺的脱氢反应表明，在含有供电子取代基的底物中，对腈的转化增强。
A family of primary amines has been catalytically dehydrogenated to nitriles by [C6H3-2,6-((OPBU2)-B-t)]IrH2 using tert-butylethylene as a hydrogen acceptor. The catalytic mechanism has been investigated by a series of kinetic and isotopic labeling experiments, in addition to the isolation of intermediates along the reaction pathway. The turnover frequency exhibits a first-order dependence on the concentration of amine, an inverse first-order dependence on nitrile, and a zero-order dependence on tert-butylethylene. The mechanism of amine dehydrogenation is proposed to proceed from an iridium(l) nitrile complex, the catalyst resting state, via two preturnover limiting equilibria, followed by a slow ss-hydride elimination event from a transient iridium(Ill) amido hydride species. Measuring rate constants for the stoichiometric dehydrogenation of isobutylamine over a 41 degrees C temperature range established activation parameters for -hydride elimination of Delta H-double dagger 24.8(9) kcal/mol and Delta S-double dagger = -10(2) eu. Dehydrogenation of a series of para-substituted benzyl amines indicated enhanced conversions to nitriles for substrates bearing electron-donating substituents.