Mechanism of alcohol oxidation mediated by copper(II) and nitroxyl radicals.
Mechanism of alcohol oxidation mediated by copper(II) and nitroxyl radicals.
复制标题
铜（II）和硝氧基自由基介导的酒精氧化机制。
DOI：
10.1021/ja5070137
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发表时间：
2014-08-27
影响因子：
15
通讯作者：
Stahl SS
中科院分区：
文献类型：
--
作者：
Ryland BL;McCann SD;Brunold TC;Stahl SS
2，2‘-联吡啶配位铜配合TEMPO(2，2，6，6-四甲基哌啶-N-氧基)是一种高效的乙醇好氧氧化催化剂。关于CUII和TEMPO介导的酒精氧化机制存在相当大的不确定性和争议。在这里，我们报告了实验和密度泛函理论(DFT)的计算研究，这些研究区分了许多以前提出的机制路径。各种自由基探针底物的氧化反应表明，在反应中没有形成长寿命的自由基。DFT计算研究支持这一结论。氢原子从CuII-醇盐转移到氮氧基的双分子途径比氢原子从CuII-醇盐转移到配位的氮氧基物种的能量更高。这里提供的数据与先前文献中报道的各种不同且似乎相互矛盾的实验和计算数据的集合相一致。由此产生的Oppenauer类反应路径进一步解释了不同类别醇(苄基与脂肪族以及伯基与仲基)相对反应性的实验趋势，以及观察到TEMPO与双环氮氧基之间的不同反应性，如ABNO(ABNO=9-氮杂双环[3.3.1]壬烷N-氧基)。
2,2′-Bipyridine-ligated copper complexes, in combination with TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), are highly effective catalysts for aerobic alcohol oxidation. Considerable uncertainty and debate exist over the mechanism of alcohol oxidation mediated by CuII and TEMPO. Here, we report experimental and density functional theory (DFT) computational studies that distinguish among numerous previously proposed mechanistic pathways. Oxidation of various classes of radical-probe substrates shows that long-lived radicals are not formed in the reaction. DFT computational studies support this conclusion. A bimolecular pathway involving hydrogen-atom-transfer from a CuII–alkoxide to a nitroxyl radical is higher in energy than hydrogen transfer from a CuII–alkoxide to a coordinated nitroxyl species. The data presented here reconcile a collection of diverse and seemingly contradictory experimental and computational data reported previously in the literature. The resulting Oppenauer-like reaction pathway further explains experimental trends in the relative reactivity of different classes of alcohols (benzylic versus aliphatic and primary versus secondary), as well as the different reactivity observed between TEMPO and bicyclic nitroxyls, such as ABNO (ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl).
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影响因子：
4.6
作者：
Belanzoni, Paola;Michel, Carine;Baerends, Evert Jan
通讯作者：
Baerends, Evert Jan
影响因子：
4.3
作者：
Kumpulainen, Esa T. T.;Koskinen, Ari M. P.
通讯作者：
Koskinen, Ari M. P.
影响因子：
3.3
作者：
Astolfi, P;Brandi, P;Lanzalunga, O
通讯作者：
Lanzalunga, O
影响因子：
3.2
作者：
Dijksman, A;Arends, IWCE;Sheldon, RA
通讯作者：
Sheldon, RA
影响因子：
4.6
作者：
Isrow, Derek;Captain, Burjor
通讯作者：
Captain, Burjor