Reaction of molecular oxygen with a PdII-hydride to produce a PdII-hydroperoxide:: Experimental evidence for an HX-reductive-elimination pathway
Reaction of molecular oxygen with a PdII-hydride to produce a PdII-hydroperoxide:: Experimental evidence for an HX-reductive-elimination pathway
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DOI：
10.1021/ja7112504
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发表时间：
2008-04-30
影响因子：
15
通讯作者：
Stahl, Shannon S.
中科院分区：
文献类型：
--
作者：
Konnick, Michael M.;Stahl, Shannon S.
分子氧与 Pd-II-氢化物反应形成 Pd-II-氢过氧化物代表了 Pd 催化需氧氧化反应中所提出的催化剂再氧化途径之一，但该反应的明确例子直到最近才被发现。在这里，我们提出了 O-2 与反式-(IMes)(2)Pd(H)(OBz), 1 (IMes = 1,3-dimesitylimidazol-2-ylidene) 反应的机理研究，该反应产生反式-(IMes)(2)Pd(OOH)(OBz), 2。通过苯-d(6) 中的 H-1 NMR 光谱监测该反应，动力学研究揭示了两项速率定律，速率 = k(1)[1] + k(2)[1][BzOH]，以及小的氘动力学同位素效应，k(Pd-H)/k(Pd-D) = 1.3(1)。该速率与氧气压力无关。数据支持将 1 转化为 2 的逐步机制，包括从 1 限速还原消除 BzOH，然后分子氧与 (IMeS)(2)Pd 度快速反应，以及 n(2)-过氧复合物 (IMeS)(2)Pd(O-2) 的 Pd-O 键质子化。苯甲酸和其他质子添加剂（H2O、ArOH）可能通过稳定从 1 还原消除 BzOH 的过渡态来催化氧化反应。这项研究首次对传统上提出的氢化钯有氧氧化机制进行了实验验证。
The reaction of molecular oxygen with a Pd-II-hydride species to form a Pd-II-hydroperoxide represents one of the proposed catalyst reoxidation pathways in Pd-catalyzed aerobic oxidation reactions, but well-defined examples of this reaction were discovered only recently. Here, we present a mechanistic study of the reaction Of O-2 with trans-(IMes)(2)Pd(H)(OBz), 1 (IMes = 1,3-dimesitylimidazol-2-ylidene), which yields trans-(IMes)(2)Pd(OOH)(OBz), 2. The reaction was monitored by H-1 NMR spectroscopy in benzene-d(6), and kinetic studies reveal a two-term rate law, rate = k(1)[1] + k(2)[1][BzOH], and a small deuterium kinetic isotope effect, k(Pd-H)/k(Pd-D) = 1.3(1). The rate is independent of the oxygen pressure. The data support a stepwise mechanism for the conversion of 1 into 2 consisting of rate-limiting reductive elimination of BzOH from 1 followed by rapid reaction of molecular oxygen with (IMeS)(2)Pd degrees and protonolysis of a Pd-O bond of the n(2)-peroxo complex (IMeS)(2)Pd(O-2). Benzoic acid and other protic additives (H2O, ArOH) catalyze the oxygenation reaction, probably by stabilizing the transition state for reductive elimination of BzOH from 1. This study provides the first experimental validation of the mechanism traditionally proposed for aerobic oxidation of Pd-hydride species.