Mechanistic Studies of the O2-Dependent Aliphatic Carbon-Carbon Bond Cleavage Reaction of a Nickel Enolate Complex
Mechanistic Studies of the O2-Dependent Aliphatic Carbon-Carbon Bond Cleavage Reaction of a Nickel Enolate Complex
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DOI：
10.1021/ic1017888
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发表时间：
2011-02-07
影响因子：
4.6
通讯作者：
Tierney, David L.
中科院分区：
文献类型：
--
作者：
Berreau, Lisa M.;Borowski, Tomasz;Tierney, David L.
单核镍烯醇配合物[（6-Ph（2）TPA）Ni（PhC（O）C（OH）C（O）Ph] ClO 4（I）是第一个被报道的含镍酸还原酮双加氧酶（ARDs）中酶/底物（ES）加合物的反应模型配合物。在这方面的贡献，其O-2依赖的脂肪族碳-碳键断裂反应的机制进行了进一步的研究。停流动力学研究表明，I与O-2的反应总体上是二级反应，并且在25 ℃下比涉及烯醇盐[Me 4 N][PhC（O）C（OH）C（O）Ph]的反应慢80倍。阴离子[PhC（O）C（OH）C（O）Ph]（-）与O-2反应的计算研究支持氢过氧化物机理，其中第一步是氧化还原过程，导致形成1，3-二苯基丙三酮和HOO-。独立的实验表明，1，3-二苯基丙三酮和HOO-之间的反应导致氧化性脂肪族碳-碳键断裂，并形成苯甲酸，苯甲酸酯和CO：CO2（类似于12：1）。在镍（II）络合物存在下的实验给出了类似的产物分布，尽管也形成了苯偶酰[PhC（O）C（O）Ph]，并且CO：CO2比率类似于1.5：1。含镍（II）反应的结果与I与O-2反应的结果相匹配，并为脂肪族碳-碳键裂解的三酮/HOO-途径提供支持。总的来说，I是一个合理的结构模型的ES加合物中形成的Ni（II）ARD的活性位点。然而，在[PhC（O）C（OH）C（O）Ph]阴离子的C（1）和C（3）处均存在苯基附加物，导致O-2依赖性脂肪族碳-碳键裂解的反应途径（通过三酮中间体）不同于C（1）-H酸还原酮物种的反应途径。这项研究，作为第一次详细调查的镍（II）烯醇络合物的相关镍（II）ARD的O-2反应性，提供了深入了解的化学因素参与的O-2反应性的金属acreductone物种。
The mononuclear nickel(II) enolate complex [(6-Ph(2)TPA)Ni(PhC(O)C(OH)C(O)Ph]ClO4 (I) was the first reactive model complex for the enzyme/substrate (ES) adduct in nickel(II)-containing acireductone dioxygenases (ARDs) to be reported. In this contribution, the mechanism of its O-2-dependent aliphatic carbon-carbon bond cleavage reactivity was further investigated. Stopped-flow kinetic studies revealed that the reaction of I with O-2 is second-order overall and is similar to 80 times slower at 25 degrees C than the reaction involving the enolate salt [Me4N][PhC(O)C(OH)C(O)Ph]. Computational studies of the reaction of the anion [PhC(O)C(OH)C(O)Ph](-) with O-2 support a hydroperoxide mechanism wherein the first step is a redox process that results in the formation of 1,3-diphenylpropanetrione and HOO-. Independent experiments indicate that the reaction between 1,3-diphenylpropanetrione and HOO- results in oxidative aliphatic carbon-carbon bond cleavage and the formation of benzoic acid, benzoate, and CO:CO2 (similar to 12:1). Experiments in the presence of a nickel(II) complex gave a similar product distribution, albeit benzil [PhC(O)C(O)Ph] is also formed, and the CO:CO2 ratio is similar to 1.5:1. The results for the nickel(II)-containing reaction match those found for the reaction of I with O-2 and provide support for a trione/HOO- pathway for aliphatic carbon-carbon bond cleavage. Overall, I is a reasonable structural model for the ES adduct formed in the active site of Ni(II)ARD. However, the presence of phenyl appendages at both C(1) and C(3) in the [PhC(O)C(OH)C(O)Ph] anion results in a reaction pathway for O-2-dependent aliphatic carbon-carbon bond cleavage (via a trione intermediate) that differs from that accessible to C(1)-H acireductone species. This study, as the first detailed investigation of the O-2 reactivity of a nickel(II) enolate complex of relevance to Ni(II)ARD, provides insight toward understanding the chemical factors involved in the O-2 reactivity of metal acireductone species.