Inaccessibility of β-hydride elimination from -OH functional groups in Wacker-type oxidation
Inaccessibility of β-hydride elimination from -OH functional groups in Wacker-type oxidation
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DOI：
10.1021/ja0533139
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发表时间：
2006-03-15
影响因子：
15
通讯作者：
Goddard, WA
中科院分区：
文献类型：
--
作者：
Keith, JA;Oxgaard, J;Goddard, WA
量子力学计算（B3LYP和MPW1K密度泛函理论）对Wacker过程中醇脱氢生成酮的机理进行了研究，结果表明，普遍接受的产物形成机理（β-氢化物消除（BHE）导致Pd-H形成）在能量上是不可行的（36.2 kcal/mol）。另一种涉及五体还原消除（RE）的途径导致18.8 kcal/mol的活化焓，这只是通常假设的瓦克过程中− OH基团的BHE的一半。我们发现，一个水分子催化这两个过程，降低到17.2 RE和25.0 BHE的障碍，但不会改变这两种机制的相对顺序。这表明，对于β原子不是烷基的情况，应该重新检查BHE机制的假设。
Quantum mechanics calculations (B3LYP and MPW1K density functional theory) on mechanisms relevant to the Wacker process for dehydrogenation of alcohol to ketone show that the commonly accepted mechanism for product formation (β-hydride elimination (BHE) leading to Pd−H formation) is not energetically feasible (36.2 kcal/mol). An alterative pathway involving a five-bodied reductive elimination (RE) leads to an activation enthalpy of 18.8 kcal/mol, which is just half that of the BHE from the −OH group usually assumed for the Wacker process. We find that a water molecule catalyzes both processes, reducing the barrier to 17.2 for RE and 25.0 for BHE, but will not change the relative ordering of the two mechanisms. This suggests that assumptions of BHE mechanisms should be reexamined for cases in which the β atom is not an alkyl group.