分子氧与Pd(II) - 化物反应以产生Pd(II) - 氧化物:实验证据表明HX-减小-消除途径
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Michael M Konnick1, Shannon S Stahl
1Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Journal of the American Chemical Society
|April 9, 2008
概括
这项研究研究了分子氧与 ((II) - 化物种的反应,这是催化有氧氧化过程中的关键步骤. 研究人员验证了一种涉及还原性消除和氧气插入的拟议机制,为催化剂再氧化途径提供了洞察力.
科学领域:
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
- 反应机制 反应机制
背景情况:
- 催化有氧氧化反应在有机合成中至关重要.
- 催化剂的再氧化,特别是通过Pd (II) - 化物到Pd (II) - 氧化物,是一种被提议但往往未得到确认的途径.
- 最近的发现使得研究精确定义的Pd (II) - 化物种成为可能.
研究的目的:
- 为了机械地研究分子氧与特定的Pd(II) - 化物复合物,转-(IMes) 2Pd(H) ((OBz) 的反应.
- 为了阐明形成相应的Pd(II) - 氧化物种的途径.
- 为在催化有氧氧化中提出的催化剂再氧化机制提供实验验证.
主要方法:
- 使用1HNMR光谱在-d6.6中监测O2与trans-{IMes) 2Pd{H}{OBz) 的反应.
- 进行动力学研究以确定速率定律并确定速率限制步骤.
- 测量的动态同位素效应 (k(Pd-H) /k(Pd-D)) 来探测反应机制.
主要成果:
- 这种反应产生了Pd(II) - 氧化复合物trans-(IMes) 2Pd(OOH) ((OBz).
- 动力学研究揭示了两项速率定律 (速率=k1[1] + k2[1][BzOH]) 和一个小的动态同位素效应 (1.3(1)).
- 发现氧气压力与反应速率无关,而酸等原性添加剂催化反应.
结论:
- 这些数据支持一个阶段性机制,涉及从Pd (II) - 化物中限制酸 (BzOH) 的减速消除.
- 接下来是分子氧与产生的Pd(0) 物种的快速反应,以及eta(2) -peroxo复合体中的Pd-O键的质子分解.
- 这项研究为Pd-化物种的有氧氧化拟议机制提供了第一个实验验证,增强了对催化剂再氧化的理解.
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