基于过渡金属的原子转移反应的基态输入的趋势
Elizabeth A Mader1, Virginia W Manner, Todd F Markle
1Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA.
Journal of the American Chemical Society
|March 12, 2009
概括
过渡金属复合物在原子转移 (HAT) 反应中与氧基发生显著的负变化. 这与有机分子形成鲜明对比,凸显了金属中心在HAT热力学中的重要性.
科学领域:
- 协调化学 协调化学
- 热化学 热化学 热化学
- 化学动力学 化学动力学
背景情况:
- 原子转移 (HAT) 是化学的一个基本反应机制.
- 了解热力学驱动力,包括,对于反应预测至关重要.
- 以前的研究经常假设有机系统中HAT反应的变化接近零.
研究的目的:
- 研究涉及过渡金属复合体作为H原子供体的HAT反应的热化学特性.
- 量化这些反应的基态变化 (ΔS°(HAT)).
- 为了比较金属基HAT中的贡献与有机系统中的贡献.
主要方法:
- 过渡金属复合物的合成和表征:[Fe (II) (H2bip) ]2+,[Fe (II) (H2bim) ]2+,[Co (II) (H2bim) ]2+,和Ru (II) (acac) 2 (py-imH).
- 测量溶液平衡以确定热力学参数.
- 热量测量研究量化证实反应和.
主要成果:
- 在与TEMPO或tBu3PhO*发生反应时,过渡金属复合物[Fe(II) ((H2bip) ]3 2+,[Fe(II) ((H2bim) 3 2+和[Co(II) ((H2bim) 3 2+显示出显著的负 ΔS° ((HAT) 值 (-30至-41 cal mol-1 K−1)).
- 鲁复合体Ru (II) (acac) (py-imH) 呈现出一个较小的正 ΔS° (HAT) (4.9 cal mol−1 K−1).
- 热量计证实了对[Fe (II) (H2bip) ]2+++TEMPO的反应度,并提供了 ΔH° (HAT) = -11.2 ± 0.5 kcal mol-1 的TEMPOH + tBu3PhO*.
结论:
- 对于基于过渡金属的HAT反应, ΔS°(HAT) ≈0的假设是无效的.
- ∆S°(HAT) 的大小与所涉及金属中心的电子转移 (ΔS°(ET)) 的趋势有关.
- 受到金属中心影响的振动贡献在基于金属的HAT反应中很重要,将HAT和ET热力学联系起来.
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