Reduction of ketones and alkyl iodides by SmI2 and Sm(II)-HMPA complexes.: Rate and mechanistic studies
Reduction of ketones and alkyl iodides by SmI2 and Sm(II)-HMPA complexes.: Rate and mechanistic studies
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DOI：
10.1021/ja026074n
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发表时间：
2002-06-19
影响因子：
15
通讯作者：
Flowers, RA
中科院分区：
文献类型：
--
作者：
Prasad, E;Flowers, RA
用停流分光光度法研究了异丁酮(2-丁酮、乙酰乙酸甲酯和N，N-二甲基乙酰乙酰胺)和烷基碘(1-碘代丁烷和2-碘代丁烷)在四氢呋喃中对二碘化钐还原反应电子转移速率的影响。ET过程的活化参数通过30-50℃范围内的温度依赖性研究来确定。比较了在不同HMPA当量存在下，上述体系的ET速率常数和活化参数，以了解HMPA对不同底物的作用机理。这些研究结果表明，SmI2/酮体系的过渡态几何构型中可能存在配位或络合作用，即使在空间要求很高的配体HMPA存在的情况下也是如此。在SML(2)/烷基碘体系中，加入4当量的HMPA后，Sm还原反应的Et速率和活化参数不再受HMPA的影响，而Et速率与HMPa当量成线性关系。这些研究结果与SmI2(和SmI2-HMPa络合物)还原酮的内球型ET和SmI2或SmI2-HMPA络合物还原烷基碘的外球型ET一致。
The effect of HMPA on the electron transfer (ET) rate of samarium diiodide reduction reactions in THF was analyzed for a series of ketones (2-butanone, methyl acetoacetate, and N,N-dimethylacetoacetamide) and alkyl iodides (1-iodobutane and 2-iodobutane) with stopped flow spectrophotometric studies. Activation parameters for the ET processes were determined by temperature-dependence studies over a range of 30-50 degreesC. The ET rate constants and the activation parameters obtained for the above systems in the presence of different equivalents of HMPA were compared to understand the mechanism of action of HMPA on various substrates. The results obtained from these studies indicate that coordination or chelation is possible in the transition state geometry for SmI2/ketone systems even in the presence of the sterically demanding ligand HMPA. After the addition of 4 equiv of HMPA the ET rate and activation parameters for ketone reduction by Sm is unaffected by further HMPA addition while a linear dependence of ET rate on the equivalents of HMPA was found in the Sml(2)/alkyl iodide system. The results of these studies are consistent with an inner-sphere-type ET for the reduction of ketones by SmI2 (and SmI2-HMPA complexes) and an outer-sphere-type ET for the reduction of alkyl iodides by SmI2 or SmI2-HMPA complexes.