Structure-Reactivity Studies, Characterization, and Transformation of Intermediates by Lithium Chloride in the Direct Insertion of Alkyl and Aryl Iodides to Metallic Zinc Powder
Structure-Reactivity Studies, Characterization, and Transformation of Intermediates by Lithium Chloride in the Direct Insertion of Alkyl and Aryl Iodides to Metallic Zinc Powder
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DOI：
10.1021/acs.organomet.6b00910
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发表时间：
2017-07-10
期刊：
影响因子：
2.8
通讯作者：
Blum, Suzanne A.
中科院分区：
文献类型：
--
作者：
Feng, Chao;Easter, Quinn T.;Blum, Suzanne A.
就业的荧光标记的烷基和芳基碘化物允许检测持久性表面中间体在其直接插入到市售的锌粉。这种亚系综显微镜技术的灵敏度，使结构反应性的研究，在形成的中间体，存在的数量足够低，以前未被检测到的传统合奏分析技术。这些表面中间体转化氯化锂，导致分配的氯化锂的机械作用，改变反应中的速率决定步骤，通过降低这些否则持久的表面有机金属中间体的溶解的障碍。直接插入步骤的温度依赖性/定性屏障独立于增溶步骤和整个反应的屏障来确定。在单分子水平上检测这些锌表面中间体，即，的个别表面有机金属物种，已首次实现。锌粉表面的元素组成的能量色散X射线光谱（EDS）测量确定氯化锂不清洁氧化物的表面;相反，用TMSCl预处理表面在先前在经验优化的合成程序中报道的2小时预处理时间之后实现表面氧化物的部分去除。目前的限制，这种显微镜的方法也确定和讨论相对于在operando成像过程中添加固体试剂。表征所得的可溶性荧光团标记的有机锌/氯化锂复合物的H-1 NMR光谱，质谱和荧光光谱提供了深入了解其溶液动力学和化学交换过程。
Employment of fluorophore-tagged alkyl and aryl iodides permitted detection of persistent surface intermediates during their direct insertion to commercially available zinc powder. The sensitivity of this subensemble microscopy technique enabled structure-reactivity studies in the formation of intermediates that are present in quantities sufficiently low as to have been undetected previously by traditional ensemble analytical techniques. These surface intermediates were transformed by lithium chloride, leading to the assignment of the mechanistic role of lithium chloride as changing the rate-determining step in the reaction by lowering the barrier for solubilization of these otherwise persistent surface organometallic intermediates. The temperature dependence/qualitative barrier of the direct insertion step was determined independently from the solubilization step and from the barrier for the overall reaction. Detection of these zinc surface intermediates at the single-molecule level, i.e., of individual surface organometallic species, has been achieved for the first time. Energy dispersive X-ray spectroscopy (EDS) measurements of the elemental composition of the surface of the zinc powder determined that lithium chloride does not clean the surface of the oxides; instead, pretreatment of the surface with TMSCl effects partial removal of surface oxides after the 2 h pretreatment time previously reported in the empirically optimized synthetic procedure. Current limitations of this microscopy approach are also determined and discussed with respect to the addition of solid reagents during in operando imaging. Characterization of the resulting soluble fluorophore-tagged organozinc/LiCl complex by H-1 NMR spectroscopy, mass spectrometry, and fluorescence spectroscopy provided insight into its solution dynamics and chemical exchange processes.