Thiolate alkylation in tripod zinc complexes: a comparative kinetic study.
Thiolate alkylation in tripod zinc complexes: a comparative kinetic study.
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三脚锌配合物中的硫醇盐烷基化：比较动力学研究。
作者：
M. Rombach;J. Seebacher;Mian Ji;Guofang Zhang;G. He;M. Ibrahim;Boumahdi Benkmil;H. Vahrenkamp
动力学研究了碘化甲基对三脚架硫代酸锌中硫代酸配体的相关生物学烷基化反应。采用吡唑基/硫代咪唑基硼酸酯型五种三脚架配体，提供N3、N2S、NS2和S3给体组。分别研究了乙基、苄基、苯基和对硝基苯基硫代锌配合物，得到了共20个二级速率常数。这些速率常数的比较表明：(1)硫代酸酯之间的电子效应，即乙硫代酸酯的反应速度比对硝基苯基硫代酸酯快3个数量级；(2)吡唑酸酯之间的空间效应，即苯基取代的吡唑酸酯比叔丁基取代的吡唑酸酯反应速度快2个数量级；(3)三脚架中给硫体的加速作用较强，（N3）Zn-SR和（S3）Zn-SR配合物的反应时间相差4个数量级。
The biologically relevant alkylations of the thiolate ligands in tripod zinc thiolates by methyl iodide were studied kinetically. Five tripod ligands of the pyrazolyl/thioimidazolyl borate type were employed, offering N3, N2S, NS2, and S3 donor sets. For each of them, the ethyl-, benzyl-, phenyl-, and p-nitrophenylthiolate zinc complexes were investigated, yielding a total of 20 second-order rate constants. The comparison of these rate constants shows three effects: (1) the electronic effect among the thiolates, i.e., the ethanethiolates react about 3 orders of magnitude faster than the p-nitrophenylthiolates; (2) the steric effect among the pyrazolylborates, i.e., the phenyl-substituted ones react about 2 orders of magnitude faster than the tert-butyl-substituted ones; and (3) the strong acceleration by the sulfur donors in the tripods, reaching 4 orders of magnitude between the reaction times of the (N3)Zn-SR and (S3)Zn-SR complexes.