The Role of Ate Complexes in the Lithium-Sulfur, Lithium-Selenium and Lithium-Tellurium Exchange Reactions
作者:Hans J. Reich、Birgir Ö. Gudmundsson、D. Patrick Green、Martin J. Bevan、Ieva L. Reich
DOI:10.1002/1522-2675(200211)85:11<3748::aid-hlca3748>3.0.co;2-0
日期:2002.11
favor the T-shaped geometry of the hypervalent intermediates. For the selenium systems, ate complex intermediates (20-Se, 26) were detected spectroscopically in THF- or THF/HMPA-containing solutions. A DNMR study showed that Li/Se exchange was substantially faster than exchange of the lithium reagents with the ate complex. Therefore, these ate complexes are not on the actual Li/Se exchange pathway.
高价配合物是金属-卤素、金属-碲和相关交换反应中的假定中间体。通过动力学技术和 NMR 光谱研究了 o,o'-联苯二基与二苯取代对碲酸盐络合物形成的影响。仅测量了关联常数 (Kate) 的适度增加。当通过间三联苯骨架 (12-S, 12-Se, 21) 在分子内实现 o,o'-联苯二硫化物和硒化物的 Li/M 交换时,Li/M 的速率大幅增加 (>109)与非循环模型相比,观察到 S 和 Li/Se 交换。显然,这些系统被理想地预先组织成有利于高价中间体的 T 形几何形状。对于硒系统,吃了复杂的中间体(20-Se,26) 在含有 THF 或 THF/HMPA 的溶液中进行光谱检测。DNMR 研究表明,Li/Se 交换比锂试剂与 ate 配合物的交换要快得多。因此,这些 ate 配合物不在实际的 Li/Se 交换途径上。