Institut für Organische Chemie, Universität Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
J Am Chem Soc. 2014 Apr 16;136(15):5765-72. doi: 10.1021/ja501055c. Epub 2014 Apr 2.
In the past the long-standing and very controversial discussion about a special reactivity of cyano- versus iodocuprates concentrated on the existence of higher-order cuprate structures. Later on numerous structural investigations proved the structural equivalence of iodo and cyano Gilman cuprates and their subsequential intermediates. For dimethylcuprates similar reactivities were also shown. However, the reports about higher reactivities of cyanocuprates survived obstinately in many synthetic working groups. In this study we present an alternative structural difference between cyano- and iodocuprates, which is in agreement with the results of both sides. The key is the potential incorporation of alkyl copper in iodo but not in cyano Gilman cuprates during the reaction. In the example of cuprates with a highly soluble substituent (R = Me3SiCH2) we show that in the case of iodocuprates during the reaction several copper-rich complexes are formed, which consume additional iodocuprate and provide lower reactivities. To confirm this, a variety of highly soluble copper-rich complexes were synthesized, and their molecular formulas, the position of the equilibriums, their monomers and their aggregation trends were investigated by NMR spectroscopic methods revealing extended iodo Gilman cuprates. In addition, the effect of these copper-rich complexes on the yields of cross-coupling reactions with an alkyl halide was tested, resulting in reduced yields for iodocuprates. Thus, this study gives an explanation for the thus far confusing results of both similar and different reactivities of cyano- and iodocuprates. In the case of small substituents the produced alkyl copper precipitates and similar reactivities are observed. However, iodocuprates with large substituents are able to incorporate alkyl copper units. The resulting copper-rich species have less polarized alkyl groups, i.e. gradually reduced reactivities.
过去，关于氰基-与碘代铜之间特殊反应性的长期且极具争议的讨论集中在是否存在更高阶的铜酸盐结构。后来，大量结构研究证明了碘代和氰基吉尔曼铜酸盐及其后续中间体在结构上是等同的。对于二甲基铜盐，也表现出类似的反应活性。然而，氰基铜盐具有更高反应活性的报道在许多合成工作组中仍然顽固存在。在这项研究中，我们提出了氰基-与碘代铜之间的另一种结构差异，这与双方的结果一致。关键是在反应过程中，碘代吉尔曼铜盐可以潜在地掺入烷基铜，而氰基铜盐则不行。在具有高可溶性取代基（R = Me3SiCH2）的铜盐的示例中，我们表明在碘代铜盐的情况下，在反应过程中形成了几种富铜配合物，这些配合物消耗了额外的碘代铜盐，并提供了较低的反应活性。为了证实这一点，我们合成了多种高可溶性富铜配合物，并通过 NMR 光谱方法研究了它们的分子公式、平衡位置、单体及其聚合趋势，揭示了扩展的碘代吉尔曼铜盐。此外，还测试了这些富铜配合物对与烷基卤化物的交叉偶联反应产率的影响，结果导致碘代铜盐的产率降低。因此，这项研究为迄今为止氰基-与碘代铜之间相似和不同反应性的令人困惑的结果提供了一种解释。在小取代基的情况下，会产生烷基铜沉淀，观察到类似的反应活性。然而，具有大取代基的碘代铜盐能够掺入烷基铜单元。由此产生的富铜物种具有极性化程度较低的烷基基团，即反应活性逐渐降低。
