Direct and Transfer Hydrosilylation Reactions Catalyzed by Fully or Partially Fluorinated Triarylboranes: A Systematic Study
Direct and Transfer Hydrosilylation Reactions Catalyzed by Fully or Partially Fluorinated Triarylboranes: A Systematic Study
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DOI：
10.1021/om501284a
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发表时间：
2015-02-23
期刊：
影响因子：
2.8
通讯作者：
Oestreich, Martin
中科院分区：
文献类型：
--
作者：
Keess, Sebastian;Simonneau, Antoine;Oestreich, Martin
本调查有几个目的。选择的缺电子硼刘易斯酸催化氢硅烷从环己-2，5-二烯-1-基取代的硅烷中释放。该两步过程包括氢化物提取以生成硅稳定的Wheland络合物和通过在前一步骤中形成的硼氢化物捕获芳烃稳定的硅阳离子。然后，相同的硼催化剂将活化Si-H键，用于分别与代表性的供π和供σ底物（烯烃/炔和酮/酮亚胺）反应。净转化是一个转移硅氢加成，和效果的取代模式的环己-1，4-二烯核心和取代基在硅原子上施加这些氢硅烷替代品进行了系统的研究。与直接使用氢硅烷得到的结果进行了比较。该全面分析的另一部分致力于比较文献已知的完全或部分氟化的三芳基硼烷在上述底物的直接和转移氢化硅烷化中的情况。数据列表和颜色编码，最后提供了一个有前途的基板/还原剂/硼烷组合的概述。通常不同的反应性的π-和σ-基本基板的解释，它表明，刘易斯酸性的硼原子，估计由Gutmann-Beckett方法，是不是唯一的决定性特征，这些硼刘易斯酸。实用的机械模型，提出合理化的刘易斯酸度和空间位阻的情况下，在硼，同样，硅原子，以及在某些情况下，需要邻位硼原子之间的相互作用。
The present survey serves several purposes. Selected electron-deficient boron Lewis acids catalyze the release of hydrosilanes from cyclohexa-2,5-dien-1-yl-substituted silanes. The two-step process consists of a hydride abstraction to generate a silicon-stabilized Wheland complex and capture of the arene-stabilized silicon cation by the borohydride formed in the previous step. The same boron catalyst will then activate the Si-H bond for the reaction with representative pi- and sigma-donating substrates, alkenes/alkynes and ketones/ketimines, respectively. The net transformation is a transfer hydrosilylation, and the effect that the substitution pattern of the cyclohexa-1,4-diene core and the subsituents at the silicon atom exert on these hydrosilane surrogates is systematically investigated. The results are compared with those obtained employing the hydrosilane directly. Another part of this comprehensive analysis is dedicated to the comparison of literature-known fully or partially fluorinated triarylboranes in both the direct and the transfer hydrosilylation of the aforementioned substrates. The data are tabulated and color-coded, finally providing an overview of promising substrate/reductant/borane combinations. The often different reactivities of pi- and sigma-basic substrates are explained, and it is shown that the Lewis acidity of the boron atom, estimated by the Gutmann-Beckett method, is not the only decisive feature of these boron Lewis acids. Practical mechanistic models are presented to rationalize the interplay between the Lewis acidity and steric situation at the boron and, likewise, the silicon atom as well as the need for fluorination ortho to the boron atom in certain cases.