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首页> 外文期刊>Chemistry: A European journal >Boron-Boron One-Electron Sigma Bonds versus B-X-B Bridged Structures
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Boron-Boron One-Electron Sigma Bonds versus B-X-B Bridged Structures

机译：硼-硼单电子Sigma键与B-X-B桥结构

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摘要

The existence of one-electron B-B sigma bonds, for two different sets of compounds, was investigated by analyzing their electron density with different tools, namely QTAIM, ELF, NCIPLOT, and NBO approaches. Our results indicate that although the generic label one-electron sigma bond is often used in the literature, the nature of these bonds varies considerably, or they even do not exist. The [B2X6](-) radical anions give place to true covalent one-electron sigma bonds, the stronger the more electronegative is the X substituent. When both boron atoms are substituents in a rigid aromatic moiety, such as naphthalene, to yield 1,8-disubstituted derivatives, two kinds of equilibrium structures are found, those also stabilized through a one-electron sigma bond (X=OH, F, Cl, CN) and those stabilized by the formation of B-X-B bridges (X=H, OMe). These 1,8-BX2 naphthalene derivatives can be considered as analogues of 1,8-NX2 naphthalene proton sponges. While the latter are able to stabilize a proton between the two basic sites, the former are able to stabilize an electron between the two electron-deficient B atoms. Interestingly, when all the H atoms attached to B are substituted by phenyl groups no one-electron sigma bonds B-B bonds are formed, due to the dispersion of the unpaired electron in the aromatic substituents.
机译：通过使用不同的工具，即QTAIM，ELF，NCIPLOT和NBO方法分析其电子密度，研究了两种不同化合物的单电子B-B sigma键的存在。我们的结果表明，尽管文献中经常使用通用标签的单电子sigma键，但这些键的性质差异很大，甚至根本不存在。 [B2X6]（-）自由基阴离子可形成真正的共价单电子sigma键，X取代基的负电性越强。当两个硼原子都是刚性芳族部分（如萘）中的取代基时，生成1,8-二取代的衍生物时，会发现两种平衡结构，它们也通过单电子sigma键稳定化（X = OH，F， Cl，CN）以及通过形成BXB桥而稳定的那些（X = H，OMe）。这些1,8-BX2萘衍生物可被视为1,8-NX2萘质子海绵的类似物。后者能够稳定两个碱性位点之间的质子，而前者能够稳定两个缺电子的B原子之间的电子。有趣的是，当所有与B相连的H原子都被苯基取代时，由于未成对电子在芳族取代基中的分散，所以没有形成单电子西格玛键B-B键。

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