Department of Chemistry , National Taiwan University , No. 1, Section 4, Roosevelt Road , Taipei 10617 , Taiwan.
Inorg Chem. 2018 Sep 17;57(18):11732-11737. doi: 10.1021/acs.inorgchem.8b01865. Epub 2018 Sep 4.
Although boron-containing radicals are promising materials for molecular electronic devices, the electronic effect of the σ-donating yet π-accepting boron center on the stability of open-shell species has been less discussed. In this work, the role of a tricoordinate boron center in π-conjugated radicals was explored through electron paramagnetic resonance measurement of several boron-linked bisphenol radicals and diradicals. Replacing the bridging methine fragment of a neutral Galvinoxyl radical with an arylboryl group led to the corresponding boron-linked radical anion that requires excessive steric protection at the boron center to be persistent in solution. Experimental and theoretical investigations revealed that the introduction of boron would diminish the quinoidal character of the phenoxyl radical and increase both the electrophilicity and nucleophilicity of the open-shell species. Therefore, it is important to consider the steric protection of the boron center in boron-containing π-conjugated organic radicals.
尽管含硼自由基是用于分子电子器件的有前途的材料，但对于 σ-给电子而 π-接受的硼中心对开壳物种稳定性的电子效应的讨论较少。在这项工作中，通过对几种硼连接的双酚自由基和双自由基的电子顺磁共振测量，探索了三配位硼中心在π-共轭自由基中的作用。用芳基硼基取代中性 Galvinoxyl 自由基的桥接亚甲基片段会导致相应的硼连接的自由基阴离子，该阴离子需要在硼中心处进行过度的空间位阻保护才能在溶液中稳定存在。实验和理论研究表明，硼的引入会降低苯氧自由基的醌型特征，并增加开壳物种的亲电性和亲核性。因此，在含硼的 π-共轭有机自由基中，考虑硼中心的空间位阻保护是很重要的。
