Segawa Yasutomo, Yamashita Makoto, Nozaki Kyoko
Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656, Japan.
Science. 2006 Oct 6;314(5796):113-5. doi: 10.1126/science.1131914.
Nucleophilic, anionic boryl compounds are long-sought but elusive species. We report that reductive cleavage of the boron-bromine bond in N,N'-bis(2,6-diisopropylphenyl)-2-bromo-2,3-dihydro-1H-1,3,2-diazaborole by lithium naphthalenide afforded the corresponding boryllithium, which is isoelectronic with an N-heterocyclic carbene. The structure of the boryllithium determined by x-ray crystallography was consistent with sp(2) boron hybridization and revealed a boron-lithium bond length of 2.291 +/- 0.006 angstroms. The structural similarity between this compound and the calculated free boryl anion suggests that the boron atom has an anionic charge. The (11)B nuclear magnetic resonance spectrum also supports the boryl anion character. Moreover, the compound behaves as an efficient base and nucleophile in its reactions with electrophiles such as water, methyl trifluoromethanesulfonate, 1-chlorobutane, and benzaldehyde.
亲核性阴离子硼化合物是长期以来一直寻找但难以捉摸的物种。我们报道，萘锂对N,N'-双(2,6-二异丙基苯基)-2-溴-2,3-二氢-1H-1,3,2-二氮杂硼烷中硼-溴键的还原裂解产生了相应的硼锂化合物，它与N-杂环卡宾等电子。通过X射线晶体学确定的硼锂化合物结构与sp(2)硼杂化一致，显示硼-锂键长为2.291±0.006埃。该化合物与计算出的游离硼阴离子之间的结构相似性表明硼原子带有阴离子电荷。(11)B核磁共振谱也支持硼阴离子特征。此外，该化合物在与水、三氟甲磺酸甲酯、1-氯丁烷和苯甲醛等亲电试剂的反应中表现为高效碱和亲核试剂。
