An Air-Stable Organoboron Compound, Dithienooxadiborepine: Preparation and Functionalization

π-Conjugated
organoboron molecules, which are easy to prepare,
stable against moisture, and easy to functionalize, are scarce. Here,
we report a one-pot synthesis of an air-stable organoboron compound,
dithienooxadiborepine 1 in 17% yield on a 600 mg scale
without separation or handling an air-sensitive intermediate. Dithienooxadiborepine 1 showed excellent stability under ambient conditions, allowing
conventional column chromatography purification. Functionalization
of 1 was realized via direct bromination using NBS and
further Stille coupling reactions, giving access to longer π-conjugated
molecules 5A and 5B. Single-crystal structures
of compounds 4, 5A, and 5B not
only unambiguously verified the chemical identity of dithienooxadiborepine 1 but also revealed that both the seven-member oxadiborepine
ring and the 5–7–5 fused dithienooxadiborepine ring
system are planar. UV–vis absorption and fluorescence emission
measurements of 5A and 5B showed bathochromic
shifted absorption and emission relative to 1, evidencing
good π-conjugation. Cyclic voltammograms of 5A and 5B displayed two reduction peaks corresponding to two electron-accepting
events at two boron atoms. These results proved dithienooxadiborepine 1 a potent π-conjugating building block for electron-accepting
materials.

易于制备、耐水解且易于功能化的π共轭有机硼分子较为稀缺。本文报道了一种空气稳定型有机硼化合物二噻吩并氧杂二硼杂环庚烷（dithienooxadiborepine）1的一锅合成方法：在600 mg规模下产率达17%，且无需分离或处理对空气敏感的中间体。该化合物在常规环境条件下表现出优异的稳定性，可通过常规柱层析法完成纯化。通过使用N-溴代琥珀酰亚胺（NBS）直接溴化，可实现对该化合物的功能化修饰，并进一步通过斯蒂尔偶联反应（Stille coupling）得到更长共轭链的π共轭分子5A与5B。化合物4、5A及5B的单晶结构不仅明确确证了二噻吩并氧杂二硼杂环庚烷1的化学结构，还揭示出七元氧杂二硼杂环庚烷环与5-7-5稠合的二噻吩并氧杂二硼杂环庚烷环体系均为平面结构。对5A与5B的紫外-可见吸收及荧光发射光谱测试结果显示，相较于化合物1，二者的吸收与发射峰均发生红移，证实其具备良好的π共轭特性。5A与5B的循环伏安图呈现出两个还原峰，对应两个硼原子位点的两次电子受体还原过程。上述结果证实，二噻吩并氧杂二硼杂环庚烷1是一类极具应用潜力的π共轭电子受体型构筑基元。