Synthesis and Characterization of a Sterically Encumbered Unsymmetrical 9-Borafluorene, Its Pyridine Adduct, and Its Dilithium Salt

The reaction of 2,6-(4-t-BuC6H4)2C6H3Li with BH2Cl·SMe2 in hexane or Et2O solution
affords the terphenyl-substituted unsymmetrical 9-borafluorene 1-(4-tert-butylphenyl)-7-tert-butyl-9-(bis-2,6-(4-tert-butylphenyl)phenyl)-9-borafluorene (1) in good to moderate yields.
Addition of pyridine gives the colorless crystalline adduct 1·py. Compound 1 is readily
reduced to the deep red heteroaromatic dianionic (μ2-η5,η5-1-(4-tert-butylphenyl)-7-tert-butyl-9-(bis-2,6-(4-tert-butylphenyl)phenyl)-9-borafluorenyl)bis(diethyl ether)dilithium (2) with
excess lithium powder in Et2O solution. Reactions of the dianionic 2 with various metal
salts leads to reduction of these salts, and bright yellow 1 is recovered in essentially
quantitative yields. Compounds 1, 1·py, and 2 were characterized by 1H, 13C, and 11B NMR
spectroscopy and compounds 1·py and 2 also by single-crystal X-ray diffraction.

将2,6-双(4-叔丁基苯基)苯基锂（2,6-(4-t-BuC6H4)2C6H3Li）与二甲基硫络合氯化硼（BH2Cl·SMe2）在正己烷或二乙基醚溶液中反应，可得到中等至良好产率的三联苯取代不对称9-硼芴类化合物1-(4-叔丁基苯基)-7-叔丁基-9-双(2,6-(4-叔丁基苯基)苯基)-9-硼芴（记为化合物1）。向体系中加入吡啶，可得到无色结晶加合物1·py。化合物1在二乙基醚溶液中与过量锂粉反应，可被顺利还原为深红色杂芳族二阴离子型化合物二(二乙基醚)合二锂(μ2-η5,η5-1-(4-叔丁基苯基)-7-叔丁基-9-双(2,6-(4-叔丁基苯基)苯基)-9-硼芴基)（记为化合物2）。二阴离子化合物2与多种金属盐反应时，可还原这些金属盐，同时以几乎定量的产率回收得到亮黄色的化合物1。采用1H、13C及11B核磁共振波谱对化合物1、1·py和2进行了结构表征，并通过单晶X射线衍射对化合物1·py和2完成了单晶结构解析。