Synthesis and characterization of a sterically encumbered unsymmetrical 9-borafluorene, its pyridine adduct, and its dilithium salt

Article abstract of DOI:10.1021/om000868y

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-t ert-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 inessentially quantitative yields. Compounds 1, 1·py, and 2 were characterized by¹H, ¹³C, and ¹¹B NMR spectroscopy and compounds 1·py and 2 also by single-crystal X-ray diffraction.