Syntheses, structures, electrochemistry and optical properties of alkyne-functionalized 1,3,2-diazaboroles and 1,3,2-diazaborolidenes

Article abstract of DOI:10.1002/zaac.200600351

The reaction of 2-bromo-1,3-ditert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (3) with lithiated tert-butyl-acetylene and lithiated phenylacetylene affords the 2-alkynyl-functionalized 1,3,2-diazaboroles 4 and 5 as a thermolabile colorless oil (4) or a solid (5). Similarly 2-bromo-1,3-diethyl-2,3-dihydro-1H- 1,3,2-benzodiazaborole (6) was converted into the crystalline 2-alkynyl-benzo-1,3,2-diazaboroles 7 and 8 by treatment with LiC≡C - tBu or LiC≡CPh, respectively. 2-Ethynyl-1,3-ditert-butyl-2,3-dihydro-1H-1,3,2- diazaborole (2) was metalated with tert-butyl-lithium and subsequently coupled with 2-bromo-1,3,-ditert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (3) to afford bis(1,3-ditert-butyl-2,3-dihydro-1H-1,3,2-diazaborol-2-yl)acetylene (9) as thermolabile colorless crystals. Analogously coupling of the lithiated species with 6 or with 2-bromo-1,3-ditert-butyl-1,3,2-diazaborolidine (11) gave the unsymmetrically substituted acetylenes 10 or 12, respectively, as colorless solids. Compounds 4, 5, 7-10 and 12 are characterized by elemental analyses and spectroscopy (IR, ¹H-, ¹¹B{¹H}, ¹³C{¹H}-NMR, MS). The molecular structures of 5, 8 and 9 were elucidated by X-ray diffraction analyses.