Syntheses, Structures, Electrochemistry and Optical Properties of Alkyne-Functionalized 1,3,2-Diazaboroles and 1,3,2-Diazaborolidines

Weber L, Penner A, Domke I, Stammler H-G, Neumann B. Syntheses, Structures, Electrochemistry and Optical Properties of Alkyne-Functionalized 1,3,2-Diazaboroles and 1,3,2-Diazaborolidines. Zeitschrift für Anorganische und Allgemeine Chemie. 2007;633(4):563-569.The reaction of 2-bromo-1,3-ditert-butyl-2,3-dihydro-1-H-1,3,2-diazaborole (3) with lithiated tert-butyl-acetylene and lithiated phenylacetylene affords the 2-alkynyl-functionalized 1,3,2-di-azaboroles 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 equivalent to C-tBu or LiC equivalent to CPh, respectively 2-Ethynyl-1,3-ditert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (2) was metalated with test-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-di-azaborol-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, H-1-, B-11{H-1}, C-13{H-1}-NMR, MS). The molecular structures of 5, 8 and 9 were elucidated by X-ray diffraction analyses