Synthesis and reactivity of 2-bromo-1,3-diethyl-2,3-dihydro-1H-1,3,2-benzodiazaborole molecular structure of Bis(1,3-diethyl-2,3-dihydro-1H-1,3,2-benzodiazaborol-2-yl

The reaction of a slurry of calcium hydride in toluene with N,N'-diethyl-o-phenylenediamine (1) and boron tribromide affords 2-bromo-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol (2) as a colorless oil. Compound 2 is converted into 2-cyano-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborole (3) by treatment with silver cyanide in acetonitrile. Reaction of 2 with an equimolar amount of methyllithium affords 1,3-diethyl-2-methyl-2,3-dihydro-1 H-1,3,2-benzodiazaborole (4). 1,3,2-Benzodiazaborole is smoothly reduced by a potassium-sodium alloy to yield bis(1,3-diethyl2,3-dihydro-1 H-1,3,2-benzodiazaborol-2-yl] (7), which crystallizes from n-pentane as colorless needles. Compound 7 is also obtained from the reaction of 2 and LiSnMe3 instead of the expected 2-trimethylstannyl-1,3,2-benzodiazaborole. N,N'-Bis(1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol-2yl)-1,2-diamino-ethane (6) results from the reaction of 2 with Li(en)C-CH as the only boron containing product. Compounds 2-4, 6 and 7 are characterized by means of elemental analyses and spectroscopy (IR, H-1-, B-11{H-1}-, C-13{H-1}-NMR, MS). The molecular structure of 7 was elucidated by X-ray diffraction analysis.