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The first deprotonation of a borohydride anion was achieved by treatment of [BH(CN)3]− with strong non-nucleophilic bases, which resulted in the formation of alkali-metal salts of the tricyanoborate dianion B(CN)32− in up to 97 % yield and 99.5 % purity. [BH(CN)3]− is less acidic than (Me3Si)2NH but a stronger acid than iPr2NH. Less sterically hindered, more nucleophilic bases such as PhLi and MeLi mostly attack a CN group under formation of imine dianions [RC(N)B(CN)3]2−, which can be hydrolyzed to ketones of the [RC(O)B(CN)3]− type. The boron-centered nucleophile B(CN)32− reacts with CO2 and CN+ reagents to give salts of the [B(CN)3CO2]2− dianion and the tetracyanoborate anion [B(CN)4]−, respectively, in excellent yields. |
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