Assessing the Broensted Basicity of Diaminoboryl Anions: Reactivity toward Methylated Benzenes and Dihydrogen

• Published in: Angewandte Chemie International Edition 2014-06, Vol.53 (24), p.6259-6262
• Main Authors: Dettenrieder, Nicole, Aramaki, Yoshitaka, Wolf, Benjamin M, Maichle-Mossmer, Caecilia, Zhao, Xiaoxi, Yamashita, Makoto, Nozaki, Kyoko, Anwander, Reiner
• Format: Article
• Language: English
• Subjects: ACTIVITY; Anions; Basicity; Boron; COPPER OXIDE; HYDROGEN; Lithium; MATHEMATICAL ANALYSIS; Reduction; Toluene
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201402175

Treatment of toluene or p-xylene with diaminoboryllithium results in consecutive reactions, involving boryl-anion-mediated deprotonation at the benzylic position followed by nucleophilic substitution at the boron center, producing benzylborane species and LiH. Diaminoboryllithium also cleaves H sub(2) heterolytically affording diaminohydroborane and LiH, while the reaction of lithium diaminoboryl(bromo)cuprate with H sub(2) takes place accompanied by reduction of Cu super(I) to give diaminohydroborane, LiH, and Cu super(0). Back to basics: The deprotonation reactions of methylated benzenes and H sub(2) by superbasic boryl anions were studied. In the reaction of methylated benzenes, subsequent nucleophilic substitution on the boron center of intermediate B-H produces benzylborane species (structure of the B unit shown in the scheme; Dip=2,6-iPr sub(2)C sub(6)H sub(3)). A general mechanism for these reactions is elaborated and the reactivity of B-Li(THF) sub(2) toward H sub(2) investigated by DFT calculations.