Boryltrihydroborate: Synthesis, Structure, and Reactivity as a Reductant in Ionic, Organometallic, and Radical Reactions

• Published in: Journal of the American Chemical Society 2010-08, Vol.132 (33), p.11449-11451
• Main Authors: Nozaki, Kyoko, Aramaki, Yoshitaka, Yamashita, Makoto, Ueng, Shau-Hua, Malacria, Max, Lacôte, Emmanuel, Curran, Dennis P.
• Format: Article
• Language: English
• Subjects: Borates - chemical synthesis; Borates - chemistry; Crystallography, X-Ray; Free Radicals - chemistry; Ions - chemistry; Models, Molecular; Molecular Structure; Organometallic Compounds - chemistry; Oxidation-Reduction; Stereoisomerism
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja105277u

Reaction of lithium 1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborol-2-ide with borane·THF provides the first boryl-substituted borohydride: lithium [1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborol-2-yl]trihydroborate. The compound is fully characterized by 11B, 1H, and 7Li NMR spectra and other means, and these data are compared to neutral and anionic benchmark compounds. The compound crystallizes as a dimer complexed to four THF molecules. The dimer lacks the bridging B−H bonds seen in neutral boranes and is instead held together by ionic Li---HB interactions. A preliminary scan of reactions with several iodides shows that the compound participates in an ionic reduction (with a primary-alkyl iodide), an organometallic reduction (Pd-catalyzed with an aryl iodide), and a radical reduction (AIBN-initiated with a sugar-derived iodide). Accordingly the new borylborohydride class may share properties of both traditional borohydrides and isoelectronic N-heterocyclic carbene boranes.