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

Reaction of lithium 1,3-bis(2,6-diisopropylpheny-1)-2,3-dihydro-1H-1,3,2-diazaborol-2-ide with borane center dot THF provides the first boryl-substituted borohydride: lithium [1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1 H-1,3,2-diazaborol-2-yl]trihydroborate. The compound is fully characterized by B-11, H-1, and Li-7 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 center dot center dot center dot 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.