Synthesis of the Long-Sought Unsubstituted Aminodiboranate Na(H3B-NH2-BH3) and Its N-Alkyl Analogs

Reduction of ammonia borane, NH3 center dot BH3, with Na or NaNH2 in refluxing tetrahydrofuran (thf) affords the new compound, the unsubstituted aminodiboranate Na(BH3-NH2-BH3) (1a). Similar N-alkyl- and N,N-dialkylaminodiboranate salts, Na(H3B-NHMe-BH3) (1b), Na(H3B-NHEt-BH3) (1c), Na(H3B-NMeEt-BH3) (1d), Na[H3B-N(C4H8)-BH3] (1e), and Na[H3B-N(C5H10)-BH3] (1f), where N(C4H8) = pyrrolido and N(C5H10) = piperido, have also been prepared, along with their adducts with dioxane Na[H3B-NRR'-BH3](diox)(x) where x = 0.5 or 1.0 (2a-f). Crystal structures of 2b, 2c, and 2e are reported. Treatment of ErCl3 with Na(H3B-NH2-BH3) in thf affords the new erbium complex Er(H3B-NH2-BH3)Cl-2(thf)(3), 3, which has been crystallographically characterized. H-1 and B-11 NMR spectra of the new compounds are reported.