Rhodium-catalyzed formation of boron–nitrogen bonds: a mild route to cyclic aminoboranes and borazines

Secondary amine–borane adducts R2NH·BH3, which are stable to H2 elimination below 100 °C, undergo efficient catalytic dehydrocoupling at 25–45 °C in the presence of RhI or RhIII complexes to quantitatively form cyclic aminoboranes [NR2–BH2]2 (1: R = Me or 2: cyclo-C4H8); under similarly mild conditions, the analogous adducts NH3·BH3 and MeNH2·BH3 yield borazines [RN–BH]3 (3: R = H or 4: R = Me) in yields limited by intermolecular coupling reactions.