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 H-2 elimination below 100 degreesC, undergo efficient catalytic dehydrocoupling at 25-45 degreesC in the presence of Rh-I or Rh-III 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.