ABINITIO STUDY OF THE FORMATION OF H2B=NH2 FROM NH3 AND B2H6

The potential energy surface for the reaction of ammonia with diborane has been calculated at the MP2/6-31 (d) level with single-point calculations at the MP4/6-31+G(2d,p) level. A mechanism is proposed to explain the formation of aminoborane (H2B=NH2) from the reaction of NH3 with diborane. The initial step is the bimolecular addition of NH3 to B2H6 to form the NH3(BH3)2 complex which is isostructural with B2H7-. Since unimolecular H2 elimination from either the complex or H3BNH3 has a high activation barrier, it is suggested that H2 elimination is either bimolecular or catalyzed in the observed reaction. Calculated vibrational frequencies (MP2/6-31G(d)) are compared with observed values for H2B=NH2, H3BNH3, the methylated derivatives (H2B=N(H)CH3 and H3BNH2CH3), and mu-aminodiborane.