High Pressure Equilibria of Dimethylamine Borane, Dihydridobis(dimethylamine)boron(III) Tetrahydridoborate(III), and Hydrogen

The interaction of hydrogen and deuterium with dimethylamine borane (Me2NHBH3) was studied at pressures from 0 to 10 GPa. Me2NHBH3 is stable to isothermal compression in noble gas pressure media up to 16 GPa. During these compressions a strong positive pressure dependence of the frequencies of BN and BH stretching fundamentals was observed. The opposite trend was observed with NH modes. Me2NHBH3 + He mixtures remain phase separated over the entire 0-16 GPa range. During the isothermal compression of Me2NHBH3 + H-2 mixtures two separate phases are observed at low pressure which subsequently collapse into one phase above 3 GPa. Prior to the formation of the Me2NHBH3/H-2 phase loss of the H-2 vibron was observed concurrently with the growth of broad features in the 3600-4000 region. Further compression of the Me2NHBH3:H-2 results in the growth of new Raman-active BN, BH, and NH modes not present in noble gas compressions. These modes are assigned to the new high pressure solid: [(Me2NH)(2)BH2+][BH4-] similar called diammoniate of diborane often observed in experiments with ammonia and diborane at ambient pressure.