EARLY STAGES OF LIX, BEH2X, AND BH3X PYROLYSIS (X-STANDS FOR NH3 OR OH2) - A THEORETICAL-STUDY OF WEAK DATIVE COMPLEX STABILITY

In this work, we study theoretically the thermal decomposition of weak dative complexes (namely, the complexes between BH3, BeH2, or LiH and ammonia or water). The most accurate calculations have been carried o ut at the MP4sdtq/6-311++G(3df,2p) level on MP2full/6-31G* fully opti mized geometries. The transition structures for hydrogen evolution are described. The rate constants were obtained using conventional transi tion-state theory. Stability conditions for the complexes were conside red. Water complexes are less stable than are the corresponding ammoni a derivatives. Lithium complexes seem to be very unstable. It seems th at beryllium compounds could be synthesized. Borane derivatives are kn own experimentally. We find, as observed, that the first hydrogen evol ution occurs only above room temperature. Iminoborane seems not to be easily accessible under pyrolysis conditions. Other reactions require less activation energy. Finally, the early stages of the ammonia-boran e pyrolysis and paths to open-chain polymers as well as to cyclic stru ctures are described. (C) 1993 John Wiley & Sons, Inc.