Ab Initio Molecular Orbital Study of the Thermochemistry and Reactions of the Chlorinated Disilenes and Their Isomers (Si2HnCl4-n)

Structures, vibrational frequencies, and energies for the chlorinated disilenes, their dibridged isomers, and the transition states connecting the chlorinated disilenes to the corresponding silylsilylenes are presented. Geometries and frequencies were obtained at the MP2/6-31G(d,p) level, and energetics were calculated at the G2, G2(MP2), MP4/6-31+G(2df,p), and/or MP2/6-31+G(2df,p) levels of theory, depending on the number of chlorine atoms in the molecule. The silylsilylene isomer with the structure HnCl3-nSiSiCl was found to be lowest in energy for all of the chlorinated compounds. The dibridged structures are all significantly higher in energy than the silylsilylene and disilene structures. Barriers for isomerization by H transfer and Cl transfer ranged from 5 to 18 kcal/mol and 9 to 23 kcal/mol above the disilene, respectively. Energies along paths for decomposition of the chlorinated disilenes to pairs of silylenes are presented, confirming that the reverse reactions are barrierless. Finally, energetics of various decomposition products of the Si2HnCl4-n compounds are considered. It is shown that for the species with two or more chlorines, decomposition to a pair of silylenes should be the dominant reaction path based on the energetics of competing paths. The isomerization barriers are much smaller than decomposition barriers, so the isomerization reactions will be fast compared to decomposition.