Structures, Energetics, and Transition States of the Silicon-Phosphorus Compounds Si2PHn (n ) 7, 5, 3, 1). An ab Initio Molecular Orbital Study

This study examines a variety of compounds containing silicon-phosphorus multiple bonds as well as a selection of hydrogen-bridged species, including a doubly bridged structure. The structures of 29 minima and 37 transition states of the form Si2PHn (n ) 7, 5, 3, 1) have been optimized at the MP2(full)/6-31G(d) level of theory; a representative subset was also optimized at the QCISD/6-311G(d,p) level. Relative energies were computed using a modification of the G2 level of theory. The stability of these compounds was investigated with respect to both unimolecular rearrangement and H2 addition/elimination. Barrier heights for 1-2 and 1-3 H-shifts and for H2 addition/elimination span wide ranges and are dependent on the nature of the bonding. Structures that contain true silicon-phosphorus double bonds are particularly stable with respect to unimolecular rearrangement.