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 mu ltiple bonds as well as a selection of hydrogen-bridged species, including a doubly bridged structure. The structures of 29 minima and 37 transition s tates of the form Si2PHn (n = 7, 5, 3, 1) have been optimized at the MP2(fu ll)/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 modif ication of the G2 level of theory. The stability of these compounds was inv estigated with respect to both unimolecular rearrangement and H-2 addition/ elimination. Barrier heights. for 1-2 and 1-3 H-shifts and for H-2 addition /elimination span wide ranges and are dependent on the nature of the bondin g. Structures that contain true silicon-phosphorus double bonds are particu larly stable with respect to unimolecular rearrangement.