Ab initio molecular orbital study of the substituent effect on phosphine–borane complexes

Ab initio molecular orbital calculations have been used to study the substituent effect on H3BPHnMe3−n and Me3−nHnBPH3 (n=0–3) phosphine–borane complexes. The ab initio results show that successive methyl substitution on the phosphine favours complex formation, contrary to successive methyl substitution on the borane. The natural bond orbitals partitioning scheme suggests that, in general, there is no correlation between the charge transfer and the complexation energies. It also shows the shortening of the P–H and P–C bond lengths, upon complexation, is due to the increasing `sʹ character of these bonds.