AB-INITIO MOLECULAR-ORBITAL STUDY OF THE SUBSTITUENT EFFECT ON PHOSPHINE-BORANE COMPLEXES

Ab initio molecular orbital calculations have been used to study the s ubstituent effect on H3BPHnMe3-n and Me3-nHnBPH3 (n = 0-3) phosphine-b orane complexes. The ab initio results show that successive methyl sub stitution on the phosphine favours complex formation, contrary to succ essive methyl substitution on the borane. The natural bond orbitals pa rtitioning scheme suggests that, in general, there is no correlation b etween the charge transfer and the complexation energies. It also show s the shortening of the P-H and P-C bond lengths, upon complexation, i s due to the increasing 's' character of these bonds. (C) 1998 Elsevie r Science B.V. All rights reserved.