ELECTRONIC AND GEOMETRICAL STRUCTURE OF H2B-O-BH2 - AN AB-INITIO STUDY

The structure of the diboroxane H2B-O-BH2 has been studied by means of ab initio calculations at the MP4/6-311G(**)//MP2/6-311G(**) level. Two minima have been characterized on the potential energy surface (PES): one is of D-2d symmetry, analogous to the isoelectronic allene molecule, and the other is of C-2v symmetry, lying 0.6 kcal/mol lower in energy than the D-2d one. The D-2h structure lies 11.3 kcal mol(-1) above the absolute minimum and is a peak on the PES (two imaginary frequencies). The preference for a bent structure of C-2v symmetry is rationalized through an orbital analysis. A reaction path between the two minima has been computed and may be described as a conrotatory motion of the two BH2 planes, coupled with the BOB angle opening. The associated activation energy is 1.2 kcal mol(-1). These results are discussed in light of the experimental data on substituted R(2)B-O-BR(2) diboroxanes.