THEORETICAL-STUDY OF SOME 1,3-SUBSTITUTED (1,3-DIKETONATO)BORONDIFLUORIDES - POTENTIAL-ENERGY CURVE RELEVANT TO THE BARRIER CROSSING REACTION

Ab initio Hartree-Fock calculations utilising STO-3G, 3-21G and 6-31G basis sets have been performed on three neutral and highly polar mol ecules, (diformylmethine)borondifluoride, (acetylacetonato)borondifluo ride and (dibenzylmethine)borondifluoride. The calculated and experime ntal structures are well correlated when using the HF/3-21G basis set , except for the structure parameters involving the boron atom. The HF /6-31G basis set does not improve the accuracy in structure calculati ons. The conformational analysis is in agreement with the experimental ly observed C-2v symmetrical structures, where the boron atom is tetra hedrally coordinated. The calculations support a one-dimensional groun d state barrier crossing reaction for (dibenzylmethine)borondifluoride , where the phenyl torsion is the most likely reaction coordinate. Bot h HF/6-31G calculations and the second-order Moller-Plesset correctio n with the 3-21G basis set suggest an activation energy of the ground state reaction of about 30 kJ mol(-1). The ground state barrier cross ing reaction kinetics is evaluated by the Kramers theory. The calculat ed ground state parameters relevant to the barrier crossing reaction a re compared with the experimentally observed excited state values.