THE BORON-CARBON TRIPLE BOND (-B=C-) - SOME THEORETICAL PREDICTIONS

The structures of the organoboron anions HB̄CH and HB̄CBH2 have been determined using ab initio methods that include the effects of dynamical electron correlation. Optimized geometries, electric dipole moments and harmonic vibrational frequencies are presented and discussed at the various levels of theory employed. The dependence of these molecular properties on the inclusion of diffuse functions in the basis set is investigated. The BC bond lengths predicted at the highest consistent theoretical level, CISD/TZ2P, are 1.319 Å for HB̄CH and 1.338 and 1.467 Å for HB̄CBH2. It may be argued that the prototypical HB̄CH anion contains a formal BC triple bond, while the larger HB̄CBH2 anion incorporates a weaker BC triple bond and a very strong CB single bond. It is postulated that the partial bonding character in the diboro anion may be understood in terms of resonance structures and hyperconjugate interactions involving orbital overlap. © 1990.