1,3,5-TRISILABENZENE - HAS IT BEEN SYNTHESIZED

The molecules 1,3,5-trisilabenzene and 1,3,5-trisilylene cyclohexane a re two isomers of Si3C3H6 which are possible products of the triple-de hydrogenation reaction of 1,3,5-trisilacyclohexane. In order to determ ine the geometries and relative energies of these potential products, ab initio quantum mechanical techniques have been employed on planar 1 ,3,5-trisilabenzene and the planar, boat and chair conformations of 1, 3,5-trisilylene cyclohexane. Basis sets as large as triple-zeta plus t wo sets of polarization functions (TZ2P) have been utilized for all of the molecules with the Hartree-Fock self-consistent field method, whi le a double-zeta plus polarization (DZP) basis set has been utilized w ith correlated methods as sophisticated as the coupled cluster approac h including all single, double, and perturbative triple excitations (C CSD(T)). The molecules 1,3,5-trisilabenzene and the chair and boat con formations of 1,3,5-trisilylene cyclohexane have been characterized as minima by the evaluation of their vibrational frequencies. Of these t he trisilabenzene is the most stable, with the chair and boat conforma tions of the silylene lying 35.0 and 36.5 kcal mol(-1) higher in energ y with the DZP CCSD(T) level of theory at the singles and doubles exci tation configuration interaction (CISD) optimized geometry points and including zero-point vibrational energies. In a further attempt to mea sure quantitatively the aromatic stabilization of 1,3,5-trisilabenzene , the heat of bond separation for this compound was determined. Result s show 1,3,5-trisilabenzene to have a bond separation energy of 53.1 k cal mel(-1), which is 83% of that of benzene at the best level of theo ry.