| Abstract
| - UDFT and CASSCF calculations with the 6-31G(d) basis set were performed to investigate theheavier group 14 element (M) effect on the ground-state spin multiplicity of cyclopentane-1,3-diylsand their reactivity. The calculations find that 2-metallacyclopentane-1,3-diyls (M = Si, Ge) thatpossess a variety of substituents (X = H, Me, F, OR, SiH3) at M(2) are singlet ground-state molecules.The energies of the 1,3-diphenyl-substituted singlet 2-silacyclopentane-1,3-diyls are calculated tobe ca. 5 kcal/mol lower than those of the intramolecular ring-closure products, i.e., 1,4-diphenyl-5-silabicyclo[2.1.0]pentanes, at the B3LYP/6-31G(d) level of theory. The energy barrier for thedisrotatory ring closure of singlet 2,2-dimethyl-1,3-diphenyl-2-silacyclopentane-1,3-diyl (λcalcd = 757nm, f = 1.01 at RCIS/6-31G(d)) to the corresponding 5-silabicyclo[2.1.0]pentane is computed to be11.6 kcal/mol, which is 13.1 kcal/mol lower in energy than that for the conrotatory ring-opening toa 3-silapenta-1,4-diene. The computational work predicts that singlet 1,3-diaryl-2-silacyclopentane-1,3-diyls are persistent molecules under conditions without trapping agents.
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