BOREPIN, BORANORBORNADIENE AND BORANORCARADIENE: SUBSTITUENT EFFECTS ON INTERCONVERSIONS AT THEORETICAL LEVELS

作者：Kassaee M Z^*; Musavi S M; Motamedi E

来源：Journal of Theoretical and Computational Chemistry, 2010, 9(1): 379-392.

DOI：10.1142/S0219633610005190

• Borepin
• 7-borabicyclo[2.2.1]heptadiene
• boranorbornadiene
• 7-borabicyclo[4.1.0]heptadiene
• boranorcaradiene
• interconversions
• electronic effects
• ab initio
• DFT
• NICS

Density-functional B3LYP and ab initio HF calculations are used to study three isomeric systems including: borepin I, boranorbornadiene II, and boranorcaradiene III as well as their X-substituted analogues at two different positions (X = F, Cl, Br, CH(3), OCH(3), CF(3), CN, and NH(2)). Geometries, enthalpies, and energy barriers for two series of interconversions, III(X) -> I(X) and III(X) -> II(X), are calculated using 6-311G* basis set. The B3LYP calculated relative stability is in the order: I (0.00 kcal/mol) > II (23.33 kcal/mol) > III (39.07 kcal/mol). Except for NH(2), the electronic effects of the substituents are generally insignificant on the relative stability. At B3LYP, the gas-phase activation enthalpies for III -> I and III -> II interconversions are estimated to be very small (0.6 and 0.75 kcal/mol, respectively). The reverse conversions, I -> III and II -> III, have activation energies of 39.67 and 16.49 kcal/mol, respectively. These energies rule out the possibility of a rapid interconversion of the isomers in the gas phase. Again, none of the substituents, X, can change this situation. Two pathways are proposed for the possible [1,3]-suprafacial sigmatropic shifts of III(X) -> II(X). The partial aromatic characters of planar borepins are estimated using magnetic (NICS) and structural criteria (bond length alternation).

• 出版日期2010-2