Generation and intermolecular trapping of 1,2-diaza-4-silacyclopentane-3,5-diyls in the denitrogenation of 2,3,5,6-tetraaza-7-silabicyclo[2.2.1]hept-2-ene: an experimental and computational study.
In our previous computational study, we found that silicon and nitrogen atoms have a notable effect on the reactivity of 1,2-diaza-4-silacyclopentane-3,5-diyls. Thus, the singlet state of the diradical was calculated to be much more stable than the corresponding ring-closing product, i.e., 2,3-diaza-5-silabicyclo[2.1.0]pentane, and the triplet state of the diradical. In the present study, derivatives of the diradical were generated experimentally in the denitrogenation of precursor azoalkanes, i.e., 2,3,5,6-tetraaza-7-silabicyclo[2.2.1]hept-2-enes, which can be prepared by cycloaddition of a diazasilole with 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) or 4-methyl-1,2,4-triazole-3,5-dione (MTAD). The diradicals were trapped intermolecularly to afford polycyclic compounds. The computational studies (UB3LYP/6-31G*) of the denitrogenation of a model azoalkane suggested that stepwise denitrogenation with an activation energy of ca. 22 kcal/mol is the thermodynamically favored pathway for generation of the singlet diradical 1,2-diaza-4-silacyclopentane-3,5-diyl derivative via a 1,4-diazenyldiradical intermediate. The low activation energy of the denitrogenation reaction was consistent with the experimental observation that the azoalkane was labile under the preparation conditions used in this study.
Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), Higashi-Hiroshima, Hiroshima 739-8526, Japan.
Takeshi
T
Nakamura
Akinobu
A
Takegami
Manabu
M
Abe