Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), Higashi-Hiroshima, Hiroshima 739-8526, Japan.
J Org Chem. 2010 Mar 19;75(6):1956-60. doi: 10.1021/jo902714c.
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.
在我们之前的计算研究中，我们发现硅和氮原子对 1,2-二氮杂-4-硅环戊烷-3,5-二基的反应性有显著影响。因此，双自由基的单重态被计算为比相应的闭环产物，即 2,3-二氮杂-5-硅双环[2.1.0]戊烷，以及双自由基的三重态更稳定。在本研究中，通过前体偶氮烷的脱氮实验生成了双自由基的衍生物，即 2,3,5,6-四氮杂-7-硅双环[2.2.1]庚-2-烯，它们可以通过二氮杂硅环戊烷与 4-苯基-1,2,4-三唑-3,5-二酮（PTAD）或 4-甲基-1,2,4-三唑-3,5-二酮（MTAD）的环加成来制备。双自由基通过分子间捕获生成多环化合物。对模型偶氮烷脱氮的计算研究（UB3LYP/6-31G*）表明，通过 1,4-二氮烯基双自由基中间体逐步脱氮，以约 22 kcal/mol 的活化能生成单重态双自由基 1,2-二氮杂-4-硅环戊烷-3,5-二基衍生物是热力学有利的途径。脱氮反应的低活化能与实验观察结果一致，即在本研究中使用的制备条件下，偶氮烷是不稳定的。
