Beijing National Laboratory for Molecular Sciences, College of Chemistry, Peking University, Beijing 100871, China.
J Am Chem Soc. 2012 Jul 25;134(29):11964-7. doi: 10.1021/ja305581f. Epub 2012 Jul 16.
A series of 2,6-diazasemibullvalenes (NSBVs) were synthesized and isolated from the reaction of 1,4-dilithio-1,3-dienes with nitriles via oxidant-induced C-N bond formation. For the first time, the activation barrier and an X-ray crystal structure of a substituted 2,6-diazasemibullvalene were determined. All NSBVs show extremely rapid aza-Cope rearrangement in solution, but the rapid aza-Cope rearrangement is "frozen" in the solid state, as shown by solid-state NMR measurements and X-ray single-crystal structural analysis. Insertion of unsaturated compounds or a low-valent metal center into the NSBV C-N bond gave diverse and interesting ring-expansion products. Theoretical analysis showed that the localized structure is predominant and that the homoaromatic delocalized structure exists as a minor component in the equilibrium.
一系列 2,6-二氮杂半环戊二烯（NSBVs）是通过氧化诱导的 C-N 键形成，由 1,4-二锂-1,3-二烯与腈反应合成并分离得到的。首次确定了取代的 2,6-二氮杂半环戊二烯的活化能垒和 X 射线晶体结构。所有 NSBVs 在溶液中均表现出极快的氮杂 Cope 重排，但通过固态 NMR 测量和 X 射线单晶结构分析表明，该重排在固态中“冻结”。不饱和化合物或低价金属中心插入 NSBV 的 C-N 键中，得到了多样且有趣的环扩张产物。理论分析表明，局域结构占主导地位，而同芳香离域结构则以较小的组成部分存在于平衡中。
