The synthesis, single-crystal X-ray structure, and 1H and 13C NMR spectrocopic analyses of an unyielding precursor molecule to a cyclic (alkyl)(amido)carbene, 1-chloro-2-(2,6-diisopropylphenyl)-4,4-dimethyl-2-azaspiro[5.5]undecane-3,5-dione, C24H34ClNO2 (1), is reported. Despite the use of several bases, 1 could not be deprotonated to afford the corresponding carbene. The crystal structure of 1 was compared to the crystal structures of two structurally similar HCl adducts of stable carbenes (compounds 4 and 5), which revealed no significant differences in the geometries about the `carbene' C atoms. To better understand the reactivity differences observed for 1 when compared to 4 and 5, modified percent buried volume (%V
bur) calculations were performed. These calculations revealed that the H atom bound to the carbene C atom is the most sterically hindered in compound 1 when compared to 4 and 5 (%V
bur = 84.9, 81.3, and 79.3% for 1, 4, and 5, respectively). Finally, close inspection of the quadrant-specific %V
bur values indicated that the approach of a deprotonating base to the H atom bound to the carbene C atom is significantly blocked in 1 (69.9%) when compared to 4 and 5 (50.4 and 56.5%, respectively).
本研究报告介绍了环状(烷基)(
氨基)碳化物 1-
氯-2-(2,6-二异丙基苯基)-4,
4-二甲基-2-氮杂螺[5.5]
十一烷-3,5-二酮
C24H34ClNO2 (1) 的合成、单晶 X 射线结构以及 1H 和 13C NMR 光谱分析。尽管使用了多种碱,但 1 无法通过去质子化得到相应的碳烯。将 1 的晶体结构与稳定碳烯的两种结构相似的 HCl 加合物(化合物 4 和 5)的晶体结构进行了比较,结果显示,"碳烯 "C 原子的几何结构没有明显差异。为了更好地理解 1 与 4 和 5 相比所观察到的反应性差异,我们进行了修正的埋藏体积百分比(%V
bur)计算。这些计算显示,与 4 和 5 相比,化合物 1 中与碳烯 C 原子结合的 H 原子受到的立体阻碍最大(%V
bur = 1、4 和 5 分别为 84.9%、81.3% 和 79.3%)。最后,仔细观察特定象限的 %V
bur值表明,与 4 和 5(分别为 50.4% 和 56.5%)相比,1(69.9%)中去质子化碱接近与碳原子 C 原子结合的 H 原子的过程明显受阻。