School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Jadavpur, 700032 Kolkata, West Bengal, India.
J Am Chem Soc. 2020 Mar 18;142(11):5331-5337. doi: 10.1021/jacs.0c00181. Epub 2020 Mar 4.
Umbrella-like inversion of pyramidalized amines proceed through a planar transition state (TS). Stabilization of the TS through N(lone-pair) → σ*(C-C) "negative hyperconjugation" in diamino--carborane () causes rapid inversion in the amine, which results in the observation of a planarized -NH from the X-ray crystal structure. This proceeds through quantum mechanical tunneling across the small and narrow barrier (low pyramidalization). Tuning this secondary orbital (donor-acceptor) interaction for various derivatives of and diamino--dodecahedron () provides a rational approach toward increasing to as large as 2.001, 2.011, and 1.807 Å for (amino oxide--carborane), (di--dimethylamino--carborane), and (di--diisopropylamino-o-dodecahedron), respectively.
伞状的胺三角锥形翻转通过平面过渡态（TS）进行。在二氨基-碳硼烷（）中，通过 N(lone-pair) → σ*(C-C)“负超共轭”稳定 TS，导致胺快速翻转，从而导致从 X 射线晶体结构中观察到平面化的 -NH。这是通过穿过小而窄的势垒（低三角化）的量子力学隧道进行的。为了调节各种 衍生物和二氨基-十二面体（）的这种次级轨道（供体-受体）相互作用，为 （氨基氧化-碳硼烷）、（二-二甲基氨基-碳硼烷）和 （二-二异丙基氨基-o-十二面体）分别提供了一种合理的方法，使 增加到 2.001、2.011 和 1.807 Å。
