Experimental and Theoretical Study of the Transannular Intramolecular Interaction and Cage Effect in the Atrane Framework of Boratrane and 1-Methylsilatrane

On the basis of the high-resolution single-crystal X-ray diffraction data and theoretical B3LYP/6-311+G(d) and
B3LYP/cc-pVDZ calculations, the electron density distribution in boratrane and 1-methylsilatrane has been investigated.
The B−N bond in the boratrane molecule was found to correspond to the “shared” (covalent) interatomic interaction
in terms of Bader's “atoms in molecules” (AIM) theory. On the contrary, the Si···N bond in 1-methylsilatrane and
B−N bond in a series of some acyclic donor−acceptor boron complexes and other boratrane derivatives correspond
to interaction of an “intermediate” type. Such character of the B−N bond is caused by an influence of the atrane
“cage effect”. The influence of this effect results in deformation of the boron atom and displacement of the bond
critical point (3,−1) to the region of the electron lone pair of the nitrogen atom. This changes the type of the
interatomic interaction in comparison to other compounds investigated and explains high hydrolytic stability of
boratrane as well as silatranes and germatranes.

本研究基于高分辨率单晶X射线衍射数据，结合B3LYP/6-311+G(d)与B3LYP/cc-pVDZ理论计算方法，对硼杂卓（boratrane）及1-甲基硅杂卓（1-methylsilatrane）中的电子密度分布展开了系统研究。根据巴德（Bader）的"分子中原子"（Atoms in Molecules, AIM）理论，硼杂卓分子中的B−N键属于共享型（共价）原子间相互作用。与之相反，1-甲基硅杂卓中的Si···N键，以及一系列无环供体-受体型硼配合物与其他硼杂卓衍生物中的B−N键，则属于中间型相互作用。此类B−N键的特性受吖烷笼效应（atrane cage effect）的影响，该效应会引发硼原子发生形变，并使键临界点(3,−1)向氮原子的孤电子对区域偏移。相较于本次研究涉及的其他化合物，这一变化改变了其原子间相互作用的类型，同时也解释了硼杂卓、硅杂卓及锗杂卓较高的水解稳定性。