Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, 7610001 Reḥovot, Israel.
J Phys Chem B. 2022 Mar 3;126(8):1799-1804. doi: 10.1021/acs.jpcb.2c00218. Epub 2022 Feb 18.
Recent quantum chemical computations demonstrated the electron-acceptance behavior of this highly reactive cyclo[18]carbon (C) ring with piperidine (pip). The C-pip complexation exhibited a double-well potential along the N-C reaction coordinate, forming a van der Waals (vdW) adduct and a more stable, strong covalent/dative bond (DB) complex by overcoming a low activation barrier. By means of direct dynamical computations using canonical variational transition state theory (CVT), including the small-curvature tunneling (SCT), we show the conspicuous role of heavy atom quantum mechanical tunneling (QMT) in the transformation of vdW to DB complex in the solvent phase near absolute zero. Below 50 K, the reaction is entirely driven by QMT, while at 30 K, the QMT rate is too rapid ( ∼ 0.02 s), corresponding to a half-life time of 38 s, indicating that the vdW adduct will have a fleeting existence. We also explored the QMT rates of other cyclo[]carbon-pip systems. This study sheds light on the decisive role of QMT in the covalent/DB formation of the C-pip complex at cryogenic temperatures.
最近的量子化学计算表明，具有哌啶（pip）的这种高反应性的环[18]碳（C）环具有电子接受行为。C-pip 络合物沿着 N-C 反应坐标表现出双势阱势能，通过克服低活化能垒形成范德华（vdW）加合物和更稳定的强共价/配位键（DB）络合物。通过使用正则变分过渡态理论（CVT）进行直接动力学计算，包括小曲率隧穿（SCT），我们展示了重原子量子力学隧穿（QMT）在溶剂相中从 vdW 到 DB 络合物转变中的显著作用接近绝对零度。在 50 K 以下，反应完全由 QMT 驱动，而在 30 K 时，QMT 速率过快（∼0.02 s），对应半衰期为 38 s，表明 vdW 加合物将短暂存在。我们还研究了其他环[]碳-pip 体系的 QMT 速率。这项研究揭示了在低温下，C-pip 络合物的 QMT 在共价/DB 形成中起决定性作用。
