Boron Tunneling in the “Weak” Bond-Stretch Isomerization of N−B Lewis Adducts,ChemPhysChem

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Boron Tunneling in the “Weak” Bond-Stretch Isomerization of N−B Lewis Adducts
ChemPhysChem ( IF 2.3 ) Pub Date : 2021-07-10 , DOI: 10.1002/cphc.202100505
Ashim Nandi ₁ , Naziha Tarannam ₁ , Daniela Rodrigues Silva _{2,

3} , Célia Fonseca Guerra _{2,

4} , Trevor A Hamlin ₂ , Sebastian Kozuch ₁

Affiliation

Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a “long bond” geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a “short bond” structure (SB, a covalent dative bond). This behavior can be considered as a “weak” form of bond stretch isomerism. Our computations reveal that complexes RCN−BX₃ (R=CH₃, FCH₂, BrCH₂, and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.

中文翻译：

NB 路易斯加合物的“弱”键-拉伸异构化中的硼隧穿

一些腈 - 卤化硼加合物表现出具有两个不同最小值的双阱势能面：“长键”几何形状（LB，范德华相互作用主要基于静电，但包括残余电荷转移成分）和“短键”键”结构（SB，共价键）。这种行为可以被认为是键拉伸异构的“弱”形式。我们的计算表明，由于硼原子隧穿机制，配合物 RCN-BX ₃（R=CH ₃、FCH ₂、BrCH ₂和 X=Cl、Br）表现出从 LB 到 SB 几何形状的快速相互转换，甚至接近绝对零. 在低温条件下，亚稳态 LB 化合物的计算半衰期在几分钟到几纳秒之间变化。因此，我们预测长键结构实际上不可能分离或表征，这与之前的基质分离实验一致。

更新日期：2021-09-15

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