Xing Yang-Yang, Liu Jian-Biao, Sun Chuan-Zhi, Huang Fang, Chen De-Zhan
College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in Universities of Shandong, Institute of Molecular and Nano Science, Shandong Normal University, Jinan 250014, P. R. China.
Dalton Trans. 2017 Jul 25;46(29):9430-9439. doi: 10.1039/c7dt01568b.
The Pd(ii)-catalyzed site-selective δ-C(sp)-H alkenylation in the presence of more accessible γ-C(sp)-H bonds is investigated by DFT calculations. Migratory insertion is found to be both the rate-limiting and the selectivity-determining step. The origin of the unusual site-selectivity is originally attributed to the different steric repulsion between the alkyne and palladacycle; however, our theoretical results reveal that the inherent electronic effect instead of steric repulsion determines the site-selectivity. The proposal is further validated by model calculations involving the less sterically hindered 1,2-dimethyl acetylene and acetylene. In addition, a novel HCO-assisted N-H activation mechanism is reported, and the origin of the regioselectivity of an unsymmetrical alkyne is also studied.
通过密度泛函理论计算研究了在更容易接近的γ-C(sp)-H键存在下，钯（II）催化的位点选择性δ-C(sp)-H烯基化反应。发现迁移插入既是速率决定步骤，也是选择性决定步骤。这种不寻常的位点选择性的起源最初归因于炔烃和钯环之间不同的空间排斥作用；然而，我们的理论结果表明，决定位点选择性的是固有的电子效应而非空间排斥作用。通过涉及空间位阻较小的1,2-二甲基乙炔和乙炔的模型计算，进一步验证了该提议。此外，还报道了一种新型的HCO辅助的N-H活化机制，并研究了不对称炔烃区域选择性的起源。
