化学
位阻效应
螯合作用
喹啉
配体(生物化学)
亚甲基
立体化学
催化作用
药物化学
基质(水族馆)
无机化学
有机化学
受体
生物化学
海洋学
地质学
作者
Yun‐Fang Yang,Gang Chen,Xin Hong,Jin‐Quan Yu,K. N. Houk
摘要
The origin of the unique effectiveness of six-membered chelates on the β-methylene C(sp3)–H activation reactions by Pd(II) catalyst was explained with density functional theory. The Pd(II) catalysts that involve five-membered chelates are inactive in this transformation. Computational studies suggest that the C(sp3)–H bond activation is the rate-limiting step in both cases. The C(sp3)–H bond activation with a five-membered chelate is unfavorable by 7.7 kcal/mol compared to the corresponding six-membered chelate with Pd(II). Two factors cause the difference: (1) the dimeric Pd species with five-membered chelation square-planar structure is more stable than that with six-membered chelation by 2.0 kcal/mol; (2) steric repulsion between the ArF group of the substrate and the quinoline group of the acetyl-protected aminomethyl quinoline ligand destabilizes the five-membered chelate transition structure by 5.7 kcal/mol. The six-membered chelate of Pd(II) with an acetyl-protected aminoethyl quinoline ligand orients the ligand away from the ArF group of the substrate and alleviates the steric repulsion.
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