We have quantum chemically studied the palladium-mediated activation of C(spn)–X bonds (n = 1–3; X = F, Cl, Br, I) in the archetypal model substrates H3C–CH2–X, H2C=CH–X, and HC≡C–X by a model bare palladium catalyst, using relativistic density functional theory at ZORA-BLYP/TZ2P. The bond activation reaction barrier decreases, for all sp-hybridized carbon centers, when the substituent X of the substrate is changed from X = F to I. Activation strain and energy decomposition analyses reveal that the enhanced reactivity along this series originates from (i) a less destabilizing activation strain due to an intrinsically weaker C(spn)–X bond; and (ii) an increasingly more stabilizing electrostatic interaction between the catalyst and the substrate. The latter is a direct consequence of the more diffuse electron density and higher nuclear charge of the X atom in the C(spn)–X bond when going from X = F to I, which, in turn, engages in a more favorable electrostatic attraction with the nucleus and electrons, respectively, of the palladium catalyst.

中文翻译：

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钯催化的碳-卤素键活化：静电控制的反应性

我们对原型模型底物 H3C–CH2–X、H2C=CH– 中的 C(spn)–X 键（n = 1–3；X = F、Cl、Br、I）进行了量子化学研究。 X 和 HC≡C–X 通过模型裸钯催化剂，在 ZORA-BLYP/TZ2P 使用相对论密度泛函理论。对于所有 sp 杂化碳中心，当底物的取代基 X 从 X = F 变为 I 时，键活化反应势垒降低。活化应变和能量分解分析表明，沿该系列的增强反应性源自 (i)由于本质上较弱的 C(spn)-X 键，不稳定的活化应变较小；(ii) 催化剂和基材之间的静电相互作用越来越稳定。