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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Density functional theory study of the mechanisms of iron-catalyzed cross-coupling reactions of alkyl grignard reagents
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Density functional theory study of the mechanisms of iron-catalyzed cross-coupling reactions of alkyl grignard reagents

机译：铁催化烷基格氏试剂的交叉偶联反应机理的密度泛函理论研究

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摘要

When compared with the established palladium and nickel catalyst systems, simple iron salts turn out to be highly efficient, cheap, toxicologically benign, and environmentally friendly precatalysts for a host of cross-coupling reactions of alkyl or aryl Grignard reagents. The inorganic Grignard reagent [Fe(MgX)_2], where X corresponds to Br or I, is a good catalyst for cross-coupling reactions. The present study reports a thorough theoretical analysis of the mechanisms of the [Fe(MgBr)_2] catalyzed cross-coupling reaction between 4-chlorobenzoic acid methyl ester and n-hexylicmagnesium bromide using density functional theory (DFT) calculations. Our calculations show that the overall catalytic cycle includes three basic steps: oxidation of [Fe(MgBr)_2] to obtain [Ar-Fe(MgBr)], addition to yield [Ar-(n-hexyl)-Fe(MgBr)_2], and reductive elimination to return to [Fe(MgBr)_2]. The energy barrier is lower if n-hexylicmagnesium bromide attacks the intermediate of the oxidative addition directly before [Cl-Mg-Br] dissociates to form the middle product [Ar-Fe(MgBr)] than if the attack occurs after the dissociation of [Cl-Mg-Br]. The solvation effect in this step clearly leads to a lowering of the energy barrier. The rate-limiting step in the whole catalytic cycle is the reductive elimination of [Ar-(n-hexyl)-Fe(MgBr)_2] to regenerate the catalyst [Fe(MgBr) 2], where the electronic energy barrier ΔE is 29.74 kcal/mol in the gas phase and the Gibb's free energy in solvent THF ΔG_(sol) is 28.13 kcal/mol computed using the C-PCM method.
机译：与已建立的钯和镍催化剂体系相比，简单的铁盐对于烷基或芳基格氏试剂的许多交叉偶联反应而言，是高效，廉价，毒理学上良好且对环境友好的预催化剂。无机格氏试剂[Fe（MgX）_2]，其中X对应于Br或I，是交叉偶联反应的良好催化剂。本研究报告使用密度泛函理论（DFT）计算方法，对[Fe（MgBr）_2]催化4-氯苯甲酸甲酯与正己基溴化镁之间的交叉偶联反应机理进行了详尽的理论分析。我们的计算表明，整个催化循环包括三个基本步骤：[Fe（MgBr）_2]的氧化以获得[Ar-Fe（MgBr）]，以及产生[Ar-（n-己基）-Fe（MgBr）_2 ]还原还原以返回[Fe（MgBr）_2]。如果正丁基溴化溴在[Cl-Mg-Br]分解形成中间产物[Ar-Fe（MgBr）]之前直接攻击氧化加成的中间产物，则能垒比在[[]] Cl-Mg-Br]。在该步骤中的溶剂化作用明显导致能垒的降低。在整个催化循环中的限速步骤是还原消除[Ar-（n-己基）-Fe（MgBr）_2]以再生催化剂[Fe（MgBr）2]，其中电子能垒ΔE为29.74气相中的kcal / mol和溶剂THF中的吉布自由能ΔG_（sol）使用C-PCM方法计算为28.13 kcal / mol。

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