Deciphering the Mechanism of the Nickel-Catalyzed Hydroalkoxylation Reaction: A Combined Experimental and Computational Study,ACS Catalysis

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Deciphering the Mechanism of the Nickel-Catalyzed Hydroalkoxylation Reaction: A Combined Experimental and Computational Study
ACS Catalysis ( IF 11.3 ) Pub Date : 2017-09-14 00:00:00 , DOI: 10.1021/acscatal.7b00616
Alexis Mifleur ₁ , Delphine S. Mérel ₁ , André Mortreux ₁ , Isabelle Suisse ₁ , Frédéric Capet ₁ , Xavier Trivelli ₂ , Mathieu Sauthier ₁ , Stuart A. Macgregor ₃

Affiliation

The [Ni(0)(cod)₂]/P^∩P-catalyzed hydroalkoxylation of butadiene to form butenyl ethers is studied mechanistically, where P^∩P = 1,4-bis(diphenylphosphino)butane (dppb) and 1,2-bis(diphenylphosphinomethyl)benzene (dppmb). Experimental studies suggest the intermediacy of [(P^∩P)Ni(0)(butadiene)] and [(P^∩P)Ni(II)(allyl)] intermediates and rule out the involvement of Ni–H species. The related species [(dppb)Ni(0)(1,4-diphenylbutadiene)], 1, and [(P^∩P)Ni(II)(crotyl)(Cl)] complexes 2 (P^∩P = dppmb) and 3 (P^∩P = dppb) have been synthesized and characterized on the basis of VT NMR spectroscopy and X-ray crystallographic studies. Compounds 2 and 3 are shown to be catalytically competent for the hydroalkoxylation reaction. Computational studies on [(dppmb)Ni(0)(butadiene)] indicate a facile protonation that forms a cationic allylic intermediate [(dppmb)Ni(II)(η-C₄H₇)]OMe. C–O bond formation then occurs via external attack by the solvent-stabilized methoxide nucleophile. Hydroalkoxylation proceeds with modest computed barriers of ca. 18 kcal/mol, and the butenyl ether product formation is only marginally exergonic. Overall, the results are consistent with initial kinetic control leading to the major branched isomer followed by a reversible isomerization process operating under thermodynamic control.

中文翻译：

镍催化的氢烷氧基化反应机理的解释：结合实验和计算研究。

从机理上研究了[Ni（0）（cod）₂ ] / ^P∩P催化的丁二烯加氢烷氧基化反应生成丁烯基醚，其中^P∩P = 1,4-双（二苯基膦基）丁烷（dppb）和1,2-双（二苯基膦基甲基）苯（dppmb）。实验研究表明，[（^P∩P）Ni（0）（丁二烯）]和[（^PPP）Ni（II）（烯丙基）]中间体具有中介作用，并排除了Ni–H物种的参与。相关物种[（DPPB）镍（0）（1,4-二苯基）] 1和[（P ^∩ P）的Ni（II）（巴豆基）（CL）]配合物2（P ^∩ P = dppmb）和3（^P∩P = dppb）已合成，并根据VT NMR光谱和X射线晶体学研究对其进行了表征。化合物2和3显示出催化加氢烷氧基化反应的能力。上计算的研究[（dppmb）镍（0）（丁二烯）]表示一个浅显的质子化，其形成阳离子烯丙基中间体[（dppmb）镍（II）（η-C ₄ H ^ ₇）] OMe。然后，由溶剂稳定的甲醇盐亲核试剂通过外部攻击而形成C–O键。加氢烷氧基化以约适度的计算的势垒进行。18 kcal / mol，而丁烯基醚产物的形成仅在很小的程度上是能动的。总体而言，结果与最初的动力学控制相一致，从而导致了主要的支链异构体，随后是在热力学控制下进行的可逆异构化过程。

更新日期：2017-09-15

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