Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
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DOI：
10.1002/anie.202001160
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发表时间：
2020-03-27
影响因子：
16.6
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
--
作者：
Martin, Johannes;Knuepfer, Christian;Harder, Sjoerd
合成了两个系列的大体积碱土金属酰胺配合物：Ae[N（TRIP）（2）]（2）（1-Ae）和Ae[N（TRIP）（DIPP）]（2）（2-Ae）（Ae=Mg，Ca，Sr，Ba; TRIP=SiiPr（3），DIPP= 2，6-二异丙基苯基）。虽然单体1-Ca是已知的，但新的复合物的结构已被表征。单体1-Ae是高度线性的，而单体2-Ae是轻微弯曲的。较大的酰胺配合物1-Ae是迄今为止在烯烃加氢中活性最高的催化剂，活性从Mg到Ba增加。催化剂1-Ba可以还原内烯烃如环己烯或3-己烯和高度挑战性的底物如1-Me-环己烯或四苯乙烯。它在芳烃氢化中也有活性，还原蒽和萘（即使被烷基取代）以及联苯。苯可以被还原成环己烷，但没有达到完全转化。催化氢化的第一步是形成（酰胺）AeH物质，其可以形成较大的聚集体。增加酰胺配体的体积减小聚集体尺寸，但不清楚真正的催化剂是什么。DFT计算表明，酰胺体也有一个显着的热力学上的（酰胺）AeH物种的形成的影响。配合物1-Ba是目前最强的Ae金属加氢催化剂。由于与以前报道的催化剂相比，活性大大增加，加氢催化的底物范围可以扩展到具有挑战性的多取代未活化的烯烃，甚至芳烃，其中苯。
Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)(2)](2) (1-Ae) and Ae[N(TRIP)(DIPP)](2) (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr(3), DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.