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首页> 外文期刊>Organometallics >Chiral phosphine-phosphite ligands with a substituted ethane backbone. influence of conformational effects in rhodium-catalyzed asymmetric olefin hydrogenation and hydroformylation reactions
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Chiral phosphine-phosphite ligands with a substituted ethane backbone. influence of conformational effects in rhodium-catalyzed asymmetric olefin hydrogenation and hydroformylation reactions

机译：具有取代的乙烷主链的手性膦-亚磷酸酯配体。构象效应对铑催化的不对称烯烃加氢和加氢甲酰化反应的影响

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摘要

A family of chiral (3,3′-di-tert-butyl-5,5′,6,6′- tetramethyl-2,2′-biphenol-derived) phosphine-phosphite ligands (P-OP) with a substituted ethane backbone has been synthesized and the performance of these ligands in the Rh-catalyzed enantioselective hydrogenation and hydroformylation of several representative olefins analyzed. Corresponding cationic rhodium complexes provide highly enantioselective catalysts for the hydrogenation of methyl (Z)-α-acetamidocinnamate (MAC) and dimethyl itaconate. The catalyst comparison indicates that, for the two substrates, product configuration is determined by the configuration of the phosphite. Regarding matching and mismatching effects in these hydrogenations, small effects were observed in the reduction of MAC, while for the itaconate the bigger difference between the matched and mismatched cases was of 21% ee. On the other hand, Rh catalysts based on P-OP ligands showed good levels of activity and regioselectivity in the hydroformylation of styrene and allyl cyanide, while moderate enantioselectivities were obtained. Participation of the two stereogenic elements has been observed in these reactions, and their mismatched combination leads to cancellation of enantioselectivity. To further investigate the influence of the ligand backbone in the course of these reactions, structures of rhodium model complexes Rh(Cl)(CO)(P-OP) were analyzed by DFT methods. The results obtained indicate the existence of two types of preferred conformations, whose relative stability depend on the backbone nature. Comparison of structures of the more stable conformers for each ligand indicates that the orientation of the biaryl phosphite group with respect to the coordination plane does not vary substantially along the series. Differently, the position of the phenyl phosphine substituents greatly depends on the backbone. On the basis of these observations it has been concluded that chiral induction in the hydrogenation is very predominantly due to the phosphite part of the ligand. Alternatively, conformation of the phosphine group has a great influence on enantioselectivity in the hydroformylation reactions, and even reversal of product configuration was observed between catalysts with an opposite axial equatorial arrangement of Ph phosphine substituents.
机译：带有取代乙烷的手性（3,3'-二叔丁基-5,5'，6,6'-四甲基-2,2'-双酚衍生）膦-亚磷酸酯配体（P-OP）已经合成了主链，并分析了这些配体在Rh催化的几种代表性烯烃的对映选择性加氢和加氢甲酰化反应中的性能。相应的阳离子铑配合物为甲基（Z）-α-乙酰氨基二十二酸（MAC）和衣康酸二甲酯的加氢提供了高对映选择性的催化剂。催化剂的比较表明，对于两种底物，产物的构型由亚磷酸酯的构型决定。关于这些氢化中的匹配和错配效应，在减少MAC方面观察到了很小的影响，而对于衣康酸酯，匹配和错配的案例之间的较大差异为ee的21％。另一方面，基于P-OP配体的Rh催化剂在苯乙烯和烯丙基氰化物的加氢甲酰化反应中表现出良好的活性和区域选择性，同时获得了中等的对映选择性。在这些反应中已经观察到两种立体生成元素的参与，并且它们错配的组合导致对映选择性的抵消。为了进一步研究配体主链在这些反应过程中的影响，通过DFT方法分析了铑模型配合物Rh（Cl）（CO）（P-OP）的结构。获得的结果表明存在两种类型的优选构象，它们的相对稳定性取决于骨架的性质。对于每个配体，更稳定的构象异构体的结构比较表明，亚磷酸亚芳基酯基团相对于配位平面的取向沿着系列基本上没有变化。不同地，苯基膦取代基的位置很大程度上取决于主链。基于这些观察，可以得出结论，氢化中的手性诱导非常主要是由于配体的亚磷酸酯部分。或者，膦基的构象对加氢甲酰化反应中的对映选择性有很大的影响，甚至在具有相反的轴向膦膦取代基轴向赤道排列的催化剂之间观察到甚至产物构型的逆转。

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