Control with an iron hand: A broad range of ketimines underwent enantioselectivehydrogenation in the presence of a chiralBrønsted catalyst and a well‐defined nonchiral iron catalyst (see scheme). This procedure constitutes an attractive and environmentally favorable alternative to well‐established asymmetric hydrogenation reactions with precious‐metal catalysts.
Cooperative Catalysis: Combining an Achiral Metal Catalyst with a Chiral Brønsted Acid Enables Highly Enantioselective Hydrogenation of Imines
作者:Weijun Tang、Steven Johnston、Chaoqun Li、Jonathan A. Iggo、John Bacsa、Jianliang Xiao
DOI:10.1002/chem.201302437
日期:2013.10.11
Asymmetric hydrogenation of imines leads directly to chiral amines, one of the most important structural units in chemical products, from pharmaceuticals to materials. However, highly effective catalysts are rare. This article reveals that combining an achiral pentamethylcyclopentadienyl (Cp*)–iridium complex with a chiral phosphoric acid affords a catalyst that allows for highly enantioselective hydrogenation
Highly Enantioselective Hydrogenation of<i>N</i>-Aryl Imines Derived from Acetophenones by Using Ru-Pybox Complexes under Hydrogenation or Transfer Hydrogenation Conditions in Isopropanol
The asymmetric reduction of N‐arylimines derived from acetophenones by using Ru complexes bearing both a pybox (2,6‐bis(oxazoline)pyridine) and a monodentate phosphite ligand has been described. The catalysts show good activity with a diverse range of substrates, and deliver the amine products in very high levels of enantioselectivity (up to 99 %) under both hydrogenation and transfer hydrogenation
A combined experimental and computational study to decipher complexity in the asymmetric hydrogenation of imines with Ru catalysts bearing atropisomerizable ligands
DFT calculations reproduce accurately the ratio of isomers observed as well as the greater thermodynamic stability of the cis isomers of 1a. Complexes 1 are efficient catalyst precursors for the asymmetric hydrogenation of N-aryl imines 5 in toluene under very mild conditions using KOtBu as a base (4 bar H2, room temperature, 5/1/KOtBu = 500/1/10). Among the catalyst precursors, 1f provides good enantioselectivities
含有可阻转异构的膦-亚磷酸酯(P-OP)和手性C 2对称二胺(N-N)的RuCl 2(P-OP)(N-N)络合物(1)可以通过连续添加P轻松制备为反式异构体RuCl 2(PPh 3)3的–OP和N–N配体。对于这些络合物,已经观察到在室温下联芳基片段的快速阻转异构化。化合物反式- 1A干净异构成的混合物中的顺式异构体在EtOH在加热。DFT计算准确地再现了观察到的异构体的比例以及顺式的更大的热力学稳定性1a的异构体。配合物1是在非常温和的条件下,使用KO t Bu作为碱(4 bar H 2,室温,5 / 1 / KO t Bu = 500/1 / ,在非常温和的条件下,N-芳基亚胺5在甲苯中不对称氢化的有效催化剂前体。10)。在催化剂前体中,1f可在多种N-芳基亚胺的氢化反应中提供良好的对映选择性(84-96%ee,16个实例)。从DFT计算中,提出了一种机制,其中包括将氢化物和质子从二氢