Institute for Research in Biomedicine (IRB Barcelona) , Barcelona Institute of Science and Technology , Baldiri Reixac 10 , 08028 Barcelona , Spain.
Departament de Química Inorgànica i Orgànica, Secció de Química Orgànica , Universitat de Barcelona , Martí i Franquès 1 , 08028 Barcelona , Spain.
J Org Chem. 2018 Apr 20;83(8):4618-4627. doi: 10.1021/acs.joc.8b00361. Epub 2018 Apr 9.
A small library of Ir-MaxPHOX catalysts has been applied to the asymmetric hydrogenation of N-aryl imines. A structure-activity analysis of the three-chiral-center MaxPHOX ligand has been performed. Using complex 1b, the hydrogenation of N-aryl imines took place with up to 96% enantiomeric excess at atmospheric pressure of hydrogen and low temperature. The impact of the stereochemical information at the phosphorus center is small with respect to the selectivity, but large with respect the catalyst activity. Non-P-stereogenic analogs of MaxPHOX were also synthesized and tested, but they provided lower selectivity. The selectivity observed could be explained by taking into account that the actual catalysts were cyclometalated imine complexes formed in situ. [IrHCl(MaxPHOX)(imine)] complexes 9 and 10 were synthesized and characterized by X-ray crystallography. These complexes, via chloride abstraction, provided the active catalytic species with the same levels of selectivity. Finally, the influence of the counterion on the catalyst performance was also studied.
已将一个 Ir-MaxPHOX 催化剂小库应用于 N-芳基亚胺的不对称氢化。对三手性中心 MaxPHOX 配体进行了结构活性分析。使用配合物 1b，在氢气常压和低温下，N-芳基亚胺的氢化最高可达到 96%的对映体过量。相对于选择性，磷中心的立体化学信息对催化剂活性的影响较小，但对催化剂活性的影响较大。还合成并测试了非 P-手性 MaxPHOX 的类似物，但它们提供的选择性较低。观察到的选择性可以通过考虑实际催化剂是原位形成的环金属化亚胺配合物来解释。通过氯化物的去除，合成并通过 X 射线晶体学对 [IrHCl(MaxPHOX)(imine)] 配合物 9 和 10 进行了表征，得到了具有相同选择性的活性催化物种。最后，还研究了抗衡离子对催化剂性能的影响。
