Department of Chemistry, Laval University, Quebec City, Quebec, G1V 0A6, Canada.
iNano and Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
Nat Chem. 2017 Jun;9(6):531-536. doi: 10.1038/nchem.2753. Epub 2017 Apr 3.
Elementary steps in enantioselective heterogeneous catalysis take place on the catalyst surface and the targeted synthesis of a desired enantiomer requires the implantation of chiral information at the surface, which can be achieved-for example-by adsorbing chiral molecules. Studies of the structures of complexes formed between adsorbed prochiral reagents and chiral molecules yield information on the forces exerting stereocontrol, but further insight could be gained by studying the dynamics of their interactions. Here, using time-lapsed scanning tunnelling microscopy and density functional theory, we observe coupling between multiple stereochemical states within individual non-covalently bonded chirality-transfer complexes on a metal surface. We identify two modes of transformation between stereochemical states and find that the prochiral reagent can sample several complexation geometries during the lifetime of a complex, switching between states of opposing prochirality in the process. These results provide insight on the contribution of individual stereochemical states to the overall enantioselectivity of reactions occurring on catalyst surfaces.
在手性异相催化的基本步骤中，反应发生在催化剂表面，而目标对映异构体的合成则需要在表面引入手性信息，这可以通过吸附手性分子来实现。研究吸附的前手性试剂和手性分子之间形成的配合物的结构，可以提供对施加立体控制的力的信息，但通过研究它们相互作用的动力学，可以获得更深入的了解。在这里，我们使用时间分辨扫描隧道显微镜和密度泛函理论，观察到在金属表面上单个非共价键手性转移配合物中多个立体化学状态之间的耦合。我们确定了两种立体化学状态之间的转变模式，并发现前手性试剂可以在配合物的寿命内采样几个配合物几何形状，在此过程中在相反的前手性状态之间切换。这些结果为了解发生在催化剂表面的反应的整体对映选择性中各个立体化学状态的贡献提供了线索。
