Scholtes Jan Felix, Trapp Oliver
Department of Chemistry, Ludwig-Maximilians-University Munich, Butenandtstr. 5-13, 81377, Munich, Germany.
Max-Planck-Institute for Astronomy, Königstuhl 17, 69117, Heidelberg, Germany.
Chemistry. 2019 Sep 6;25(50):11707-11714. doi: 10.1002/chem.201902017. Epub 2019 Aug 8.
Well-defined supramolecular interactions are a powerful tool to control the stereochemistry of a catalytic reaction. In this paper, we report a novel core motif for fluxional 2,2'-biphenyl ligands carrying (S)-amino acid-derived interaction sites in 5,5'-position that cause spontaneous enrichment of the R rotamer. The process is based on strong non-covalent interlocking between interaction sites, which causes diastereoselective formation of a supramolecular ligand dimer, in which the axial chirality of the two subunits is dictated by the stereochemical information in the amino acid residues. The detailed structure of the dimer was elucidated by NMR spectroscopy and single-crystal X-ray analysis. Three different phosphorus-based ligand types, namely a bisphosphine, a bisphosphinite and a phosphoramidite were synthesized and characterized. Whereas the first one was found to exist in a strongly weighted equilibrium, the two others each exhibited stereoconvergent behavior transforming into the diastereopure R rotamer. Enriched ligands were used in rhodium-mediated asymmetric hydrogenation reactions of prochiral olefins in which very high enantioselectivities of up to 96:4 were achieved.
明确的超分子相互作用是控制催化反应立体化学的有力工具。在本文中，我们报道了一种新颖的核心基序，用于在5,5'-位带有（S）-氨基酸衍生相互作用位点的可旋转2,2'-联苯配体，这些位点会导致R旋转异构体的自发富集。该过程基于相互作用位点之间强烈的非共价互锁，这会导致超分子配体二聚体的非对映选择性形成，其中两个亚基的轴向手性由氨基酸残基中的立体化学信息决定。通过核磁共振光谱和单晶X射线分析阐明了二聚体的详细结构。合成并表征了三种不同的基于磷的配体类型，即双膦、双亚膦酸酯和亚磷酰胺。虽然发现第一种配体存在于强烈加权的平衡中，但另外两种配体均表现出立体收敛行为，转化为非对映纯的R旋转异构体。富集的配体用于前手性烯烃的铑介导不对称氢化反应，其中实现了高达96:4的非常高的对映选择性。
