Chiral Separation And Characterization Of Molecular Face-rotating Polyhedra

Design and synthesis of molecular cages with novel structures and functionalities have draw broad research interests in supramolecular chemistry due to their potential applications in gas adsorption,chiral separation,and molecular catalysis.Among them,chiral cages are the most important one,but the construction and separation of chiral cages are still challenging.On one hand,the chirality of chiral cages generally originated from chiral building blocks with chiral carbon atoms or chiral metal centers,but chiral cage exhibiting supramolecular chirality is still rarely reported.On the other hand,chiral separation and thus thorough characterization of the diastereoisomers ofchiral cages are technically challenging and rarely reported,because most of chiral cages are constructed through weak interactions and not appropriate for chromatography.Organic cages constructed through dynamic covalent bonds are more stable than cages based on non-covalent interaction.Recently,our group developed a series of face-rotating polyhedra(FRP),exhibiting novel supramolecular chirality and chiral optical properties.Based on our previous work,this dissertation systematically.separated and analyzed several chiral FRPs,including detailed characterization of all the diastereoisomers.In Chapter 2,we studied the self-sorting phenomena using different facial buildingblocks and vertice.First,we assembled a C3-symmetric truxene derivative TR with racemic diphenylethylenediamine(DPEDA)into octahedra through dynamic imine bonds,and investigated whether racemic vertice can be chiral self-sorted.TR was first assembled with(1R,2R)-DPEDA to quantitatively gave[4+6]octahedra.Although there are five possible diastereoisomers,i.e.CCCC,CCCA,CCAA,CAAA and AAAA,the product contained only 6R-(AAAA)and 6R-(CAAA),confirmed by nuclear magnetic resonance(NMR)spectra,chiral high-performance liquid chromatography(HPLC),circular dichroism(CD)and X-ray crystallography.Interestingly,when the vertice changed from homochiral to racemic mixtures of DPEDA,the assembly process underwent high-degree chiral self-sorting process.Although there are 124 possible diastereoisomers,this assembly produced only 6R-(AAAA)and 6S-(CCCC).On contrary,using D3h-symmetric facial building block such as triazine derivatives TFPT or triformyl-benzene,their assembly with racemic diamines exhibited no apparent chiral self-sorting phenomenon.Our work demonstrates the regulation of facial interactions in the chiral self-sorting process.Second,we mixed two facial building blocks(TR and TFPT)with homochiral cyclohexanediamine and investigated whether this assembly process exhibit self-sorting phenomenon.Chiral HPLC analysis and mass spectroscopy results indicated that there are five diastereoisomers in the product,exhibiting no self-sorting of facial building blocks.Each diastereoisomer was thoroughly characterized by NMR and CD spectroscopy.In Chapter 3,several cages were constructed using larger facical or vertex building blocks.All those building blocks assembled into large molecular cages were confirmed by mass spectroscopy.Assembly of TITR and CHDA resulted in[4+6]cages with excellent rigidity and large cavity,but there are four diastereoisomers due to lack of facial interactions.TFPTR and CHDA also assembled into[4+6]cages,but due to existence of carbon-carbon single bonds in facial building blocks,these cages can not be separated.Assembly of TR and Cx[4]or Cx[5]resulted in larger polyhedra,but due to the flexibility of calixarene and unstability of aromatic imine bonds,these assemblies would decompose at high concentration and can not be characterized.In the final part of this dissertation,the author summarized some useful principles and guidelines for the separation of diastereoisomers using chiral HPLC.Besides,by introducing fluorine atom into the building block,preliminary exploration of monitoring the assembly process using 19F NMR was achieved.