Study On The Precise Control Of Reaction Process And Chiral Memory Based On A Phosphate Tetrahedron Cage

Recently,due to the significant similarity between supramolecular chemistry and biological system in recognition,catalysis,and sensing,lots of elegant supramolecular assemblies with potential applications have been constructed.Hydrogen bonding is one of the weak interactions in supramolecular chemistry,multiple anion receptors have been designed and synthesized base on hydrogen bonding.The anion-coordination-driven assembly(ACDC)has been recognized by researchers in recent years.This thesis focuses on the design and synthesis of a C₃-symmetric tris-bis(urea)ligand,which assemblies with phosphate anions to form an A₄L₄(A=anion,L=ligand)type tetrahedral anion cage through hydrogen bonding.The host-guest chemistry,the precise control of reactive activity,the chiral induction and chiral memory were studied with this cage.This thesis consists of four parts,as follows:The first chapter is introduction,the supramolecular chemistry is briefly introduced.The research on the constructions,supramolecular flasks and chiral memory of metal-coordination-driven cages were briefly described.Urea anion receptors,the constructions and chirality of anion self-assembled supramolecular cages were also introduced.And expounds the purpose and significance of this thesis.Starting from Chapter 2 is the main research content.Our group has reported a series of A₄L₄-type(A=anion,L=ligand)anion tetrahedral cages based on the assemblies of C₃-symmetric tris(bis-urea)and phosphate ion.The linkers of ligand L¹ and L² are triphenylamine and 1,3,5-triphenylbenzene,and successfully constructed tetrahedral cage 1and 2 with phosphate ion,respectively.In this thesis a C₃-symmetric tris-bis(urea)ligand L³ based on 2,4,6-triphenyl-1,3,5-triazine spacer has been designed and synthesized.The assembly of L³ and phosphate ion formed cage 3,due to the intramolecular hydrogen bonds of triphenyltriazine the rotations of phenyl rings were restricted,and the ligand L³ is more rigid.Cage 3 would encapsulate lots of alkyl ammonium guests with different sizes and configurations by bending of the triphenyltriazine planes.And the effective utilization of cavity has also been improved,the packing coefficients of cage 3 is as high as 99.5%.Compare with cage 2,3 would selectively bind larger guests.In chapter 3,the different degrees of DABCO methylation(1,4-diazazbicyclo[2.2.2]octane)were regulated precisely by cage 3.Normally,there are two products in the methylation reaction of DABCO.The cavity of cage 3 is not larger enough to accommodate the dimethyl-substituted DABCO cation,so cage 3 could be used as a“microreactor”to control the nature of the alkylation products.Due to the encapsulation of monomethyl-substituted species by cage 3 the second methylation process was precluded despite the excessive iodomethane.Only when adding TEA⁺to“extruded”the monomethyl-substituted species the dimethyl-substituted DABCO can be detected.What's more,the formation of asymmetric product can be controlled by this method.In chapter 4,the chiral induction and chiral memory of cage 3 was studied.A series of chiral choline derivatives including R-?-methycholine(G^1R),S-?-methycholine(G^1S),R-?-methycholine(G^2R),and S-?-methycholine(G^2S)can be trapped by cage 3,and a given stereochemistry can be straightforward imprinted by these chiral guests.The CD spectra confirmed the chiral induction of guests.The chiral guests can be released partially or totally by the adding of achiral guests(TEA⁺,TMA⁺,Ch⁺)with higher binding affinity but the chiral of cage 3 would be remembered.The CD signals decay in the form of first-order kinetics,and the kinetic and thermodynamic parameters of the memory process were calculated.This is the first example of a chiral memory effect within the anion-coordination tetrahedral cages.