Bipyridine-containing multitopic ligands for supramolecular chemistry

含雙呲 [sic] 啶多配位模式配體的超分子化學

Student thesis: Doctoral Thesis

View graph of relations


  • Kiu Chor SHAM


Awarding Institution
Award date14 Feb 2014


The use of bipyridine-containing ligands in supramolecular chemistry has been of great interest. This thesis reports the use of bipyridine-containing ligands for formation of different types of supramolecular assemblies. Chapter 1 is an introduction section. Literature examples are reviewed. With chiral 2,2':6',2'':6'',2''':6''',2'''':6'''',2'''''-sexipyridine L1, the diastereoselective synthesis of copper double-stranded helicate [Cu3(L1)2](ClO4)3 is reported in Chapter 2. The synthesis was carried out by reaction between L1 and [Cu(MeCN)4]ClO4 in a two to three molar ratio. The complex was characterized by ESI-MS, NMR, and elemental analysis. X-ray crystal structure and circular dichroism spectroscopy (CD) of [Cu3(L1)2](ClO4)3 show that it is a P-helicate. When compared with the 2,2':6',2'':6'',2'''-quaterpyridine which bears the same isopinocamphenol-based chiral substituents at the 5,6-position L2, the binuclear double-stranded copper helicate formed by L2 has reversed helical chirality. Theoretical calculations on the formation of [Cu3(L1)2](ClO4)3 and [Cu2(L2)2](ClO4)3 were carried out. The stereochemical outcome is explained by the steric hindrance present in the helicates. The preparation of manganese double-stranded helicates [Mn2(L)2](ClO4)4 based on bridged bis-bipyridines L4–6, which have the chiral bipyridine units linked by different number of phenyl rings at the 6'-position, is represented in Chapter 3. The complexes were characterized by ESI-MS, NMR, CD, and elemental analysis. The complexes of L5 and L6 were structurally characterized. Both helicates have P-helical chirality. The distorted octahedral manganese centers are coordinated to two 2,2'-bipyridine units of two different ligands. The other sites are either completed by solvent molecules or perchlorate ions. These manganese helicates are excellent epoxidation catalysts, which catalyze the epoxidation of both aliphatic and aromatic alkenes with peracetic acid as oxidant in good yield (up to 99%). Chapter 4 reports a study on metallomacrocycles. The manganese metallomacrocycles [Mn2(L)2](ClO4)4 (L = L8 and L9) were prepared by reacting oligopyridines which have bipyridine units connected by a phenyl group at the 5'-postion with Mn(ClO4)2 in a one to one molar ratio. The complexes were characterized by ESI-MS, NMR, CD, and elemental analysis. Although the ligand backbone structures are very similar, crystal structures show that [Mn2(L8)2(H2O)4](ClO4)4 and [Mn2(L9)2(H2O)2(ClO4)2](ClO4)2 are metallomacrocycles with significantly different structure. One has a fac-configured metal centers and the other has mer-configured metal centers. Their potential application in epoxidation of olefins has been explored and both are found to be active catalysts with peracetic acid as oxidant. A study on acid-base controlled chiroptical switching based on reversible formation of a hydrogen-bonded double helix with chiral biphenyl-bridged oligopyridine L5 is presented in Chapter 5. Protonation of L5 with HFeCl4, HOTf, or HClO4, gives intense CD signals. With HClO4, the induced CD signal is reversible and a chiroptical switch is developed. The results of CD, NMR, ESI-MS, and the X-ray crystal of [(L5)2H2](FeCl4)2 suggest that the induced CD signal comes from the formation of a hydrogen-bonded double helix of monoprotonated L5. Crystal structure of [(L5)2H2](FeCl4)2 and minimized energy models of [(L5)2H2](FeCl4)2 and [(L5)2H2](ClO4)2 suggest that the exterior hydrogen-bonds between the anions and the backbone are important to the helix formation. Chapter 6 reports the self-assembly reaction between chiral 2,2':5',5'':2'',2'''- quaterpyridine L10 and zinc(II) salts to form M4L6 tetrahedral cages [Zn4(L10)6](X)8 X = ClO4-, OTf-, and PF6-. These complexes were characterized by ESI-MS, NMR and elemental analysis. 19F NMR spectra of the OTf- and PF6- complexes suggest that the tetrahedral cages have cavity that can capture an anion and X-ray crystal structures of the ClO4- and OTf- complexes confirm this finding. The cage binding preference is in the order: PF6- > OTf- > ClO4- and the captured anion is exchangeable. The exchange rate is significantly affected by the anions involved in the exchange process. It is suspected that the difference in exchange rate is related to the exterior binding anions. Kinetic studies were carried out. The presence of perchlorate shows an increase in displacement rate of OTf- by PF6-. The effect of anion to the host–guest dynamics is demonstrated by using non-captured TsO- anion. The presence of TsO- accelerates the displacement rate of OTf- by PF6- at the beginning, but inhibits the displacement when the concentration of TsO- is sufficiently large. The binding of the TsO- to the exterior of the cage can be observed using 1H NMR and the binding constants can be calculated by curve fitting of chemical shift obtained in titration experiment with software WinEQNMR2. With the binding constants, the composition of exterior anions bound to the surfaces of the cage with respect to the concentration of TsO- was examined and the relationship between the composition of the exterior anions bound and the rate of exchange was studied.

    Research areas

  • Bipyridine, Ligands (Biochemistry), Supramolecular chemistry