UBC Theses and Dissertations
Synthesis of triple-stranded supramolecular complexes using poly(dipyrromethene) ligands Zhang, Zhan
Composed of conjugated dipyrromethene moieties connected by a linker, poly(dipyrromethene)s are useful ligands for the formation of well-defined architectures through self-assembly. Analogous to porphyrins, poly(dipyrromethene) ligands can endow their metal complexes with intense absorption bands in the visible region. The primary objectives of this project were to synthesize triple-stranded poly(dipyrromethene) complexes and explore the octahedral coordination chemistry of poly(dipyrromethene) ligands. A series of α,α’-linked and β,β’-linked bis(dipyrromethene) ligands were synthesized and examined for the formation of triple-stranded complexes. It was found that the size of α-substituent was the key factor. To facilitate the synthesis of the novel α-free bis(dipyrromethene) ligands, a method was developed to prepare the unknown key precursors, β,β’-linked α-unsubstituted diformyldipyrromethanes (201, for example) and diacyldipyrro- methanes (238 and 257, for example). Alkyl-substituted α-free bis(dipyrromethene) proligand 220-H₂•2HBr was synthesized from the β,β’-linked 201. Due to the presence of four exceedingly reactive α-positions, the proligand is unstable in solution. In order to improve the stability of the α-free proligand, aryl-substituted bis(dipyrromethene) proligands 250-H₂ and 260-H₂ were also developed from 238 and 257, respectively. Upon coordination with trivalent metals, these α-free proligands produced uncharged triple-stranded complexes which have intense absorption around 500nm. Intriguingly, the complexation led to both helicate and mesocate. The diastereomers were, for the first time, isolated and found inconvertible to each other under the reaction conditions. The case provids a new scenario for the formation of helicates versus mesocates and indicates the empirical odd-even rule is too simple to predict the product(s) of such a process.
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