Preparation, characterization and applications of macrocycle-dendrimer conjugates

[摘要] ENGLISH ABSTRACT: In this thesis we describe various attempts at incorporating macrocycles intodendritic architectures to form macrocycle-dendrimer conjugates with the aim ofpreparing materials that would exhibit properties that are more than the sum of theconstituent parts, in this case macrocycles and dendrimers. A further aim was thesynthesis and characterization of metallodendrimers based on such scaffolds and totest these as catalyst precursors in the catalytic oxidation of alcohols.The synthesis of two different types of conjugate systems was attempted; viz.dendrimers functionalized with macrocycles on the peripheries and dendrimers withmacrocyclic cores.The synthesis of conjugate systems based on cyclam as the macrocycle wasattempted. This required the mono functionalization of cyclam with a linker moleculecapable of further reaction with the functional groups at the periphery ofcommercially available N,N,N,N-tetrakis(3-aminopropyl)-1,4-butanediaminedendrimer. Several approaches were taken in trying to make such conjugatesystems but they were not entirely successful. One of the major issues was the finaldeprotection step, of the Boc-protected cyclam units which proved difficult in ourhands.Another approach to prepare the target conjugates involved the use of clickchemistry in order to synthesize a dendrimer with an aromatic core and cyclamperipheries. A dendrimer with Boc-protected cyclam peripheries that are bondedthrough triazole groups to the aromatic core was synthesized. However, subsequentattempts at de-protection of the cyclam functionalities of this conjugate failed to yieldthe pure de-protected dendrimer.Greater success was achieved with the preparation of a dendrimer with amacrocyclic core. A cyclam cored dendrimer with salicylaldimine peripheries wassuccessfully synthesized and characterized. This dendritic ligand was complexed toCu(II), Ni(II) and Zn(II) metal ions respectively to form a series of newmetallodendrimers. These metallodendrimers were fully characterized using a range of analytical techniques including FT-IR spectroscopy, mass spectrometry, elementalanalysis, thermogravimetric analysis, magnetic susceptibility measurements andNMR spectroscopy where appropriate.The Cu(II) and Ni(II) metallodendrimers were tested as catalyst precursors in thecatalytic oxidation of benzyl alcohol to benzaldehyde. The catalytic system consistedof the appropriate metallodendrimer, the free radical, 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) and O2 as the oxidant. The reaction parameters, namely the natureof the solvent, catalyst loading, substrate concentration and reaction temperaturewere sequentially optimized to achieve the best catalytic efficiency. The Cu(II)catalyst precursor exhibited relatively high catalytic activity and achieved TOF'sbetween 40 and 30 when operating under the optimized conditions, while the Ni(II)catalytic system showed very poor catalytic activity.

[发布机构] Stellenbosch University