Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis we describe various attempts at incorporating macrocycles into
dendritic architectures to form macrocycle-dendrimer conjugates with the aim of
preparing materials that would exhibit properties that are more than the sum of the
constituent parts, in this case macrocycles and dendrimers. A further aim was the
synthesis and characterization of metallodendrimers based on such scaffolds and to
test 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 with
macrocyclic cores.
The synthesis of conjugate systems based on cyclam as the macrocycle was
attempted. This required the mono functionalization of cyclam with a linker molecule
capable of further reaction with the functional groups at the periphery of
commercially available N,N,N,N-tetrakis(3-aminopropyl)-1,4-butanediamine
dendrimer. Several approaches were taken in trying to make such conjugate
systems but they were not entirely successful. One of the major issues was the final
deprotection step, of the Boc-protected cyclam units which proved difficult in our
hands.
Another approach to prepare the target conjugates involved the use of click
chemistry in order to synthesize a dendrimer with an aromatic core and cyclam
peripheries. A dendrimer with Boc-protected cyclam peripheries that are bonded
through triazole groups to the aromatic core was synthesized. However, subsequent
attempts at de-protection of the cyclam functionalities of this conjugate failed to yield
the pure de-protected dendrimer.
Greater success was achieved with the preparation of a dendrimer with a
macrocyclic core. A cyclam cored dendrimer with salicylaldimine peripheries was
successfully synthesized and characterized. This dendritic ligand was complexed to
Cu(II), Ni(II) and Zn(II) metal ions respectively to form a series of new
metallodendrimers. These metallodendrimers were fully characterized using a range of analytical techniques including FT-IR spectroscopy, mass spectrometry, elemental
analysis, thermogravimetric analysis, magnetic susceptibility measurements and
NMR spectroscopy where appropriate.
The Cu(II) and Ni(II) metallodendrimers were tested as catalyst precursors in the
catalytic oxidation of benzyl alcohol to benzaldehyde. The catalytic system consisted
of the appropriate metallodendrimer, the free radical, 2,2,6,6-tetramethylpiperidinyl-
1-oxyl (TEMPO) and O2 as the oxidant. The reaction parameters, namely the nature
of the solvent, catalyst loading, substrate concentration and reaction temperature
were sequentially optimized to achieve the best catalytic efficiency. The Cu(II)
catalyst precursor exhibited relatively high catalytic activity and achieved TOF’s
between 40 and 30 when operating under the optimized conditions, while the Ni(II)
catalytic system showed very poor catalytic activity. / AFRIKAANSE OPSOMMING: In hierdie tesis beskryf ons pogings om makroringe in die dendritiese argitektuur te
inkorporeer om makroring-dendrimeer gekonjugeerdes te vorm met die hoop dat
sulke molekules eienskappe sal toon wat meer is as die somtotaal van die
afsonderlike eenhede. ‘n Verdere doel was die sintese en karakterisering van
metallodendrimere gebaseer op sulke draers sowel as die toetsing van hierdie
molekules as pre-katalisore in die katalitiese oksidasie van alkohole.
Pogings tot die sintese van twee verskillende tipes makroring-dendrimeer
gekonjugeerdes word beskryf naamlik, dendritiese ligande met makroringe by die
buiterand sowel as dendritiese ligande met ‘n makroring as kern word bespreek.
Die sintese van makroring-dendrimeer gekonjugeerdes gebasseer op die makroring
cyclam word beskryf. Hierdie sintese vereis die gebruik van ‘n monogefunksioneerde
cyclam wat ‘n gepaste koppelingsgroep besit. Hierdie
koppelingsgroep kan dan verder met funksionele groepe op die oppervlak van die
kommersieel beskikbare DAB-dendrimeer reageer. Verskeie pogings is aangewend
om sulke gekonjugeerde stelsels te sintetiseer maar hierdie pogings was nie
volkome suksesvol nie. ‘n Groot uitdaging was die gebruik en gevolglike latere
verwydering van beskermende groepe soos Boc.
‘n Ander benadering het gebruik gemaak van “click” chemie met die doel om ‘n
dendrimeer bestaande uit ‘n aromatiese kern en cyclam periferie te vorm. ‘n
Dendrimeer met Boc beskermde cyclam eenhede op die buiterand geheg aan ‘n
aromatiese kern deur triasool groepe is gesintetiseer. Die verwydering van die
beskermende groepe geheg aan die cyclam eenhede was egter weereens ‘n
probleem en hierdie metode kon nie die suiwer dendrimeer lewer nie.
Groter sukses is behaal met die sintese van ‘n dendrimeer met ‘n cyclam kern en
salisielaldimien periferieë. Die dendritiese ligand is vervolgens met metaalsoute van
Cu(II), Ni(II) en Zn(II) gereageer om verskeie multikern metaalkomplekse te vorm.
Die metaalkomplekse is volledig gekarakteriseer deur verskeie analitiese tegnieke insluitende infrarooi spektroskopie, massa spektrometrie, termografiese analiese,
mikroanaliese asook KMR spektroskopie waar moontlik.
Die Cu(II) en Ni(II) metaalkomplekse is geëvalueer as pre-katalisatore in die
katalitiese oksidasie van alkohole. Hierdie katalitiese sisteem bestaan uit die
metaalkompleks, die radikaal TEMPO en molekulêre suurstof. Die invloed van
verskeie reaksie- parameters soos die tipe oplosmiddel, die hoeveelheid katalisator,
die konsentrasie van die alkohol asook die temperatuur is ondersoek. Gevolglik is
die optimale kondisies bepaal om die hoogste opbrengs van bensaldehied te lewer.
Die Cu(II) kompleks het ‘n relatief hoë omset van bensielalkohol na bensaldehied
getoon met omset frekwensie waardes tussen 30 en 40 onder die optimale kondisies.
Die Ni(II) kompleks het egter swak aktiwiteit getoon vir hierdie transformasie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85568 |
| Date | 12 1900 |
| Creators | Wilbers, Derik |
| Contributors | Mapolie, S. F., Luckay, R. C., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxi, 107 p. : ill. |
| Rights | Stellenbosch University |
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