Thesis (PhD)--University of Stellenbosch, 2011. / In this thesis we describe the application of novel salicylaldimine and iminopyridyl
nickel metallodendrimer complexes as catalysts in the transformation of รก-olefins as well as
in the polymerization of norbornene.
New cyclic dendrimers based on cyclam as a core (L1-L8) were synthesized and
characterized via FTIR and NMR spectroscopy, mass spectrometry and microanalysis.
Subsequently the generation 1 cyclam-based dendrimers as well as the commercial
generation 1 to generation 3 DAB-PPI dendrimers were functionalized with salicylaldimine
and iminopyridyl moieties on the periphery to produce new ligands, DL1-DL10. These
modified dendritic ligands were subsequently complexed to Ni salts to obtain the
metallodendrimer complexes, C1-C8. The metallodendrimers were characterized by FTIR
spectroscopy, mass spectrometry, microanalysis, magnetic susceptibility measurements,
UV-Vis spectroscopy and thermal gravimetrical analysis (TGA).
The DAB G1-G3 salicylaldimine ligands (DL1-DL3) were subjected to
computational studies and the optimized structures were obtained by density functional
theory (DFT) calculations. The effect of the increase in dendrimer generation on the
structural arrangement of the dendrimer was also investigated. The following aspects were
probed using molecular modeling: a) the possible coordination site for the Ni to the first
generation dendrimer ligand, DL1, and b) the optimized structure of the first generation
salicylaldimine nickel complex, C1.
We subsequently evaluated catalysts, C1-C7, in the vinyl polymerization of
norbornene, using methylaluminoxane (MAO) as a co-catalyst. All the catalysts were found
to be active for norbornene polymerization with the weight of the polymers obtained ranging
from 5.12 x 105 - 11.17 x 106 g/mol. The DAB-based iminopyridyl catalysts (C4-C6)
exhibited higher activities than its analogous salicylaldimine catalysts (C1-C3) under the
same reaction conditions. Also, the cyclam-based salicylaldimine nickel catalyst (C7)
exhibited higher activities than the DAB-based salicylaldimine nickel catalyst, C1. A
negative dendritic effect was observed for the G1-G3 DAB salicylaldimine catalysts since the
optimum activity for the G3 catalyst, C3, was lower than that for the G2 catalyst, C2.
These nickel complexes were also evaluated as ethylene oligomerization catalysts and
were found to produce a range of ethylene oligomers (C4-C18) as well as some longer chained
oligomers, when employing EtAlCl2 as a co-catalyst. We observed however that the free
EtAlCl2 mediates the Friedel-Crafts alkylation of the solvent, toluene, in the presence of the
obtained ethylene oligomers to give uneven carbon number products, which are mixtures of
alkylated benzenes.
Our metallodendrimer catalysts also isomerized and in some cases dimerized
1-pentene. In both ethylene oligomerization and 1-pentene isomerization processes, the
salicylaldimine catalysts exhibited higher activity towards olefin transformation than the
iminopyridyl catalysts. The cyclam-cored dendrimer catalyst again showed the highest
activity. From the results obtained thus far it can be concluded that these nickel
metallodendrimers exhibit great potential as catalysts in the transformation of unsaturated
hydrocarbons.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6596 |
| Date | 03 1900 |
| Creators | Malgas-Enus, Rehana |
| Contributors | Mapolie, S. F., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
Page generated in 0.0022 seconds