M.Sc. / In this study, the pyrazolyl-based ligands were synthesised and used in the synthesise of new ruthenium pyrazolyl-based complexes. The ruthenium pyrazolyl-based complex 2.4 was tested as a catalyst for the self-metathesis reaction of 1-octene. The N^N ligands: 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 4-(3,5- dimethylpyrazol-1-ylmethyl)pyridine (L2) were prepared from the reaction of 2- picolyl chloride (for L1) and 4-(bromomethyl)pyridine (for L2) with 3,5- dimethylpyrazole. Reactions of L1 and L2 with [RuCl2(PPh3)3] and [RuCl3·3H2O] produced [2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine) dichlorotriphenylphosphine]ruthenium (2.1) and bis[4-(3,5-dimethylpyrazol-1- ylmethyl)pyridine-trichloride]ruthenium (2.3), respectively. The N^O ligands: 2- (3,5-dimethylpyrazol-1-yl)ethanol (L3), 2-(3,5-diphenylpyrazol-1-yl)ethanol (L4), were prepared from the reaction of 2-hydroxyethylhydrazine (for L3) and dibenzoylmethane (for L4) with 2-hydroxyethylhydrazine. Reaction of L3 with (3-phenylindenylidene)dichlorobis-(triphenylphosphine)ruthenium produced [3-phenylindenylidene-(3,5-dimethylpyrazol-1-yl)-ethanolate chlorotriphenylphosphine]ruthenium (2.4). Ligands, 2-(3,5-dimethylpyrazol-1-ylmethyl)-phenol (L5) and bis(3,5- dimethylpyrazol-1-yl)acetic acid (L6), were prepared from the reaction of o-(α- bromo-methyl) phenyl methanesulfonate (for L5) and dibromoacetic acid (for L6) with 3,5-dimethylpyrazole. Reaction of L6 with [RuCl2(PPh3)3] produced bis-[(3,5-dimethylpyrazol-1-yl)-acetic-acid-chloro(bistriphenylphosphine)] ruthenium (2.6). The C^N ligands: 1-[2-(3,5,-dimethylpyrazol-1-yl)-ethyl]-3- methyl-3H-imidazol-1-ium bromide (L7) and 1-[2-(3,5,-dimethylpyrazol-1-yl)- ethyl]-3-methyl-3H-imidazol-1-ium bromide (L8) were prepared from the reaction of 1-(2-bromoethyl)-3,5-dimethyl-1H-pyrazole (for L7) and 1-(2- bromoethyl)-1H-pyrazole (for L8) with 1-methylimidazole. Reactions of L7 and L8 with silver(I) oxide (Ag2O) produced 3,5-dimethyl-1-[2-(3-methyl-2,3- dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.7) and 1-[2-(3- methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazole]silver bromide (2.8), respectively. Reactions of silver complexes (2.7) and (2.8), respectively, with [RuCl2(PPh3)3] produced 3,5-dimethyl-1-[2-(3-methyl-2,3-dihydro-imidazol-1- yl)-ethyl-1H-pyrazole-dichloro(triphenylphosphine)]ruthenium (2.9) and 1-[2- (3-methyl-2,3-dihydro-imidazol-1-yl)-ethyl-1H-pyrazoledichloro (triphenylphosphine)]ruthenium (2.10). The synthesised complexes were obtained in moderate to low yields and were characterised by 1H, 13C{1H}, 31P{1H} NMR, IR spectroscopy, mass spectrometry, elemental analyses and ligand L5 was also characterised by X-ray crystallography. Complex 2.4 was screened for self-metathesis reaction of 1-octene. Initial run from 30-90 oC showed no activity for 1-octene metathesis below 105 oC. At 105 oC small amounts of 7-tetradecene was obtained, indicating that metathesis reaction occurs at very high temperatures (105 oC). Thermal stability test of complex 2.4, showed that rearrangement in the proposed structure of complex 2.4 occurs after heating at 90 oC for 16 h, this was evident by the 31P{1H} NMR spectrum of complex 2.4 obtained as a singlet at 28.9 ppm (after being heated), (complex 2.4 appears at 30.0 ppm before heating). From the 31P{1H} NMR study, it could be proposed, that the pyrazole arm of the ligand dissociates thus influencing the environment of the phosphorus (of the triphenylphosphine), and therefore a shift in the peaks is observed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:6772 |
| Date | 12 April 2010 |
| Creators | Chonco, Zandile Hlengiwe |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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