M.Sc. / Six pyrazole and pyrazolyl compounds, 3,5-dimethylpyrazole (L1), 3,5-diphenylpyrazole (L2), 3,5-di-tert-butylpyrazole (L3), bis(3,5-dimethylpyrazol-1-yl)methane (L4), bis(3,5-diphenylpyrazol-1-yl)methane (L5) and bis(1,2-bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L6), were reacted with Zn(II) and Cu(II) benzoates to form pyrazole and pyrazolyl metal benzoates. The complexes are [Zn(C6H5COO)2(L1)2] (1), [Zn(3,5-NO2-C6H3COO)2(L1)2] (2), [Zn(4-OH-C6H4COO)2(L1)2] (3), [Zn(2-Cl-C6H4COO)2(L1)2] (4), [Zn(C6H5COO)2(L2)2] (5), [Zn(3,5-NO2-C6H3COO)2(L2)2] (6), [Zn(4-OH-C6H4COO)2(L2)2] (7), [Zn(2-Cl-C6H4COO)2(L2)2] (8), [Zn(3,5-NO2-C6H3COO)2L4] (9), [Zn(4-OH-C6H4COO)2L6] (10), [Zn2(C6H5COO)4L6]n (11), [Zn(3,5-NO2-C6H3COO)2L6] (12), [Zn(2-Cl-C6H4COO)2L6] (13), [Cu(C6H5COO)2(L1)2] (14), [Cu(3,5-NO2-C6H3COO)2(L1)2] (15), [Cu(4-OH-C6H4COO)2(L1)2] (16), [Cu(2-Cl-C6H4COO)2(L1)2] (17), [Cu(C6H5COO)2(C6H5COOH)]2 (18), [Cu(2-Cl-C6H4COO)2(L3)2] (19), [Cu(C6H5COO)2L4] (20), [Cu(2-Cl-C6H4COO)2L4] (21), [Cu(C6H5COO)2DMSO]2 (22), [Cu(C6H5COO)2L6]2 (23), [Cu(2-Cl-C6H4COO)2L6]2n (24), [Cu(4-OH-C6H4COO)2L6]2(25) and [Cu(3,5-NO2-C6H3COO)2L6]n (26). The molecular structures of the Zn(II) and Cu(II) complexes 6, 9, 11, 14, 17-19, 22-26 were determined by X-ray diffraction studies that revealed four types of geometries adopted by these complexes: (i) 4-coordinate tetrahedral (6, 9, 14), (ii) 6-coordinate octahedral (17), (iii) paddle wheel (18, 19, 22, 23, 25) and (iv) polymeric structures (11, 24, 26). Catalysis studies performed with selected complexes (1-4, 9-17, 23-26) revealed that they initiate the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and D,L-lactide at elevated temperatures, and under solvent-free conditions and in toluene respectively. Polycaprolactone (PCL) and poly(D,L-lactide) (PLA) produced were of moderate molecular weights (858-4 757 Da for PCL and 602-3 185 Da for PLA) and polydispersity indices (1.36-2.16 for PCL and 1.42-2.35 for PLA). End group of the iv polymers, determined by MALDI-TOF MS, were benzoates, hydroxyl, methoxy groups and cyclic. From the 13C{1H} NMR spectra of polymers synthesized, the stereochemistry of PLA was predominantly isotactic.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8668 |
| Date | 07 June 2012 |
| Creators | Appavoo, Divambal |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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